ii

These materials are to be used only for the purpose of individual, private study and may not be reproduced in any form or medium, copied, stored in a retrieval system, lent, hired, rented, transmitted, or adapted in whole or in part without the prior written consent of Jeppesen.

Copyright in all materials bound within these covers or attached hereto, excluding that material which is used with the permission of third parties and acknowledged as such, belongs exclusively to Jeppesen. Certain copyright material is reproduced with the permission of the International Civil Aviation Organisation, the United Kingdom Civil Aviation Authority, and the Joint Aviation Authorities (JAA).

This book has been written and published to assist students enrolled in an approved JAA Air Transport Pilot Licence (ATPL) course in preparation for the JAA ATPL theoretical knowledge examinations. Nothing in the content of this book is to be interpreted as constituting instruction or advice relating to practical flying.

Whilst every effort has been made to ensure the accuracy of the information contained within this book, neither Jeppesen nor Atlantic Flight Training gives any warranty as to its accuracy or otherwise. Students preparing for the JAA ATPL theoretical knowledge examinations should not regard this book as a substitute for the JAA ATPL theoretical knowledge training syllabus published in the current edition of “JAR-FCL 1 Flight Crew Licensing (Aeroplanes)” (the Syllabus). The Syllabus constitutes the sole authoritative definition of the subject matter to be studied in a JAA ATPL theoretical knowledge training programme. No student should prepare for, or is entitled to enter himself/herself for, the JAA ATPL theoretical knowledge examinations without first being enrolled in a training school which has been granted approval by a JAA-authorised national aviation authority to deliver JAA ATPL training.

Contact Details: Sales and Service Department Jeppesen GmbH Frankfurter Strasse 233 63263 Neu-Isenburg Germany Tel: ++49 (0)6102 5070 E-mail: fra-services@jeppesen.com For further information on products and services from Jeppesen, visit our web site at: www.jeppesen.com

© Jeppesen Sanderson Inc., 2004 All Rights Reserved

JA310103-000 ISBN 0-88487-353-6 Printed in Germany

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PREFACE_______________________ As the world moves toward a single standard for international pilot licensing, many nations have adopted the syllabi and regulations of the “Joint Aviation Requirements-Flight Crew Licensing" (JAR-FCL), the licensing agency of the Joint Aviation Authorities (JAA). Though training and licensing requirements of individual national aviation authorities are similar in content and scope to the JAA curriculum, individuals who wish to train for JAA licences need access to study materials which have been specifically designed to meet the requirements of the JAA licensing system. The volumes in this series aim to cover the subject matter tested in the JAA ATPL ground examinations as set forth in the ATPL training syllabus, contained in the JAA publication, “JAR-FCL 1 (Aeroplanes)”. The JAA regulations specify that all those who wish to obtain a JAA ATPL must study with a flying training organisation (FTO) which has been granted approval by a JAA-authorised national aviation authority to deliver JAA ATPL training. While the formal responsibility to prepare you for both the skill tests and the ground examinations lies with the FTO, these Jeppesen manuals will provide a comprehensive and necessary background for your formal training. Jeppesen is acknowledged as the world's leading supplier of flight information services, and provides a full range of print and electronic flight information services, including navigation data, computerised flight planning, aviation software products, aviation weather services, maintenance information, and pilot training systems and supplies. Jeppesen counts among its customer base all US airlines and the majority of international airlines worldwide. It also serves the large general and business aviation markets. These manuals enable you to draw on Jeppesen’s vast experience as an acknowledged expert in the development and publication of pilot training materials. We at Jeppesen wish you success in your flying and training, and we are confident that your study of these manuals will be of great value in preparing for the JAA ATPL ground examinations. The next three pages contain a list and content description of all the volumes in the ATPL series.

iv

ATPL Series

Meteorology (JAR Ref 050)

• The Atmosphere • Air Masses and Fronts • Wind • Pressure System • Thermodynamics • Climatology • Clouds and Fog • Flight Hazards • Precipitation • Meteorological Information

General Navigation (JAR Ref 061)

• Basics of Navigation • Dead Reckoning Navigation • Magnetism • In-Flight Navigation • Compasses • Inertial Navigation Systems • Charts

Radio Navigation (JAR Ref 062)

• Radio Aids • Basic Radar Principles • Self-contained and • Area Navigation Systems External-Referenced • Basic Radio Propagation Theory

Navigation Systems

Airframes and Systems (JAR Ref 021 01)

• Fuselage • Hydraulics • Windows • Pneumatic Systems • Wings • Air Conditioning System • Stabilising Surfaces • Pressurisation • Landing Gear • De-Ice / Anti-Ice Systems • Flight Controls • Fuel Systems

Powerplant (JAR Ref 021 03) • Piston Engine • Engine Systems • Turbine Engine • Auxiliary Power Unit (APU) • Engine Construction

Electrics (JAR Ref 021 02)

• Direct Current • Generator / Alternator • Alternating Current • Semiconductors • Batteries • Circuits • Magnetism

v

Instrumentation (JAR Ref 022)

• Flight Instruments • Automatic Flight Control Systems • Warning and Recording Equipment • Powerplant and System Monitoring Instruments

Principles of Flight (JAR Ref 080)

• Laws and Definitions • Boundary Layer • Aerofoil Airflow • High Speed Flight • Aeroplane Airflow • Stability • Lift Coefficient • Flying Controls • Total Drag • Adverse Weather Conditions • Ground Effect • Propellers • Stall • Operating Limitations • CLMAX Augmentation • Flight Mechanics • Lift Coefficient and Speed

Performance (JAR Ref 032)

• Single-Engine Aeroplanes – Not certified under JAR/FAR 25 (Performance Class B) • Multi-Engine Aeroplanes – Not certified under JAR/FAR 25 (Performance Class B) • Aeroplanes certified under JAR/FAR 25 (Performance Class A)

Mass and Balance (JAR Ref 031)

• Definition and Terminology • Limits • Loading • Centre of Gravity

Flight Planning (JAR Ref 033)

• Flight Plan for Cross-Country • Meteorological Messages Flights • Point of Equal Time • ICAO ATC Flight Planning • Point of Safe Return • IFR (Airways) Flight Planning • Medium Range Jet Transport • Jeppesen Airway Manual Planning

Air Law (JAR Ref 010)

• International Agreements • Air Traffic Services and Organisations • Aerodromes • Annex 8 – Airworthiness of • Facilitation Aircraft • Search and Rescue • Annex 7 – Aircraft Nationality • Security and Registration Marks • Aircraft Accident Investigation • Annex 1 – Licensing • JAR-FCL • Rules of the Air • National Law • Procedures for Air Navigation

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Human Performance and Limitations (JAR Ref 040)

• Human Factors • Aviation Physiology and Health Maintenance • Aviation Psychology

Operational Procedures (JAR Ref 070)

• Operator • Low Visibility Operations • Air Operations Certificate • Special Operational Procedures • Flight Operations and Hazards • Aerodrome Operating Minima • Transoceanic and Polar Flight

Communications (JAR Ref 090)

• Definitions • Distress and Urgency • General Operation Procedures Procedures • Relevant Weather Information • Aerodrome Control • Communication Failure • Approach Control • VHF Propagation • Area Control • Allocation of Frequencies

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CHAPTER 1

Basic Radio Theory

Wave Motion .................................................................................................................................................1-1 Introduction ...................................................................................................................................................1-1 Electro-Magnetic Waves ...............................................................................................................................1-2 Properties of Radio Waves ...........................................................................................................................1-2 Refraction, Diffraction, and Reflection...........................................................................................................1-2 Relationship between Frequency, Wavelength, and Velocity .......................................................................1-3 Phase Difference ..........................................................................................................................................1-5 Radio Spectrum ............................................................................................................................................1-6 Wave Propagation ........................................................................................................................................1-7 Surface Wave ...............................................................................................................................................1-8 Type of Surface.............................................................................................................................................1-8 Sky Wave......................................................................................................................................................1-9 Critical Angle.................................................................................................................................................1-9 Dead Space ................................................................................................................................................1-10 The Ionosphere...........................................................................................................................................1-10 Frequency and Skip Distance .....................................................................................................................1-11 Ionisation and Skip Distance.......................................................................................................................1-11 Space Wave................................................................................................................................................1-11 Duct Propagation ........................................................................................................................................1-12 Aerials ........................................................................................................................................................1-13 Aerial Characteristics ..................................................................................................................................1-13 Aerial Length...............................................................................................................................................1-14 Polar Diagrams ...........................................................................................................................................1-14 Omni-Directional Aerials .............................................................................................................................1-14 Simple Half-Wave Dipole ............................................................................................................................1-14 Marconi Quarter Wave Aerial......................................................................................................................1-14 Aerial Feeders.............................................................................................................................................1-15 Aerial Directivity ..........................................................................................................................................1-15 Modulation ..................................................................................................................................................1-17 Keying.........................................................................................................................................................1-17 Amplitude Modulation (AM).........................................................................................................................1-19 Frequency Modulation (FM) ........................................................................................................................1-20 Pulse Modulation (PM)................................................................................................................................1-20 Classification of Emissions..........................................................................................................................1-21 Basic Radar Theory ....................................................................................................................................1-21 Radar Frequencies .....................................................................................................................................1-22 Principles ....................................................................................................................................................1-22 Pulse Radars ..............................................................................................................................................1-22 Radar Direction Finding ..............................................................................................................................1-23 Lobe Comparison........................................................................................................................................1-24 Beam Direction Finding...............................................................................................................................1-24 Radar Terminology .....................................................................................................................................1-24 Choice of Frequency...................................................................................................................................1-26

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CHAPTER 2

VHF Direction Finding

Introduction .................................................................................................................................................. 2-1 Principles of Operation................................................................................................................................. 2-1 Frequency .................................................................................................................................................... 2-1 Emission Characteristics.............................................................................................................................. 2-1 Operation ..................................................................................................................................................... 2-2 Services ....................................................................................................................................................... 2-2 Siting ............................................................................................................................................................ 2-2 Receiving a Bearing ..................................................................................................................................... 2-2 Asking For a Bearing.................................................................................................................................... 2-3 Position Fix .................................................................................................................................................. 2-3 VDF Approach.............................................................................................................................................. 2-3 Decoding the Chart ...................................................................................................................................... 2-5 Part 1 – Administration................................................................................................................................. 2-5 Part 2 – The Plan View ................................................................................................................................ 2-6 Part 3 – The Elevation View......................................................................................................................... 2-7 Refusal of Service ........................................................................................................................................ 2-7 Automatic VDF............................................................................................................................................. 2-7 Range and Errors......................................................................................................................................... 2-8

CHAPTER 3

Non-Directional Beacons and Automatic Direction Finding

Introduction .................................................................................................................................................. 3-1 Principles of Operation................................................................................................................................. 3-1 Frequency .................................................................................................................................................... 3-1 Emission Characteristics.............................................................................................................................. 3-1 Loop Theory................................................................................................................................................. 3-2 Sensing ........................................................................................................................................................ 3-3 NDB Operation............................................................................................................................................. 3-3 ADF Operation ............................................................................................................................................. 3-4 Bearing Determination ................................................................................................................................. 3-5 Types ........................................................................................................................................................... 3-5 Control Panels and Indicators ...................................................................................................................... 3-6 Control Panel ............................................................................................................................................... 3-6 TEST Switch ................................................................................................................................................ 3-7 Bearing Indicators ........................................................................................................................................ 3-7 Relative Bearing Indicator (RBI)................................................................................................................... 3-7 Radio Magnetic Indicator (RMI).................................................................................................................... 3-9 Direct Wave Limitations ............................................................................................................................... 3-9 Sky Wave Limitations................................................................................................................................. 3-10 Night Effect ................................................................................................................................................ 3-10 Errors of the ADF ....................................................................................................................................... 3-11 Quadrantal Error ........................................................................................................................................ 3-11 Dip (Bank) Error ......................................................................................................................................... 3-11 Coastal Refraction...................................................................................................................................... 3-12 Multipath Signals........................................................................................................................................ 3-12 Noise.......................................................................................................................................................... 3-13 Synchronous Transmission........................................................................................................................ 3-14 Promulgated Range ................................................................................................................................... 3-14 Absence of Failure Warning....................................................................................................................... 3-14 Accuracy .................................................................................................................................................... 3-14

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CHAPTER 4

NDB Navigation

Introduction ...................................................................................................................................................4-1 ADF Bearing .................................................................................................................................................4-1 Line of Position (LOP) Using the RBI............................................................................................................4-1 Line of Position (LOP) Using the RMI ...........................................................................................................4-2 Homing .........................................................................................................................................................4-2 Intercepting a Course....................................................................................................................................4-3 Inbound to the Beacon..................................................................................................................................4-4 Outbound From the Beacon..........................................................................................................................4-5 Tracking ........................................................................................................................................................4-7 NDB Approach ..............................................................................................................................................4-9 Part 1 Administration...................................................................................................................................4-10 Part 2 the Plan View ...................................................................................................................................4-11 Part 3 the Elevation View............................................................................................................................4-12 Part 4 Limits and Other Information ............................................................................................................4-12

CHAPTER 5

VHF Omnidirectional Radio Range (VOR)

Introduction ...................................................................................................................................................5-1 Principle of Operation ...................................................................................................................................5-1 Frequency.....................................................................................................................................................5-1 Polarisation ...................................................................................................................................................5-1 Emission Characteristics...............................................................................................................................5-1 Conventional VOR ........................................................................................................................................5-2 Reference Signal ..........................................................................................................................................5-2 Variable Signal..............................................................................................................................................5-2 Aircraft Receiver ...........................................................................................................................................5-2 Bearing Measurement...................................................................................................................................5-2 Aircraft Equipment ........................................................................................................................................5-3 Aerial.............................................................................................................................................................5-3 Receiver........................................................................................................................................................5-3 Frequency Selector.......................................................................................................................................5-3 Indicators ......................................................................................................................................................5-4 Monitoring .....................................................................................................................................................5-4 Terrain ..........................................................................................................................................................5-4 Designated Operational Coverage (DOC) ....................................................................................................5-4 Cone of Confusion or Cone of Silence..........................................................................................................5-5 Accuracy .......................................................................................................................................................5-5 Airway Navigation .........................................................................................................................................5-6 Test VOR ......................................................................................................................................................5-6 Doppler VOR.................................................................................................................................................5-6

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CHAPTER 6

VOR Navigation

Introduction .................................................................................................................................................. 6-1 Radio Magnetic Indicator ............................................................................................................................. 6-1 Omni-Bearing Selector................................................................................................................................. 6-2 Using the OBS ............................................................................................................................................. 6-4 Horizontal Situation Indicator (HSI) .............................................................................................................. 6-6 VOR Navigation ........................................................................................................................................... 6-8 Establishing Position .................................................................................................................................... 6-8 Tracking a Radial Inbound From a Present Position .................................................................................... 6-8 Intercepting a Radial .................................................................................................................................... 6-8 VOR Approaches ......................................................................................................................................... 6-9 Part 1 – Administration............................................................................................................................... 6-11 Part 2 – Plan View...................................................................................................................................... 6-11 Part 3 – Elevation View .............................................................................................................................. 6-12 Part 4 – Notes ............................................................................................................................................ 6-12

CHAPTER 7

Distance Measuring Equipment (DME)

Introduction .................................................................................................................................................. 7-1 Principle of Operation................................................................................................................................... 7-1 Frequency .................................................................................................................................................... 7-1 Emission Characteristics.............................................................................................................................. 7-1 Aircraft Equipment........................................................................................................................................ 7-2 Transponder................................................................................................................................................. 7-2 Frequency Allocation.................................................................................................................................... 7-2 Jittered PRF ................................................................................................................................................. 7-3 Reflected Transmissions.............................................................................................................................. 7-4 Memory ........................................................................................................................................................ 7-4 Beacon Saturation........................................................................................................................................ 7-4 Co-Location of Beacons............................................................................................................................... 7-5 Slant Range ................................................................................................................................................. 7-6 DME Navigation ........................................................................................................................................... 7-6 DME Procedures.......................................................................................................................................... 7-7 Slant Range ................................................................................................................................................. 7-7 Flight Overhead the DME............................................................................................................................. 7-8 Failure Indications ........................................................................................................................................ 7-8 Accuracy ...................................................................................................................................................... 7-8

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CHAPTER 8

Instrument Landing System (ILS)

Introduction ...................................................................................................................................................8-1 Principle of Operation ...................................................................................................................................8-1 Frequency.....................................................................................................................................................8-2 Emission Characteristics...............................................................................................................................8-2 Localiser........................................................................................................................................................8-2 Localiser Coverage .......................................................................................................................................8-4 Glidepath.......................................................................................................................................................8-5 Glidepath Coverage ......................................................................................................................................8-6 Airborne Equipment ......................................................................................................................................8-6 Frequency Pairing.........................................................................................................................................8-6 Localiser and Glidepath Receivers ...............................................................................................................8-7 ILS Indicator..................................................................................................................................................8-7 Horizontal Situation Indicator (HSI)...............................................................................................................8-8 ILS Accuracy.................................................................................................................................................8-9 False Beams ...............................................................................................................................................8-10 Localiser Back Beam ..................................................................................................................................8-10 ILS Performance Categories.......................................................................................................................8-13 ILS Operational Performance Categories ...................................................................................................8-13 Protection Range and Monitoring................................................................................................................8-14 Use of ILS ...................................................................................................................................................8-15 ILS Identification .........................................................................................................................................8-15 Flying the Localiser .....................................................................................................................................8-15 Flying the Glidepath ....................................................................................................................................8-15 ILS Without Glidepath .................................................................................................................................8-16 Distance Measuring Equipment ..................................................................................................................8-19 Rate of Descent (ROD)...............................................................................................................................8-19 Height Passing on the Approach.................................................................................................................8-19

CHAPTER 9

Marker Beacons

Introduction ...................................................................................................................................................9-1 Principle of Operation ...................................................................................................................................9-1 Frequency.....................................................................................................................................................9-1 Emission Characteristics...............................................................................................................................9-1 Airborne Equipment ......................................................................................................................................9-1 Airway Marker ...............................................................................................................................................9-3 Ground Installation........................................................................................................................................9-3

CHAPTER 10

Microwave Landing System

Introduction .................................................................................................................................................10-1 Principle of Operation .................................................................................................................................10-1 Frequency...................................................................................................................................................10-1 Polarisation .................................................................................................................................................10-1 Ground Installation......................................................................................................................................10-2 Azimuth Coverage ......................................................................................................................................10-2 Elevation Coverage.....................................................................................................................................10-3 DME/P ........................................................................................................................................................10-4 Back Azimuth ..............................................................................................................................................10-4 Signal Transmission Format .......................................................................................................................10-4 Time Reference Scanning Beam ................................................................................................................10-5 Angular Measurement in Azimuth and Elevation ........................................................................................10-5 Airborne Equipment ....................................................................................................................................10-6 Accuracy .....................................................................................................................................................10-6

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CHAPTER 11

Radar Principles and the Cathode Ray Tube

Pulse Techniques and Associated Terms .................................................................................................. 11-1 The Components of a Radar Unit............................................................................................................... 11-1 The Timebase ............................................................................................................................................ 11-2 The Display ................................................................................................................................................ 11-2 The Transmitter.......................................................................................................................................... 11-2 Choice of Frequency .................................................................................................................................. 11-2 The Aerial................................................................................................................................................... 11-4 Beamwidth ................................................................................................................................................. 11-4 The Receiver.............................................................................................................................................. 11-5 Timer – Cathode Ray Tube........................................................................................................................ 11-6 Cathode ..................................................................................................................................................... 11-6 Grid ............................................................................................................................................................ 11-6 Focussing Assembly .................................................................................................................................. 11-6 Electronic Beam Deflection ........................................................................................................................ 11-7 Screen ........................................................................................................................................................ 11-7 Time Base.................................................................................................................................................. 11-7 Saw Tooth Voltage..................................................................................................................................... 11-8 Radar Performance.................................................................................................................................... 11-8 Secondary Radar ....................................................................................................................................... 11-9

CHAPTER 12

Ground Radar

Introduction ................................................................................................................................................ 12-1 Long Range Surveillance Radar ................................................................................................................ 12-1 Terminal Surveillance Radar ...................................................................................................................... 12-2 Aerodrome Surveillance (Approach) Radar ............................................................................................... 12-2 Range, Accuracy, and Limitations of Surveillance Radar........................................................................... 12-3 Surveillance Radar Procedures.................................................................................................................. 12-3 Enroute ...................................................................................................................................................... 12-3 Approach.................................................................................................................................................... 12-3 Precision Approach Radar (PAR)............................................................................................................... 12-4 PAR Procedure .......................................................................................................................................... 12-5 Airfield Surface Movement Indicator (ASMI) .............................................................................................. 12-6 Weather Radar........................................................................................................................................... 12-7

CHAPTER 13

Secondary Surveillance Radar (SSR)

Introduction ................................................................................................................................................ 13-1 Principles of Operation............................................................................................................................... 13-1 Pulse Spacing ............................................................................................................................................ 13-2 Side Lobe Suppression .............................................................................................................................. 13-3 Operation ................................................................................................................................................... 13-5 SPI Code.................................................................................................................................................... 13-6 Use of Transponder ................................................................................................................................... 13-6 Presentation and Interpretation.................................................................................................................. 13-6 Limitations.................................................................................................................................................. 13-7 Fruiting ....................................................................................................................................................... 13-7 Garbling ..................................................................................................................................................... 13-7 Mode S....................................................................................................................................................... 13-8 Operation of Mode S .................................................................................................................................. 13-8 ATC Services ............................................................................................................................................. 13-9

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CHAPTER 14

Airborne Weather Radar (AWR)

Introduction .................................................................................................................................................14-1 Principle of Operation .................................................................................................................................14-1 Frequency...................................................................................................................................................14-1 Frequency Range .......................................................................................................................................14-1 AWR Aerial .................................................................................................................................................14-2 Control Panel ..............................................................................................................................................14-2 Power Switch and Timebase Range Switch................................................................................................14-2 Function Switch...........................................................................................................................................14-4 Weather Function (WEA) ............................................................................................................................14-4 Contour Function (CON) .............................................................................................................................14-4 Mapping Function (MAP) ............................................................................................................................14-5 Manual Function (MAN) ..............................................................................................................................14-6 Contrast ......................................................................................................................................................14-6 Manual Gain................................................................................................................................................14-6 Tilt Control...................................................................................................................................................14-6 Colour Displays...........................................................................................................................................14-7 Cloud Height Determination ........................................................................................................................14-8 Shadow.......................................................................................................................................................14-9 Test.............................................................................................................................................................14-9 Hold ............................................................................................................................................................14-9 Target Alert .................................................................................................................................................14-9 Use of the Radar on the Ground .................................................................................................................14-9

CHAPTER 15

Doppler

Introduction .................................................................................................................................................15-1 Frequency...................................................................................................................................................15-1 Doppler Effect .............................................................................................................................................15-1 Doppler Measurement of Groundspeed......................................................................................................15-3 Two Beam Janus Array...............................................................................................................................15-4 Further Janus Arrays ..................................................................................................................................15-5 Doppler Aerial .............................................................................................................................................15-6 Signal Characteristics .................................................................................................................................15-6 Output and Presentation .............................................................................................................................15-6 Accuracy and Limitations ............................................................................................................................15-8 Sea Bias......................................................................................................................................................15-8 Memory Mode .............................................................................................................................................15-8 Pitch and Roll Error.....................................................................................................................................15-8 Height Hole Error ........................................................................................................................................15-8 Sea Movement Error...................................................................................................................................15-9 Computational Errors ..................................................................................................................................15-9 Heading Error..............................................................................................................................................15-9 Summary of Errors......................................................................................................................................15-9 Advantages .................................................................................................................................................15-9 Disadvantages ..........................................................................................................................................15-10

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CHAPTER 16

Hyperbolic Navigation

Introduction ................................................................................................................................................ 16-1 Hyperbolic Family....................................................................................................................................... 16-1 Lines of Position (LOP) .............................................................................................................................. 16-4 Errors of Hyperbolic Navigation.................................................................................................................. 16-4 Propagation Errors ..................................................................................................................................... 16-4 Height Error................................................................................................................................................ 16-5 Simple Hyperbolic Calculation ................................................................................................................... 16-5

CHAPTER 17

LORAN C

Introduction ................................................................................................................................................ 17-1 Principle of Operation................................................................................................................................. 17-1 Frequency .................................................................................................................................................. 17-2 Typical LORAN C Chain ............................................................................................................................ 17-2 LORAN C Transmission............................................................................................................................. 17-2 Operation ................................................................................................................................................... 17-2 Coverage, Limitations, and Accuracy......................................................................................................... 17-5 LORAN C Coverage................................................................................................................................... 17-5 Sky Waves ................................................................................................................................................. 17-5 Static Disturbances .................................................................................................................................... 17-5 Radio Propagation Speed .......................................................................................................................... 17-5 Geometry of Crossing Angles .................................................................................................................... 17-6 Use of LORAN C........................................................................................................................................ 17-6 LORAN C Navigation ................................................................................................................................. 17-7 Transmitter Fault Indication........................................................................................................................ 17-7 Range and Accuracy.................................................................................................................................. 17-8 Accuracy Limits .......................................................................................................................................... 17-8

CHAPTER 18

Global Navigation Satellite Systems (GNSS)

Introduction ................................................................................................................................................ 18-1 System Capability ...................................................................................................................................... 18-1 Frequency .................................................................................................................................................. 18-2 Basic Principle of Operation....................................................................................................................... 18-2 The GPS System ....................................................................................................................................... 18-4 The Space Segment .................................................................................................................................. 18-4 GPS Timing................................................................................................................................................ 18-5 Frequency and Coding............................................................................................................................... 18-6 Navigation Message................................................................................................................................... 18-7 The Control Segment ................................................................................................................................. 18-8 The User Segment ..................................................................................................................................... 18-8 GPS Operating Principles .......................................................................................................................... 18-9 Pseudo Range ......................................................................................................................................... 18-10 Velocity Measurement.............................................................................................................................. 18-12 GPS Receiver .......................................................................................................................................... 18-13 System Limitations ................................................................................................................................... 18-14 Number of Users ...................................................................................................................................... 18-14 Coverage ................................................................................................................................................. 18-14 Reliability/Integrity .................................................................................................................................... 18-14 Receiver Autonomous Integrity Monitoring (RAIM) .................................................................................. 18-15 GPS Integrity Broadcast (GIB) ................................................................................................................. 18-15 Coverage Problems ................................................................................................................................. 18-15 Accuracy and Error Sources .................................................................................................................... 18-16 Accuracy for Civil Use .............................................................................................................................. 18-16

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User Equivalent Range Errors ..................................................................................................................18-16 Dilution of Precision (DOP) .......................................................................................................................18-17 Error Predictions .......................................................................................................................................18-17 Differential GPS (DGPS)...........................................................................................................................18-17 DGPS Principle of Operation ....................................................................................................................18-18 Summary of GPS Error Sources ...............................................................................................................18-18 Pseudolite/DGPS ......................................................................................................................................18-19 Satellite Based Augmentation Systems (SBAS) .......................................................................................18-20 RAIM in the Wide Area Augmentation System..........................................................................................18-22 GLONASS.................................................................................................................................................18-22 Basic concepts of the GLONASS system .................................................................................................18-22 Integrated Navigation Systems .................................................................................................................18-23 GNSS Applications ...................................................................................................................................18-24

CHAPTER 19

Area Navigation Systems

Introduction .................................................................................................................................................19-1 Area Navigation Concepts ..........................................................................................................................19-2 Accuracy of RNAV Equipment ....................................................................................................................19-3 Basic RNAV ................................................................................................................................................19-3 Use of Basic RNAV.....................................................................................................................................19-5 RNAV Limitations........................................................................................................................................19-7

CHAPTER 20

Introduction to the Flight Management System (FMS)

Introduction .................................................................................................................................................20-1 The Role of FMS.........................................................................................................................................20-1 Use of FMS.................................................................................................................................................20-3 Output Information ......................................................................................................................................20-5

CHAPTER 21

An Overview of CNS/ATM

Introduction .................................................................................................................................................21-1 Communications .........................................................................................................................................21-1 Air Traffic Management and FANS 1 ..........................................................................................................21-1 Controller/Pilot Data Link Communication (CPDLC) ...................................................................................21-2 Aeronautical Telecommunications Network (ATN)......................................................................................21-3 Navigation ...................................................................................................................................................21-3 Eurocontrol BRNAV and PRNAV................................................................................................................21-3 Required Navigation Performance (RNP) ...................................................................................................21-3 Terminal Area Initiatives .............................................................................................................................21-3 Surveillance ................................................................................................................................................21-4 Automatic Dependent Surveillance (ADS) ..................................................................................................21-4 Automatic Dependent Surveillance Broadcast (ADS-B)..............................................................................21-4 Mode S Data Link .......................................................................................................................................21-4

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CHAPTER 22

Electronic Display Systems

Glossary of Terms...................................................................................................................................... 22-1 Introduction ................................................................................................................................................ 22-1 General ...................................................................................................................................................... 22-2 General Certification Considerations.......................................................................................................... 22-2 Display Function Criticality ......................................................................................................................... 22-2 Loss of Display........................................................................................................................................... 22-2 Navigation Information ............................................................................................................................... 22-3 Propulsion System Parameter Displays ..................................................................................................... 22-3 Crew Alerting Display................................................................................................................................. 22-3 Flight Crew Procedures.............................................................................................................................. 22-3 Information Display .................................................................................................................................... 22-3 Information Display Colours ....................................................................................................................... 22-4

CHAPTER 23

Boeing 737 Electronic Flight Instrument System (EFIS)

Introduction ................................................................................................................................................ 23-1 System Architecture ................................................................................................................................... 23-1 EFIS Symbol Generator ............................................................................................................................. 23-2 EFIS Control Panel .................................................................................................................................... 23-3 EADI Controls ............................................................................................................................................ 23-4 EHSI Controls ............................................................................................................................................ 23-5 Electronic Attitude Direction Indicator ........................................................................................................ 23-6 EADI General ............................................................................................................................................. 23-6 Attitude Display .......................................................................................................................................... 23-7 Mode Annunciations................................................................................................................................... 23-7 Flight Director (F/D) Commands ................................................................................................................ 23-7 Glideslope (G/S) and Localiser ................................................................................................................. 23-7 (LOC) Deviation Displays........................................................................................................................... 23-7 ILS Deviation Warning ............................................................................................................................... 23-8 Rising Runway Symbol .............................................................................................................................. 23-8 Attitude Comparator ................................................................................................................................... 23-8 Digital Radio Altitude and Decision Height................................................................................................. 23-8 Mach Display.............................................................................................................................................. 23-9 Groundspeed Display................................................................................................................................. 23-9 Pitch Limit Symbol...................................................................................................................................... 23-9 Speed Tape Scale...................................................................................................................................... 23-9 Digital Airspeed Readout ........................................................................................................................... 23-9 Airspeed Trend Arrow .............................................................................................................................. 23-10 Command Speed ..................................................................................................................................... 23-10 Max Operating Speed (VMO/MMO or Gear/Flap Placards) ..................................................................... 23-10 High Speed Buffet Margin ........................................................................................................................ 23-10 Next Flap Placard Speed ......................................................................................................................... 23-10 Flaps Up Manoeuvring Speed.................................................................................................................. 23-10 V1 (Decision Speed) ................................................................................................................................. 23-10 VR (Rotation Speed)................................................................................................................................. 23-11 VREF (Reference Speed)........................................................................................................................... 23-11 Minimum Flap Retraction Speed.............................................................................................................. 23-11 Minimum Manoeuvring Speed.................................................................................................................. 23-11 Stick Shaker Speed.................................................................................................................................. 23-12 EADI Symbols .......................................................................................................................................... 23-12 Radio Altitude Dial.................................................................................................................................... 23-14 Speed Tapes............................................................................................................................................ 23-15 EFIS – EADI Fault Displays ..................................................................................................................... 23-20 EADI Failure Flags and Annunciations..................................................................................................... 23-20 EFIS Typical EHSI Centre Map, Map and Plan Displays ......................................................................... 23-21 EHSI Display Orientation ......................................................................................................................... 23-22 PLAN Mode.............................................................................................................................................. 23-22

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Features of PLAN Mode ...........................................................................................................................23-23 MAP and CTR MAP Modes ......................................................................................................................23-23 Features of MAP Mode .............................................................................................................................23-24 Features of CENTRE MAP Mode .............................................................................................................23-25 NAV Mode Displays ..................................................................................................................................23-25 Features of EXPANDED NAVIGATION Mode ..........................................................................................23-25 Features of FULL NAVIGATION Mode .....................................................................................................23-26 VOR and ILS Displays ..............................................................................................................................23-26 Expanded VOR Mode ...............................................................................................................................23-27 Full Rose VOR Mode ................................................................................................................................23-28 Expanded ILS Mode .................................................................................................................................23-29 Full Rose ILS Mode ..................................................................................................................................23-30 EHSI Symbology.......................................................................................................................................23-30 EHSI System Failure Flags and Annunciation ..........................................................................................23-39 Range Disagreement Annunciations.........................................................................................................23-39 Weather Annunciations.............................................................................................................................23-40 Instrument Transfer Switching ..................................................................................................................23-42 Light Sensing and Brightness Controls .....................................................................................................23-43

CHAPTER 24

Boeing 737 Flight Management Computer (FMC)

General .......................................................................................................................................................24-1 Operation Overview ....................................................................................................................................24-3 CDU Function .............................................................................................................................................24-4 CDU Page Display General ........................................................................................................................24-4 Function and Mode Keys ............................................................................................................................24-5 Line Select Keys .........................................................................................................................................24-5 Keyboard.....................................................................................................................................................24-6 CDU Page Display ......................................................................................................................................24-7 Page Status ................................................................................................................................................24-8 Function and Mode Keys ............................................................................................................................24-8 Lights ........................................................................................................................................................24-11 System Components.................................................................................................................................24-11 Databases.................................................................................................................................................24-12 Operation ..................................................................................................................................................24-13 Lateral Navigation .....................................................................................................................................24-14 Vertical Navigation ....................................................................................................................................24-14 Required Time of Arrival (RTA) Navigation ...............................................................................................24-15 Radio Tuning.............................................................................................................................................24-15 Electrical Power ........................................................................................................................................24-17 Terminology ..............................................................................................................................................24-17 Executing ..................................................................................................................................................24-17 Inactive .....................................................................................................................................................24-17 Active ........................................................................................................................................................24-17 Page Status ..............................................................................................................................................24-18 Modification...............................................................................................................................................24-18 Initialisation ...............................................................................................................................................24-18 Line Select ................................................................................................................................................24-18 Enter .........................................................................................................................................................24-18 Access ......................................................................................................................................................24-18 Propagate .................................................................................................................................................24-18 Page Concepts .........................................................................................................................................24-19 General .....................................................................................................................................................24-19 Page Sequence Logic...............................................................................................................................24-19 CDU Messages.........................................................................................................................................24-21 Waypoint ...................................................................................................................................................24-22 Waypoint Identifiers ..................................................................................................................................24-22 Created Waypoints ...................................................................................................................................24-22 Conditional Waypoints ..............................................................................................................................24-23

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CHAPTER 25

Boeing 737 Navigation Equipment and Flight Management

Inertial Reference System.......................................................................................................................... 25-1 IRS Mode Selector ..................................................................................................................................... 25-1 Align Light (White)...................................................................................................................................... 25-2 Fault Light (Amber) .................................................................................................................................... 25-2 On DC Light (Amber) ................................................................................................................................. 25-3 DC Fail Light (Amber) ................................................................................................................................ 25-3 Inertial Reference System.......................................................................................................................... 25-3 General ...................................................................................................................................................... 25-3 Alignment ................................................................................................................................................... 25-4 Alignment on the Ground ........................................................................................................................... 25-4 Fast Realignment on the Ground ............................................................................................................... 25-4 Loss of Alignment....................................................................................................................................... 25-4 IRS Display Unit ......................................................................................................................................... 25-5 Display Selector ......................................................................................................................................... 25-5 Brightness Control...................................................................................................................................... 25-6 Data Displays ............................................................................................................................................. 25-6 Enter Key ................................................................................................................................................... 25-6 Keyboard.................................................................................................................................................... 25-6 Instrument Transfer Switch/Instrument Transfer Switch Light.................................................................... 25-7 DME System .............................................................................................................................................. 25-7 Radio Distance Magnetic Indicator............................................................................................................. 25-8 VOR/ILS Navigation ................................................................................................................................... 25-9 Marker Beacon Switch ............................................................................................................................. 25-10 ADF Navigation ........................................................................................................................................ 25-10 SSR Transponder Selections................................................................................................................... 25-11 Weather Radar......................................................................................................................................... 25-13 Radio Altimeters....................................................................................................................................... 25-15

Radio Navigation 1-1

WAVE MOTION INTRODUCTION A wave is a progressive disturbance in a medium, formed by alternating pressures and tensions, without any permanent displacement of the medium itself in the direction in which these stresses are propagated. This condition is readily observed on the surface of a pond. Throwing a stone into the water produces a series of waves which radiate out until they reach the bank. A plastic duck in the pond rises and falls as the wave pass underneath, demonstrating that there is no movement in the direction of wave travel. While the wave moves toward the bank, the water does not. The wave possesses the following characteristics:

The form of the wave moves outward although the water itself does not. The wave possesses energy obtained from the stone. With the passage of the wave,

energy is lost due to friction. The wave becomes smaller as it moves away from the source.

The wave travels at a constant speed. The wave is sinusoidal; it travels as a sine wave.

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The radio wave is an alternating waveform and, as such, the following terms are used: Cycle — a complete sequence of positive and negative values (AB). Period — the duration of one cycle (T). In the figure above it is T = 1/100 seconds. Velocity — the speed and direction of movement through a given medium. Frequency — the number of complete waves passing a fixed point in one second, denoted by the symbol f and usually expressed as Hertz (Hz). Wavelength — the distance between similar points on successive waves, or the distance occupied by one complete cycle when traveling in free space (AB), and denoted by the symbol λ (Lambda). Amplitude — the maximum height of the wave. This can be positive or negative. The positive amplitude is represented by b.

ELECTRO-MAGNETIC WAVES The atmosphere carries light, heat, and radio waves. These waves differ only in their wavelength and the effects they have on different materials. Because of their electrical and magnetic nature, they are termed electro-magnetic. All of these waves travel at the same velocity, denoted by the letter c. For the Radio Navigation syllabus, this velocity is:

300 000 000 m/sec or 162 000 nm/sec For simplicity, the speed of light in m/sec can expressed as 300 X 106 m/sec

PROPERTIES OF RADIO WAVES Radio waves leaving a transmitter have the following properties:

They consist of oscillating electric and magnetic fields that are at right angles to each other and at right angles to the direction of propagation.

They require no supporting medium. They can be reflected, refracted, and diffracted as discussed below. They are subject to interference and Doppler effect. They can pass through an opaque object such as a building, although they do suffer

attenuation in doing so.

Attenuation of an RF signal is the reduction in signal strength due to absorption, scattering, or dispersion and diffraction. REFRACTION, DIFFRACTION, AND REFLECTION All radio waves are subject to refraction, diffraction, and reflection, and even combinations of these phenomena. Refraction occurs when the speed of the radio wave is affected differently on either side of the centreline of the ray. This causes a difference in the propagation speed either side of the centreline that bends the wave. The most common cause of refraction is when the wave travels obliquely through mediums that have differing effects on the speed of propagation.

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Diffraction occurs principally when a radio wave travels close to the Earth’s surface. The wave travelling over the Earth’s surface induces a micro-voltage into the Earth, during which the wave tends to attach itself to the Earth. As this induction takes place, the signal is attenuated and slowed, causing the wave to bend and follow the Earth’s curvature. Some surfaces exhibit reflective properties to radio energy, accepting the incoming signal and then re-radiating it. Where a reflected signal is at a small angle to the direct line between transmitter and receiver, the energy lost is minimal and can combine with the direct signal at a different phase, causing significant interference at the receiver. RELATIONSHIP BETWEEN FREQUENCY, WAVELENGTH, AND VELOCITY The frequency of a sinusoidal wave is the number of cycles occurring in one second. The JAR exam requires conversion of frequency to wavelength and vice versa. Frequency uses the symbol f and the unit is the Hertz. Wavelength is λ and the unit used is metres.

c=f λ Because of the large figures used in frequency, the following prefixes are used:

Prefix Magnitude

Kilo Mega Giga

103 106 109

Example 1000 Hertz = 1 Kilohertz = 1 kHz 1 000 000 Hz = 1 MHz 1 000 000 000 Hz = 1 GHz

Likewise, radio wavelength units can be small, so the following prefixes are used:

Prefix Magnitude Milli

Micro or µ Nano

10-3 10-6 10-9

Example: Convert 2 MHz to a wavelength

λ = c = 300 x 106 = 150 metres f 2 x 106

Example: Convert 60 metres to a frequency

f = c = 300 x 106 = 5 MHz λ 60

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Remember: The higher the frequency, the shorter the wavelength and vice versa. Examples: Convert the following wavelengths into the corresponding frequencies

(The answers are given below):

1. 1500 m 2. 20 cm 3. 3500 m

Convert the following frequencies into the corresponding wavelength:

1. 300 kHz 2. 75 MHz 3. 600 MHz 4. 8800 MHz 5. How many wavelengths, to the nearest whole number, of frequency 200 MHz are

equivalent to 35 ft? Answers: Wavelength to Frequency

1. 200 kHz 2. 1500 MHz 3. 85.7 kHz

Frequency to Wavelength

1. 1000 m 2. 4 m 3. 50 cm 4. 3.41 cm

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5. Number of wavelengths in 35 ft for a frequency of 200 MHz λ = c = 300 x 106 = 1.50 metres

f 200 x 106

1 m is equivalent to 3.28 ft

1.5 m = 4.92 ft

The number of wavelengths in 35 ft = 35 4.92

which is approximately 7.

PHASE DIFFERENCE In the diagram below the two waves are said to be in phase. The waves pass the same point of their cycle at the same time.

In the diagram below the waves are said to 90° out of phase:

Wave B leads wave A by 90°, or Wave A lags wave B by 90°

A B

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Where two waves have a phase difference of 180°, then they are said to be in anti-phase.

RADIO SPECTRUM The diagram below shows the electromagnetic spectrum. Frequency determines the different effects brought about by electro-magnetic waves. The lower limit is determined by the size and efficiency of the aerials required and the upper limit by the attenuation and absorption of the radio waves by the atmosphere.

RadioWaves

GammaRays

CosmicRays

UltraVioletInfra Red X-Rays

LIGHT

3 KHz 300 GHz

Wavelength

The part of the frequency spectrum of interest to the pilot is further sub-divided below.

VLF LF MF HF VHF UHF SHF EHF

3 30 300 3 30 300 3 30 300

kHz MHz GHz

Radio Spectrum

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WAVE PROPAGATION There are three principle paths that radio waves may follow between the transmitter and the receiver:

Surface Waves follow the contours of the Earth’s surface. Sky Waves are refracted by the ionosphere and returned to Earth. Space Waves are line of sight.

A combination of a surface and a space wave is called a ground wave. The radio energy reaching a receiver may be made up of components of any one or more of these mechanisms but depending on the part of the radio spectrum concerned, one of the three predominates. In general:

Low frequencies are propagated by surface wave. Middle range frequencies are propagated by sky wave. Upper range frequencies are propagated by space wave.

Surface

Wave

Sky

Space

Wave

Ionosphere

Wave

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SURFACE WAVE The surface wave follows the curvature of the Earth, a process known as diffraction. The Earth’s attenuation of the radio energy helps the process. The wave is slowed as it touches the Earth’s surface. As a result, the wave front nearest the surface lags behind the wave farther from the surface.

The wave front tilts and diffractive bending occurs. The stability of this type of propagation makes the low frequency surface wave suited to systems requiring consistency of signal over long distances. The propagation does require large aerials and the cost of transmission can be considerable. TYPE OF SURFACE High conductivity favours the passage of a radio signal. Therefore, passage over the sea is better than over rock or desert.

Transmitter Power Surface absorption and free space loss reduce the signal strength of a radio wave. If there is no restriction in the available transmitter power, then global ranges can be achieved by VLF radio waves. Different types of surfaces will affect the transmission of a ground wave differently, but all power to range ratios follow a square law rule. The basic rule of thumb formula to calculate required transmitter power from a given range is: 3√P (in watts) for transmission over water and 2√P (in watts) for transmission over land. In both cases note that to double the range, the power must increase by a factor of 4.

Wave front falls toward the Earth as it progresses

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Noise and Interference Noise affects the lower frequencies, consequently affecting the signal/noise ratio. This can limit the usable range.

For maximum ground wave range:

Use low frequency for maximum diffraction and least attenuation. Use vertical polarisation (see polarisation).

SKY WAVE The sky wave ascends into the upper atmosphere and encounters a region containing electrically charged particles (the ionosphere) where it is refracted sufficiently to return to Earth.

β Is the Critical Angle. Note that it is measured from the vertical down.

When the wave enters the ionosphere it changes direction due to a change in velocity. If the wave penetrates halfway through the layer before being bent parallel to the layer it will bend back in the opposite direction to emerge from the top of the layer as an escape ray. This is likely if:

The ionisation is insufficiently intense The frequency is too high The angle of entry is too acute

CRITICAL ANGLE For a particular frequency and degree of ionisation, it is possible to define a critical angle below which total refraction does not take place. Defining the critical angle also establishes the minimum range or the skip distance. Any ray travelling away from the aerial at greater than the critical angle will be freely refracted down to about 5° above the horizon.

β

Dead Space

Ground Wave

Skip Distance

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400 km 200 km 100 km

F2 F1 E D

Day Night

DEAD SPACE Because of the high frequencies used in sky wave transmission, the ground wave travel is not as far as the returning sky wave. The distance between the limit of the ground wave and the first returning sky wave is the dead space. THE IONOSPHERE The ionosphere consists of a series of conducting layers between heights of 50 and 400 km. It exists because of the transmission of ultra-violet radiation from the sun. Because of this dependence upon radiation from the sun, the heights and densities of the layers vary according to the time of day and season of the year. There is also a connection between the 11-year sunspot cycle. Short-term effects occur in a random fashion resulting in the ionised layers being in a state of constant turbulence. Three main layers have been identified, designated as D, E, and F. The F layer splits into two separate layers during the day, the time of highest ionisation. The D layer is a region of low ionisation that only persists during the day. The E layer is more marked and remains weakly ionised by night with little change in height. The F layer is the most strongly ionised and has the greatest diurnal change in height.

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FREQUENCY AND SKIP DISTANCE At a fixed level of ionisation, an increase in frequency will cause the ray, previously the critical ray, to become an escape ray. This causes an increase in skip distance. IONISATION AND SKIP DISTANCE At a fixed frequency, if ionisation decreases, the effect is the same as above. The critical ray becomes an escape ray. This causes an increase in skip distance. SPACE WAVE Transmissions at VHF and above cannot propagate by either surface or sky wave. Attenuation is so severe that the surface wave is virtually non-existent. These frequencies are too high to be refracted by the ionised layers aloft. As a result, transmission is by straight line, or the direct wave. In addition to the direct wave, a reflected wave can also exist. The two components make up the space wave.

Because of the different emission paths, the direct and reflected wave is sometimes in phase and sometimes out of phase. This produces lobes and nulls particularly when the receiver is close to the station.

The range of a space wave appears to be line of sight. In practice it is termed quasi-optical:

The lower atmosphere causes some refraction of the wave, which bends it beyond the optical horizon.

A further small increase is gained from diffraction when the wave becomes tangential to the Earth’s surface

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This range can be approximated by the following formula:

R = 1.25(√HT + √HR)

Where: R Range in nautical miles HT Height of the transmitter in feet HR Height of the receiver in feet

Example: An aircraft flying at 10 000 ft receives a transmission from a station at 400 ft. What is the maximum distance communications can occur between the two stations?

R = 1.25(√10 000 + √400) R = 1.25(100 + 20) R = 150 nm DUCT PROPAGATION Under certain abnormal climatic conditions, transmissions on a frequency greater than 50 MHz can be received at ranges in excess of the quasi-optical expected.

PRESSURE900mb920mb945mb

TEMPERATURE+7.1+7.5-3.5

DEW POINT-40.0-28.0-3.9

MODIFIED REFRACTIVE INDEX250.8257.3295.8

25 JANUARY 1989 - 0001 GMT. ST. HUBERT, BELGIUM

VERY DRY AND RELATIVELY WARM

COOL AND MOISTLOW CLOUDS TRAPPED BELOW INVERSION

INVERSION BASE

SUBSIDINGAIR

+7°

-3°

-40°

AIR TEMPERATURE

DEW POINT TEMPERATURE

The conditions that cause this abnormal propagation are a temperature inversion and a rapid decrease in humidity with height (steep humidity lapse rate). This forms a duct between the Earth and a few hundred feet above the surface. Radio waves have a wavelength that is small compared with the duct height. This allows the duct to refract the wave back to Earth. The Earth’s surface then reflects the wave back to the duct ceiling. A series of these refraction/reflection hops occur and thus the wave can be received well in excess of the quasi-optical range. The same conditions can occur when there is an inversion aloft.

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These conditions are normally associated with large high-pressure systems, a condition that is a regular feature in the tropics. AERIALS A transmitter/receiver is only as good as the aerial. An aerial is a device used for the efficient transmission and reception of electromagnetic energy. Generally, aerials that radiate are looked at; however, the properties of a transmitting aerial apply equally to the receiving aerial. AERIAL CHARACTERISTICS When an aerial radiates an electro-magnetic wave it transmits two radio frequency fields:

The E Field is the electric or electrostatic field. The H Field is the magnetic field.

These fields transmit at right angles to each other.

Note: The H field is always at right angles to the aerial and the E field is always parallel to the plane of the aerial. By convention, the wave is said to be vertically polarised if the E Field is perpendicular to the Earth and horizontally polarised if parallel to it. A vertical aerial produces a vertically polarised wave, and conversely, a horizontal aerial produces a horizontally polarised wave.

TRANSMITTER

TRANSMITTER

ELEVATED DUCT

SURFACE DUCT

EARTH

LAYER OF HIGHDIELECTRIC CONSTANT

LAYER OF HIGHHUMIDITY

LAPSE RATE ANDTEMPERATURE

INVERSION

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A standard dipole receiver aerial must be aligned in the same polarity as the signal to be received for maximum transfer of energy. For instance, a transmitted signal from a horizontal aerial needs to be received by an aerial that is itself horizontal for optimum reception. AERIAL LENGTH The aerial is manufactured to a specific length dependent on the frequency to be used. POLAR DIAGRAMS The effective radiation or reception of an aerial is shown by a polar diagram. These can be oriented to show the pattern as horizontal (looking down on the aerial from above) or vertical (looking at the aerial from the side). OMNI-DIRECTIONAL AERIALS SIMPLE HALF-WAVE DIPOLE In its simplest form, a dipole consists of a metal rod or a wire cut to a specified length. The aerial is cut to a half wave-length. Example For a frequency of 30 MHz λ = 10 m

The aerial for this wavelength is λ /2 or 5 m.

This is called the Electrical Length. In an ideal world, the Electrical Length would be the length of aerial required for a given frequency. The speed of electro-magnetic radiation through a vacuum is constant. When an aerial feeder is used, the speed of the radiation is slower. This slower speed is approximately 5% less than the in-vacuo speed and we must consider this by factoring the Electrical Length to 95% of its value. This is the Physical Length of the aerial for a given frequency.

Example For a frequency of 100 MHz λ = 3 m

Electrical Length of the aerial = λ /2 = 150 cm Physical Length = 95% of λ /2 = 142.5 cm

MARCONI QUARTER WAVE AERIAL Most practical aerials are cut to one quarter of the wavelength (λ /4). By using the reflective properties of electro-magnetic waves, the aerial compensates for the missing half of the dipole.

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The Marconi aerial is particularly suitable for fitting into aircraft structures. To ensure that the aerial can be used over a range of frequencies, an aerial loading unit (ALU) is fitted. This unit electronically matches the aerial to the frequency selected. AERIAL FEEDERS There must be a connection between the transmitter/receiver and the aerial; this is a feeder. The type of feeder depends upon the frequency to be used. The most common feeder in use in aircraft communications is the co-axial cable (better known as the TV aerial wire). Higher frequencies require a more sophisticated feeder, for example, radar requires a wave guide. AERIAL DIRECTIVITY The dipole radiates power evenly in all directions or omnidirectionally. The plan and side views show the radiating pattern.

Plan View

AERIAL

AERIAL

Side View Note: The radiating polar diagram is from the centre of the aerial not the tip. To modify the omni-directional properties and give the aerial directivity requires adding parasitic elements. The most common directional aerial in everyday use is the TV antenna, or the Yagi. The directional properties are derived by adding parasitic elements in front and behind the dipole.

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To change the omni-directional properties, a parasitic reflector 5% larger than the dipole is placed at a distance of λ /4 from the dipole. The normally circular polar diagram now changes into an elongated heart shape with the reflector reflecting the power back toward the aerial. Note that the dipole is the only part of the aerial that has any power.

To enhance the directional properties, parasitic directors are added on the opposite side to the parasitic reflector. These elements are 5% shorter than the dipole.

The resulting polar diagram is narrow in beam width and gives excellent directional properties. One disadvantage is the production of unwanted side lobes. The side lobes are approximately 50% of the power of the main beam and can give spurious indications if not dealt with. Methods of suppression or removal of the side lobes are discussed in individual chapters on equipment.

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Side Lobes

Different polar diagrams can be achieved for different aerial combinations. An example of this is the figure of eight produced by two dipoles.

The significance of changing the polar diagram becomes apparent upon discussing each piece of equipment in detail.

MODULATION Modulation is the superimposing of intelligence, such as speech or Morse identification, onto a carrier wave. Varying a parameter of the carrier, such as its amplitude or frequency does this. When electro-magnetic energy is radiated as a sinusoidal wave, it transmits no intelligence. The frequency is beyond the scope of human hearing and the wave itself would be meaningless. KEYING Interrupting the wave, a process known as keying, makes it possible to transmit Morse code.

OFF

DOT DOTDASH

OFF OFFON ON ONTransmitter

The signal may be identifiable as Morse code, but it is still outside the audible range. Converting the carrier frequency into a signal within the audio range helps with audible reception.

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Mixing the received frequency with another known radio frequency produces a signal in the audio range. The mixing of two radio frequencies, known as heterodyning rather than modulation, is the mixing of a radio frequency and an audio frequency.

Example: Received frequency 500 kHz Known frequency 501 kHz

Produces four frequencies:

500 kHz} 501 kHz} outside the audible range 1001 kHz} 1 kHz} an audible frequency

Selecting the BFO function (Beat Frequency Oscillator) enables heterodyning. The incoming signal is received and mixed with the BFO frequency and the resulting audio frequency is fed to the intercom system. As a result, an audio tone is only heard when the two frequencies are present.

Detector

500 kHz

500 kHz501 kHz1001 kHz1 kHz

On

Off

BeatFrequencyOscillator(BFO)

501 kHz Note: The only piece of equipment that uses a BFO in the aircraft is the ADF. Normally, electromagnetic radiation is modulated by one of the three methods listed below:

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AMPLITUDE MODULATION (AM) AM is where the modulating frequency alters the amplitude of the wave.

Amp

Audio Note

UnmodifiedTransmitterOutput

AmplitudeModitiedOutput

Time ModulatingWaveform

CarrierWave

AmplitudeModulatedCarrier Wave

Where a carrier is amplitude-modulated by a single tone, the resultant waveform consists of three components:

The carrier wave fc The upper sideband (fc + fs) The lower sideband (fc - fs), where fs is the modulating signal

The AM signal consists of:

1 500 kHz the carrier 2. 501 kHz the upper sideband 3. 499 kHz the lower sideband

Both sidebands carry intelligence. The spread of the side frequencies is known as the bandwidth. For an amplitude modulated signal the bandwidth is 2 fs. Both sidebands carry the same information. If one of the bands is suppressed (e.g. the upper sideband) then the only frequencies that need transmitting are 500 kHz and 499 kHz. This type of transmission has two main advantages:

It requires less power to transmit one sideband and the carrier. The signal occupies less of the radio spectrum, meaning that the frequency band can

be used more efficiently. HF transmissions make use of the single sideband transmission.

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FREQUENCY MODULATION (FM) FM is where the modulating frequency alters the frequency of the wave.

The frequency of the carrier varies by an amount proportional to the instantaneous amplitude of the modulating signal. The rate of change of the carrier frequency is proportional to the frequency of the modulating signal with the amplitude of the modulated carrier remaining constant throughout. FM signals are relatively noise free. Unfortunately, this type of broadcast uses a much wider bandwidth than AM, so FM has limited application in commercial aviation. FM is used in:

VOR Radio Altimeters Doppler

PULSE MODULATION (PM) PM is where the carrier is transmitted in short pulses. These pulses can be coded to carry information. Two types of PM need consideration:

Pulse Amplitude Modulation (PAM) In a manner similar to AM, it is possible for an audio waveform to modify the amplitude of a fixed train of pulses.

Pulse Code Modulation (PCM) PCM is a system where each pulse amplitude is assigned a binary number.

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CLASSIFICATION OF EMISSIONS Radio regulatory agencies have designed a coding system that fully describes the form that a radio transmission may take. The table below details the coding system.

First Character Type of Modulation

Second Character Nature of the Modulating

Signal

Third Character Type of Information Being

Transmitted N – Unmodulated carrier 0 – No modulation N – No information

transmitted A – Amplitude 1 – Interrupted carrier A – Telegraphy – for aural

reception J – Single sideband (no carrier)

2 – Keyed or digital audio modulation

E – Telephony – including sound broadcasting

F – Frequency 3 – Telephony (voice or music)

W – Combination of the above

P – Unmodulated pulses 8 – Two or more channels of analogue information

X – Cases not otherwise covered

9 – Composite systems comprising of 1 & 2 above with 3 or 8

X – Cases not otherwise covered

The emission characteristics pilots need to know for civil aviation use are: ADF N0N A1A N0N A2A HF J3E VHF A3E VDF A3E ILS A8W VOR A9W DME P0N

BASIC RADAR THEORY INTRODUCTION Radar is derived from the expression radio detection and ranging. It may be defined as any system employing radio to detect the presence of objects and to determine their position and movement.

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RADAR FREQUENCIES Radar occupies the frequency bands from VHF upward. Higher frequencies are used because:

They are free from external noise. Narrow beams operate more efficiently with a short wavelength. Primary radar uses pulses, and higher frequencies can utilise shorter pulses. The efficiency of reflection depends upon the size of the target in relation to

wavelength. High frequencies are reflected more efficiently. PRINCIPLES A transmitter sends out, via the aerial, a brief pulse of radio energy. Every 6.2 microseconds (µs) this pulse travels 1 nautical mile. If this pulse strikes a target, a small proportion of the radio energy reflects back to the aerial. The aerial picks up this reflected energy and passes it to the receiver. By measuring the time of travel, the range can be calculated.

Transmitter Receiver

Tx pulses

Echo pulses

PULSE RADARS Pulse radars are employed as:

Primary radars - ATC surveillance radars, airborne weather radars Secondary radars - DME and SSR Doppler

The radar transmits energy in very short bursts of high energy. Timing the pulse yields a direct measurement of the range and requires a sensitive receiver. The transmission, travel, and reception of the pulse must occur before the next pulse is transmitted. This ensures having an unambiguous target.

Primary Radar Primary radar relies on the weak reflections from a passive target. The effectiveness of the radar depends upon the transmitter power and the receiver sensitivity.

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Because primary radar transmits a pulse and receives an echo, range is affected by propagation outbound and inbound, both of which are subject to the range/power formula discussed earlier under Type of Surface/Transmitter power. Therefore, to double the range of a primary radar the transmitter power must be increased by a factor of 16. Secondary Radar Secondary radar relies on the target co-operating with the transmitter. The target transmits a reply signal to an interrogatory signal such as in SSR and DME. The interrogation and reply are usually on different frequencies.

Secondary radar has both advantages and disadvantages over primary radar:

Advantages

Primary radars require much more power to achieve the same range. Target size and aspect are irrelevant because the target transmits the response. Responses on the secondary radar are much more reliable. Information can be encoded to give the transmitter and receiver information. Clutter on the radar screen can be eliminated.

Disadvantages

The radar requires the co-operation of the target. Bearing resolution can be inferior. Side lobes can be a problem at short range. Beacon saturation can be a problem.

RADAR DIRECTION FINDING There are two principle means of radar direction finding:

Lobe Comparison Beam Direction Finding

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LOBE COMPARISON Mainly used by secondary radars two aerials are used to define direction. The aerials are rotated until an equal strength signal is received.

BEAM DIRECTION FINDING By using a parabolic aerial, a near parallel beam can be achieved. Because the direction of the aerial is known and the pulse is transmitted and received before the next pulse is transmitted, the azimuth of the target can be calculated.

The beamwidth of a parabolic aerial can be calculated by the formula:

Beamwidth = 70λ/d Where: λ = wavelength of the radar d = diameter of the parabolic aerial Remember with this calculation that λ and d must be in the same units.

RADAR TERMINOLOGY Certain terms used in radar need to be understood.

Pulse Recurrence Frequency (PRF) The radar transmits pulses at this rate. The unit of measurement is pulses per second (pps). The fact that each pulse must be able to reach the most distant target and return before transmission of the next pulse determines the maximum PRF. Otherwise there is a possibility of ambiguous range measurement.

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Pulse Recurrence Interval (PRI) PRI is the time interval between pulses with the unit of measurement normally being microseconds. The PRI determines the maximum range of the radar. The relationship between PRI and PRF is simple.

PRI = 1 ÷ PRF

Example: For a radar with a PRF of 250 pps, find the maximum range: PRI = 1/PRF = 1/250 = 0.004 seconds 0.004 seconds = 4000 µs

4000 µs = 4000 X 10-6 seconds (To convert seconds into microseconds multiply by 1 000 000) Distance = speed X time The total time of travel out and back for the pulse is 4000 µs The time of travel one way, to calculate the range = 2000 µs or 2000 X 10-6 seconds Distance = (2000 X 10-6) seconds X (300 X 106) m/second Distance = 600 000 metres = 600 kilometres This is the maximum unambiguous range of the radar.

Pulse Width (PW) PW is the duration of the pulse. This determines the minimum range of a radar. The pulse must travel half its distance before it hits a target and returns to the radar. Otherwise, the radar will still be transmitting the same pulse when the reflected signal returns.

Example: What is the minimum range of a radar with a PW of 2 µs?

The minimum range must be half the time of travel, or 1 µs. Distance = speed X time = (1 X 10-6) seconds X (300 X 106) metres per second Distance = 300 metres

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Radio Navigation 1-26

CHOICE OF FREQUENCY To produce a narrow beam, a high frequency must be used. The advantages of using a narrow beam are obvious:

Bearing accuracy is greater. There is an increase in effective power. The radar is able to resolve closely spaced targets. High frequencies also generate a more square pulse shape. Wavelength must be shorter than the target size.

All of the above must be taken into consideration.

Basic Radio Theory Chapter 1

Radio Navigation 1-27

The basic radar has seven elements:

Master Timer This is the trigger unit and has two functions:

It generates the basic PRF. It synchronises the firing of the transmitter.

Modulator The output from the modulator switches the transmitter on and off controlling the pulse length of the transmitter output. Transmitter This delivers the pulse to the aerial. Receiver This is a sensitive superhet that can amplify the very weak returning echoes. These are then processed for display. T/R switch The same aerial is used for both transmission and reception. The receiver must be protected from the high power transmitter. This is accomplished by electronically isolating the waveguides for both. A duplexer performs this isolation. In real terms, it is the brains of the radar. Indicator Radar information is usually displayed on a Cathode Ray Tube. Aerial This is a parabolic dish on older aerials. Now a flat bed array electronically simulates a parabolic dish.

Chapter 1 Basic Radio Theory

Radio Navigation 1-28

Radio Navigation 2-1

INTRODUCTION Certain aerodromes have VHF Direction Finding (VDF) equipment. VDF provides an ATC Controller with the means of determining the direction of the VHF signal from an aircraft. The only onboard equipment required to obtain this service is a standard aircraft VHF radio. This is one of the main advantages of the VDF service.

PRINCIPLES OF OPERATION The basic VDF uses a phased array system based on the Doppler Principle. The modern VDF aerial is shown below.

Frequency VHF – 118 to 137 MHz Emission Characteristics A3E

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OPERATION If the communications transmitter on an aircraft is tuned to the VDF frequency and the transmitter activated, the aerials at the VDF unit detect the incoming transmission and each aerial element feeds a signal to the VDF receiver.

The aerial elements are all at slightly different distances from the source of the signal. Each detects a slightly different phase of the signal from the aircraft at the same

moment in time. The value of these detected phase differences directly relate to the direction of the

incoming signal. The phase differences are used to drive the bearing indicator.

On some VDF units a simple digital read-out gives the bearing. The ground VDF station can give true or magnetic bearings.

SERVICES It is common to use the Q codes to represent the bearings from a VDF station. The codes originate from the days of telegraphy where it was convenient to transmit short codes instead of full text messages. The Q codes are not abbreviations.

Listed below are the codes that are relevant to direction finding:

QTE: True track from the station QDR: Magnetic bearing from the station QUJ: True track to the station QDM: Magnetic bearing to the station QGH: DF controlled approach QDL: DF steer

In practice, only QDM and QDR are normally used.

The accuracy of the bearing is measured in degrees. Accuracy is classified in accordance with the ICAO defined classifications:

Class A accurate within ± 2° Class B accurate within ± 5° Class C accurate within ± 10° Class D accuracy less than Class C

SITING Due to topography, some VDF stations are approved for use only within certain sectors. Specific information for an aerodrome is given in the AIP. Generally, the class of bearing is no worse than class B (many states will not permit Class C & D bearings to be provided). Do not use ground VDF stations as enroute navigation aids, as they do not provide the aircraft with continuous tracking information. However, in case of emergency, or where other essential navigation aids fail, their service is available. When flying VFR under marginal weather conditions, a VDF station is a useful navigation tool for any pilot.

RECEIVING A BEARING To request a bearing or a heading to steer, the pilot should call the aeronautical station on the listed frequency. The pilot should then specify the type of service desired by using the appropriate Q code.

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Radio Navigation 2-3

Automatic VDF stations only require a short transmission, while older manual stations may require a short preparatory period before being able to provide the service. After requesting the bearing or heading to steer, the VDF station advises the aircraft station the following way:

The appropriate Q code The bearing or heading to steer The class of bearing and time of observation (if necessary)

The pilot will read back the bearing or heading to steer immediately upon receiving the message. ASKING FOR A BEARING Assume that the pilot of an aircraft G-BOBA needs to confirm its position.

Aircraft Cranfield Tower, G-BOBA, request QDM Tower G-BOBA, QDM 180°, Class B Aircraft QDM 180°, G-BOBA

Initially the pilot asks for the magnetic bearing from the aircraft to the airport (QDM). To home to Cranfield, the pilot should fly a magnetic heading of 180°. Remember that the bearing applies to a still air condition. If there is any wind, the initial QDM must be corrected for drift. Note that a QDM only provides a line of position, not a fix position. POSITION FIX When a position fix is necessary, the request must be made to a station with the capability for triangulation, such as the Distress and Diversion Cell on the international emergency frequency of 121.5. A bearing derived from one station is a line of position (LOP), while two LOPs are necessary to get a position fix. VDF APPROACH The pilot may request a QGH procedure provided one is listed for the airfield. This is a procedure in which the controller provides the pilot with a series of QDMs so that the pilot can follow a laid down approach path. This approach path involves a number of steps described in the appropriate approach chart, and are summarised as follows:

Guiding the pilot into a position over the airfield Establishing the pilot on an outbound leg (about 20° off the reciprocal of the desired

final approach path). This path is flown at a safe level above the airfield and the surrounding obstructions. The pilot times the outbound leg (allowing for wind effect and using the distances

given in the approach plate) and, using the QDM information supplied, establishes the drift being experienced.

At the end of the appropriate time, the pilot carries out a rate one turn to intercept the inbound final approach path.

On intercepting the final approach, the course is maintained by using the drift established outbound (with the sign changed) as an inbound wind correction angle. This can be adjusted as the controller provides new QDM information.

At the prescribed time, the let-down commences.

On the next page is an example VDF chart for Cranfield.

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VHF Direction Finding Chapter 2

Radio Navigation 2-5

DECODING THE CHART The chart is in three parts: PART 1 – ADMINISTRATION

Right Side The airfield the chart refers to The procedure VDF 210° to Aerodrome The VDF frequency in MHz

Left Side

The Minimum Safe Altitude circle valid for the 4 quadrants shown out to 25 nm from the aerodrome reference point (ARP)

Centre

The four letter ICAO code for Cranfield (EGTC) The categories of aircraft that can fly this approach (A & B) The airfield data The airfield frequencies

Note that:

The approach frequency is also the primary VDF frequency The tower frequency is the secondary VDF frequency

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PART 2 – THE PLAN VIEW

The plan view shows a range circle out to 10 nm from the aerodrome, which is the

centre point. Inside the circle are marked airspace restrictions such as D206. Significant obstacles are also marked.

The Approach

The aircraft initially homes to the Cranfield overhead, the initial approach fix (IAF), which is co-located with the VDF.

The outbound leg is 016° and the inbound leg is 210°. Overhead the VDF is the missed approach point (MAPt).

The above shows the course of the aircraft over the ground but shows no elevation information. This is given in the bottom part of the chart.

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PART 3 – THE ELEVATION VIEW The elevation view is as a bystander would see on the ground looking at the aeroplane from the side.

Initially the aircraft homes to the IAF at an altitude of 2200 ft. This is QNH; the QFE figures are given in the brackets.

On the outbound leg, the aircraft descends to 1664 ft QNH (1300 ft QFE). After the inbound turn, the aircraft can then descend to the appropriate MDA for the

category of aircraft shown in the boxes to the bottom right of the diagram. If the airfield is not seen by the time the aircraft is over the VDF, a missed approach must be carried out. REFUSAL OF SERVICE DF stations have the authority to refuse to give bearings when conditions are unsatisfactory or when the bearings do not fall within the calibrated limits of the station. The station will state the reason at the time of refusal. Full R/T procedures to be used, when requiring VDF assistance, are contained in the Communications section of your notes. AUTOMATIC VDF Automatic VDF stations assist in the radar identification for ATC procedures. They do not provide a normal VDF service to aircraft.

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RANGE AND ERRORS Being a VHF transmission, the range is line of sight and the maximum range formula applies:

Range = 1.25(√HT + √HR)

Where: R = the maximum range between the stations HT = the height of the transmitter HR = the height of the receiver

Other factors that affect the expected range are:

Intervening Terrain This can screen the transmitter/receiver path (remember that VHF is a line of site transmission). Atmospheric Refraction An increased refractive index (resultant from the inversions of temperature and/or humidity) can cause super refraction and increased ranges. Sub-refraction reduces the expected range. Transmitter Power The bearing signal measured may be in error. The major sources of error are:

Ground Reflections These can cause VHF and UHF signals to reach the DF station aerial from multiple paths. Additional phase differences are detected which deflect the bearing indication. Synchronous Transmissions The DF station detects signals from other aircraft communications equipment at the same time as the desired signal. This causes a deflection of the measured bearing. This is a problem in congested airspace when atmospheric conditions favour super refraction and cause detection of transmissions from beyond the radio horizon.

The signal quality may decrease if an aircraft is not flying straight and level. VHF radio signals are vertically polarised and reception is only optimal when the aircraft has a small amount of pitch and bank. To ensure good reception, avoid asking for bearings or headings to steer during steep turns.

Radio Navigation 3-1

INTRODUCTION Non Directional Beacons (NDB) are ground-based transmitters that transmit radio energy equally in all directions. The airborne system in the aircraft is the Automatic Direction Finder (ADF). The indicator in the aircraft always points toward the tuned NDB. (Exceptions to this are discussed later in this chapter.)

PRINCIPLES OF OPERATION The NDB transmitter is very simple. An RF oscillator provides a carrier wave. This carrier wave is the NDB signal that the airborne equipment (ADF) uses to determine the direction of the transmitting station. A low-frequency oscillator provides the identification signal of the transmitting station or ident. The low-frequency signal modulates the carrier wave in the modulator. Frequency LF/MF – 190 to 1750 kHz. In Europe, the frequencies are normally between 225 and 455 kHz. EMISSION CHARACTERISTICS

Long Range Beacons N0N A1A Short Range Beacons N0N A2A

It is important to bear in mind that, although the airborne equipment only needs the bare carrier signal to indicate the direction to the transmitter, there must be a way of identifying the selected station. In the above emission characteristics, both the long and short range beacons transmit N0N. This is the unmodulated carrier wave on which the indication relies. It is the A1A or A2A that provides the identification. The A1A emission keys the carrier wave. The paragraph in Chapter 1 on heterodyning states that to have an audio frequency input to the headphones there must be two radio frequencies. As a result, the BFO must be turned on to provide the second frequency. This means that the audio tone is heard during the entire N0N phase of the incoming signal and during the active part of the keyed A1A signal. The A2A emission modulates the audio tone frequency directly onto the carrier and therefore the BFO selection should be turned off. In this case, it is the demodulator within the ADF that feeds the audio ident tone to the headphones. The ICAO recommended emission characteristic is A2A, unless operational or environmental considerations dictate the use of A1A, such as long range coastal installations.

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LOOP THEORY To understand direction finding, an understanding of a loop aerial is necessary. Below is a representation of a loop aerial. The loop has two vertical elements shown as A and B.

A B

Phase Difference (AC) = AB Cosß The NDB transmits a vertically polarised signal which induces voltage in vertical elements A and B, but no voltage in the horizontal elements of the loop. If the loop is lying across the path of the incoming signal, the voltages induced in elements A and B are equal, and vary with the incoming signal at the same rate. Because an electric current only flows when a voltage difference occurs, no current flows in the loop when it is across the path of the incoming signal. Now consider the loop aerial aligned with the incoming signal as in the diagram above. The magnitutde of the signal wave form is different across elements A and B, and this induces voltages of different levels which causes an AC current to flow in the loop. By plotting the strength of the iduced current in the loop for one complete revolution of the signal source around the loop a figure of eight polar diagram is developed.

The polar diagram shows two ill-defined maxima (90° and 270°) and two well-defined minima at (0° and 180°). The minima are usually used in direction finding. Even with two well-defined minima, there is no indication as to which side of the loop the transmitter is sited. A sensing aerial resolves the ambiguity.

β

+ -

A B

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SENSING Inserting a vertical di-pole into the loop resolves the ambiguity of the polar diagram above as shown in the diagram below.

The polar diagram of the sensing di-pole appears below.

Combining the polar diagram for the loop aerial and the sensing aerial forms a polar diagram in the shape of a cardioid.

A cardioid diagram has only one null position, and resolves the 180° ambiguity. The principle of the ADF is that the loop is turned to the position for minimum which corresponds to the null position of the cardioid. The instrument’s needle indications are also relative to the position of the loop aerial. The system is called the Automatic Direction Finder because the aerial rotation and the interpretation of its relative signal strength are done automatically. The indicator information is such that, by laying the instrument panel down flat, the ADF needle points directly at the transmitting station. The system component which drives the indicator in response to the sensed direction of the signal source is called a ‘Goniometer’.

+ - +

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Radio Navigation 3-4

NDB OPERATION In this method of operation, an amplified signal radiates omni-directionally. The transmission mast may be either a single mast or a large T-aerial strung between two masts. These aerial arrangements produce a vertically polarised signal. The polar diagram for the aerial is omni- directional in the horizontal plane but, as shown below, exhibits directional properties in the vertical plane.

Above the station, marked by the points at which the radiated power has fallen to 0.5 of its maximum value, is a conical area in which signal strength may be too low for use. This volume of space is called the cone of silence or cone of confusion. For an NDB, this angle is 40° from the vertical.

ADF OPERATION The Automatic Direction Finder (ADF) consists of a receiver, a sense aerial, a loop aerial, and an indicator. The receiver control panel and the indicator are on the instrument panel, and the loop and sense aerials are normally combined in a single aerial unit, normally mounted under the fuselage. The pilot uses the receiver control panel to enter the frequency corresponding to the NDB for intended use. The ADF indicator consists of a needle, which indicates the direction from which the signals of the selected NDB ground station are coming. The most basic ADF indicator is known as a Radio Compass. In this configuration, the needle moves against a scale calibrated in degrees from 0° - 359°. The datum for the direction measurement is the nose of the aircraft and therefore, the radio compass indications are relative bearings.

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BEARING DETERMINATION The loop, or directional aerial, rotates electronically and, by combining information from the loop and sense aerials, the unit derives the bearing to the station internally. When a looped conductor, such as the loop aerial encounters electromagnetic waves it induces voltages in the two halves of the loop. These voltages depend on the angular position of the loop relative to the incoming electromagnetic (EM) waves. The total voltage induced in the loop is the algebraic difference between the voltages from the two halves. This total voltage is the signal output from the loop aerial. TYPES Typical associated power outputs and uses are as follows:

Locator Beacon Radiating between 15 and 40 watts and used for intermediate approach guidance toward establishing the final approach path of an ILS, these beacons are short range and are normally N0N A2A. Their maximum range is 15 - 25 nm. Homing These beacons primarily serve as an approach and holding aid near an aerodrome. They are medium range beacons, normally N0N A2A. Their maximum range is 50 nm. Airways/Route Beacons Radiating at up to 200 watts and used for track guidance and general navigation, these beacons are normally N0N A2A. Long-Range Beacons Radiating at up to 4 kilowatts, and generally located on islands or oceanic coastlines, these beacons serve to provide guidance and navigation resources to transoceanic flights. These beacons are normally N0N A1A.

Besides NDBs, other transmitters operate within the NDB band of frequencies and can be detected by the aircraft’s receiver. These include:

Broadcast stations (i.e. those carrying entertainment, news, etc.). Broadcast stations can have repeater transmitters at different locations causing synchronous transmission errors.

Marine Beacons. Do not use stations if their details are not published in the AIP or appropriate Flight Guides. Where information on Marine Beacon is published, pilots need to be aware that a number of beacons are grouped together on the same frequency, and each beacon transmits for a period of 60 seconds in a cycle of six minutes. The use of signals from such published stations guarantees that, within the published range by day, the signal from the desired station is at least three times stronger than any other signal on the same or near frequency. The use of transmissions from non-published sources may lead to errors, as they are not protected from such harmful interference.

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Radio Navigation 3-6

CONTROL PANELS AND INDICATORS CONTROL PANEL There are different types of ADF control panels, but their operational use is almost the same. An example appears below. The mode selector, or function switch, has several positions, enabling the pilot to select the desired function. Typical markings are: OFF, ADF, ANT, and LOOP.

ADF is the position when the pilot wants the needle to automatically display bearing information. ANT is the abbreviation of antenna. In this position, only the signal from the sense aerial is used. This results in no satisfactory directional information to the ADF needle.

There are two reasons for selecting the ANT position:

Easier identification of the NDB station Better understanding of voice transmissions

BFO stands for Beat Frequency Oscillator. Sometimes this position is labeled CW, the abbreviation for Carrier Wave. The BFO circuit imposes a tone onto the carrier wave signal to make it audible to the pilot, enabling identification of the NDB signal. The emission characteristics determine the position of the BFO switch:

Tuning Identification N0N A1A ON ON N0N A2A ON OFF

For N0N A2A, the BFO is on for tuning in order to check the integrity of the incoming signal by providing an uninterrupted tone for an uninterrupted carrier signal. Once the station has been properly tuned and identified, switch the Mode Selector back to ADF. This is important, as no bearing information shows unless the switch is in the ADF position. When a pilot selects BFO or ANT, some ADFs automatically default to the 180° position, while others remain on the last bearing computed. Never leave the mode selector in ANT or BFO position if navigating using the ADF.

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Radio Navigation 3-7

In order to avoid the dangers of this problem, NDBs transmitting on A2A are identifiable with the mode selector in the ADF position, so it becomes possible to avoid the ANT position. There is no failure flag on an ADF receiver or indicator. The only way to be sure that the instrument is receiving a valid signal from the NDB is to continuously monitor the station’s identification. Each NDB is identifiable by a two or three lettered Morse code identification signal, transmitted together with its normal signal and known as its IDENT. When tuning an NDB it is absolutely essential to correctly identify the facility before using it. TEST SWITCH If the unit has a test switch, pressing it swings the indicator needle. If the needle does not swing, this indicates the unit is not working properly. If the needle swings, but does not return to its previous position, the signal is too weak to be used for navigation. If it swings and returns to its previous position, the system is working properly and the received signal is good. BEARING INDICATORS Bearings to the station display on an indicator consisting of a bearing scale (calibrated in degrees) and a pointer. There are four types of bearing scale with varying degrees of sophistication. They are:

The fixed card The manually rotatable card The radio magnetic indicator (RMI) The fixed card indicator, or relative bearing indicator (RBI)

This manual discusses only two systems, the RBI and the RMI. RELATIVE BEARING INDICATOR (RBI) The bearing displayed on a fixed card indicator is a relative bearing; thus the name Relative Bearing Indicator (RBI). Since the card is fixed, zero is always at the top and 180° always at the bottom.

3

612

15

30

33

21

24

0

18

9

27

HDG

A relative bearing is always measured clockwise from the nose of the aircraft. In the diagram above, the needle is pointing to 100°. This means that the station is 100° to the right of the aircraft nose.

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Radio Navigation 3-8

In the diagram below the relative bearing is 340°. The NDB is 340° right of the nose.

3

612

15

30

33

21

24

0

18

9

27

HDG

A more convenient way of expressing this is that the station is 20° left of the nose. It is sometimes convenient to describe the bearing of the NDB in relation to the NOSE or TAIL of the aircraft. Since the card is fixed, the indicated relative bearing must be combined with the magnetic heading of the aircraft in order to obtain the magnetic bearing to the station (QDM). If the result of this addition exceeds 360°, it is necessary to subtract 360° from the result in order to obtain a meaningful bearing.

Example: Assume for the diagram above that the aircraft is heading 230°M The bearing to the NDB is:

230° + 340° = 570° Because this is more than 360, it is necessary to subtract 360 from 570 = 210° The QDM is 210°. This means the QDR is 030°.

The magnetic bearing of the aircraft from the station, the QDR, is the reciprocal of the QDM. A quicker way to determine the QDM is to mentally superimpose the RBI needle onto the directional gyro. This is not very accurate, but it is a good double check for calculations. Visualise the QDR as the tail of the needle when it is mentally transferred from the RBI onto the directional gyro indicator.

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RADIO MAGNETIC INDICATOR (RMI) This combines the Relative Bearing Indicator and Remote Indicating Gyro Compass into a single instrument, with the compass card being aligned automatically with Magnetic North. In the diagram below:

The heading is 332°M. The VOR or ADF can be indicated by either pointer depending upon the switching. The QDM is continuously indicated by the arrow head of the pointer. The QDR is continuously indicated under the tail.

VOR

VOR

ADF ADF

33 N3

6E

30W

24

21S 15 12

This is now the most common type of presentation.

If the double pointer represents the ADF then the QDM is 300° and the QDR is 120°. DIRECT WAVE LIMITATIONS The Direct Wave follows the line of sight. Its range can be determined using the line of sight formula. In most cases, the direct wave range is considerably less than that of the Ground Wave. Height may become significant when it is desirable to receive the direct wave, to minimise the risk of ADF error, when flying in mountainous areas, or when using coastal NDBs.

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SKY WAVE LIMITATIONS

F1

E

TX

Skip Distance

At some frequencies there will be a gap in coverage between the ground wave and the first return of the sky wave. The ground wave coverage might extend out to 300 miles, while the first sky wave returns at 1000 miles. The name for this gap is the dead space. The exact length of the dead space depends on frequency and the state of ionisation of the atmosphere. At frequencies in the lower MF and the LF bands, intense ionisation by day attenuates (absorbs) RF signals and no sky wave return is noticeable. By night, the ionisation levels fall and returning sky waves can be detected.

NIGHT EFFECT At short range (30 to 80 miles), the sky waves mix with the ground wave signal (there is no dead space). Because the returning sky waves travel over a different path, they have a different phase from the ground wave. This has the effect of suppressing or displacing the aerial null signal, in a random manner. The needle on the RMI or RBI wanders. This effect is at its most variable during twilight at dusk and dawn. A further effect occurs due to the design of the loop aerial system. The loop uses a vertically polarised signal. As the radio wave travels through the ionosphere, the vertical polarisation changes as the wave refracts back toward the Earth, so the returning wave has a horizontal polarisation component. A current is now induced in the horizontal members of the loop:

The horizontal member AB, and The two smaller feeds to the bottom of the aerial

The resultant current flow further degrades the null position and an accurate reading is impossible.

A B

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Radio Navigation 3-11

At longer ranges, the sky wave signal becomes progressively stronger. Ionospheric refraction may cause the plane of polarisation of the signal to shift randomly. This can cause the random introduction of a horizontally polarised component into the loop aerial, which causes displacement of the null signal. In summary, the airborne ADF is designed and optimised for use in conjunction with the more predictable ground wave signal from the selected NDB.

ERRORS OF THE ADF The ADF bearing is subject to a number of error sources including any or all of the following. QUADRANTAL ERROR The metal components of the aeroplane’s structure behave as an aerial. They absorb signals at all frequencies, but more readily so at frequencies in the MF band. Once absorbed, these then re-radiate as weak signals but, being close to the ADF aerial, are strong enough to detect. The effect of this signal is to displace the measured null toward the major electrical axis of the aeroplane creating an error that is maximum on relative bearings 045°, 135°, 225°, 315° (the quadrantals). Calibration and electro-mechanical compensation at installation minimises this error.

POSITIVECORRECTION

REQUIRED

MAJOR ELECTRICALAXIS OF AIRCRAFT

CORRECTBEARING OF

TRANSMITTER

INCOMINGRADIO WAVE

BEARINGACTUALLYMEASURED

DIP (BANK) ERROR During turns, the horizontal member of the loop aerial detects a signal. This causes displacement of the null and the display of a short-term erroneous bearing.

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COASTAL REFRACTION When flying over the sea and using a land based beacon, the changes in propagation properties of the signal as it passes from land to sea causes displacement of the wave front. This results in a bearing error.

CORRECT BEARINGOF BEACON

ACTUAL PATHOF RADIO WAVE

(INDICATED BEARING)

REFRACTIONTOWARDS COAST

WAVE CROSSINGAT 90°

NO REFRACTIONLAND

SEA

NDB

Coastal refraction errors may be minimised by any or all of the following:

Do not use beacons unless they are situated on islands or near to the coast. If using an inland NDB, only use bearings at or near 90º to the coast. Remember that coastal refraction decreases as height increases.

MULTIPATH SIGNALS When flying in mountainous regions, signals may refract (bend) around and/or reflect from mountains. Such multipath signals may affect the ADF, making the bearings unreliable.

TRANSMITTER

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NOISE The definition of noise is any signal detected at the receiver other than the desired signal.

Man Made Noise Each published NDB has an associated published range. If use of that NDB is restricted to that range, the desired signal is protected from the harmful interference of ground waves from other known transmitters on the same or adjacent frequencies. Remember that, from sunset to sunrise, sky wave propagation of signals in the LF and MF bands is possible. This causes the signal to noise ratio to decrease and results in errors as null displacement occurs, usually randomly. Another localised source of man-made noise is overhead power cables. Many of these cables carry not only electrical power but also modulated signals used by the power companies for communication. These modulated signals radiate from the power cables and create mini NDBs. Such emissions are monitored but, in some states, monitoring may not occur. The rule is use with extreme caution if unsure.

Lightning There are an average of 44 000 thunderstorms over the Earth’s surface in every 24 hour period and more than half of these occur over or near land surfaces within 30º latitude of the Equator. Each thunderstorm generates electro-magnetic signals and these radiate in all directions from that storm. When flying near one of these storms, the aircraft’s ADF detects the signal and the bearing indication may well deflect toward that storm. Such noise levels are normally quite low, but they do increase under the following conditions:

In temperate latitudes during the summer As one moves toward the tropics At night as a result of sky wave propagation

Charged Water Droplets Water droplets held in a cloud have an electric charge. As an aircraft flies through the cloud, the water droplets that contact the aircraft discharge on the metal surface. The collective effort of the water droplet discharge can distort and blur the polar diagram enough to displace the null position.

Noise effects are indicated by:

Random wandering of the bearing indication Using the audio output and noting audible signals such as voice/music/static

If noise effect is suspected, only use the published NDBs when well within the notified range. The aircraft could be at half the published range before finding a reliable signal.

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SYNCHRONOUS TRANSMISSION Where two or more beacons are transmitting on the same frequency, the measured bearing becomes the resultant of the two received signals.

As long as the NDB is used within its promulgated range, the effects of synchronous transmission should be a minimum. PROMULGATED RANGE Most NDBs are given a daytime-only protection range where the unwanted signals are limited to ± 5°. Outside this range the error increases. The propagation conditions at night also increase the bearing errors. ABSENCE OF FAILURE WARNING There is no visible indication to the user that there is a system failure. ACCURACY When used within the published range by day, the ADF should give a bearing accuracy within ± 6°.

Radio Navigation 4-1

INTRODUCTION This chapter discusses the uses of the NDB. Even though pilots are unlikely to use the instrument for plotting position lines, they need to understand this procedure as it helps a General Navigation course. The process of homing and understanding the Jeppesen plate is essential in instrument flying for the Instrument Rating.

ADF BEARING The procedure for obtaining an ADF bearing is:

Determine the frequency, identification, and modulation of the required beacon and ensure that the aircraft is within the published (promulgated) range.

Switch on the ADF and adjust volume. Tune the frequency and identify the station using ANT and BFO as necessary. Select ADF on the control panel and note the bearing on the indicator.

LINE OF POSITION (LOP) USING THE RBI With the help of the information provided by instruments, the pilot is now able to determine the line of position along which the aircraft is situated. To draw this LOP on the chart, the pilot needs the QDR or the QTE. Assume the aircraft is on a heading of 015°M:

3

612

15

30

33

21

24

0

18

9

27

HDG

The relative bearing from the indicator is 340°. The QDM is the relative bearing plus the heading.

340 + 015 = 355°

The QDR is the reciprocal, or 175°.

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LINE OF POSITION (LOP) USING THE RMI An RMI solves the bearing automatically. The RMI continuously provides QDMs and QDRs. Magnetic Bearings can only be used on charts that are oriented to magnetic north. The beacons on most instrument charts have the direction of magnetic north attached with an arrow.

V O R

VOR

ADF ADF

33 N3

6E

30W

24

21S 15 12

Assuming that the single pointer is the ADF:

The QDM is 017 The QDR is 197

HOMING The ADF needle always points toward the station, and the easiest way to reach the beacon is to constantly fly with the needle pointing to the top of the indicator. This procedure is known as homing. The easiest way to home to a station is to turn the aircraft in the direction of the needle until the needle points to the top of the indicator. This points the nose of the aircraft directly toward the station. Once aimed at the station, any crosswind component displaces the aircraft to either side of the straight track to the station and the ADF needle swings away from the top of the indicator. The pilot must then make a correction of the heading toward the needle in order to continue heading to the station. This process must be repeated again and again, since the crosswind continues to push the aircraft away from the straight track. As a result, the path to the station is a curved one.

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36

1215

3033

2124

0

18

9

27

3 6

1215

3033

2124

0

18

9

27

3 6

121530

33

2124

0

18

9

27

3

612

15

30

33

21

24

0

18

9

27

The crosswind component requires the aircraft to turn further and further into the wind in order to continue toward the station. The aircraft must turn until eventually reaching a point where the aircraft faces directly into the wind. At that point, the aircraft no longer drifts off the direct track and is now heading straight to the station. The actual curved path that results is different for each combination of crosswind and TAS. A strong crosswind component and low TAS results in a large deviation. A weak crosswind component and a high TAS results in a small deviation. Since the actual track over the ground varies with every wind and airspeed combination, there is no way to ensure that any given aircraft stays within the boundaries of an airway or approach path when homing. Homing is a very simple but extremely inefficient procedure. Because of the uncertain demands on airspace, it is not commonly used. INTERCEPTING A COURSE To navigate with the help of ADF and NDB:

Visualise the aircraft’s position Intercept the desired course Maintain the course to or from the station

The first step is to visualise the aircraft’s position. Once this is completed, intercept the desired course, which in this case is 035° inbound. The second step is to make any turn necessary to the heading that provides a suitable intercept. Observe the instrument readings during the turn.

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INBOUND TO THE BEACON

Now look at the corresponding plan view. The heading of 090° provides an intercept angle of 55°. Since the desired QDM is 035°, the aircraft is on track when the RBI indicates a relative bearing of 305° as shown in the diagram on the next page.

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Radio Navigation 4-5

3

6

9

12

1518

21

24

27

30

330

When the needle nears the desired relative bearing, in this case 305°, begin the turn toward the station. This places the aircraft on the desired inbound track. Compare with the instrument indications. OUTBOUND FROM THE BEACON To intercept a track outbound, follow the same procedures. First of all, visualise the aircraft’s position.

3

612

15

30

33

21

24

0

18

9

27

HDG

The relative bearing of 100° combined with the magnetic heading of 125° indicates a location North and East of the NDB.

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Radio Navigation 4-6

The desired track is 050° outbound. The intercept angle is 40°. When the relative bearing is 140° the aircraft has reached its outbound course. Observe the instruments’ indications. When the needle reaches 135° degrees, start turning to intercept the outbound course. Look at the instrument. Heading 050°, with relative bearing 180°, places the aircraft on course. This heading will only maintain the course in still air. A crosswind component will require a drift correction. Example 1: In order to intercept a specific course:

First determine the aircraft’s position relative to the desired course. Then establish a suitable interception angle.

Consider the following situation. To assist in visualising the situation, draw a plan and the instrument indications.

The aircraft is on a heading of 340°. The relative bearing to the NDB is 080°. The required course is 090° inbound.

By maintaining a heading of 340°, the aircraft eventually intercepts the 090 course. This would be a rather untidy intercept because a turn of 110° would be required when the aircraft is on track. A more efficient intercept can be achieved by turning onto an initial heading of 360°, for a 90° intercept. A heading of 030° leads to a 60° intercept with the required inbound course.

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Since the aircraft is on QDR 240, a heading of 060° would turn the aircraft directly toward the station, and the QDM 090 would never be intercepted. Once the aircraft is on a correct intercept heading, the rule is a simple one. When the angle formed by the aircraft’s heading and the desired course is the same as the angle between the zero mark at the top of the indicator and the pointer, then the aircraft is on the desired course (QDR or QDM). When intercepting OUTBOUND, the aircraft is on the desired course when the intercept angle is the same as the angle between the zero mark at the top of the indicator and the TAIL of the needle. To intercept a specific course from an assigned heading using this technique requires knowing the interception angle. For instance, with a heading of 220° and a clearance to intercept QDM 180, the intercept angle is 40°. When the needle is 40° to the left of zero, the track has been intercepted. Example 2: The aircraft heading is 265° and the RBI indicates 005°. The aircraft must join QDM 240 at an intercept angle of 60°. The first step is always to visualise the aircraft’s position:

What is the QDR? In this instance, it is east of the station. Which way must the aircraft turn to make the intercept, left or right?

The course is to the right of the aircraft, so a right turn has to be made for the interception. Which heading is required in order to intercept the QDM 240 with an intercept angle of 60°? To intercept QDM 240 at 60°, the aircraft should turn to a heading of 300°. Maintain a heading of 300°, and observe the RBI needle. Since this is a 60° intercept, wait until the pointer falls 60° to the left of the zero indication on RBI. Mentally superimposing the RBI needle on the directional gyro always provides a good crosscheck for the calculations. To avoid overshooting the intended course, turn a few degrees before reaching the desired QDM. Observe the instruments and initiate the turn a few degrees before reaching QDM 240.The RMI eliminates the need to do any mental calculation. It always displays the QDM under the pointer and the QDR under the tail. The procedure of intercepting QDRs and QDMs becomes a lot easier if the pilot maintains a mental picture of where the aircraft is and where it should be. TRACKING With no crosswind, a direct inbound course is achieved by:

Heading the aircraft directly at the NDB Maintaining the ADF needle on the nose of the aircraft.

If there is no drift, the aircraft homes straight to the NDB.

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Any crosswind will cause the aircraft to be blown off track. In the cockpit, the ADF needle indicates this as it starts to move away from the top of the indicator. To fly a straight course to the station is called TRACKING. To track to the station requires establishing a wind correction angle (WCA) to compensate for the drift caused by the crosswind. If the exact W/V is not known, then use an estimated WCA obtained from the available information (forecasts, pilot reports, etc.). Remember that the higher the crosswind, the greater the WCA and, for the same crosswind, slower aircraft must establish a greater WCA than faster aircraft. Once the aircraft is on a course with a wind correction angle to compensate for drift, observe the instruments and look at where the crosswind is coming from and what the impact is on the aircraft. If the ADF needle indicates a constant relative bearing while maintaining a constant magnetic heading, the current wind correction angle is correct and the aircraft is tracking directly to or from the station. A wind correction angle that does not compensate for the present wind allows the aircraft to drift off course, and the ADF needle shows a gradually changing relative bearing. If the head of the ADF needle moves to the right, it indicates that a turn to the right is necessary to maintain the course to the NDB and, conversely, if the head of the needle moves to the left, a left turn is required. How large each correcting turn should be depends upon the deviation from the course. A simple method is to double the angle of bearing change. Observe that if the aircraft deviates 10° to the left, the needle has moved 10° to the right. Doubling the angle of bearing change simply means the pilot must alter the heading 20 degrees to the right. Having regained the course, turn left by half of the correcting turn of 20°. In other words, turn left 10° to maintain the track. This WCA should provide reasonable tracking. In real life, the perfect track is difficult to achieve and the pilot makes a number of minor corrections to the heading, a technique known as bracketing the track. The ADF needle becomes more and more sensitive as the aircraft nears the NDB station. Minor displacements to the left or right of the track cause larger and larger changes in the relative bearings and the QDM. When passing overhead the NDB, the ADF needle oscillates then moves toward the bottom of the dial and settles down. When close to the NDB, do not change heading. Maintain the heading until obtaining accurate readings on the outbound flight. To facilitate the QDR calculations when tracking outbound, remember that the QDR is equal to the Magnetic Heading plus or minus the deflection of the tail of the needle. Suppose that the desired course outbound from an NDB is QDR 040 and the pilot estimates a WCA of 10° to the right to counteract the wind from the right. To fix the QDR 040 in a no wind condition fly heading 040°. With a right crosswind that requires a 10° WCA, the heading is 050°.

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Radio Navigation 4-9

NDB APPROACH The approach chart (plate) shown below is for the Coventry NDB(L) Runway 23.

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To facilitate discussion, the plate is split into 3 parts in a similar method to the Cranfield VDF discussed in an earlier chapter. PART 1 – ADMINISTRATION

The top of the chart follows the same profile as the VDF chart. In the top right:

The name of the airfield Coventry The approach to be flown NDB(L) The L indicates that the beacon being used is a locater beacon. Normally, this

beacon is associated with the ILS. The frequency and identification CT 363.50 kHz

On the left:

The minimum safe altitude sectors. In the centre:

The four letter identifier for Coventry The categories of aircraft that can use the approach Airfield elevation, threshold elevation, transition altitude and variation Frequencies in use at Coventry

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PART 2 - THE PLAN VIEW

The plan view shows information around the environs of Coventry:

Coventry airfield Coventry NDB (CT 363.5), which is also the Initial Approach Fix (IAF) The prominent obstacles Major airfields (Birmingham) Minor airfields (Baxterly, Bruntingthorpe) Disused airfields

The plan view shows a circle radius 10 nm from Coventry. Superimposed on the chart are the tracks to fly:

From the VOR at Daventry (DTY) From the NDB at Lichfield (LIC) The tracks to fly for category A, B, C, and D aircraft. Note that the two tracks are

different The missed approach Warnings

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Radio Navigation 4-12

PART 3 - THE ELEVATION VIEW

The profile is complementary to the plan view. The altitude (height in brackets) and tracks appear on the elevation view. Timing for the outbound (OUBD) legs is in a box to the right of the diagram. The missed approach is a written commentary from the Minimum Descent Altitude (MDA). PART 4 - LIMITS AND OTHER INFORMATION

The bottom part of the chart is split into four columns:

The recommended profile The rate of descent and time to the MAPt from the Final Approach Fix (FAF) for

different groundspeeds The Obstacle Clearance Altitude (OCA) or Obstacle Clearance Height (OCH) which

is used in calculating the MDA. The Visual Manoeuvring (Circling) Altitude (VM(C) OCA)

The bottom two rows show an alternate procedure and a note as to the lowest altitude from which the aircraft can begin a procedure.

Radio Navigation 5-1

INTRODUCTION Recognised in 1949 by ICAO as the international standard for short-range navigation, VOR is the most commonly used beacon in radio navigation. As opposed to the NDB, which transmits a non-directional signal, the signal transmitted by the VOR contains directional information. This chapter discusses two types of VOR; Conventional VOR (CVOR) and Doppler VOR (DVOR). For the user in the aircraft there is no apparent difference in the indications.

PRINCIPLE OF OPERATION Two independent modulations are placed on a VHF frequency, known as the reference and variable phase. The aircraft equipment measures the magnetic bearing of the station by phase comparison of these two waves. FREQUENCY VHF – 108 to 117.95 MHz It is prudent to discuss the allocation of the VHF frequency band in this section. VORs are used for two separate purposes, as Terminal VORs (TVOR) and Airway VORs. These beacons occupy different parts of the frequency band. Further complicating the allocation, Instrument Landing System (ILS) occupies frequencies in the same range as well.

TVOR uses the first even decimal and first even decimal + 50 kHz up to 112 MHz (e.g. 108.00 MHz, 108.05 MHz, 108.20 MHz, 108.25 MHz etc.). ILS uses the first odd decimal and first odd decimal + 50 kHz up to 112 MHz (e.g. 108.10 MHz, 108.15 MHz, 108.30 MHz, 108.35 MHz etc.). Airways VOR occupies the remainder of the frequency band 112 MHz to 117.95 MHz at 50 kHz spacing.

POLARISATION Horizontal EMISSION CHARACTERISTICS A9W

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Radio Navigation 5-2

CONVENTIONAL VOR REFERENCE SIGNAL Conventional VOR is an omni-directional continuous wave transmission on the VOR frequency. The signal is frequency modulated (FM) at 30 Hz. The polar diagram of this omni-directional signal is circular, meaning that the phase detected by the aircraft’s receiver is the same on all bearings. This reference signal effectively tells the VOR receiver where magnetic north is. VARIABLE SIGNAL The variable signal is transmitted from an aerial that is effectively a loop and is amplitude modulated (AM) at 30 Hz. As with the ADF, this produces a figure 8 polar diagram. Unlike the ADF, the “loop” aerial electronically rotates at 30 revolutions per second. By combining the reference and variable signal, the resulting polar diagram is similar to a cardioid with the exception being it does not have a null position. This polar diagram is called a limacon, the French for edible snail. AIRCRAFT RECEIVER The aircraft VOR receiver splits the received signal into three parts. The first connects to the aircraft communications system so that the beacon can be identified. The second and third parts pass through a filter that separates the AM and FM reference signals. The 30 Hz FM reference signal is then electronically changed so that it can be compared with the AM variable signal. Thus the principle of operation of VOR is bearing measurement by phase comparison.

BEARING MEASUREMENT The absence of a null position is compensated for by varying the power relationship between the reference and variable signals. This difference in field strength is graphically illustrated below.

A BOTH SIGNALSARE IN PHASEON A BEARINGOF MAGNETIC

NORTH

FM REFERENCE30 HZ

AM VARIABLESIGNAL 30 HZ

A

B

C

DTX

ROTATINGLIMACON REFERENCE

REFERENCE

REFERENCE

D90° PHASE DIFFERENCE

= 090 RADIAL

C

B

180° PHASE DIFFERENCE

270° PHASE DIFFERENCE

= 180 RADIAL

= 270 RADIAL

7

4

1

4

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Radio Navigation 5-3

The resultant shape is that of an elongated cardioid, called a limacon. In the diagram above, the reference signal appears at the four cardinal headings. If the line of the variable phase plots the power curve, then it can be seen that at North it is 4 units of power, West 7 units, South 4 units and East 1 unit. The variable phase is rotated at the same rate as the reference signal is modulated so that at:

North The limacon is set in the start position (remember that the aerial is rotating at 30 revolutions per second). By comparing the variable signal wave for magnetic north with the reference signal wave it is obvious that the wave diagrams are the same. By looking at the limacon signal strength start North 4, West 7, South 4, and East 1. Comparing this with the reference signal whose amplitude varies 4, 7, 4, and 1 shows that the two waves are in phase. East On East, the sequence starts East 1, North 4, West 7, and South 4. When drawn as a sine wave and compared with the reference wave, it shows that the variable signal lags the reference signal by 90°. Hence, the aircraft is on a bearing of 090°M. South On South, the sequence starts South 4, East 1, North 4, and West 7. When drawn as a sine wave and compared with the reference wave, it shows that the variable signal lags the reference signal by 180°. Hence, the aircraft is on a bearing of 180°M. West On West, the sequence starts West 7, South 4, East 1, and North 4. When drawn as a sine wave and compared with the reference wave, it shows that the variable signal lags the reference signal by 270°. Hence, the aircraft is on a bearing of 270°M.

AIRCRAFT EQUIPMENT AERIAL The aerial is a small, horizontal dipole, designed to receive the horizontally polarised signals transmitted from the ground station. Designed for the frequency band of 108 MHz – 118 MHz, the aerial has to be mounted so that it offers 360° reception. It must also be shielded from transmissions from the VHF communication radio aerial. Aerials are frequently mounted on the fin of an aircraft. RECEIVER The receiver compares the reference signal and the variable signal in order to detect the phase difference. The signal from the aerial is filtered through the high-frequency part of the receiver and only the signals from the desired VOR station pass through to the detectors and filters. FREQUENCY SELECTOR The frequency selector switch on the control panel selects the desired station. The phase comparator compares the phase of the two signals and the difference is fed to the indicator. Special circuitry within the receiver detects the identification signal and amplifies it for a speaker or headphones. Some VORs can also transmit “voice”, either radio communication, identification, met-information, or other voice transmissions. The receiver panel has a frequency selector knob, a dial indicating the selected frequency and a selector switch with a position for IDENT and Voice.

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Select the IDENT position to hear the identification signal of the VOR. The identification transmits according to ICAO recommendations and consists of a two or three letter Morse code transmitted at a rate of:

Seven words a minute Repeated at least once every 30 seconds Modulated at 1020 Hz

Selecting the VOICE position improves the reproduction of speech, and is selected when the transmission contains voice messages (for instance ATIS), or if the station serves as a regular voice transmitter. INDICATORS The indicator can be in many different forms, from the simplest to the most complex electronic flight information system. The parts and functions of the basic indicator are covered in the next chapter. MONITORING All VOR stations are monitored by automatic equipment located approximately 50 ft from the transmitter. The monitor performs functions when it detects any malfunction:

It warns the control point. It removes the identification and navigation component of the beacon. It switches the beacon off in extreme cases.

The monitor limits are:

A change in bearing information of >1° A reduction of more than 15% in the signal strength of either of the 30 Hz

modulations The monitor failing

If the beacon is switched off, the standby system comes into operation. The standby beacon requires time to become operational, so no transmission of identification happens until a full changeover occurs. TERRAIN Uneven ground, high ground, or man made obstacles nearby the VHF wave can affect VOR signals. If the terrain causes erroneous indications, they are listed in the AIP under the Designated Operational Coverage. DESIGNATED OPERATIONAL COVERAGE (DOC) VOR operates in a range where the signals are line of sight, so the line of site formula can be used to calculate the maximum range in which a signal is receivable. The AIP lists the VORs and provides the maximum range, altitude, and bearings where reliable signals are obtainable. As with the promulgated range for an NDB, only use the VOR with confidence within the DOC. VORs on the same frequency must be spaced at least 500 nm apart to ensure there is no mutual interference. The DOC is applicable for both day and night operations, as returning sky waves do not affect the VHF wave as they do the NDB.

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CONE OF CONFUSION OR CONE OF SILENCE Unlike the NDB, which has a cone of confusion of 40° from the vertical, the VOR cone of confusion is 50° from the vertical. The area above the VOR gives no signal, which causes problems with the indicators in the aircraft. Rapid bearing changes may be displayed near the beacon, making it impractical to home or follow a radial. The easy option is to fly the required heading through the overhead until receiving reliable indications. The cone of confusion is easily calculated by trigonometry.

Radius of the cone of silence = altitude (nm) x Tan 50°

Example: An aircraft is flying at 30 000 ft overhead a VOR, what is the diameter of the cone of confusion?

30 000 ft = 30 000 ÷ 6080 ft = 4.93 nm

Radius = 4.93 x tan 50° = 4.93 x 1.19 = 5.9 nm

The diameter is twice the radius = 11.8 nm

ACCURACY A number of sources account for the total accuracy of a VOR:

Site Error is due to the nature of the terrain or obstacles in the vicinity of the transmitter. The limitation for course displacement errors is ± 1°. This site error is monitored as stated earlier.

Propagation Error occurs due to signal travel over terrain or obstructions. These errors are in the region of ± 1°.

Airborne Equipment Error occurs due to the tolerances of the equipment in the aircraft. These errors are normally no more than ± 3°.

The normal accuracy of the VOR is ± 5°.

50° 50°

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AIRWAY NAVIGATION The student may be asked to calculate the maximum distance between two VORs. Again, this is a matter of using simple trigonometry.

Distance = width of the airway ÷ tan 5° (accuracy of the VOR) x 2

Example: What is the maximum distance between two VORs on an airway which is

10 nm wide (5 nm from the centreline to the edge of the airway)? 5 / tan 5° x 2 = 5 / .087 x 2 = 115 nm Where the figures are easy, try the 1 in 60 rule: There exists an effective track error of 5 nm caused by a 5° angle error. With the knowledge that 1° in 60 nm causes a 1 nm error, 5° must cause 5 nm, so the distance is twice this = 120 nm.

TEST VOR Certain airports have VOT transmitters installed. These are VOR test transmitters and allow a pilot to check the airborne equipment on the ground. The test can be conducted at any position on the aerodrome:

Tune the VOT frequency Centre the needle on the Course Deviation Indicator (discussed in the next chapter) The bearing indicates 180° with a TO flag 000° with a FROM flag If the indications are not within ± 4° of 180°/000°, the aircraft installation should be

repaired.

5°

Airway Centre Line

width

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DOPPLER VOR CVORs suffer from reflections originating with objects in the vicinity of the site. It was found that reducing these errors is possible by increasing the horizontal aerial dimensions. This was impractical as the CVOR uses a mechanical rotating aerial, so a new system was devised.

The Doppler VOR is the second generation VOR, providing improved signal quality and accuracy. A fundamental change is that the reference signal of the DVOR is amplitude modulated, while the variable signal is frequency modulated. This means that the modulations are the opposite of conventional VORs, so the variable signal rotates anticlockwise to maintain the same phase relationship at the receiver. Because the frequency-modulated signal is less subject to interference than the amplitude modulated signal, the received signals provide a more accurate bearing determination. The Doppler effect is created by “electronically rotating” the variable signal. Circular placed aerials (diameter 44 ft), rotate at a speed of 30 revolutions per second. The diameter of the circle is 13.4 metres, making the radial velocity of the variable signal 1264 m/s. This causes a Doppler shift, increasing the frequency as the signal rotates toward the observer and decreasing as it rotates away, with 30 full cycles of frequency variation per second. This results in an effective FM of 30 Hz. A receiver situated at some distance in the radiation field continuously monitors the transmitter. When certain prescribed deviations are exceeded, either the identification is switched off, or the complete transmitter is taken off the air. This is similar to the CVOR. The VOR receiver does not know if it is receiving a signal from a CVOR or a DVOR. As a result, the pilot treats both types in the same way. Reference Signal Variable Signal

CVOR Frequency Modulated Amplitude Modulated DVOR Amplitude Modulated Frequency Modulated

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Radio Navigation 5-8

Radio Navigation 6-1

INTRODUCTION This chapter discusses the uses of VOR. Three types of VOR indicators are covered:

Radio Magnetic Indicator (RMI) Omni-Bearing Selector (OBS) Horizontal Situation Indicator (HSI)

RADIO MAGNETIC INDICATOR The RMI combines the information from the radio navigation instruments with the directional information from the directional gyro. The RMI has two needles, which can indicate both ADF and VOR information. The two needles usually have single and double lines to make it easier for the pilot to identify the stations.

VOR

VOR

ADF ADF

33 N3

6E

30W

24

21S 15 12

There are two small buttons on the bottom of the instrument. These enable the pilot to select either VOR or ADF information to be displayed by each needle. The indicator needles constantly point toward the tuned station. The RMI card is slaved to the directional gyro, so that the heading of the aircraft can be read directly off the lubber line at the top. In this way, the needles show the bearing to the ground stations continuously:

The tip of the needles indicate a magnetic bearing to the ground station, the QDM. The tail indicates magnetic bearing from the ground station to the aircraft, the QDR.

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When tuned to a VOR, the tail of the needle indicates the VOR radial. In our example, the single needle points to a VOR station, indicating that the aircraft is on radial 195°. The needle marked with a double line indicates QDM 302° (QDR 122°). Be aware that the bearing registered from the ADF is a magnetic bearing against the magnetic meridian passing through the aeroplane. If there is a significant variation change or meridian convergence between the station and the aeroplane, the bearing indicated is not the same as a QDM. Consider a flight at high latitudes, and tuning a station with both a VOR and an NDB where there is a marked difference of variation and longitude between the station and the aeroplane. If the VOR is fed to the single needle and the NDB to the twin needle of the RMI, will they have the same bearing indications?

OMNI-BEARING SELECTOR The indicator shown below has three components:

The Omni Bearing Selector A TO/FROM Indicator A LEFT/RIGHT Course Deviation Indicator

TO

FR

When using this instrument the pilot has certain selections to make:

OBS Selector The control knob selects the desired magnetic track that a pilot wishes to fly TO or FROM a VOR beacon. In the case above, the pilot has selected a track of 100°M. TO/FROM Indicator When the required magnetic track is set, the TO or FROM arrow appears showing where the aircraft is relative to the beacon. The case above shows the TO arrow. The indication changes as the aircraft passes over the beacon.

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Course Deviation Indicator The indicator has 4 small dots and one large central dot. Each of these dots represents 2°, with a full-scale deflection of the needle being 10°. The vertical bar moves left or right according to the relative position of the aircraft to the magnetic track selected. With the vertical bar centred, the aircraft is on the magnetic track selected. In the instrument above, the bar shows 3½ dots left. This means that the aircraft has a deviation of 7° from the selected course. To get back to track the aircraft must fly toward the needle, in this case left. Warning Flag: A warning flag appears when:

There is a failure of the aircraft’s receiving equipment. There is a failure of the ground station. There is a failure of the indicator. Signals received are too weak or the aircraft is out of range of the beacon.

The indications are totally independent of aircraft heading. The instrument shows the aircraft position in relation to the course selected.

TO Flag If the TO flag is visible, the number shown by the arrow at the bottom of the instrument (if the vertical bar is central) is the radial of the aircraft. FROM Flag If the FROM flag is visible, the number selected at the top of the instrument (if the vertical bar is central) is the radial of the aircraft.

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USING THE OBS The diagram below shows three aircraft at different positions. The OBS indication for each is discussed in turn. (Note that the angles shown are exaggerated.)

Aircraft 1

TO

FR

The aircraft in position 1 has the indications shown above. The aircraft is flying TO the beacon and must fly left to regain the track. Note that when centralising the needle, the aircraft homes to the beacon. When flying on an airway, an aircraft must regain track as quickly as possible. With TO showing, if the aircraft were on track (vertical bar central) it would be on the 280° radial. The lubber line shows this at the bottom of the OBS indicator. In this case, the vertical bar shows a fly left situation of 3½ dots, which is the amount of deviation from the selected track. 3½ dots are equal to 7°.

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Because the displacement of the vertical bar provides an angular measurement of deviation, it is easy to determine the radial the aircraft is on. With TO in the window, the deviation shown by the vertical bar should be:

ADDED to the OBS radial if the aircraft is left of track SUBTRACTED from the OBS radial if the aircraft is right of track

Subtracting the deviation from the selected radial (because the aircraft is right of track) reveals the radial the aircraft is now on: 280 – 7 = 273°. In the case of Aircraft 2, where the aircraft is within the area of ambiguity, 10° either side of the perpendicular cutting track, no positive indications exist. Aircraft 3

TO

FR

The aircraft in position 3 has the indications shown above. The aircraft is flying FROM the beacon and must fly left to regain the track. With FROM showing, if the aircraft were on track (vertical bar central) it would be on the 100° radial. The top of the OBS indicator shows the radial. As with Aircraft 1, the vertical bar shows a fly left situation of 3½ dots, which is the amount of deviation from the selected track. 3½ dots are equal to 7°. To determine which radial the aircraft is on with FROM in the window, the deviation shown by the vertical bar should be:

ADDED to the OBS radial if the aircraft is right of track SUBTRACTED if the aircraft is left of track

Taking the radial plus the deviation (because the aircraft is right of track) allows the pilot to work out the radial of the aircraft (100 + 7) = 107°.

Chapter 6 VOR Navigation

Radio Navigation 6-6

HORIZONTAL SITUATION INDICATOR (HSI) A more modern derivative of the CDI, this instrument is widely used and pilots need to be familiar with its presentation and interpretation. As the name suggests, the HSI (shown below) provides the pilot with a pictorial presentation of the aeroplane’s navigational situation in relation to a selected course, as defined by a VOR radial or ILS localiser beam. It also displays glide slope information, a heading reference and, on many units, a DME range indication.

The instrument consists of a number of discrete elements:

1. The HORIZONTAL SITUATION INDICATOR (HSI) provides a pictorial presentation of aircraft deviation relative to VOR radials or localiser beams. It also displays glide slope deviations and gives heading reference with respect to magnetic north.

2. The NAV FLAG is in view when the NAV receiver signal is inadequate. When a NAV flag is present, the navigation indicator of the autopilot operation is not affected. The pilot must monitor the navigation indicators for NAV flags to ensure that the Autopilot and/or Flight Director are tracking valid navigation information.

3. The LUBBER LINE indicates the aircraft magnetic heading on the compass card (10).

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4. The HEADING WARNING FLAG (HDG) is in view when the heading display is invalid. If a HDG flag appears and a lateral mode (HDG, NAV, APR or APR BC) is selected, the autopilot disengages. It is possible to re-engage the autopilot in the basic wings-level mode along with any vertical mode.

5. The COURSE BEARING POINTER indicates the selected VOR course or localiser

course on the compass card (10). The selected VOR radial or localiser heading remains set on the compass card when the compass card rotates.

6. The TO/ FROM INDICATOR FLAG indicates direction of the VOR station relative to the

selected course.

7. The DUAL GLIDE SLOPE POINTERS indicate, on the glide slope scale (8), aircraft displacement from the glide slope beam centre. Glide slope pointers in view indicate the reception of a usable glide slope signal. The glide slope pointers bias out of view if the glide slope signal is lost.

8. The GLIDE SLOPE SCALES indicate displacement from the glide slope beam centre. A

glide slope deviation bar displacement of 2 dots, represents full scale (0.7°) deviation above or below the glide slope beam centre line.

9. The HEADING SELECTOR KNOB positions the heading bug (14) on the compass card

(10). The bug rotates with the compass card.

10. The COMPASS CARD rotates to display the aeroplane’s heading with reference to lubber line (3) on HSI.

11. The COURSE SELECTOR KNOB positions the course-bearing pointer (5) on the

compass card (10) by rotating the course selector knob.

12. The COURSE DEVIATION BAR (D-BAR) moves laterally to pictorially indicate the relationship of aircraft to the selected course utilising the centre portion of the omni-bearing pointer. It indicates degrees of angular displacement from VOR radials and localiser beams, or displacement in nautical miles from RNAV courses.

13. The COURSE DEVIATION SCALE functions with a course deviation bar displacement of

5 dots representing full scale (VOR = ± 10°, LOC = ± 2.5°; RNAV = 5 nm, RNAV APR = 1 nm) deviation from the beam centre line.

14. The HEADING BUG shows the desired heading, as selected using the heading bug

knob (9).

Chapter 6 VOR Navigation

Radio Navigation 6-8

VOR NAVIGATION The VOR is a very versatile navigational aid, and forms the basis of the Airway routes structure. It can assist VFR pilots, as the main navigational aid for enroute navigation, a holding aid, or also as an approach to landing aid. Before looking at the different ways of using the VOR, there are a few important things that must be done prior to using the information indicated by the instruments;

Always make sure the aircraft is within the coverage area of the VOR stations planned for use. Do this by checking the official AIP (Aeronautical information publication) or other published enroute manuals. After having turned the receiver on, dial the frequency of the aid and listen to the identification signal to ensure the aircraft is receiving the correct and desired station, and that it is “on the air”. Make sure that the warning flag (NAV or OFF) is not visible, indicating reception of a satisfactory signal and that the aircraft installation is working properly.

ESTABLISHING POSITION Using the VOR to find the aircraft’s present position requires either a VOR in combination with DME, or two VOR stations. Turning the OBS to centre the needle with a FROM indication determines the radial on which the aircraft is located. Performing this procedure using two different VOR stations provides two crossing position lines, good enough to determine a fix position. TRACKING A RADIAL INBOUND FROM A PRESENT POSITION Flying to a VOR station from the aircraft’s present position requires turning the OBS to centre the CDI needle with a TO indication and flying the heading indicated in the selected course window. The inbound track is the reciprocal the aircraft’s present radial. In a no-wind condition, a heading equal to the inbound track takes the aircraft to the VOR with the CDI needle centred. Any crosswind calls for heading corrections in order to keep the CDI needle centred. Initially make a small heading correction. If the needle drifts to one side, turn toward the needle, since the needle actually indicates the position of the desired track. Use only small changes in heading at any one time and wait for the needle to move back to centre position. This procedure of changing the heading to stabilise the needle in centre is called “bracketing”. Use small changes of heading and keep the new heading for a while to await needle movement. If the needle remains still at a position off centre, the aircraft is using the correct WCA, but still requires a correction in order to regain the desired track. INTERCEPTING A RADIAL To plan an intercept and follow a specific radial, first determine the aircraft’s position in relation to the desired track. If tracking a radial outbound, set the CDI to the desired radial. CDI deflection now shows which way to turn in order to make an intercept. The intercept angle depends on different factors. If ATC wants the pilot to join the new track as soon as possible, the pilot should make an initial intercept of up to 90° and, when the CDI starts to move, start leading the turn to establish on the new radial. If the aircraft is close to the VOR station, the needle moves quite fast. Conversely, if the aircraft is far from the station the needle moves more slowly. Aircraft speed also affects the needle movement.

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Radio Navigation 6-9

If there are no restrictions regarding the intercept, an intercept angle of 30° or 45° is normally a good alternative. This is part of a pilot’s practical training. If the intent is to intercept a radial and track it inbound, the procedure is as above, except that the pilot sets the reciprocal of the radial, which is the inbound course. The procedure is otherwise the same. Upon intercepting the selected course, the procedure is the same as described earlier. If tracking TO a VOR station and the aircraft is to continue on the same course after passing the station, needle-movement becomes very erratic when close to the station. The TO/FROM flags flicker during the passage of the station and the warning flag (NAV/ OFF) appears momentarily. This is due to the cone of confusion that is directly overhead the VOR. When tracking along an airway between two VORs, the normal procedure is to switch from tracking FROM one VOR to tracking TO the next VOR when midway between the two facilities. Sometimes the changeover point is specified elsewhere on the route segment. This is usually because of signals being restricted by terrain or by frequency interference. When this is the case, the changeover point will be specified on the appropriate instrument chart. When tracking from one VOR to another, the published radial for the inbound track to one VOR should match the outbound track or radial from the other, but this is not always so. Radials are magnetic tracks from the VOR and the directions of the radials depend on the magnetic variation at the different VORs. The difference between the corresponding radials equals the difference in variation at the position of the two VORs. At high latitudes, convergence of the meridians also contributes noticeable differences. VOR APPROACHES VOR approaches may be published for an approach to an aerodrome. The example shown on the next page is for Cranfield.

Chapter 6 VOR Navigation

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VOR Navigation Chapter 6

Radio Navigation 6-11

PART 1 – ADMINISTRATION

080° 270°

180° 360°

22

22

20

20

MSA 25 NM ARP

000 50W 000 40W 000 30W 000 20W

EGTCVOR RWY 22

CFD 116.50

CRANFIELDCAT A,B,CAD ELEV

364FTAPPROACH

122.850TOWER122.850

THR ELEV357FT

VAR4°W

TRANSITION ALT3000

As with the NDB, the top part of the chart contains the details of:

The airfield and the type of approach The categories of aircraft that can fly the approach The Minimum Safe Altitude

PART 2 – PLAN VIEW

Part 2 shows a plan view of the airfield out to 10 nm. Restricted areas, danger areas, and significant obstacles are marked. In the centre of the plan is the airfield with a plan view of the track to be flown.

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PART 3 – ELEVATION VIEW

The elevation view is used in co-ordination with the plan view. Timings and altitudes to fly are included (as with all charts QFE heights appear in brackets). The MAPt is the IAF and a commentary of the missed approach is given in a box to the left of the diagram. PART 4 – NOTES

The notes given include:

The rate of descent for a given groundspeed The OCA for the approach The OCA for visual Manoeuvring (Circling)

The holding procedure for the approach is included. The notes box at the bottom gives the restrictions applicable to the approach.

Radio Navigation 7-1

INTRODUCTION DME is a secondary radar providing the pilot with an accurate slant range from a ground transmitter. Normally paired with VOR, the combination provides the standard for ICAO short-range navigation systems (know as rho-theta). More recent uses see the DME paired with ILS and MLS to give range from touchdown during a precision approach.

PRINCIPLE OF OPERATION The system works on the principle of secondary radar:

The interrogator on board the aircraft transmits an interrogation signal. The ground-based transponder (transponder meaning a transmitter that is

responding to an interrogation) transmits to the aircraft. The interrogation signal from the aircraft and the response are on different frequencies.

Frequency UHF – 960 to 1215 MHz Emission Characteristics P0N

Aircraft transmits the interrogation signal

DME Ground Aerial Replies

Chapter 7 Distance Measuring Equipment (DME)

Radio Navigation 7-2

AIRCRAFT EQUIPMENT The airborne unit (interrogator) consists of:

An omni-directional blade aerial A transmitter A receiver A time measuring device A tracking unit

The interrogator transmits pulse pairs on the selected frequency. These pulse pairs are spaced by either 12µ seconds (X channel) or 36µ seconds (Y channel). Discussion regarding the X and Y channels occurs later.

Note: For the X channel, the transponder replies with a pulse pair spacing of 12µ

seconds. The Y channel reply is at 30µ seconds. When the pilot switches the equipment on, or when a new DME channel is selected, the pulse pairs transmit at 150 pulse pairs per second (pps). This is the search mode. The equipment stays in search mode until the equipment either:

Locks on (normally 4 to 5 seconds) 15 000 pulse pairs have been transmitted

If lock-on occurs, then the transmitter reduces the pulse recurrence frequency (PRF) of pulse pairs to 24 to 30 pps, known as tracking mode. If the system transmits 15 000 pulse pairs, the PRF drops to 60 pps until the system locks on. TRANSPONDER The ground transponder consists of a receiver and a transmitter. When it detects an interrogating signal, it transmits a response after a delay of either 50 µs or 74 µs, depending on the channel. Response is at a different frequency to that received, with the transponder being capable of generating up to 2700 pps. When replying to a signal, the ground transponder replies at a rate of 24 – 30 pps. FREQUENCY ALLOCATION Interrogator and transponder operating frequencies are grouped into pairs, the two frequencies being 63 MHz apart. The airborne interrogator uses frequencies from 1025 MHz to 1150 MHz for transmissions, while the ground-based transponder answers on frequencies in two groups, 962 MHz to 1024 MHz (low) and from 1051 MHz to 1213 MHz (high). The range of the interrogator frequencies from 1025 to 1150 provides 126 channels. To double the available response channels to 252, the response frequencies are split into groups 63 MHz higher and lower than the corresponding interrogation channel. For the interrogation channels from 1 to 63, an X beacon would prompt a response 63 MHz lower and a Y beacon, 63 MHz higher. For interrogation channels 64 to 126, the X beacon would obtain a response 63 MHz higher and the Y beacon, 63 MHz lower. To differentiate between the two beacon types, the interrogation pulse pairs are separated by 12µs for an X beacon and 36µs for a Y beacon. The response to an X beacon has the same 12µs

Distance Measuring Equipment (DME) Chapter 7

Radio Navigation 7-3

separation whereas the response to a Y beacon has a 30µs separation. The delay at the transponder (50µs for the X beacon and 74µs for the Y beacon) provides further differentiation. ICAO recommends the pairing of DME channels with VOR/ILS or MLS. Consequently, a VOR on 112.30 MHz is always paired with the DME on Channel 70X (1094 MHz interrogation – 1157 MHz reply). A VOR on 112.35 MHz would pair with the DME on Channel 70Y (1094 MHz interrogation – 1031 MHz reply). Each DME channel has an identifiable number and a letter (X or Y). The following table is an illustration of some of the available channels with their paired frequencies.

DME Channel VOR/ILS/MLS Paired frequency

20X 20Y 21X 21Y

- 70X 70Y

- 126X 126Y

108.3 108.35 108.4 108.45

- 112.3 112.35

- 117.9 117.95

The channel numbers and paired frequencies can be found in the relevant communications documents. Pilots never select a DME frequency because of the pairing. Even though the system works in the UHF band, the frequency is selected by tuning the paired VHF frequency. The major reason for this procedure is to reduce the workload on the flight deck. JITTERED PRF If two aircraft transmit to a DME at the same time, the replies are on the same frequency. If both signals received by the aircraft are the same, how can the receiver differentiate the correct reply? To which aircraft is each reply being directed?

Chapter 7 Distance Measuring Equipment (DME)

Radio Navigation 7-4

The equipment in the aircraft “jitters” the PRF before transmission. This random PRF is unique to the aircraft. When the ground station replies, it manufactures exactly the same PRF reply for the aircraft. Any reply taken by the airborne equipment that does not match the PRF of the initial transmission is rejected. The responder now responds to the new rate, and since the interrogator PRF randomly varies, only the responses to that interrogation will have the same random variation of PRF. Within the airborne receiver, the tracking unit looks for responses around the anticipated time interval compatible with the current range from the ground responder. This effectively creates a gate, and only responses that arrive within that gate receive consideration. The receiver then determines a match between the PRF of the response and those that were transmitted. Once matched, the time difference is measured, and, allowing for responder fixed delay, a range is derived. This is tracking mode. REFLECTED TRANSMISSIONS The advantage of using secondary radar is that the aircraft equipment does not process reflected transmissions from the ground or cloud, as the frequency of reply is incorrect. MEMORY Interruption of the responding signals whilst the system is in tracking mode activates a memory circuit. The system holds the following:

The last measured range value The receiver gate at the last measured time interval

The system returns to the search mode after holding the memory mode for 8 to 10 seconds. BEACON SATURATION The ground-based responder beacon has a limit of a maximum PRF of 2700 pps and interrogations occur at 24 - 30 pps (27 pps average). This means that one DME beacon can handle up to 100 aircraft.

?

Same frequency used for the reply

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Radio Navigation 7-5

Normal Gain Level

Saturation GainLevel

A B C D The ground transponder has a set gain level that a signal must exceed in order to receive a reply. This ensures that receiver noise or other weak returns are ignored. In the diagram above:

Signal A is too weak to break the normal gain level and so receives no reply. Signals B & D exceed the normal gain level and consequently receive a reply from the transponder as long as the beacon is not saturated. Signal C exceeds the normal gain level the most. If the beacon is saturated, the normal gain level elevates to a saturation gain level and only the strongest 100 signals receive replies.

CO-LOCATION OF BEACONS As stated in the introduction, the DME is usually paired with a VOR to provide the primary short range fixing required by ICAO. Where a VOR and DME transmit the same callsign in a synchronised manner the stations are considered “associated”. This means:

The VOR and DME transmitter are co-located. The aerials are a maximum of 100 ft apart in a terminal area that uses the VOR/DME

for approach purposes. The aerials are at a maximum of 2000 ft apart in instances not using VOR and DME

for approach purposes. Where co-location occurs, the identification is synchronised and transmitted 7½ seconds apart. In a 30 second period:

The VOR idents 3 times The DME idents once

Where a VOR and DME serve the same area (within 7 nm) they may be frequency paired but the DME generally uses Z as the last letter of the ident.

VOR ident MAC DME ident MAZ

Where a VOR and TACAN are co-located, the system is called VORTAC. The VOR uses the DME portion of the TACAN.

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Radio Navigation 7-6

Where DME works with an ILS or MLS, the 50 µsecond time delay is gradually reduced to a minimum to allow the DME to read zero when the aircraft passes the runway threshold. SLANT RANGE All aircraft displays show the value of the measured slant range while some contain an arithmetic unit, which calculates the instant ground speed and time to the station. It is possible on most modern installations to select “GS” or “TIME” for this purpose. Some indicators show distance, ground speed, and time simultaneously. It is important to note that the indications of ground speed and time are only correct when flying directly toward the ground station. If the aircraft is flown in any other direction, both the DME indicated ground speed and time to the station would be too low. In this case, only slant distance is correct.

DME NAVIGATION All navigational aids provide the pilot with a position line, depending on the type of radio aid. The position line resulting from the DME is a circle. When an aircraft’s DME indicator shows 55 nm, the pilot knows the aircraft is at a slant range of 55 nm from the station, but not whether it is south, east, north, or west of the station. As a result of this, the position line from one DME station alone is of little help. A radial from a VOR at some distance from the DME station provides a second position line that could intersect the DME circle at two places. This results in an ambiguity situation as seen in the diagram below.

If the VOR and DME are associated, the pilot has one clearly-defined fix position. As an approach aid, the DME provides, together with the tracking facility, positions like initial approach fix (IAF), final approach fix (FAF), and missed approach point (MAPt).

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Radio Navigation 7-7

DME PROCEDURES A DME procedure is one that is published for use with a particular ground facility. The most common type of DME procedure is flying the arc. This procedure requires the pilot to maintain a specific range from a DME, generally between two stated VOR radials.

SLANT RANGE The DME indicates a slant range, that is, the straight line from the aircraft to the ground station, not the distance along the ground. The true range can be calculated by using Pythagoras’s theorem.

A2 + B2 = C2

Example An aircraft is flying at 45 000 ft with an indicated DME of 175 nm. What is the true range?

45 000 ft = 7.4 nm Range = 1752 – 7.42

Distance = 174.84 nm

This results in a slant range error of 0.16 nm or 0.09%, which is negligible. Problems start when the aircraft is closer than 20 nm to the beacon.

Example The aircraft is at 30 000 ft, with an indicated DME of 20 nm.

What is the true range?

30 000 ft = 4.9 nm Ground distance = 19.39 nm The error is 0.61 nm or 3%

The slant error is almost negligible at long distances, but increases both with altitude and with decreasing DME distance. When using a DME at less than 20 nm range, a pilot must apply a slant range correction.

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Radio Navigation 7-8

FLIGHT OVERHEAD THE DME When an aircraft passes directly overhead a DME station, the DME indicates the altitude of the aircraft in nautical miles. For instance, if the aircraft passes at an altitude of 40 000 ft, the indication is about 6.6 nm. There is a cone of silence directly above the ground station. However, the arithmetic unit in the aircraft remembers the last computed data and continues to indicate the altitude for some time. FAILURE INDICATIONS If the system receives no signals of an acceptable strength it unlocks and only regains the tracking mode upon receiving the correct signal of an acceptable strength. The unlock condition is indicated by:

An off flag on the rotary indicator A red bar across the face of the digital indicator

Failure indications also appear upon switching the equipment on, and:

No signal is being received The received signal is below the minimum strength required The aircraft is out of range of the transponder

Switching the equipment off also results in an off indication. ACCURACY The DME is extremely accurate. ICAO prescribes a maximum system error of ± (0.25 nm + 1.25% of the slant range) on 95% of occasions.

Chapter 8 Instrument Landing System (ILS)

Radio Navigation 8-1

INTRODUCTION The instrument landing system is the primary precision approach facility for civil aviation. The definition of a precision approach is an approach that provides both glideslope and track guidance. ILS signals are transmitted continuously, and provide pilot-interpreted approach guidance. When flying the ILS approach, the ILS provides approach guidance for the descent to the decision height (DH), at which point the pilot makes the final decision to land or go around. All installations must conform to the standards laid down in ICAO Annex 10 and must include allocation of an appropriate performance category. Exceptions to these standards are published in NOTAMs. Many ILS installations use an associated DME to provide a more accurate and continuous ranging facility than that provided by the markers. A low power NDB, known as a locator beacon, may also complement ILS installations to provide guidance during the intermediate approach and into the final approach path marked by the ILS. The ideal flight path on an ILS approach is where the localiser plane and the glide slope plane intersect. To fly this flight path, the pilot follows the ILS cockpit indications.

PRINCIPLE OF OPERATION The ILS consists of the following components:

Localiser The localiser transmitter and aerial system provide the azimuth guidance along the extended runway centerline. Glidepath The glidepath and its aerial system provide the approach guidance in the vertical pane.

Marker Beacons Separate beacons (up to three) along the approach path provide the aircraft with range check points on the approach (discussed in Chapter 9).

Chapter 8 Instrument Landing System (ILS)

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OUTER MARKER

.

5 MILES 3250 FT

MIDDLEMARKER

INNERMARKER

GLIDEPATH TRANSMITTER(MAY BE EITHER SIDE)

LOCALISER TRANSMITTER

RUNWAY

Frequency The localiser and glidepath operate on separate frequencies:

Localiser VHF – 108 to 112 MHz using the odd first decimals and the odd first decimals plus 50 kHz: 108.10 MHz, 108.15 MHz, 108.30 MHz, 108.35 MHz, etc. Glidepath UHF – 329.15 MHz to 335 MHz at 150 kHz spacing: 329.15 MHz, 329.3 MHz, 329.45 MHz, etc. (The frequency band allocated is 328.6 MHz to 335.4 MHz. It is not necessary to remember these figures.)

The localiser and glidepath frequencies are paired. The glidepath is automatically selected upon selection of the ILS VHF frequency (the localiser).

Marker Beacons VHF – 75 MHz

Emission Characteristics A8W The localiser and marker beacons also radiate an A2A identifier.

LOCALISER The localiser transmitter aerial is located in line with the runway centre line, at a distance of approximately 300 metres from the “up-wind” end of the runway. The aerial, which is of frangible construction, may be 20 metres wide and 3 metres high, and consists of a number of dipole and reflector elements. The radio signal transmitted by the localiser aerial produces a composite field pattern consisting of two overlapping lobes. The two lobes are transmitted on a single ILS frequency, but are modulated differently so that the receiver can distinguish between them.

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The lobe on the left-hand side of the approach has a 90 Hz tone. The lobe on the right hand side has a 150 Hz tone. A receiver located to the left of the centre line detects more of the 90 Hz modulation tone and relatively less of the 150 Hz modulation. This difference is called DDM (Difference in Depth of Modulation) and causes the vertical indicator needle of the ILS to indicate that the centerline is to the left. Conversely, a receiver right of the centre line receives more 150 Hz than 90 Hz modulation and, as a result, the needle indicates that a correction to the left is necessary. With the needle in the centre the difference in depth of modulation is zero. Because the beam of the ILS localiser is very directional, unwanted side lobes are produced. To ensure that the aircraft does not pick up a false localiser signal the basic pattern shown above is covered with a clearance pattern. This changes the localiser signal to the one shown below.

COURSE SIDE LOBES PRODUCING SPURIOUS

EQUISIGNALS

1000 FT 90 Hz

RUNWAY

20° APPROX 150 Hz

RUNWAY EXTENDED CENTRE LINE NIL DDM

MAIN LOBE

THE COURSE RADIATION PATTERN

CLEARANCESIDE LOBES

RUNWAYAPPROX 70°

NIL DDMAPPROX 20°

COMBINED COURSE AND CLEARANCE RADIATION PATTERNS

Chapter 8 Instrument Landing System (ILS)

Radio Navigation 8-4

LOCALISER COVERAGE The ILS localiser covers:

± 10° of the centreline to 25 nm range ± 35° of the centreline to 17 nm range

17 NM

25 NM

Cen

tre

of L

ocal

iser

Ant

enna

Sys

tem

Course Line

25°

25°

10°

10°

Localisers paired with steep-angle glideslopes provide coverage from the centre of the localiser to distances of:

± 10° of the centreline to 18 nm range ± 35° of the centreline to 10 nm range

7°

P

300 m

The coverage of the localiser in elevation is determined as follows:

First calculate point “P”, which is the higher of a point 600 metres above the threshold and a point 300 metres above the highest point within the approach area.

Connect this point to the threshold. Draw a line 7° above the horizontal. The resulting shaded area corresponds to the localiser vertical coverage within its

horizontal coverage. The vertical coverage extends from ¾° above the surface up to 7°. The maximum field strength is directed along the centreline out to a range of 10 nm. If an aircraft is outside the coverage of the course and clearance patterns, it can lead to receipt of false localiser signals. In some cases these signals, caused by side lobes, can give reverse indications.

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The localiser signals are protected out to a range of 25 nm and up to a height of 6250 ft. The localiser is checked for accuracy out to a range of 10 nm. The above criteria should enable the aircraft to undertake the manoeuvres that are necessary to capture the localiser course at the outer limit of the coverage pattern and to carry out the subsequent descent on the glide path.

GLIDEPATH Placement of the glidepath aerial is 300 metres upwind from the threshold and 150 metres from the centre line. Placement is at the optimum touch down point at which the extension of the glide path intersects the runway. This ensures adequate wheel clearance over the threshold and over any other object or terrain during landing approach. Glide path transmission is in the UHF band on 40 spot frequencies from 329.15 to 335 MHz. UHF is used to produce an accurate beam. The transmission is beamed in the vertical plane in two lobes similar to that of the localiser. The upper lobe has a 90 Hz modulation, while the lower lobe has a 150 Hz modulation. The DDM (Difference in Depth of Modulation) energises the horizontal needle of the instrument, in order to indicate whether the aircraft is in the 90 Hz lobe or in the 150 Hz lobe. In this way, it gives the position of the centre line of the glide path. The line along which the two modulations are equal in depth, defines the centre line of the glide path. It is generally 3° from the horizontal, but could be adjusted between 2° and 4° to suit the particular local conditions. A glide slope much in excess of 3° requires a high rate of descent and is not common in public transport operations. In the vicinity of the landing threshold, the glide path becomes curved and gradually flattens. This is of consequence when considering a fully automatic landing. It is one of the reasons a Category III landing requires the use of a radio altimeter. The siting of the glide path aerial and the choice of the glide path angle depend on many interrelated factors:

Acceptable rates of descent and approach speeds for aircraft using the airfields Position of obstacles and obstacle clearance limits resulting Horizontal coverage Technical siting problems The desirability of attaining the ILS reference datum 50 ft above the threshold on the

centre line Runway length

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GLIDEPATH COVERAGE The coverage in azimuth extends 8 degrees on either side of the localiser centreline, to a distance of 10 nm.

10 NM

RunwayCentre Line

8°

8°

The coverage in the vertical plane extends from 0.45 θ to 1.75 θ where θ is the nominal glidepath angle above the surface (1.35° to 5.25° for a 3° glidepath). Remember that correct signals are guaranteed only within the approved coverage zones, and false indications can be received outside these zones.

(or to such lower angle, down to 0.30 θ, as required to safeguard the promilgated Glide Path Procedure).

Runway

1.75

0.45θ

θ

θ

Use of the glidepath below 0.45 θ that is below 1500 ft QFE at 10 nm range (for a 3° glidepath) should only be attempted when the Promulgated Glide Path Intercept Procedures requires the aircraft to fly at this level. The aircraft should never fly below 0.3 θ (0.9° for a 3° glidepath) which is 1000 ft at 10 nm range. When the procedure is designed to join a glidepath from above the pilot must bear in mind that a false glidepath may exist at approximately 2 θ (discussed later in this chapter).

AIRBORNE EQUIPMENT The ILS airborne equipment consists of:

A frequency control box A VHF localiser receiver A UHF glide path receiver A 75 MHz marker beacon receiver An ILS indicator

The installation includes three separate aerials, one for each receiver. Since all the marker beacons transmit on the same frequency, there is no need for a marker beacon control box. An audio coded signal automatically identifies markers, by the related transmission audio tone and a coloured light. FREQUENCY PAIRING Both localiser and glidepath are tuned using the same unit. This is possible because of international agreement under ICAO standards. Every localiser frequency has a paired glidepath frequency. Since the frequencies come in pairs, only the correct localiser frequency needs to be selected. The glide path receiver is then automatically tuned to the appropriate UHF channel. The VHF navigation receiver panel tunes the ILS frequency.

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LOCALISER AND GLIDEPATH RECEIVERS Once the localiser frequency has been tuned, both the localiser and the glide path receiver are activated, and they send the received signal to the indicator. The two receivers are similar to each other in that they both detect the modulations on the carrier wave. The modulations (90 Hz and 150 Hz) are compared and the Difference in Depth of Modulation (DDM) is measured. This output, which is in the form of a DC electrical signal, is used to drive the pointers on the display. If the aeroplane is on the centre line, the 90 Hz and the 150 Hz signals will have the same amplitude and the indicator needle will be centred. If the aircraft is not on the centre line, one signal will be stronger than the other and the resultant DC output energises the needle displacement. To indicate whether the received signals are adequate or not, a warning system is incorporated into the receivers. A red warning flag appears on the ILS indicator if the signal is not reliable. There are separate flags for the localiser and for the glide path signals. ILS INDICATOR The indicator consists of a dial, similar to the VOR indicator, but with an additional needle. Localiser signals displace the vertical needle, while glide path signals displace the horizontal needle. The same indicator normally provides for both ILS and VOR guidance. When the localiser receiver detects that the 150 Hz signal is stronger, it feeds a voltage to the localiser needle moving it to the left. This indicates that the localiser centre line is to the left of the aircraft on approach. If the 90 Hz signal is stronger, the voltage moves the localiser needle to the right, indicating that the pilot must turn right to get back on centre line. Full-scale deflection occurs when the aircraft is displaced 2.5° or more from the centre line. In other words, when tuned to a localiser frequency, the indicator is four times more sensitive than it is when tuned to a VOR (full scale deflection for a VOR corresponds to 10°). Unlike the VOR, which gives the pilot a choice of 360 radials using the omni-bearing selector (OBS), the localiser course is a single, fixed beam. Once a localiser frequency is selected, all the needle indications refer exclusively to the localiser centre line. Consequently, the fact that the instrument also contains the OBS selector has absolutely no significance and rotating it has no effect on the ILS indications. However, pilots should always turn the OBS to the correct inbound course for the sake of reference when flying the ILS. The localiser indicator does not provide any heading information. It only gives information regarding the geographical position of the aircraft. It displays how many degrees the aircraft is displaced from the localiser centre line.

Localiser PointerShows 3 DotsFly Right

Warning FlagAppears if Signalis Unusable

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The diagram on the previous page shows only the vertical localiser needle. A full illustration with the glidepath needle is below. The important features of the localiser needle are:

Full scale deflection is 2.5°. Each dot represents a deviation of 0.5°. A warning flag appears when the signal is unusable.

The horizontal needle of the indicator indicates the position of the glide path, relative to the aircraft. The vertical glide path scale on the usual cockpit indicator consists of 5 dots above and below the central position.

Glide Path PointerShows 21/2 DotsFly Up

Warning FlagAppears if Signalis Unusable

The full instrument has the horizontal glidepath needle with important features being:

Full scale deflection is only 0.7°. Each dot represents a deviation of 0.14°. As with the localiser, a warning flag appears if the signal is unusable.

If the 90 Hz signal is the stronger one, the aircraft is above the glide path and the indicator needle deflects down. This indicates that the aircraft must fly down to recapture the glide path. Conversely, if the receiver detects a stronger 150 Hz signal, the needle moves up, known as a fly-up indication. The glide path has a total depth of 1½°, making the glide path indicator considerably more sensitive than the localiser indicator. This means that for a full-scale deflection of the needle the aircraft must be at least 0.7° above or below the glide path. A “half-scale” (2½ dots) fly-up indication indicates the maximum safe deviation below the glide path. Deviation from the glide path is referred to in terms of dots instead of degrees, in that there are 5 dots above it and 5 dots below it on the instrument. Very accurate control is necessary when flying down a glide path. A more sophisticated instrument, used to fly an ILS approach, is the horizontal situation indicator.

HORIZONTAL SITUATION INDICATOR (HSI) With the HSI, the course arrow must be manually aligned with the localiser inbound course. Using the deviation bar provides localiser guidance. A scale alongside the instrument provides the glide path position.

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ILS ACCURACY Up to now, the ILS has been viewed as an instrument that provides assistance in landing approaches. This means that the ILS provides guidance down to a specified height above the threshold. If the visibility at this point is good enough for landing, then the pilot may legally land the aircraft. If the existing weather does not permit the pilot to see the visual references at the prescribed minima, the aircraft cannot land. Operators were not happy about the prospect of delaying a flight or wasting time and fuel while holding overhead an aerodrome and waiting for the weather to clear. This required an improved ILS system. Obtaining these improvements requires considering certain limitations of the system. The main problems come from bends and scallops in the beams.

Bending

Scalloping

Bending of the beam is a single angular displacement from the approach path. Scalloping is where the guidance beam direction varies from side to side of the

intended approach path. Reflections from obstacles on and around the aerodrome produce these bends, such as airport structures, vehicles, aircraft flying overhead the localiser aerial, etc. The ability to use ILS installations for fully automatic landing has necessitated that ICAO lay down stringent requirements and that both ground and airborne equipment are constantly improved. These requirements concern the quality of the transmitted signal data and the suppression of bending of the radio beams by improvement in aerial design in order to reduce unwanted reflections.

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FALSE BEAMS Even with strict monitoring of all the ILS ground equipment, there are unavoidable factors to consider. The first of these is false signals. This problem is particularly associated with the glide path transmission and occurs because of the aerial’s propagation characteristics. The number of such false glidepaths produced at any ILS site depends on several factors, such as the design of the aerial, transmission power, obstacles and other such factors. These false glide paths occur at multiples of the nominal glide path. As a result, the first occurs at approximately 6° above the horizontal for a glide path of 3°. There is never a false glide path below the true one. Consequently, the recommended practice when carrying out an ILS approach is to lock onto the localiser first and then intercept the glide path from below.

Outside the localiser ‘protected area’, it is possible to encounter false localiser beams. The angle from the actual centre line to the false beams varies with the number of aerial elements. Six elements produce a false beam at approximately 40° and 12 elements at 50° to 60°. LOCALISER BACK BEAM Some localisers transmit in the opposite direction of the ILS inbound course and the signal is receivable when flying behind the aerial. This signal, called the back beam, should normally not be used. Some transmitters, however, are designed to radiate a back beam. This beam can provide a back course approach to the reciprocal runway. Note that when using a back course pilots do not have the benefit of a glide path. Usually, back beams are less accurate than front beams. They are not checked for accuracy unless they are a part of published procedure. Do not use a back beam unless it has a published procedure.

SIDE-LOBES PRODUCINGFALSE GLIDE PATHS

GP NOT CORRECTLYDELINEATED INFINAL STAGES

ILS REFERENCE

RUNWAY

1000 FT

GP AERIAL OFFSETA SAFE DISTANCE

FROM RUNWAY

50 FT APPROX. ABOVE THRESHOLD

VERTICAL COVERAGE

TO 1.75 ABOVE HORIZONTALηAT LEAST FROM 0.45 BELOWη

η BETWEEN 2° AND 4°(NORMALLY 3°)

90 Hz PREDOMINATES

G.L. GLIDE PATH - NIL DDM

150 Hz PREDOMINATES

SIMPLIFIED DIAGRAM OF GLIDE PATH RADIATION PATTERN

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Note that, when flying the localiser back beam approach, pilots must be very careful in interpreting the course selector. When using a conventional ILS indicator for a back beam approach, the localiser needle gives a “fly left” indication when the aircraft is left of the centre line and vice versa. In other words, the pilot experiences a reverse sensing. Such reverse sensing occurs regardless of course selector setting. Conversely, when flying with an HSI display, the pilot receives normal indications (i.e. “fly left” when the aircraft is to the right of the centre line) if the course selector is set to inbound track on the localiser front beam. When the course selector is set to the back beam course, it provides reverse sensing.

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The graphic above shows a plate for a back beam approach at Lista in Norway. Back beam procedures are not common in Europe.

ILS PERFORMANCE CATEGORIES A system of facilities performance categories defines the capability of a particular ILS system. These categories state that the ILS must be capable of providing guidance from the coverage limit as follows for:

Category I to a height of 60 metres above the horizontal plane containing the threshold

Category II to a height of 15 metres above the horizontal plane containing the

threshold Category III with the aid of ancillary equipment when necessary, down to and along

the runway. ILS OPERATIONAL PERFORMANCE CATEGORIES A similar categorisation exists for operational purposes, and it is to these limits that the pilot flies. These categories establish practical weather minima for an approach. Pilots must be familiar with the following ILS operational minima.

ILS Cat I: DH down to 200 ft, RVR 550 metres ILS Cat II: DH down to 100 ft, RVR 350 m ILS Cat IIIA: DH 0 to 100 ft, RVR 200 m ILS Cat IIIB: DH 0 to 50 ft, RVR 50 – 200 m ILS Cat IIIC: No external visual reference

When flying a Category I approach, reference is to the barometric altitude, but for a Category II or III approach reference is to the radio altimeter. In a Category I ILS approach, also called CAT I, the pilot may manually follow the ILS indications down to the decision height (DH), which is not less than 200 ft. At that point, if visual contact has been established, the landing can be made. If not, the pilot must initiate a go-around. Note that the ILS coverage, described earlier in this chapter, refers to ILS Category I. Category II and III requirements are more stringent. ILS CAT I, although still widely used, is gradually being replaced by CAT II & CAT III facilities. On a CAT II approach, the aircraft must be flown by the autopilot down to the DH. From there, if visual contact has been made, the pilots can make the landing. Otherwise, they must initiate a go-around. A CAT II approach can only be made at a Category II certified airport. The localiser and glide path transmissions must meet stricter standards than for a CAT I system. The transmissions must be monitored and failure indications must be available in the control tower. In addition, two RVR (Runway Visual Range) transmissometers must be operating on the runway, and extensive airport lighting requirements must be met. A CAT II approach requires an aeroplane with CAT II equipment certified by the regulatory authority. Additionally, special training programmes must be certified and conducted for the flight crews. Category III approaches require the same criteria as those for CAT II but with additional, more stringent, requirements. This is because the aircraft must have guidance all the way down to the runway. The autopilot must perform the CAT III approach.

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The performance of the airborne equipment must match the improvement in the ground equipment. To this end, operational performance categories have been established. They correspond to the facility performance categories. In accordance with its airborne equipment, an aircraft is certified in one of the listed categories. Naturally, aircraft and airport performance categories are required to conduct any of the approaches. Remember that in order to perform a CAT II or CAT III approach, not only must the airport and the aircraft be properly equipped and checked, but so must the flight crew. Unqualified and untrained pilots may not carry out a precision approach. PROTECTION RANGE AND MONITORING National and regional frequency plans have been established by the ICAO and are adhered to by contracting states. These plans take many factors into account, such as the sensitivity and selectivity of receivers, and the channel spacing and geographical proximity of transmitters. In this way, interference between facilities is reduced to negligible proportions. Within Europe, the congested radio frequencies have resulted in FM transmissions from aerials that are close enough to allow side band interference to spill over into the ILS frequencies. These can cause random displacement of the localiser, so be aware. Monitoring equipment automatically and continuously checks both localiser and glide path transmitters. The monitors take action whenever they sense a shift or change in the basic transmission. If the ILS is Category II or III the transmissions are stopped within 2 seconds. If Category I, the transmissions are stopped within 6 seconds. The localiser and glidepath monitors take action when:

The mean course line shifts by: Category I: ± 35 ft Category II: ± 25 ft Category III: ± 10 ft

The glidepath angle changes by > 0.075θ

3° Glidepath: 0.225°

A reduction in power of 50% or more in any transmission If a monitor operates, the standby unit will be used. Before this happens:

All radiation stops The identification stops For a Category II or III operation, the system may allow degradation to a lower

category operation

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USE OF ILS ILS IDENTIFICATION Because the localiser and glide path frequencies are paired, selecting a localiser frequency automatically activates the glide path receiver so that the corresponding glide path signal is automatically received. The ILS must be identified before use. The identification is transmitted on the localiser frequency and is amplitude modulated by a 1020 Hz (A2A transmission) tone. A two or three letter Morse code transmitted at a rate of seven words per minute. The letter “I” may precede the identification. When an ILS is undergoing maintenance or is being used for test purposes, the identification is completely removed and a continuous tone replaces the coding. In both cases, the ILS must not be used. FLYING THE LOCALISER When initiating the approach, the localiser indicator shows the position of the aircraft in relation to the centre line and provides no heading information. Thus the term “follow the needle” is only valid when flying inbound within the coverage area. For an aircraft on approach, the localiser needle indicates which way the aeroplane should move to regain the centre line. If the localiser needle is to the right, then the aircraft should be flown to the right. To regain the centre line, fly toward the needle. The aim is to fly a heading that maintains the aircraft on the centre line. If a crosswind exists, a wind correction angle (WCA) is required and the aircraft heading differs slightly from the published inbound course. The localiser beam narrows as the aircraft approaches the runway. As a result, corrections should become smaller and smaller.

FLYING THE GLIDEPATH The horizontal glide path needle should be flown in the same way as the localiser needle. To regain the glide path, fly toward the needle. The needle is the pilot’s glide path. If the glide path needle is below centre, the aircraft is too high and requires a steeper descent. Remember that the closer the aircraft is to the threshold, the more dangerous a high descent rate is. If the aircraft is not properly established on the glide path, stop the approach. Do not continue to hunt the glide, and if in doubt, carry out a missed approach. With an angular depth of only 1.4° (0.7° above and below), the glide path needle is three times more sensitive than the localiser and 15 times more sensitive than the VOR. When following a glide path, the rate of descent is the pilot’s reference, so the vertical speed indicator becomes important. Determine the proper vertical speed before starting the descent on the glide path. Instrument approach plates usually give the rate of descent related to the ground speed of the aircraft during the approach. As a rule of thumb or guide, the rate of descent (in fpm) may be calculated as half the ground speed, in knots, with a zero added. This is valid for a glide path of 3°. A ground speed of 120 kt during final approach requires a 600 fpm descent rate.

1000 FT NOMINAL

LOCALIZERTRANSMITTER

(100 WATTS)

4° ON LONG RUNWAY6° ON SHORT RUNWAY

TOTAL COURSE WIDTHIS 700 FT WIDE AT THRESHOLD

5 DOTS OR FULL SCALEDEFLECTION

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As a general rule, use the pitch attitude to control the glide path and the throttle to control the airspeed. When flying the ILS procedure the pilot must continuously monitor all the instruments, and follow both ILS needles at the same time. This phase of flight requires a great deal of accuracy and attention. Look at the indications of the needles relative to the aircraft’s position. The same rules apply when using the horizontal situation indicator, but naturally the localiser tracking is simpler. Normally the HSI has a scale along either side of the instrument, on which glide path information appears. As shown, many instruments are involved in an ILS approach: The localiser and glide path indicators, the directional gyro, the airspeed indicator, the vertical speed indicator, and the altimeter. Recently, there has been a tendency to group all these instruments into a single display. ILS WITHOUT GLIDEPATH If glide path information is not available, either because of equipment failure on the ground or glide path receiver failure in the aircraft, the ILS automatically becomes a localiser approach. In some cases, ILS installations may be purposely commissioned without glide slope. Since no vertical guidance is provided, localiser approaches are non-precision approaches. They are similar to VOR approaches except for the fact that a localiser course is four times more sensitive than a VOR course. In addition, localiser approaches normally include marker range indicators. The minimum descent height (MDH) for a localiser approach is never lower than 250 ft, whereas the DH for ILS with glide path can be 200 ft (ILS Category I). The next two pages show the approaches to Coventry on Runway 23. The first plate is for a normal ILS approach. The second plate is for the localiser-only approach.

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Note: For a Category A aircraft the OCA is 431 ft.

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The OCA on the localiser only approach for a Category A aircraft is 635 ft. The Category A aircraft OCA for the ILS on the previous page is 431 ft. The difference occurs because a precision approach, such as an ILS, allows the aircraft to a lower DH than the localiser only non-precision approach where a MDA is used. DISTANCE MEASURING EQUIPMENT It is common to find a DME paired with an ILS frequency to supplement the marker beacons or very often, to replace them. All information is zero-referenced to the threshold. The ILS DME is protected from other DME services only within the localiser service area described earlier up to a height of 25 000 ft. RATE OF DESCENT (ROD) The rule of thumb is only valid for a 3° glidepath. To calculate the ROD for any other glidepath, use the 1 in 60 rule:

ROD = θ x groundspeed (miles per minute) x 101.3

Example: For a 4° glidepath at a groundspeed of 120 knots, the rate of descent should be:

4 x 2 x 101.3 = 810 fpm

HEIGHT PASSING ON THE APPROACH Using a similar method, the height an aircraft should be passing at any given range from either the threshold or touchdown can be calculated.

Height Passing = θ x Range from touchdown (nm) x 101.3

Example: For a 4° glidepath, an aircraft is 4.5 nm from touchdown. What height should it be passing?

4 x 4.5 x 101.3 = 1824 ft

If range from the threshold is provided, add 50 ft to the answer as the aircraft is assumed to be passing 50 ft as it passes over the threshold.

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Radio Navigation 9-1

INTRODUCTION Marker beacons are radio beacons transmitting their power vertically toward the sky. All marker beacons transmit on the same frequency. The marker beacon is only received when the aircraft is directly overhead. The marker beacon cannot be used as a tracking aid for navigation purposes.

PRINCIPLE OF OPERATION The transmitted beam forms a polar diagram in the shape of a vertical fan or funnel-shaped lobe. There are four types of markers:

Airway marker (fan marker) Outer marker Middle marker Inner marker

The indicators for marker beacons are small coloured lights on the instrument panel marked:

A Airways Marker O Outer Marker M Middle Marker

No inner marker indicator is shown. The inner marker is now part of military installations only. The beacon and its limitations are included since military airfield systems are used for both training and commercial practices. Frequency VHF - 75 MHz Emission Characteristics Amplitude modulated, A2A emission, with different audio frequencies in order to distinguish between the different types of markers.

AIRBORNE EQUIPMENT All marker beacons transmit on the same frequency and there is no need for a frequency selector in the receiver. Besides the receiver unit, the airborne equipment consists of three coloured lamps and a sensitivity switch. Audio output is channelled through the audio panel of the nav/com installation of the aircraft.

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Signals received from the marker beacons first pass through a 75 MHz filter, then to the RF amplifier and detector. The sensitivity switch (HI/LO) acts as a gain control on the RF-amplifier input. Whichever audio tone is modulating the carrier triggers detector output. Three audio filters discriminate audio tones. The diagram below shows passage of the different markers.

250 FT.(±25 FT.)

500 FT.(±160 FT.)

1000 FT.(±325 FT.)

2000 FT.(±650 FT.)

3500 FT.(±500 FT.)

31/2 to 5 NM

Runway

InnerMarker

MiddleMarker

OuterMarker

Glide Path (Exaggerated)

The outer, middle, and inner markers are parts of the ILS installation and are used when conducting an ILS approach to an airfield. Remember that the inner marker is only used at military installations.

The Inner Marker has a modulating signal frequency of 3000 Hz with an audio tone of 6 dots per second. The white indicator lamp flashes on the indicator panel. The Middle Marker has a modulating signal frequency of 1300 Hz with an audio tone of alternate dots and dashes at a rate of 2 dashes per second. The amber indicator lamp flashes on the indicator panel. The Outer Marker has a modulating signal frequency of 400 Hz with an audio tone of continuous dashes at a rate of 2 dashes per second. The blue indicator lamp flashes on the indicator panel

Position Marker Distance From Threshold

Deviation Allowed

Light Signal Modulation

Outer 3.5 to 5 nm - Blue Continuous dashes

400 Hz

Middle 3500 ft ± 500 ft Amber Alternate dots and dashes

1300 Hz

Inner 250 ft ± 25 ft White Continuous dots

3000 Hz

Since the transmission pattern is fan-shaped, the horizontal area of reception depends on aircraft altitude. Where the aircraft is on the glidepath, the distance of travel where the beacon is received is:

Outer Marker 2000 ft ± 650 ft Middle Marker 1000 ft ± 325 ft Inner Marker 500 ft ± 160 ft

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With airways markers, in order to get a more precise indication and to avoid receiving ILS markers at high altitude, the ILS Marker sensitivity switch on the panel is set to low. AIRWAY MARKER As the name indicates, the airway marker is used while route-flying along airways as follows:

To identify certain fixes along routes where there are no other means of establishing the fix

When flying over mountainous areas, it works where it is difficult or impossible to receive other navigation aids aside from the one being tracked

To supplement an NDB by providing vertical cover above the cone of silence

Some markers, usually modulated with 3000 Hz, function to mark important points such as significant positions in a noise abatement procedure. Airway markers are becoming rare, as are the inner markers of ILS.

GROUND INSTALLATION Airway marker usage is decreasing; however, they still appear along airways in order to establish accurate reporting points. In areas with poor radio-coverage, such as mountainous areas, airway markers can provide a point source fix. With the sensitivity switch set to high, these markers can reach as high as 50 000 ft. The outer, middle, and inner markers are parts of the ILS installation, and are all installed along the extended centre line from the approach end of the runway. The outer and middle markers are no more than 75 metres from the extended centreline. The inner marker is installed no more than 30 metres from the extended centreline. Glidepath crossing heights at the different markers are published on the appropriate approach plate for the actual ILS approaches. When on the glide slope, the outer marker crossing height is approximately 1500 to 2000 ft dependent on the glideslope angle. The purpose of the outer marker is to provide height, distance, and ‘equipment functioning’ checks to aircraft on intermediate or final approach. The middle marker is crossed at approximately 200 ft AAL, which is close to decision height for a Category I ILS approach. The purpose of the middle marker is to indicate the imminence, in low visibility conditions, of visual approach guidance. The purpose of the inner marker is to indicate to the pilot that the aircraft is about to pass the threshold. The height is the lowest decision height applicable in Category II operations.

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Radio Navigation 10-1

INTRODUCTION ILS has served as the primary precision approach and landing aid since the last war. Since the mid 1980s, the limitations of the system prompted ICAO to develop a replacement system to fulfill the needs for future aviation. The limitations of the ILS are:

Procedurally, ILS limits aircraft to long straight-in final approaches of at least 7 miles. This creates potential airspace conflicts in multi-airport environments and constrains the number of possible approach paths. Each ILS provides only one approach path for one aircraft at a time.

Direct and ground-reflected signals form part of the ILS guidance signal, and require a significant level of site preparation. ILS can only be installed at locations where site preparation is practical.

ILS is limited to 40 frequency channels constraining the number of sites that can be allocated a frequency in a given geographical area.

The ILS frequency band suffers from interference from high power FM transmitters operating in adjacent bands. Aircraft receivers contain FM filters, which narrow the band of reception and reduce this ‘noise’ interference but this is still a limitation. At some airports, interference can cause the ILS to receive local radio broadcasts.

ILS is sensitive to signal diffraction and blockages caused by ground traffic, necessitating the use of large protected areas on the airport surface (critical areas). Within these areas, the ground movement of vehicles and aeroplanes must be prohibited. This reduces the effective capacity of the airfield during low visibility operations.

These limitations led to the development of a microwave landing system. Parallel to the development of MLS, the civilian use of satellite-based Global Positioning System (GPS) was also under development, both as an enroute navigation aid and, with augmentation systems, as an approach aid. The development of GPS has advanced so that, in some countries, further development and installation of MLS has been abandoned. In practice, this chapter describes a system pilots may never encounter in their careers.

PRINCIPLE OF OPERATION The MLS system is a precision approach system that provides the pilot with highly accurate azimuth and elevation information. It also utilises a precision DME (DME/P) which provides highly accurate ranging information. The MLS system can also transmit other types of information to the aircraft such as station identification, system status, runway information, and weather. Frequency SHF – 5031 to 5090.7 MHz. Spacing 300 kHz, giving 200 channels Polarisation Vertical

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GROUND INSTALLATION This is a completely digital system that is not influenced by weather or other common sources of disturbances. The system allows for several approach paths, both in azimuth and elevation at the same time. As with visual approaches, MLS lets the air traffic controller clear the aircraft for curved approach paths, with a straight-in final segment being as short as 1.5 nm. This leads to a significant reduction in air traffic delays. The ground installation consists of the following three main elements:

Azimuth (AZ) Elevation (EL) Precision DME (DME/P) Some installations may also contain Back Azimuth (BAZ)

AZIMUTH COVERAGE The azimuth (AZ) part of the installation is comparable to the localiser of the ILS except that it provides a much wider area of information, up to 40° on each side of the extended centre line.

APPROACHELEVATIONANTENNA

APPROACHAZIMUTHANTENNA

45 m (150 ft)

45 m (150 ft)MLS DATUM

POINT

THRESHOLD

40°

40°

37 km (20 NM) CL

APPROACHDIRECTION

LATERAL COVERAGE ADDITIONALCOVERAGERECOMMENDED

6000 m (20 000 ft)

600 m (2 000 ft)

30°20°

15°

2.5 m (8 ft)

APPROACHAZIMUTHANTENNA

0.9°

HORIZONTAL

37 km (20 NM)

VERTICAL COVERAGE

COVERAGE OF LOCALIZER EQUIVALENT

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The system provides the AZ out to 20 nm and the BAZ to 5 nm (ICAO minimum). The azimuth coverage is:

± 40° of the runway centreline out to 20 nm Vertical coverage of the beam is 0.9° to 15° Has a beam no more than 4° wide

ELEVATION COVERAGE

The elevation (EL) part is comparable to the glide path of the ILS. The main difference is that the pilot can choose the desired glide path angle (up to 15°). The elevation coverage is:

± 40° of the centreline to 20 nm The aerial scans vertically from 0.9° to 7.5° above the horizontal (most systems can

scan to 15°) The system has a beam no more than 2.5° wide

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DME/P The DME/P is an integral part of the MLS system. The DME/P signal defines two operating modes, Initial Approach (IA) and Final Approach (FA). The IA mode design improves accuracy for the initial stages of approach and landing. The FA mode provides substantially improved accuracy in the final approach area. The DME/P coverage is at least 22 nm from the ground transponder. The interrogator does not operate in the FA mode at ranges greater than 7 nm from the transponder site, although a transition from the IA mode may begin at 8 nm from the transponder. These ranges assume that the transponder location is beyond the stop-end of the runway at a distance of 2 nm from the threshold. BACK AZIMUTH The back azimuth (BAZ) provides navigational guidance for precision departures and for missed approach procedures. In practical installations, the coverage in the horizontal plane can vary according to local conditions and needs and does not have to be symmetrical on each side of the centre line. SIGNAL TRANSMISSION FORMAT The AZ and EL elements transmit on the same frequency, while the DME uses a paired channel in the UHF band. The format of the digital signal is very flexible and the information from the different elements can be sent in any desired order. A preamble precedes each group, which tells the processor in the receiver which functions are being sent. As soon as decoding is complete for one group, the processor is ready and waiting for the next element. There are two types of signals sent, basic data and auxiliary data:

Basic Data directly relate to the operation of the landing guidance system. Station identification is a part of the basic data. Auxiliary Data is other data used for siting information and other information not directly related to the guidance system.

Measuring the time difference between successive passes of the highly directional fan-shaped beams derives the angular measurements required by the aircraft. The DME/P provides the distance measurement. Using a system called time division multiplexing allows accommodation of all information required by the aircraft on the same channel. This means that an aircraft can decode the incoming signal in a sequential manner. Each function is a separate entity within the format and a preamble identifies all functions This preamble sets up the receiver processing circuits, which then decode the remainder of the function transmission. Once the decode is complete, the receiver waits for the next function preamble and the process repeats itself. The diagram below explains the approach azimuth signal. As well as information regarding the position of the aircraft, this signal can carry extra information.

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Each angle function transmission consists of four elements:

The preamble consisting of a synchronising code plus a function identity code A series of pulses for azimuth guidance The “TO” and “FRO” angle scan Two pulses which provide a system check

If the aircraft is close to the ground, the process then begins for the flare information. TIME REFERENCE SCANNING BEAM ANGULAR MEASUREMENT IN AZIMUTH AND ELEVATION The aerial transmitting the AZ beam, forms a vertical narrow fan-shaped beam, which scans from one side to the other and back at a constant angular velocity.

+40°

-40°

+40°

-40°

AzimuthAerial

'To' Scan

Time interval isDirectly Related to

Azimuth Angle'To' ScanBegins

'Fro' ScanEnds

ReceivedSignals

Amplitude

MeasurementThreshold

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The total scan of the beam lasts 9000 microseconds (µs):

4000 µs for the “TO” scan 1000 µs resting time 4000 µs for the “FRO” scan

In the diagram above, the aircraft is 15° left of the centreline. The system receives the “TO” scan after x microseconds. The “FRO” scan occurs after y µs. The measured intervals of time provide the aircraft’s azimuth. Calculating the vertical position (EL) occurs exactly in the same way as the horizontal with one exception. The scanning beam moves in the vertical plane, first up and then down. Normally the horizontal AZ- scan repeats 13 times per second, while the vertical EL- scan repeats 39 times per second.

AIRBORNE EQUIPMENT The aircraft receiver measures the time passage between the “TO” and “FRO” scans of both the AZ and the EL elements. These time measurements allow calculation of both the azimuth and elevation angles. When coupled with a range measurement from the DME/P, they allow the pilot to establish a three-dimensional aircraft position. In its simplest form, this position can be compared with a planned approach path and, if not on that path, can be used to create an error signal, which can drive the conventional ILS indicator to show displacement from the selected azimuth and glide path approach. The conventional ILS indicator is used since it is also required for conventional ILS approaches. Therefore, the indicator is multi-mode. More sophisticated computerised systems would allow the full potential of MLS to be realised, making it possible to follow curved and segmented approaches. If the DME/P is not available, the system still provides an ILS look-alike approach. ACCURACY When used with a Category III system, accuracy is ± 20 ft in azimuth and ± 2 ft in elevation.

Radio Navigation 11-1

PULSE TECHNIQUES AND ASSOCIATED TERMS This chapter discusses the uses of radar. To understand how these various types of radar operate requires refreshing and expanding some fundamentals and expressions related to radar. Chapter 1 gives some of the basic principles of radar. This chapter expands on those principles. The following is a review of some of the terms used:

Frequency f Hertz Hz Wavelength λ metres m Speed of light C metres per second m/s Time intervals – t milliseconds ms t microseconds µs Pulse Width PW microseconds µs Pulse repetition interval PRI microseconds µs Pulse repetition frequency PRF pulse per second pps Duty cycle DC no units Radar mile microseconds

THE COMPONENTS OF A RADAR UNIT A radar unit consists of:

A transmitter An aerial A receiver (and possibly a receiver aerial) A timebase A display

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Look at each of those elements in simple terms:

Magnetron

Modulator

T/R Switch

Timebase

Receiver

Display

Within the transmitter, the timer unit triggers a supply of RF signals to the modulator. The modulator forms the pulses and passes these to the magnetron where they are amplified to a very high energy level. This high-energy pulse travels through a waveguide via the T/R switch to the aerial where it radiates outward. The receiver is isolated from the aerial to ensure that there is no damage from this high-energy pulse. After the pulse passes the T/R switch, the switch recovers and the receiver, using the same aerial, waits for an echo of the energy returning, after it bounces off a target. THE TIMEBASE The timebase connects to the transmitter and receiver and knows when a pulse is sent and when an echo received. Measuring time between these two events and using the speed of an electromagnetic wave determines a range. THE DISPLAY In simple radar systems, the timer and display are a single unit known as a plan position indicator or PPI. In many modern applications, the information from this timer is processed and sent, with other information, to a suitable display. This is particularly evident in modern Air Traffic Control systems. THE TRANSMITTER Like other transmitters, the radar transmitter consists of a RF generator, a modulator, and an amplifier. The RF generator creates the transmission frequency and the modulator creates the pulses of energy. CHOICE OF FREQUENCY A number of factors govern the choice of frequency (wavelength):

Attenuation Attenuation due to intervening weather can be high so returning signals are very weak.

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Target Size The relative size of the desired target must be considered. Smaller targets require shorter wavelengths in order to create reflection of energy. Aerial Size If space is limited and aerial size is restricted, shorter wavelengths give narrower beams. Pulse Length The energy content of a pulse increases with the number of cycles transmitted during the pulse.

The following are commonly used frequencies:

1000 MHz 30 - 50 cm Long Range Surveillance 3000 MHz 10 cm Surveillance Radar & Approach Radar 10 000 MHz 3 cm Approach Radar

The modulator creates pulses of the desired length and at the desired rate. Factors affecting the choice of pulse length include:

Minimum Detection Range Since the aerial is common to both transmitter and receiver, it is important to protect the sensitive receiver from the high power pulse. As a result, the receiver is disconnected from the aerial during the transmission of the pulse (and for a short interval after). Range Discrimination The ability to detect separate targets that are on the same bearing (azimuth) and are close together depends on pulse length. For example, if a pulse length is 4 microseconds (4 µs) its physical length is 1200 m. If two targets lie on the same bearing and are within 600 m of each other, they both illuminate at the same time and their echoes merged at the receiver. If the two targets are so close that the beamwidth covers both aircraft then only one target is visible. Range The longer the pulse the greater the energy content, permitting the pulse to travel farther before attenuation and increasing the return of detectable energy from distant targets.

Choice of PRF is also affected by a number of factors including:

Design Maximum Range The transmitter must remain ‘silent’ while the receiver is ‘listening’ for echoes. If the design maximum range is 200 nm from the receiver it is necessary to allow it to listen for the period of time from when a pulse transmits until it can go 200 nm and then return. That is a round trip of 400 nm, which would require a silent period of 2473.3 ms. This would be the minimum PRI (pulse repetition interval). In practice, the minimum PRI would be increased to allow for receiver recovery time. The PRF is the inverse of the PRI so that, if the PRI was 2500 ms the PRF is 400 pps.

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Data Acquisition If the pulses are of short duration (1 m or less) it takes up to six echoes to cause the radar display to show the target echo. The PRF must be sufficiently high to allow this to occur in the period of time that the effective part of the aerial is pointing toward the target.

THE AERIAL A highly directional aerial system is necessary in order to concentrate the transmitter power and increase the effective pulse power and provide azimuth information. The systems most commonly used consist of either a wave-guide horn and parabolic dish or a flat plate “phased array” system. Both systems are designed to focus the radiated energy into a narrow beam.

The radar pulses go through the wave-guide horn and reflect from the parabolic dish. This acts very much as the reflector in a car headlamp. BEAMWIDTH The polar diagram from such an aerial assembly appears with a main lobe and a number of smaller side-lobes. The side-lobes are not desirable and may, on some systems, be suppressed by modification of the reflector or by use of suppression systems.

Beamwidth Main Beam

The beam width is the angle contained between the ½ power points on the polar diagram. This determines the radar’s ability to discriminate between targets that are close together and at the same range. If, for example, two targets are at a range of 60 nm and are separated by 1 nm, a beam of more than 1° allows both targets to be ‘illuminated’ at the same time (1 in 60 rule). The reflections from these targets merge at the receiver and they appear as one echo on the display. As long as a target is within the beam, it remains illuminated and continues to paint an echo. All targets therefore appear to have an azimuth dimension equal to the beam width irrespective of the physical size of the target.

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For a parabolic reflector, the beam width can be calculated from the following relationship:

Beam width° = 70λ ÷ d

In this formula, λ is the wavelength of the transmission and d is the dish diameter. Both λ and d must have the same units.

Example: What dish diameter is needed to get a 1° beamwidth at a 25 cm wavelength?

1 = (70 x 25) ÷ d d = 70 x 25 d = 1750 cm = 17.5 m

On 10 cm radar the same beam width is possible with a 7 metre dish. 1 = (70 x 10) ÷ d

d = 70 x 10 d = 700 cm = 7 m

In order to provide coverage, the aerial is rotated in azimuth so that the beam rotates. The direction in which the aerial points when illuminating a target provides the azimuth (or bearing) information. An electronic link relays this direction to the display. The display may be either analogue or digital. The rate of the aerial rotation must be matched to the criteria that affect the PRF selection. It must be sufficiently high to allow for renewal of target information at short enough intervals of time, while at the same time, it must be slow enough to allow for sufficient echo comparison in order to allow the display to show the target. THE RECEIVER This unit detects the extremely low energy signals reflected from a target. The receiver is, consequently, extremely sensitive and has a very powerful amplifier circuit. It must be protected from the very high energy of transmissions from the same aerial, so it is electronically disconnected during transmission. This means that the receiver is dead during transmission and for a short period afterward, known as receiver recovery time. The duration of time that the receiver is inactive governs the minimum range at which a target is detectable. After detection and amplification, echoes from the target go to the display. In the case of ATC radar, the echoes include returns from fixed objects on the ground, and these may well hide the returns from aeroplane targets. In order to remove these stationary targets, signals are filtered by a circuit known as Moving Target Indicator (MTI). If the target is moving radially toward or away from the aerial, the frequency of the echo pulseschange due to Doppler effect, increasing if the target is moving toward the aerial and decreasing if moving away. There is no frequency change from stationary targets, so the receiver circuit can be designed to reject all signals that do not exhibit a change in frequency. This introduces another problem if a moving target happens to fly so as to stay at the same distance from the radar. In that case, there is no radial motion and no Doppler effect. The MTI circuit could reject such targets unless measures occur to counteract this problem. Varying the transmissions achieves this in modern units.

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TIMER – CATHODE RAY TUBE In its simplest form, the timer is combined with the display, and consists of an electron gun and screen assembled into a unit known as a Cathode Ray Tube (CRT), as illustrated below.

The elements of this unit have the following functions: CATHODE When heated, the cathode emits electrons. Due to the great heat required to expel the electrons from the parent metal, tungsten is generally used. GRID The annular grid restricts the flow of electrons. By applying a negative voltage the electron flow can be:

Cut off if the grid is at a maximum negative voltage A maximum if the grid has no voltage applied

The grid controls the brilliance of the CRT. FOCUSSING ASSEMBLY The focussing assembly consists of 3 anodes at different potentials. These anodes both focus and accelerate the electrons. The electrons are attracted at high speed to this group of annular anodes which are all at a high positive potential with respect to the cathode. The higher the potential used the higher the electron velocity. Due to this high velocity, large numbers pass through the apertures. This means the emerging beam has enough energy to strike the screen at the end of the tube. The potential in anodes 1 and 3 are constant with the potential in anode 2 being variable. By using a variable potential in anode 2 the focal length of the beam can be adjusted.

FIRST ANODE

THIRDANODE

HEATER/CATHODE /GRID ASSEMBLY

SECONDANODE

X PLATES

Y PLATES

AQUADAG-WALL ANODE (INTERNALLY CONNECTED

TO THIRD ANODE)

FLUORESCENT SCREEN

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ELECTRON BEAM DEFLECTION To write usable information on the screen the beam must be deflected in a controlled manner. Two plates are set in the CRT, the X for horizontal scanning and the Y plates for vertical scanning. SCREEN The screen is coated with a chemical salt that gives a fluorescent glow when the electron beam strikes it. When the electrons strike the screen, the heat produced allows electrons from the chemical screen to be freed (called secondary emission). This forms a cloud of electrons which can inhibit the energy of the electron beam and cause a loss of brilliance. Covering the screen wall with a carbon coating – Aquadag, removes the secondary emission. The aquadag is charged to a high positive potential which attracts the secondary emissions. The screen wall is also known as the final wall anode. TIME BASE In the CRT, the stream of electrons striking the interior surface of the screen causes the screen to fluoresce at the point of impact. If the electron stream is deflected, the spot leaves a trace image.

T

0 200

X2 X1

Y1

Y2 In the illustration above, if a high negative electrical potential is applied to plate X1, the electron beam is held to the left at plate X2. This equates to zero range. Changing this negative potential at X1 at a constant rate from negative to positive causes the electron beam to move toward X1. The spot moves from the left to the right at a constant speed, leaving a straight line traced behind. Knowing the speed of travel allows us to calibrate across the scope for range. This can also be done for the Y plates allowing the possibility of moving the beam around any part of the screen. If the frequency at which the potential applied to the plate is made to match the PRF then the time taken for a single movement of the spot will match the interval between pulses and is therefore compatible with the maximum range. The trace left by the spot is called a time-base.

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SAW TOOTH VOLTAGE Once the electron beam is fully displaced, the right hand plate X1 is made rapidly negative. This causes the electron beam to “fly back” to X2. If nothing happens in this fly back period, a visible trace would remain on the screen. During the fly back, a high negative voltage is applied to the grid, stopping any electron flow. This ensures that no visible trace is left on the screen. This is known as a saw tooth voltage and is illustrated below.

+

0

-

0

-VE

SAW-TOOTHVOLTAGE

GRIDBIAS

VOLTS

TIME

CUT-OFF BIAS

ELECTRONS DO NOT FLOWDURING FLY-BACK PERIODS

VARIABLE BIAS(BRILLIANCE)

ELECTRONS FLOW

Most radar timer/display CRTs use a rotating time base. The time base is rotated by varying the potentials, in sequence, to the deflector arrangement. By connecting the receiver output to the grid and causing the flow of electrons to be increased momentarily when an echo is detected, targets are shown by causing the spot to become brighter. Rotating the time base in sympathy with the aerial allows the derivation of bearing information.

RADAR PERFORMANCE Radar uses frequencies that are normally in the higher bands of the electromagnetic spectrum. Propagation typically follows a direct wave path, so the range of radar is generally line of sight. Certain factors, other than those of design, affect radar’s performance:

Atmospheric Conditions At the very high frequencies used, super refraction caused by inversions of temperature and/or humidity (Anaprop) may cause a considerable increase in the direct wave range. It is possible for echoes to return from a range greater than the design maximum range, and to appear on the screen as false targets at any range. Sub-refraction causes poor radar performance at the upper range limits.

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Weather Rain and snow attenuates the radar signal and causes at least decreased performance and possibly even blind sectors. Target Size, Shape and Aspect As previously mentioned, the size and shape of the target have a tremendous effect on its ability to reflect radar signals. How it appears to the radar is also important. A B747 head-on is much harder to see than one that is side-on. Radar has the same difficulty with targets of differing size.

By the same reasoning, a flat surface at right angles (to the direction to the radar aerial) produces a much stronger return than a similar sized curved surface.

SECONDARY RADAR The principles of primary radar operation and some of the factors that affect a radar’s performance have been illustrated. Using Secondary Radar techniques can minimise some of the effects. The principle of measuring range from a time delay is still applicable, but the target plays an active role. The interrogating radar unit sends out a pulse (interrogation pulse). When the target detects this pulse, it triggers a transmitter to respond, sending a signal back to the interrogator. This signal is stronger than an echo, is not dependent on how well the target has reflected the energy and could be coded with additional information.

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Radio Navigation 12-1

INTRODUCTION In today’s Air Traffic Control systems, the role of radar is crucial for the safe and efficient controlling of an ever-increasing air traffic density. To provide for the needs of this task, the differing Air Traffic Control environments demand different performance parameters from radar. The main categories of ground radar are:

Surveillance Radar

Long range surveillance radar TMA surveillance radar Aerodrome surveillance radar

Secondary surveillance radar (SSR) – discussed in Chapter 13 Precision approach radar Surface movement radar Weather radar – a meteorological service

LONG RANGE SURVEILLANCE RADAR The radar has the following properties:

A range capability of 200 nm to 300 nm An ability to penetrate intervening weather The ability to detect small targets out to maximum range Moderate target discrimination capability in range and bearing

Using two radar systems generally fulfils these needs:

Primary Radar Wavelength of 30 - 50 cm Pulse length 4 µs PRF 270 pps Horizontal beamwidth 1.7° Aerial rotation 5 rpm

Secondary Radar This serves as a complement to the primary radar, improving the

possibility of detecting targets at long ranges and allowing for the identification of co-operating targets.

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TERMINAL SURVEILLANCE RADAR This radar provides separation between aircraft within the terminal area during transit, approach, and departure. It may be used to provide a radar approach. The service is provided by primary radar with the following characteristics:

Ranges up to about 60 or 80 nm Ability to refresh the target information at short intervals Ability to penetrate intervening weather Good target discrimination properties Good accuracy

The radar has the following properties:

Wavelength of 25 cm Pulse length 3.9 µs PRF 350 pps Beamwidth 1.2° Aerial rotation rate 8 rpm

An SSR element is also normally used in the terminal surveillance radar environment. Surveillance radar displays for long range and terminal radars are normally processed and combined with the information from the primary radar. The superimposing of the SSR information on the primary display shows the controller a complete situational picture of the relevant airspace on an easily viewed screen.

AERODROME SURVEILLANCE (APPROACH) RADAR Where provided, the aerodrome surveillance radar is normally a short-range (25 nm) primary radar that is capable of providing guidance during the initial, intermediate, and even final approach phases of the flight. As such it requires the following:

Very accurate range and bearing Excellent target discrimination Rapid refreshing of the information.

The properties of the radar are:

Wavelength 10 cm which allows a very short pulse length to be produced (pulse length1 µs)

PRF of 700 pps Beamwidth 1° Aerial rotation rate increased to 15 rpm

The shorter pulse length and narrower beam width improve both accuracy and target discrimination. The increased speed of aerial rotation allows for an increase in the rate of target information renewal. This type of radar can provide a Surveillance Radar Approach.

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RANGE, ACCURACY, AND LIMITATIONS OF SURVEILLANCE RADAR Surveillance Radar is capable of providing coverage to ranges greater than 200 nm. However, both primary and secondary elements are strictly “line of sight” so if an aircraft is below the radar horizon it will not be detected. If the aircraft is above the horizon, there are still other considerations:

The size of the aircraft If the aircraft is heading straight toward or away from the radar aerial If the aeroplane is made of glass reinforced plastic

Any of the above make the aircraft a poor target for primary radar. SSR provides information that is not size or aspect related, but depends on:

The ground unit being equipped with an interrogator The aeroplane having a transponder The pilot using the transponder correctly

The accuracy of Surveillance Radar depends on the type of unit used but is sufficiently effective to allow for a traffic separation of 5 miles. This may decrease to 3 nm within a range of 40 nm of the radar aerial.

SURVEILLANCE RADAR PROCEDURES ENROUTE Procedures are limited to those required for identification. This may involve:

Carrying out turns as directed by the controller Identifying the aircraft’s position as a radial and range from a VOR/DME beacon at

the request of the controller Identifying the aircraft’s position as a geographical point at the request of the

controller In European regions, identification occurs more frequently using the SSR element. In the event of a primary radar failure, the controller introduces non-radar separation standards using SSR to assist. APPROACH Surveillance radar may be used to provide the pilot with approach guidance including azimuth information and altitude advisories. The success of such an approach depends upon:

The skill of the controller The ability/willingness of the pilot to carry out the controller’s instructions.

Remember that this type of radar has no height-finding capability, so all height information is advisory. This is the height the aircraft should be flying at the range and bearing observed by the controller. Also remember that if the pilot cannot see the runway upon reaching Minimum Descent Height (MDH), the pilot must not descend below this height. When the aircraft reaches the Missed Approach Point (MAPt) a go-around is necessary.

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PRECISION APPROACH RADAR (PAR) Many military airfields have PAR installations. These are primary radar units designed to provide guidance during final approach to landing. The PAR consists of two elements:

One providing azimuth and range information The other providing elevation/range information

Each element utilises 3 cm wavelength (10 GHz) radar with high PRF and short pulse length (less than 1 µs). Both elements must be capable of providing detection to:

Range of 9 nm Elevation of 7° Azimuth sector of 20° (10° each side of the extended runway centre line)

Within this volume of airspace, the PAR must be capable of detecting a target with a radar cross section of 15 m2 or greater. The maximum allowable error is ± 30 ft on azimuth and ± 20 ft in elevation.

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The two elements are sited at the approach end of the runway to the side of the landing threshold.

Azimuth The azimuth element scans a very narrow beam (0.6°) backward and forward over a sector covering the required minimum azimuth sector. Elevation The elevation element has a narrow vertical beam width (0.6°) but a broader azimuth beam width (up to 30°). It sector-scans vertically from an elevation of about 0.5° up to 8°.

Both scans are at a rapid rate in order to ensure that the target information is refreshed quickly. Target information is presented to the controller on two screens mounted one above the other. The upper screen shows the range to the target and its position relative to the nominal glide path. The lower screen shows the range and the position relative to the extended runway centre line.

PAR PROCEDURE A typical procedure is detailed below:

Prior to commencing the approach, the controller advises the pilot of the Aerodrome QFE. All heights refer to this datum. Instructions are designed to help pilots on the glidepath and centreline by providing regular azimuth and glidepath correction information to the pilot. Remember it is the pilot’s responsibility to ensure that the runway is in sight before DH. Initiate a missed approach procedure if the runway is not in sight at DH.

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AIRFIELD SURFACE MOVEMENT INDICATOR (ASMI) This is a highly specialised primary radar unit designed to assist controllers in maintaining safe separation between aircraft and vehicles on the ground and to monitor all ground movements. The maximum range is approximately 2.5 nm. It requires only short range but must be capable of:

Very low minimum range 360° cover Very high level of accuracy Excellent target discrimination

For some time it was necessary to use a radar operating in the “Q” band (35 000 MHz) as this provided:

A very narrow beam width with a small aerial Excellent bearing discrimination

Modern signal processing techniques have led to the achievement of equivalent definition with a cheaper “X” band (10 000 MHz) radar. This is now the favoured option. The following are the typical specifications for an ASMI:

Frequency 10 000 MHz PRF 15 000 pps Pulse length 0.05 µs Beam width 0.4° Aerial rotation 60 to 75 rpm

Here is a typical ASMI picture:

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WEATHER RADAR The weather radar found at an airfield is not an ATC radar but is for the use of the meteorological services to supplement their forecast information.

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Radio Navigation 13-1

INTRODUCTION The primary radar element of the ATC Surveillance Radar System provides detection of suitable targets with good accuracy in bearing and range measurement, but with certain limitations: Targets that are too small, built of materials that reflect radar energy poorly, or have a poor aspect may not be detected.

Targets cannot be identified directly Radar energy suffers attenuation (losses) both on the path out to the target and on

the return path of the reflections To overcome these problems, a Surveillance Radar installation often consists of both a primary and a secondary radar, the latter being the Secondary Surveillance Radar (SSR). The role of the SSR is to complement the primary radar element.

PRINCIPLES OF OPERATION SSR operates on secondary radar principles. An SSR “link” uses one ground-based transmitter and receiver, called the interrogator, and one airborne transmitter and receiver, referred to as the ATC transponder, or simply transponder. The interrogator transmits pulses. A receiver within the interrogator’s beam receives these pulses and decodes them. The transponder then responds by transmitting a pulse train (many pulses in a stream) back to the interrogator. The pulse train contains information according to what the interrogator requested. All interrogations transmit at a frequency of 1030 MHz and all transponders respond at a frequency of 1090 MHz.

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The SSR aerial consists of a radiator and reflector similar to that used in the primary radar. Since the return is much stronger than that of a primary radar reflection, it is much smaller. As a result of this small size and the frequencies used, the beam width tends to be large. This results in the transmission of a considerable number of side lobes.

PULSE SPACING There are four modes and their applications and pulse intervals are as follows:

Mode Use Pulse spacing A ATC 8 µs B ATC 17 µs C Auto Pressure Altitude report 21 µs D Not Assigned 25 µs

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Mode A is known to the military as Mode 3. Modes B and D are not currently in use and the conventional aeroplane transponder is designed to use only modes A and C.

SIDE LOBE SUPPRESSION The large beam width reduces the bearing accuracy and increases the chances of reflections from buildings and other obstacles generating false interrogations. The side lobes can cause aircraft responses from any direction. Aerial design has minimised this problem.

Side lobes still create a problem since aeroplane receivers, especially at close range, detect them. This triggers a false response outside the main beam and can result in the effect of side lobe clutter, illustrated below. A process known as side lobe suppression (SLS) can counteract this by modifying the method of interrogation so as to electronically cancel the effect of side lobe radiation.

SIDE LOBECLUTTER

AIRCRAFT ATLONG RANGE

RING-A-ROUND

MEDIUMRANGE

SHORTRANGE

Interrogations are sent in the form of a group of three pulses identified as P1, P2, and P3. P2 is a control pattern placed over the main beam.

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The spacing between P1 and P2 is constant at 2.0 µs. Pulse P2 is used in the electronic side lobe suppression. The spacing between P1 and P3 is set at a value dependent upon the mode required from the aeroplane transponder as shown earlier.

Position 1 The control pattern is omni-directional except in the direction of the main beam. This means that an aircraft painted by the main beam receives a P2 pulse that is lower in amplitude than the P1 and P3 pulse, as in the diagram shown above. Position 2 If an aircraft is painted by one of the side lobes, the P2 pulse is of greater amplitude than the P1 and P3 pulse. The side lobes only have 50% of the power of the main beam and thus P2 appears as the pulse with the greater amplitude (see diagram below).

Whenever the transponder receives P1 and P3 at greater amplitude than P2, it transmits a reply. Should P2 be greater than P1 and P3, it indicates that the aircraft is being painted by side lobes, and the transponder suppresses any reply transmission.

2µs

2µs

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OPERATION The pilot sets the transponder to the mode and code as instructed by ATC.

OFFL R

ALT RPTGOFF ON

ATC

IDENT

FAULT

0767

TRANSPONDER SELECTOR- SELECTS DESIRED TRANSPONDER

ATC CODE INDICATOR- DISPLAYS CODE SET BY ATC CODE SELECTOR

ALTITUDE REPORTING SELECTORON - ENABLE ALTITUDE REPORTING

ATC FAULT LIGHT (AMBER)- ILLUMINATES WHEN A TRANSPONDER

MALFUNCTION HAS BEEN DETECTED

ATC CODE SELECTORSROTATE - SETS CODE IN ATC CODE INDICATOR

AND BOTH TRANSPONDERS

ATC IDENT SWITCHPUSH - TRANSMITS IDENT SIGNAL

TYPICAL TRANSPONDER CONTROL If the transponder is set to the “ON” position, the unit responds to Mode A interrogations. If set to ALT, the transponder responds to Mode A and C interrogations, sending identification and automatic altitude information. The transponder’s response occurs in the form of a pulse train. This consists of two framing pulses separated by 20.3 µs. Between the framing pulses is the facility for transmitting up to 13 coding pulses. Pulse ‘X’ is not used at this time, utilising only 12 pulses. The pulses are used as follows:

A pulses form the first digit of the four-figure code B the second C the third D the fourth

The diagram below shows the arrangement of A, B, C, and D pulses for sending the digits. Note that for each digit, there are 8 possibilities ranging from 0 to 7. This leads to a total of 4096 selectable codes (8 x 8 x 8 x 8).

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After the main framing pulses, a special position indicator (SPI) pulse is transmitted 4.35 µs after the last pulse when the ident button is used on the main control panel. The SPI code paragraph discusses this. The system uses a form of binary numbering to identify the code. The altitude information is relative to the 1013.2 hPA level no matter what pressure setting is on the altimeter.

SPI CODE Utilising a special “IDENT” feature allows ATC to confirm an aeroplane’s identity. The pilot activates this when instructed by ATC. When the IDENT button is pushed, an additional pulse is transmitted 4.35 µs after the second framing pulse. At the controller’s display, the ident pulse causes the particular aeroplane’s echo to brighten or flash. This lasts for approximately 15 – 30 seconds.

USE OF TRANSPONDER Pre-departure the transponder is set to stand by. This allows the equipment to warm up but not transmit. The test function is then activated to establish the operational status of the equipment. When instructed, the pilot sets the mode and code given by ATC, and when told to “Squawk” sets the controller to “ON” or “ALT” as appropriate. Normally ALT is selected, as the altitude encoding has to be selected in all cases unless ATC instructs otherwise. In order to avoid causing interference, do not change the mode or code without first selecting “STBY” on the controller. When in an abnormal situation, there are three codes to alert the controller. These codes have a predefined meaning and, with one of these selected, triggering a signal indicating a “special condition” on the controller’s screen. The aircraft symbol may change colour to attract more attention. On some radar systems, an aural alarm sounds together with the target on the screen either flashing or brightening.

Code 7500 Hijack Code 7600 Radio failure Code 7700 Emergency

From time to time, the ATC controller may ask the pilot to “SQUAWK IDENT”. Pushing the “IDENT” button activates the transponder to transmit the additional pulse. This appears on the radar display as a flashing target. This function, when first enabled, continues for approximately 15 - 30 seconds. Do not press the “IDENT” button unless instructed by air traffic. PRESENTATION AND INTERPRETATION SSR information is presented together with the primary radar information. The difference between the two is that the primary information is very accurate in bearing and range, but does not consist of any extra information. The secondary radar information is inaccurate in bearing and range, although it can serve as a back up, but provides reliable information that can identify every aircraft and provide altitude information.

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The primary radar element provides the necessary bearing and range. The use of computer-generated displays allows calculated information, such as course and ground speed, to be shown. Here is a common style of displaying combined (primary and secondary surveillance radar) information on the air traffic controller’s radar screen.

LIMITATIONS SSR complements the primary radar system and, although effective, is likely to be replaced by Mode S in the near future. Previously noted is the fact the bearing and range information is not as good as that of the primary radar. In addition there are two other major problems: FRUITING Although ground based interrogators have a nominal range of approximately 200 nm, the propagation is “line of sight” and it is not unusual for aeroplanes, especially at cruising altitudes over well-developed ATC regions, to be within range of two or even more ATC interrogators. Since all SSR units operate at the same frequency, this can result in detection of an aeroplane’s response to one interrogator by other ground units. Such responses occur out of synchronisation causing random responses to appear. This is called fruiting. Electronic circuits are employed (de-fruiters) to remove this effect but they do not remove all random responses and the situation becomes worse as traffic density increases. GARBLING Another problem is garbling, which occurs when targets are close to one another (e.g. in a holding pattern or progressing along an airway one above the other). If both aircraft are in the interrogation beam at the same time, and are close enough to each other, the ground interrogator cannot differentiate between them and records only one confused return. Although fruiting and garbling effects are manageable at this time, future traffic growth places more and more stress on the system and the controllers.

Chapter 13 Secondary Surveillance Radar (SSR)

Radio Navigation 13-8

MODE S This is a development of the basic SSR, which is being introduced. The Mode S ground interrogators and airborne transponders are fully compatible with the conventional Mode A and C units and use the same basic frequencies of 1030 MHz and 1090 MHz. Mode S units working together have much greater capabilities. OPERATION OF MODE S The Mode S interrogator and receiver operate on the same frequency as standard SSR. The initial part of the interrogation signal is such that a normal airborne transponder unit recognises the standard SSR modes. The second part of the Mode S interrogation consists of a message of up to 112 data bits of which 24 bits are allocated to aircraft address. This permits the controller to interrogate a specific aircraft. The 24 bits allocated are sufficient to provide for over 16 million individual addresses. This is considered sufficient for the registration of all aircraft in the world. In order to detect further Mode S transponders, a special feature known as SSR/Mode S “ALL CALL” is broadcast at intervals. Normal SSR transponders respond to this in Mode A or C (dependent on the P1/P3 relationship). Mode S transponders recognise the special character of the “ALL CALL” interrogation as a roll call request and transmit a response that includes the aircraft’s identity/address along with details of the capability of the relevant on-board equipment. This is a 56-bit message. The other interrogations and responses are as follows:

INTERROGATION RESPONSE Type Content Type Content Surveillance

16 control bits 16 altitude echo 24 address

Surveillance

13 SSR identify & altitude 19 control purposes 24 address

Comm A As for Surveillance + 56 bits ground to air data

Comm B As above + 56 bits air to ground data

Comm C 112 bits for data transmission of long messages

Comm D 112 bits data transmission of long air to ground messages

The altitude echo function in the Surveillance interrogation indicates (to the pilot) the flight level that the aeroplane’s transponder is providing ATC. Comm A and Comm C interrogations can send longer messages by breaking the messages up into suitable sized blocks and transmitting on successive cycles. Comm D, from the airborne transponder, has a similar capability. Comm D cannot be used for position update, as the messages contain no altitude information.

Secondary Surveillance Radar (SSR) Chapter 13

Radio Navigation 13-9

The expanding use of Mode S has the following benefits over standard SSR:

Elimination of synchronous garbling Elimination of ‘fruiting’ Increased traffic capacity Improved accuracy

In addition, the ability to send messages allows for a reduction of congestion on the current R/T communication frequencies. Transmitted data can be presented to the pilot on a CDU either integral with the Mode S transponder or on the FMS screen. Mode S information, transponder to transponder, can also be integrated with the airborne Collision Avoidance system allowing the systems of conflicting aircraft to communicate and resolve convergent situations.

ATC SERVICES Mode S data link can serve as a back-up to many ATC services provided today by VHF voice communications. This data link back-up improves system safety by reducing communications-related errors within the ATC system. Many types of messages are potential candidates for data link back up and other ATC services. These include:

Flight identification Altitude clearance confirmation Take-off clearance confirmation New communication frequency for sector hand-off Pilot acknowledgement of ATC clearance Transmission to the ground of aircraft flight parameters Minimum safe altitude warning

Chapter 13 Secondary Surveillance Radar (SSR)

Radio Navigation 13-10

Radio Navigation 14-1

INTRODUCTION All transport aircraft, and some small general aviation aircraft, are equipped with weather radar. The weather radar has four main functions:

Locating clouds ahead of the aircraft Assisting the pilot to avoid turbulent clouds Determining the location and height of cloud tops Mapping of the terrain ahead

Weather radar is an airborne pulse radar designed to locate turbulent clouds ahead of an aircraft. Some weather radars have a secondary ground mapping capability.

PRINCIPLE OF OPERATION Cumuliform clouds are associated with both rising and descending currents of air, which lead to turbulence. In the case of towering cumulus and cumulonimbus cloud, this turbulence can be severe. The turbulence within the cloud retains the water droplets within the cloud until they are of a size to fall as precipitation. It is the precipitation, and in particular, the large water droplets, that reflect the radar energy. The reflection depends upon the form and size of the droplets within the cloud:

Hail is covered by a film of water and gives the strongest return. Light Rain and Snow give the weakest returns.

Weather radar does not detect non-turbulent clouds, as the water droplet size is too small. Frequency 9 to 12 GHz Frequency Range The frequency range above provides good returns from droplets of water, rain, or hail in clouds.

Using a frequency that is too high causes the smaller wavelength to reflect off the smaller water droplets of non-turbulent clouds.

Using a frequency that is too low causes the radar to penetrate the cloud and to provide inadequate returns from turbulent clouds.

Chapter 14 Airborne Weather Radar (AWR)

Radio Navigation 14-2

AWR AERIAL The aerial consists of either a parabolic dish or, in modern units, a flat-plate phased array. It is mounted in the nose of the aeroplane and scans ahead of the aircraft from side to side with a narrow beam. The sweep can be up to 90° to each side of the aircraft nose. The beam can be tilted manually ± 15° in the vertical plane. A gyro stabilises the scan horizontally to prevent loss of target if the aircraft rolls or pitches. This stabilisation is effective up to ± 20° of combined roll, pitch, and tilt. The radar can be selected to either “weather” or “mapping” beam. The weather beam is used for detecting clouds and is a conical pencil beam with a width of 5°. The directional properties of the radar produce side lobes. One side lobe goes vertically down to the ground and is received back by the radar receiver. This received signal produces a height ring on the display. The ring indicates that the radar is working and appears at the approximate height of the aircraft above the ground. An aircraft flying at 12 000 ft will have a permanent return at approximately 2 nm.

CONTROL PANEL

POWER SWITCH AND TIMEBASE RANGE SWITCH These two switches are used together. On the ground, the timebase range switch is set to standby. The power switch is then set to either STAB ON or STAB OFF (the significance of these positions will be explained later in this chapter). The radar warms up but does not transmit.

OFF

OFF

POWERONSTAB

STANDBY

20

50

150

CONTRAST

DOWN

MARKBRILL

UP TILT15

15

10

10

5

5

0

CONTWEA

MAN

MAP

POWER SWITCH MARKER BRILLIANCE

TIMEBASERANGESWITCH

CONTRASTCONTROL

TILTCONTROL

MANUALGAIN

CONTROL

FUNCTIONSWITCH

Airborne Weather Radar (AWR) Chapter 14

Radio Navigation 14-3

When the aircraft is airborne, the pilot makes the appropriate range selection, in this case 20 nm, 50 nm, or 150 nm.

The angle markings are permanently etched on the radar screen every 15°. The angles represent the relative bearing of a return left or right of the nose. The range markers are electronically produced depending on the range selected. The marker brilliance control determines the brightness of these settings. It has no other function.

30 30

45 45

60 60

0 5 10 15

30 30

45 45

60 60

0 10 20 30 40

30 30

45 45

60 60

0 50 100

20 nm range scale

50 nm range scale

150 nm range scale

Chapter 14 Airborne Weather Radar (AWR)

Radio Navigation 14-4

FUNCTION SWITCH The function switch selects the mode of the radar:

WEA/CON This mode shows Weather and Contour. Both of these selections assist in cloud detection. These selections have automatic gain control. MAN/MAP This mode shows Manual and Mapping. Both selections assist with ground mapping. Gain is controlled manually in these selections.

WEATHER FUNCTION (WEA) When WEA is selected a conical beam is produced by the radar. A form of “swept gain” is used. Swept gain is an automatic gain setting that adjusts the returns within a radius of 25 nm. A short-range non-hazardous return at 5 nm may show up on the radar while a hazardous return at 25 nm may only just be painted. The swept gain adjusts these returns to remove the non-hazardous cloud off the screen but enhances and amplifies the hazardous cloud return. CONTOUR FUNCTION (CON) With a monochrome screen it is difficult to distinguish between the severities of turbulent clouds. When CON is selected an ISO-ECHO circuit is activated. An ISO-ECHO level supplements the Automatic Gain Visual Threshold set in WEA mode. The shape of the return on the radar depends upon the gain level of the cloud:

Automatic Gain Visual Threshold When a cloud return breaks this threshold, it still appears on the radar scope but only as a normal cloud return. Iso-Echo Level When this gain level is broken, the effect is to create a black hole in the cloud by reversing and amplifying the signal. This reversal brings the signal below the Automatic Gain Visual Threshold and so no return appears in the middle of the cloud.

Airborne Weather Radar (AWR) Chapter 14

Radio Navigation 14-5

Turbulence severity is assessable using the above picture:

The hole shows an area of high turbulence. The outer ring shows the severity of the turbulence gradient within the cloud. • The narrower the retaining ring, the steeper the gradient. • The wider the outer ring, the more slack the gradient.

MAPPING FUNCTION (MAP) For MAP functioning, the conical beam used in the WEA and CON modes is modified into a fan- shaped or cosecant2 beam. To spread the beam, a system of spoilers is placed on the aerial. When MAP is selected, these spoilers and the aerial position change the conical beam into the one shown in the diagram below. In MAP, the power is spread across the beam so that the maximum range usage is approximately 60 nm.

Aircraft

A B

ParasiticElements

IN P U T S IG N A L - IN V E R TE DA B O V E TH E IS O -E C H O L E V E L

IS O -E C H O LE V E L

A U TO M A TIC G A INV IS U A L TH R E S H O LD

3 0 30

4 54 5

6 06 0

R E S U L T IN G P A IN T

T U R B U L E N T C L O U D P A IN T - C O N T O U R M O D E

Chapter 14 Airborne Weather Radar (AWR)

Radio Navigation 14-6

MANUAL FUNCTION (MAN) This mode uses the conical beam. Because of the concentration of energy within the beam, ranges of up to 150 nm can be seen on the radar. CONTRAST The contrast rotary switch determines the degree of amplification to the video pulse. It influences the brightness of the display. MANUAL GAIN Signal strength can vary with altitude and the type of terrain the aircraft is flying over. This control varies the amount by which the returning echoes are amplified by the video processing unit. TILT CONTROL The dish aerial sweeps in azimuth and the setting of the tilt control, normally 15° up or down, determines the variation in elevation. In association with the tilt control, the aerial settings STAB ON and STAB OFF are used:

STAB OFF: The beam is fixed to the aircraft nose.

STAB ON: The beam is gyroscopically-fixed to the Earth horizontal. The beam always looks at the tilt angle selected regardless of the aircraft’s pitch angle.

UP

TILT

DOWN

15

15 10

10

5

5

0

ZERO TILT SELECTED

STAB OFF

PENCIL BEAM LOCKED INAIRCRAFT PITCHING PLANE

EARTH HORIZONTAL

Airborne Weather Radar (AWR) Chapter 14

Radio Navigation 14-7

COLOUR DISPLAYS The airborne weather radar displays echoes from clouds having a sufficient concentration of liquid water. It cannot discriminate between clouds that are likely to produce turbulence and those that are not likely to do so. Introducing an iso-echo contour circuit overcomes this. Any clouds having heavy concentrations of large water drops will be associated with turbulence and will also be good reflectors of radar, especially at 3 to 5 cm. When the contour circuit has been selected and echoes return above a pre-set level, they are processed to show as black holes on a monochrome (single colour) screen. Most modern weather radars use colour, and the processing of the returns produces graded colour paints as follows:

Green Light concentration, slight turbulence Yellow Moderate concentration, light turbulence Red Heavy concentration, moderate/severe turbulence Magenta Heavy concentration of large drops, severe turbulence

Chapter 14 Airborne Weather Radar (AWR)

Radio Navigation 14-8

CLOUD HEIGHT DETERMINATION On detecting an active cloud, it is possible to determine the height of the top of the cloud by using the tilt control. Tilt the beam upward until the cloud echo disappears, then note the tilt angle and range. Finally, using the 1/60 rule, determine the height above the aeroplane level. Remember to allow for beam width.

Echo range 60 nm Tilt angle at disappearance 4° Beam width 4° = 4 nm at 60 nm Beam bottom 2° above horizontal. Range 60 nm Beam height 2 nm = 12 000 ft above aeroplane The simple formula to use is:

Cloud height = (tilt angle – ½ beamwidth) x 100 x range Cloud height = (4 – 2) x 100 x 60 Cloud height = 12 000 ft above the aircraft A negative figure means that the cloud is below the aircraft.

At lower altitudes, tilting the aerial down may increase ground returns, and pilots may find it impossible to differentiate between ground and cloud returns. This may require an upward tilt of the aerial.

4°5°3°

BEAMWIDTH

EARTH HORIZONTAL(STAB ON)

RANGE 30 NM

AIRCRAFTALTITUDE

5000 FT

Airborne Weather Radar (AWR) Chapter 14

Radio Navigation 14-9

SHADOW Water surfaces at any reasonable range reflect the radar energy away from the aeroplane and give little or no return, causing the screen to remain quite clear. Beware, shadow areas appear behind hills and could easily be mistaken for water. Adjusting the gain control can often make a substantial improvement to the radar picture. In order to interpret the bearing and range information, the pilot must interpret between the bearing marks to obtain the relative bearing, and between the range markers for the range (which are a slant range for ground targets). Contamination of the radome with ice, snow, or rain causes degradation of the radar performance. TEST Most modern radars have a built-in test equipment (BITE) selection. This enables checks of the display colour patterns and the internal workings of the radar. HOLD The hold selection is a method of assessing cloud movement. Once selected, a cloud position is frozen on the radar screen. Deselecting hold releases the cloud paint to its current position, allowing the pilot to assess the mean track of the cloud relative to the aircraft. TARGET ALERT When the target alert is activated, a yellow T in a red square appears at the top of the screen. If the system detects a turbulent cloud beyond the selected range, the T changes to TGT and the symbol flashes.

USE OF THE RADAR ON THE GROUND The following is a short checklist for using an AWR on the ground:

Prior to start, set the AWR to “off” to avoid any surge currents passing through the system.

Post start, set the range to SBY and the power to STAB OFF. Selecting STAB OFF fixes the radar aerial to the aircraft axis and prevents any damage to the gyroscopic system used in the gimbals of the radar. The radar warms up.

Tilt should be fully up. When clear of all personnel, buildings, etc., check the timebase for radar returns on

all ranges. Return to standby. Before take-off on the runway – power STAB ON, select WEA and tilt as required. The radar can be switched on before take-off if the aircraft is lined up on the runway.

Chapter 14 Airborne Weather Radar (AWR)

Radio Navigation 14-10

Radio Navigation 15-1

INTRODUCTION Airborne Doppler Radar systems provide a pilot with ground speed and drift angle information continuously and automatically. Doppler, unlike most airborne navigation equipment, does not need any active system outside the aircraft. Although more modern systems have superseded the use of Doppler, they may still be encountered on older transport aircraft and helicopters. In 1842, the Austrian scientist, Christian Doppler, noted the changing pitch of the sound generated by moving vehicles as they approached and then passed beyond a stationary point. Moving a wave propagation source toward a person, causes the frequency of the sound observed by that person to be higher than the actual frequency at the source. The shift of frequency (increasing when the source moves toward the object, decreasing when it is moving away) is proportional to the velocity of the source. This phenomenon is called Doppler shift. Other names are Doppler effect or Doppler frequency. When applying the Doppler principles to an aircraft in flight, with no relative motion between the radiating source and the receiver (both transmitter and receiver are on board the aircraft), a Doppler shift still occurs if the transmitted energy returns to the receiver from the Earth. In this case, the surface of the Earth acts as a reflector. Frequency 8.8 GHz or 13.5 GHz

DOPPLER EFFECT

1

2

3

4

Blueshift Redshift+ + + + +

P4 P3 P2 P1

Doppler Effect

As the Transmitter moves to the left, the waves are compressed toward the blueshift. The intervals between the waves diminish and this apparent shortening in wavelength causes an

Chapter 15 Doppler

Radio Navigation 15-2

increase in frequency or pitch. The frequency appears to increase. As the transmitter passes, the waves are now stretched. The interval between each wave increases and causes a decrease in frequency and pitch at the redshift side of the diagram. The frequency appears to decrease.

The diagram above shows a stationary transmitter. Assume that the frequency of transmission is f Hz. The receiver receives the successive wave fronts at f Hz.

Now assume the transmitter is moving toward the receiver and the velocity is V m/s. The first wave front is centred on 1, the second on 2, etc. The effect is to decrease the wave front spacing as the transmitter travels toward the receiver. This appears to the receiver as an increase in the received frequency. Behind the transmitter, the wave front spacing increases, and a receiver placed opposite Rx would experience a reduced frequency. This change in frequency is the Doppler shift. The change in frequency, the Doppler shift, is represented by fd and is proportional to the transmitter’s velocity:

fd = Vf = V c λ

c is the speed of propagation f is the transmitted frequency V is the velocity of the transmitter

Doppler Chapter 15

Radio Navigation 15-3

Example: Assume a transmitter (9 GHz) is moving toward a stationary receiver at 300 km/h. What frequency will the receiver record?

First convert 300 km/h to m/s 300 x 1000 ÷ 3600 = 83 m/s The wavelength for a frequency of 9 GHz is = 0.03 m

fd = V λ

fd = 83.3 ÷ 0.03 = 2777 Hz

This is the Doppler shift that must be added to the transmitted frequency to arrive at the received frequency. (If the transmitter is moving away from the receiver then the Doppler shift would be subtracted from the transmitted frequency.)

Received frequency = 9 000 000 000 + 2777 = 9 000 002 777 Hz

It is not likely students will have to make any Doppler calculations for the JAR exam. The example above is probably the style of question that would be asked.

DOPPLER MEASUREMENT OF GROUNDSPEED Since the aircraft cannot fly directly toward a reflecting surface, the radar beam must tilt downward. The measured Doppler shift must be mathematically corrected for a tilt angle (θ) in order to resolve the aircraft’s forward horizontal velocity. The diagram below shows an aircraft transmitting a narrow radar beam toward the ground at an angle θ (called the depression angle). The system receives the beam at a different frequency than that transmitted.

The basic Doppler shift formula becomes:

fd = 2VF cos θ C

Chapter 15 Doppler

Radio Navigation 15-4

The frequency received (Fr) on a forward facing beam will be:

Frequency transmitted (Ft) + 2VF cos θ C

Where θ is the angle of depression of the beam (the angle between the horizontal and the direction of the beam). The equation shows that the Doppler shift is at its highest when the angle θ is shallow, or when the beam faces forward in the flight direction. This is impossible, as there is no reflecting surface in front of the aircraft. If the pilot makes the beam depression too large, the Doppler shift is very small, becoming zero when the beam is directed vertically downward. The choice of beam depression angle is a compromise between these two extremes, a matter of trying to obtain reliable energy returns with sufficient Doppler shift to be accurately measured. An angle of approximately 67° normally achieves this. The system considered here is a single-beam system that has certain disadvantages:

Pitch Error Changing the aircraft’s pitch changes the θ. If the aeroplane pitches nose down, the reflected beam in front would depress greater than θ and the Doppler frequency shift would decrease, even if aircraft speed remains constant. For the system to work correctly, the aircraft must either fly straight and level at all times, or the aerial must be stabilised in the pitching plane. Vertical Motion Any vertical motion of the aircraft generates a change in the Doppler shift not associated with the groundspeed. Drift If the aerial is fixed, the system measures the speed along the heading. However, groundspeed is calculated along track. A system design should allow the aerial to move in azimuth to obtain maximum Doppler shift. This would provide a drift angle as well as a groundspeed. In practice, this is not done, and the system remains inaccurate.

TWO BEAM JANUS ARRAY A common way of solving this problem is to transmit a second beam backward from the aircraft, at the same depression angle as the front beam. The system then algebraically adds the two sensed Doppler shifts and calculates the ground speed based on this information. This is termed a Janus system, named after the Roman god, Janus, who could look forward as well as aft at the same time.

DepressionAngle θ

DepressionAngle θ

Surface

Doppler Chapter 15

Radio Navigation 15-5

The frequency received from the forward beam (fr) is higher than the frequency transmitted.

fr = f + fd

The frequency received from the rear beam (fr) is lower than the frequency transmitted.

fr = f - fd

Using a two-beam system requires adding the two received frequencies to yield a total received Doppler shift ft as follows:

ft = (f + fd) - (f - fd) = 2 fd or

4VF cos θ C

The total frequency received is double that received from a single beam system.

Pitch Error Aircraft pitch causes an increase in depression angle for one beam and a decrease in depression angle in the other beam; thus effectively cancelling each other out. Vertical Speed Both front and back beams sense the change in vertical speed and in the summation process they cancel each other out.

FURTHER JANUS ARRAYS Four different types of array appear below.

By using any of the systems above, the drift angle will be sensed since drift occurs across the intended track. To ensure the calculation of drift angle requires using three or four beams, each pointing in different directions. The configurations have names that reflect their appearance. For example, the three-beam lambda configuration is similar to the Greek letter λ.

Chapter 15 Doppler

Radio Navigation 15-6

In the four-beam system, the aerials transmit front left/rear right and then front right/rear left. If the aircraft has no drift, the Doppler shift measured by the two sets of aerials is the same in each sequence of transmissions. If there is sideways drift, one set of aerials receives a larger Doppler shift than the other set. The system electronically calculates this difference as an error signal that rotates the aerial to ensure that the two signals received are the same. The angle of movement is the drift.

DOPPLER AERIAL The Doppler aerial system consists of three or four slotted arrays giving shaped beams, each with a width that varies between 5.5° to 11°. The beams are depressed to an angle of 67° to provide a measurable Doppler shift. Aerial systems may be hard strapped to the airframe and, if so, cause some small errors in measured groundspeed during prolonged climbs. Alternatively, they may be gyro stabilised in pitch to reduce these errors. SIGNAL CHARACTERISTICS The sensitivity, and thereby the accuracy, of a Doppler radar increases with frequency. However, the higher frequency, the more rain reflections, scattering effects, and absorption affect the signal. A compromise is made, and as a result Doppler airborne radar equipment operates on two frequency bands: 8.8 GHz and 13.5 GHz. In selecting the actual frequency to use, the pilot must take into account:

The operational height required The power output available The speed of the aircraft

A helicopter Doppler normally uses the higher frequency in order to increase the Doppler shift at the low speeds. OUTPUT AND PRESENTATION Doppler equipment measures drift and groundspeed. If combined with a heading input, it gives track and ground speed. This can feed into a specific display or, more commonly, be integrated into a navigation computer, which can add the measured values to a start position to produce outputs such as:

Position Distance to go Bearing and distance to a waypoint Current W/V

Doppler Chapter 15

Radio Navigation 15-7

As shown in the diagram below, the functions important to the pilot on a Doppler control unit are:

25 15 5 2 2 5 15 25

TRACK ERRORN

S

EW

SEALAND

STBY

DOPTEST

SLEW

LAT

LONG

BRGDIST

WP

GSDFT

POSFIX

HDGVAR

LMPTEST

10

WAYPOINT

DIM

GF

E

D

C

B

A

H

J

K

L

A Display Switch B Latitude/Longitude selection switch C Slew switches D Light bars E/W or N/S as selected E Track error indicator F Warning bars G Power supply test bars H Numeric displays J Function switch K Display dimmer switch L Waypoint selection Certain functions require understanding for the syllabus:

STBY is the setting used during equipment warm-up. SLEW allows the pilot to set a drift and ground speed if the equipment is operating in Memory mode. LAND/SEA creates a mathematical solution to compensate for partial loss of the beam. When flying over the sea or flat surfaces, the switch should be set to ‘sea’. (See sea bias.)

Chapter 15 Doppler

Radio Navigation 15-8

ACCURACY AND LIMITATIONS Modern Doppler radar systems are quite accurate. Expect errors in the order of 0.1 % on ground speed and 0.15% on drift angle. SEA BIAS When flying over the sea, the leading edge of the forward beam and trailing edge of the rear beam are lost due to increased reflection away from the aircraft. This causes the measured values of ground speed to be lower than the true ground speed. Selecting the ‘Sea’ position on the land/sea switch provides a bias, which offers some compensation for this effect. The Land/Sea switch discriminates between the Doppler frequency over water (fdw) and land (fdl) when switched to sea. The calibration of the tracker unit is altered to increase the groundspeed by a nominal 1 – 2%.

Ret

urne

d P

ower

fdw fdl

Measured fd Correct fd forBeam Centre Line

Over WaterCalibrationShift

WaterSpectrum

LandSpectrum

f

MEMORY MODE If the sea becomes too smooth, (surface wind less than 5 kt) nearly all the energy scatters away from the aeroplane and no measurements are possible. Under these circumstances the system, activates a Memory Mode and the drift and ground speed are frozen at the last measured values. These may not be correct values, but will be used by any associated equipment. Examples of other situations that cause the system to go into Memory are:

Flight over hot desert regions where the attenuation is high Flight in adverse weather such as severe thunderstorms. The water content of such

storms causes excessive scattering of the energy. PITCH AND ROLL ERROR Errors due to pitch or roll are cancelled by the Janus array. When both pitch and roll occur simultaneously, an error is likely to occur. Limitations for pitch and roll are typically ± 20° and ± 30°, respectively. Beyond these, the system loses data and enters the Memory Mode. HEIGHT HOLE ERROR In a pulse-modulated system, when the Doppler radar is transmitting, the receiver is shut off. Low flying may introduce an error to the system because the transmitted signals reflect back to the aircraft before the receiver is functioning again. Likewise, when flying at high altitudes, the time delay between transmission and reception may cause problems, reception may occur at exactly the same time that a new transmission is taking place. In such cases, the receiver is short-circuited.

Doppler Chapter 15

Radio Navigation 15-9

SEA MOVEMENT ERROR Doppler measures the drift and groundspeed relative to the terrain beneath the aircraft. If the surface is moving, as is the case with the sea, the following factors may induce errors:

Tidal Stream Tidal streams normally affect narrow waterways. Since the time the aircraft will be over this type of feature is small the effect is minimal. Ocean Currents Ocean current speeds are slow, and thus have little effect. Water Transport The surface wind causes wave movement on the surface of large tracts of water. This error is complex to understand but the resultant error can affect both drift and groundspeed.

COMPUTATIONAL ERRORS Processed Doppler information may be subject to heading input errors that are probably more significant than those of the measured ground speed. The Doppler is based on an assumption that 1 nm is equivalent to 1 minute of latitude. This is only correct at 47°42’N/S, and on the surface of the Earth. As soon as an aircraft is at height, the assumption is again not true. Both errors are small and are not corrected for. HEADING ERROR This is the greatest error in Doppler. The system relies on the accuracy of the heading input information, which, if wrong, can cause considerable cumulative errors. SUMMARY OF ERRORS

Error Measurement of Error Distance Track

Aerial Misalignment No Yes Pitch Error Yes No

Sea Movement A vector error dependent on the time spent over the water, the direction and movement of the sea and the wind velocity

Sea Bias Yes No Heading Error No Yes

Altitude and Latitude Yes No ADVANTAGES As mentioned above, the Doppler navigation system is quite accurate. It does not require any external equipment for basic operation (although updating would require external means). The system has good, long-term accuracy irrespective of flight time, and the measured ground speed and drift retain the same accuracy potential. If combined with a short-term accuracy system, the overall accuracy is excellent.

Chapter 15 Doppler

Radio Navigation 15-10

DISADVANTAGES Doppler can only give an instantaneous value of drift and ground speed and requires a link to other equipment. This makes the derived position information dependent upon the accuracy of such inputs as heading and TAS.

The equipment is very prone to ‘loss of signal’ and entry into Memory Mode. The equipment is costly to maintain.

Radio Navigation 16-1

INTRODUCTION Hyperbolic navigation systems determine present position from the intersection of lines of position. While radials and bearings from VOR and NDBs are straight lines, in hyperbolic navigation a line of position is based on a curved line - specifically, a hyperbolic curve and, more precisely, a hyperbolic surface.

A Hyperbola is a line joining all points where the difference of distance between two fixed points is the same.

HYPERBOLIC FAMILY

Draw a straight line of 4 cm and label the ends M and S. Draw a line perpendicular to M – S, 2 cm from M. Label it A-B. Draw circles starting with a radius of 1 cm from M and S. Do this for 2 cm, 3 cm, 4 cm, etc. This produces a diagram like the one below:

M S

3 3

B

A

Look at the line AB. Where AB cuts the line MS is the meeting point of the 2 cm radius circle drawn from M and the 2 cm circle drawn from S. The difference between the two circles is an answer to the equation 2 – 2, or zero.

Chapter 16 Hyperbolic Navigation

Radio Navigation 16-2

The 3 cm circles meet at two points on the line AB, one above the line MS and one below. The same for the 4 cm line, etc. The difference between the circles is zero (3 – 3, 4 – 4, etc). The line AB is a hyperbola. Now plot the following points on the diagram. Label each point from X and X1 to Z and Z1.

Distance from S – 5 cm, Distance from M – 3 cm Distance from S – 4 cm, Distance from M – 2 cm Distance from S – 3 cm, Distance from M – 1 cm

Each of the circles intersects the others at two points. With the line X-X1 drawn, the diagram should look like the one below.

M S

B

A

x

y

z

y1

x1

The difference between the circles is 2 (5 - 3, 4 – 2, 3 – 1, etc). By plotting all the variables, it is possible to establish a family of hyperbolas, shown by the curved lines. Now assume that these are range lines. By establishing the difference in range between that from the aircraft’s own position to the M and S points respectively, it becomes possible to use these hyperbolas as LOPs. Hyperbolic radio navigation aids operate on the principle that the difference in time of arrival of signals from two stations is a measure of the difference in distance from the point of observation to each of the stations. Since radio signals travel at a constant speed (essentially the speed of light), these measurements can translate the differences in time directly into differences in distance.

Hyperbolic Navigation Chapter 16

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The base line is the line joining M – S, in a hyperbolic navigation system. Note that each hyperbola cuts the base line at half the difference in range from the central 0 hyperbola.

The 1 cm line cuts the base line at ½. The 2 cm line cuts the base line at 1.

The lines behind M and S are referred to as base line extensions while the straight line at right angles to the centre of the base line is called the base line bisector.

Area ofAmbiguityand PoorAccuracy

MostAccurate

The base line extensions and the base line bisector are straight hyperbolas. The spacing of the position lines varies. They are constant along the base line but diverge with increasing distance from the base line. The rate of divergence is least near the base line bisector, increasing toward the base line extensions. As a result, the accuracy decreases more rapidly in the vicinity of the base line extensions.

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LINES OF POSITION (LOP) Due to the curvature of the hyperbola, the same LOP exists on both sides of the base line extensions. This gives the risk of an ambiguous situation that is not acceptable. In the application of this principle, one transmitter (M) is used to stabilise or control the transmissions of the second transmitter (S). The control transmitter is known as the Master and the other is called the Slave (or Secondary). Since the signals from the Master are used for control and synchronisation of the master/slave pair it follows that there must be reliable communication between the two beacons. This communication is normally done by radio so the two transmitters must be within radio range of each other, ensuring predictable and reliable signal to noise ratios. It requires one Master/Slave combination to produce a single LOP (line of position). To determine a fix requires a minimum of two LOPs and therefore the use of two Master/Slave combinations. Like all fixes, however, the angle of intersection of the LOPs affects the fix accuracy. Each LOP has a band of error. If the LOPs intersect at 90° the respective bands of error form a small rectangle enclosing the position of the receiver. If the LOPs intersect at 30° the area becomes an elongated diamond. This considerably increases the area of possible positions. In a hyperbolic system, base line bisectors intersecting at 90° provide the best fixes.

ERRORS OF HYPERBOLIC NAVIGATION PROPAGATION ERRORS Since the determination of the LOP depends upon the comparison of time of arrival of the two signals, anything that affects the accuracy of that timing causes errors. The timing assumes that the speed of propagation is constant and the same for both signals. If the Master signal travels over the sea to reach the receiver, and the Slave signal propagates over the land, the propagation speeds are slightly different and the accuracy of the timing disrupted. Where these propagation errors are known to exist, either distorting the hyperbola or publishing corrections generally accounts for them.

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HEIGHT ERROR Note that the hyperbolas are indeed three-dimensional. A constant range differential is observable not only along the Earth’s surface but also on a three-dimensional curved hyperbolic surface. The hyperbolic surface is a vertical plane over the base line bisector but, in the vicinity of the transmitters, it becomes noticeably more curved. For charts drawn for a hyperbolic navigation system, it is normal for the hyperbola to be drawn for Sea Level. Although an aircraft at altitude may be on the same curved hyperbolic surface represented by a plotted LOP, the plotted LOP shows only the line where this curved surface intersects Sea Level. Using the plotted LOP introduces an error, termed Height Error.

SIMPLE HYPERBOLIC CALCULATION

Example: A hyperbola cuts the base line 100 km from the Master end and 150 km from the Slave end. When on the same hyperbola at a range of 120 km from the Master, the range from the slave will be:

Draw the situation.

Hyperbola is a line joining all points where the difference of distance from two fixed points is the same. The difference between the M – S base line cut is 50 km. Therefore the difference in distance must be the same at 120 km. Therefore the distance from the slave is 120 + 50 km = 170 km if the aircraft is on the same hyperbola.

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Example: An aircraft is 120 km from the Master and 170 km from the Slave. How

far from the Slave will the hyperbola cut the base line? Master – Slave distance is 250 km:

Draw the situation.

M S125 km 125 km

120 km 170 km

Look at the range difference between the Master and the Slave = 50 km. Halve this difference = 25 km. This is the distance the hyperbola crosses the base line from the central perpendicular. Therefore, the hyperbola cuts 125 + 25 km = 150 km from the Slave.

Radio Navigation 17-1

INTRODUCTION LORAN is an acronym for LOng RAge Navigation, developed in the Second World War with the intention of providing aircraft with a hyperbolic navigation system that did not suffer from sky wave contamination.

PRINCIPLE OF OPERATION LORAN C is a hyperbolic navigation system. The system was scheduled to be discontinued in 2000 but some users made strong moves to retain its operational status. LORAN C stations are grouped in a network or chain, with one station as a master and the other stations arranged around it as secondary (slave) stations. Secondary stations are identified by the letters W, X, Y or Z. The chains covering the North Atlantic appear below. The distance between master and slave is between 600 and 1000 nm.

SWEDEN

NORWAY

GERMANY

IRELAND

GREENLAND

U. K.

ICELAND

W 7930

M 7930

X 7930W 9980

M 7970

7970 Y

Z 7970

X 7970

X 9980M

9980

W 7970

Labrador Sea ChainLoran GRI 7930

Icelandic ChainLoran GRI 9980

Norwegian Sea ChainLoran GRI 7970

M Fox Harbour LBW Cape Race NFLDX Angissog GRLD

M Sandur ICLDW Angissog GRLDX Eidhi Faroes DNK

M Eidhi Faroes DNKW Sylt GERX Bo NRWYY Sandur ICLDZ Jan Mayen NRWY

LABRADOR

Coverage extends from Asia, over the USA, North Atlantic Region and Europe.

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LORAN C uses the principle of differential range by pulse technique. Frequency 90 to 110 kHz

TYPICAL LORAN C CHAIN In the diagram above, three chains cover the North Atlantic. Looking at the individual composition of the Norwegian Sea Chain:

Station Position Designation Location Eidhi Faroes Master 7970 Faroe Islands

Sylt Slave 7970W Germany Bo Slave 7970X Norway

Sandur Slave 7970Y Iceland Jan Mayen Slave 7970Z Arctic

The coverage requirements determine a station’s location with respect to other stations in the chain. A monitor station is also part of a LORAN C chain, and is usually located at one of the transmitting stations. The distance between master and secondary stations (base line) varies between 600 and 1000 nm. LORAN C signals are transmitted at low frequencies, around 100 kHz. Low frequency signals travel as surface waves over the earth giving LORAN C a theoretical range of up to 1500 nm over water. The master station in a chain transmits first, and its signal is used as a reference. Each secondary station has a unique emission delay that allows the aircraft to receive the signal from the master before the secondary transmits. LORAN signals are transmitted in pulses in the shape of an elongated pear. Signals from the master stations are sent out in groups of nine pulses with a pause after the eighth. Signals from the secondary stations are sent out in groups of eight pulses.

LORAN C TRANSMISSION All the masters and slaves transmit on the same frequency of 100 kHz. To ensure that there are no chain identification problems, each chain is allocated a specific PRI. The time that elapses from the beginning of one master pulse group to the beginning of the next is different for each LORAN chain. The name for this time interval is the group repetition interval (GRI). For each chain, a minimum GRI is selected. It must be of sufficient length to allow time for the transmission of the pulse group from each station, plus the time between each pulse group. The GRI is also used as a way to label LORAN chains. For example, a GRI of 79 700 microseconds becomes chain 7970 by dropping the last significant zero. Chain 7970 corresponds to the Norwegian Sea Chain. Permissible GRIs are multiples of 10 microseconds from 40 000 through 99 990 microseconds.

OPERATION Using the principle of differential range by pulse technique, it is necessary to look at the way an operator deciphers the system. Weather or static build up can affect transmissions. The multi-pulse system minimises the problems of low frequency long-range transmissions. The master and slave pulses are sent in groups of eight, with each pulse separated by 1000 microseconds. The master pulse is identified by an extra pulse which is transmitted 2000 microseconds after the main group. The pulses are then summated to give one strong pulse. Each pulse is between 180 and 270 microseconds long.

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The operator will receive a train of pulses as shown above. The master transmits first followed by, the slaves in the order W, X, Y, and Z. The operator looks at the chain and chooses the two slaves that will give the most accurate fix. At the same time the master is gated to align the timing of the system.

Once the system has been gated, the matching of the received signals is carried out to match the cycles. The measurement of time difference between the master and relevant slave is obtained from the pulse. The third cycle is always used, as this is never contaminated by returning sky waves once it has been identified. For a 100 kHz radio frequency, the period (1/T) is 10 microseconds which is also the accuracy obtainable.

The LORAN C receiver uses the pulse envelope to find the timing point on a particular cycle. If the pulse is distorted, due to a poor signal for instance, the cycle tracking point may jump to the next pulse causing an error. This is how the 10 microsecond accuracy is determined. An error of 10 microseconds in the time measurements equals a typical 1 nm position error in the area around the base line. The position error increases away from the base line.

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1 nm 10 M sec

3 nm 10 M sec

10 nm 10 M sec

W

M

Baseline

To minimise this error, LORAN C determines the time intervals by calculating the time between pulses and cycle matching within the pulses by comparing the cycles of radio frequency within the master signal with those within the slave signal. This makes it possible to determine the time interval to an accuracy of 10 microseconds. The measured difference depends on the aircraft’s position in relation to the master slave pair. On the slave base line extension, the total time difference is base-line propagation time plus slave delay and will be the smallest value. On the master base line extension, the delay is twice base line propagation time plus slave delay and will be the largest value. The area in the vicinity of the base line extensions is not a good LOP area due to spread of the hyperbola and high risk of ambiguity. Each pulse within a group may have its radio frequency cycles organised in a pattern of regular or inverted pulses. This phase coding enables the receivers to distinguish the master signal from the secondary stations and also helps to reduce sky wave and noise interference. In summary, the propagation delay between the pulses from the master and slave at every chain are:

Baseline Extension from the Slave is the time delay at the slave. Baseline Extension from the Master is twice the time the pulse takes to travel from the master to the slave plus the time delay at the slave. The Baseline Bisector is the time of travel of the pulse to the slave plus the time delay at the slave.

All other propagation delays are between the above figures.

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COVERAGE, LIMITATIONS, AND ACCURACY LORAN C COVERAGE Even though most of the major avionics manufacturers now produce LORAN C systems, LORAN C’s nautical origin is still evident in several ways. One of the most obvious is LORAN C’s continuing orientation toward over-water areas. Most of the existing chains exist in coastal areas or on islands, providing fairly complete North Atlantic and Pacific coverage. The western part of northern Europe and the Mediterranean Sea has almost complete LORAN C coverage. No coverage currently exists in the Southern Hemisphere. This limits LORAN C capability as an international long-range navigational system. SKY WAVES LORAN C is a low frequency system, which means that LORAN C unit sometimes receives the sky wave in addition to the normal and preferred ground wave. Since the sky wave travels a greater distance than the ground wave, it takes a longer period of time to reach the receiver. At certain distances from the transmitter this may adversely affect the accuracy of the plotted LOP. Up to distances of 1000 nm from the transmitter, the ground wave dominates and the receiver can fairly easily distinguish ground waves from sky waves. At greater distances however, usually over 1500 nm, the ground wave becomes so weak that the sky wave begins to dominate. The ground wave is more stable and reliable than the sky wave and is preferred for navigation purposes. Modern LORAN C receivers have circuits that enable them to differentiate between the stronger ground wave and the weaker sky wave. Most LORAN C receivers are able to make use of the sky wave signals at this range, but accuracy is reduced. The problems arise at the intermediate distances, from approximately 1000 to 1500 nm. At these distances, the sky wave and the ground wave are about equal in strength. This may confuse the receiver and distort the results, particularly at night. The phase coding of the transmitted pulses helps the receiver in solving the problems of interfering sky waves. STATIC DISTURBANCES The modern LORAN C receiver constantly monitors the signal to noise ratio (SNR). The SNR is a ratio given by the signal received, divided by noise due to static or other disturbances. Precipitation static causes electronic noise, and this noise causes the SNR to drop. LORAN C receivers normally issue a warning when the ratio drops below a certain minimum level. The static charge picked up when flying through precipitation can seldom be completely eliminated but it can be reduced by airframe grounding and by installing static discharge wicks. Other electrical disturbances, such as those produced by thunderstorms, may also have an influence on LORAN C accuracy. RADIO PROPAGATION SPEED The accuracy of LORAN C is related to the propagation speed of the radio waves, which is assumed to be constant. This is not the case. The speed of radio waves is influenced by factors such as the time of day, the season, and especially by different kinds of terrain. LORAN C was designed as an over-water system, and all of the assumptions as to the signal speed and transmission are based on signals propagated over seawater. Position calculations based on signals propagated over land have slight errors. Modern LORAN C receivers have compensating circuits, called additional secondary factors (ASF) circuits, to correct for this condition. These propagation errors are usually not significant. They only affect the accuracy slightly and within predictable limits. The pilot should be aware that peak accuracy can only be obtained with LORAN C when operating over oceanic areas using signals from transmitters situated on islands or coastal regions.

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GEOMETRY OF CROSSING ANGLES A factor that affects accuracy is the angle at which the hyperbolic LOPs intersect each other. LOPs that cross at 90° angles produce small, square areas of position between hyperbolae. LOPs that cross at oblique angles produce large, diamond shaped areas between hyperbolae. Furthermore, the distance from the LORAN C station affects accuracy by increasing the distance between LOPs. A 10-microsecond change represents approximately one nautical mile close to the base line, compared to eight nautical miles near the base line extension. These distances both increase since the hyperbolae spread with a distance increase from the base line. Due to ambiguity, the area around the base line extension is not usable for LORAN C navigation even though the aircraft may be close to the station. Interference from navigation and communication stations within the same band as LORAN C may influence LORAN C accuracy. To cope with interference from other transmitters within the same band, the manufacturers install notch filters at the receiver input, which reduce interference from transmissions on adjacent frequencies. USE OF LORAN C The use of LORAN was more complex before the introduction of new electronic processors. Signals from the master and secondary stations were presented on the horizontal trace of a cathode ray tube and appeared initially as vertical blips on the linear time base (as shown on page 17-3). The cathode ray tube displayed the master and secondary pulses. The operators electronically moved the two pulses and compared them, reading the time difference between the master and secondary pulses as the distance X. This distance corresponded to a hyperbolic LOP. The operator plotted this line of position on a LORAN chart that had all the hyperbolic lines drawn on it. The process was repeated to find another line of position by using another master/secondary pair in the chain. With the introduction of electronic processors came the development of a new generation of LORAN C receivers. These very sophisticated receivers perform the same operations the navigator did, but in a much shorter time. They also provide present position instantaneously. The new LORAN receivers not only provide position fixes, but can also provide additional information such as bearing, track, groundspeed, and drift angle without the need of any manual operation. There are many different types of control display units (CDU) for LORAN C operations.

There are also more expensive and sophisticated CDUs, which are intended for larger aircraft and are generally designed to fit in the control stand on the pilot’s side with the bulk of the electronics located in a remote unit. Although still found in many aircraft, it is unlikely that newer aircraft will have them since the future of the system is very much in doubt. There are currently 15 chains worldwide. Most LORAN C units require the pilot to manually select a specific LORAN C chain. The pilot uses the GRI to tune the desired chain. For instance, the GRI for the Norwegian Sea is 79 700 microseconds. The identification for this station is 7970. In more sophisticated units, an internal memory remembers the unit’s position when the set is shut off. This position is used to find the applicable chain when power is switched on again. Once a GRI has been selected, the unit then goes into search, identify, and track cycle. During the cycle, the unit attempts to receive the master station for the GRI selected and then looks for the two best secondary signals in that chain.

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LORAN C NAVIGATION LORAN C can provide point-to-point navigational guidance with great reliability and accuracy and is easy to use. Specific procedures vary from unit to unit, but essentially, once the unit establishes the point of origin, the pilot can determine a route between waypoints and follow it, using the additional information provided by the unit. Several methods of entering the point of origin into the unit exist. For instance, latitude and longitude co-ordinates can be entered manually. Selecting a previously stored airport identifier or waypoint can also enter Latitude and Longitude. Finally, selecting position mode and allowing the LORAN C to determine the present position by itself can automatically enter the point of origin. This last procedure is usually accomplished in flight. Once present position has been entered, the destination waypoint is entered, either by LAT/LONG co-ordinates, or by waypoint identifier. At this point, the unit can be switched to navigation mode and track guidance is provided on a CDI, an HSI, or on a dedicated LORAN instrument. The most direct method of tracking using LORAN C is by using the cross track distance (XTD,) or the distance between the desired track and the actual track. Directly displayed on the receiver’s monitor, XTD is the actual distance the aircraft is off track. If, for instance, the LORAN C unit indicates a cross track distance 1.2 nm right of track, the pilot can simply correct to the left and monitor the cross track distance decreasing as the aircraft approaches the desired track. Many modern sophisticated Navigation Processing units accept LORAN C position information for use alongside that from other sources. The development of GNSS would appear to mean that the use of LORAN will become rapidly less important in aviation. TRANSMITTER FAULT INDICATION The ninth pulse in the master transmission can be coded to indicate a variety of problems. Normally the blink is the Morse code letter R (• – •). A slave station can also blink the first two pulses of transmission to indicate a fault. Using a blink code indicates:

Station not transmitting Incorrect phase coding Incorrect number of pulses Incorrect pulse spacing Incorrect pulse shape Time difference outside specified limits

Both master and slave stations blink if either station is operating incorrectly.

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RANGE AND ACCURACY Both range and accuracy can be affected by the following:

The power and accuracy of the ground transmission The path of the surface wave The propagation conditions for sky waves The receiver and aerial employed Noise in the reception area The aircraft’s position in the chain

The approximate daytime ranges of LORAN are:

Ground Wave 1200 nm over water 900 nm over land

Sky Wave Up to 2500 nm by day or night

ACCURACY LIMITS Ground Wave ± 0.5 nm on 95% of occasions, up to 1000 nm over the sea Sky Wave Sky wave should only be used when out of ground wave range. 10 – 15 nm at 1500 nm. Up to 20 nm at 2500 nm

Radio Navigation 18-1

INTRODUCTION Satellite navigation was initially developed for military operations. The civil aviation world now extensively uses the system. Available 24 hours a day, the system provides accuracy and reliability never seen before in aviation systems.

Two systems of satellite navigation exist: GPS or Navstar Global Positioning Service developed by the USA, and GLONASS, the Russian equivalent. This chapter refers primarily to GPS. A discussion of GLONASS follows at the end of this text.

SYSTEM CAPABILITY For civil aviation, GPS is capable of providing users with the following information:

Position, in three dimensions Velocity determination Time

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FREQUENCY

Fundamental Frequency f0 10.23 MHz Carrier Frequency L1 1575.42 MHz Carrier Frequency L2 1227.60 MHz

The use of the frequencies is discussed later in this chapter.

BASIC PRINCIPLE OF OPERATION GPS uses a similar principle of operation to radar:

The satellite transmits a signal. The receiver notes the time the satellite signal is received. Comparing the time of transmission to the time of receipt provides a distance from

the satellite. Example: Assume that 2 people on the surface of the Earth are a set distance away from a

satellite (also on the Earth’s surface).

Suppose the satellite transmits a sound signal that both people receive 10 seconds after transmission. If the speed of sound is 340 m/s, each person is 3400 m from the satellite. The distance measurement depends upon:

The satellite transmitting at the correct time The speed of sound being exactly 340 m/s The clocks of the receivers being correct and synchronised to the satellite clock

The example above provides only one range measurement, indicating only that each person is somewhere on a circular line of position at a range of 3400 m.

10 seconds

10 seconds

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If the pilot of an aircraft receives the same satellite signal 10 seconds after transmission, the aircraft could be anywhere on a spherical surface with a radius of 3400 metres from the satellite.

For a person on the ground, one satellite only gives one position line. Three satellites will give a three position line fix. As soon as a fix is required in 3 dimensions, a fourth satellite is required.

10 seconds

10 seconds

10 seconds

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If the timepiece in the receiver is in error then the range from each satellite will have the same range error. This would present a pilot with three possible positions. By biasing each of these ranges equally, the pilot could deduce the accurate position and, at the same time, determine the magnitude of the clock error (known as clock bias).

THE GPS SYSTEM The GPS system consists of three segments:

The Space Segment The Control Segment The User Segment

THE SPACE SEGMENT The space segment consists of a group of satellites known as a constellation, which provides the navigation signals. GPS consists of 24 satellites, 21 of which are operational, and 3 operational spares. The constellation is arranged in six orbital paths with four satellites in each orbit. The orbits are inclined at 55° to the equator, and are separated from each other by 60° of latitude as they cross the Equator. A satellite is considered masked when it is less than 5° above the observer’s horizon. Masked satellites are not used in the navigation solution.

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Orbit Height: Approximately 20 200 km Orbit Time: Approximately 12 hours

There is a time difference of 3 minutes 57 seconds between two orbits of the satellite and one rotation of the earth around its axis. This is due to the difference between the length of the sidereal day and that of the solar day. The system is designed so that an observer can always detect signals from a minimum of five satellites. The receiver system usually has a back-up capability for failures of any part of the system. GPS TIMING GPS timing is measured in seconds from a start date of 00:00:00 UTC, 06 January 1980. The system then runs for 1024 weeks, after which the clock restarts at zero. Because the start date was UTC the GPS has to run referenced to UTC. The time difference between the satellite clock and UTC at present is approximately 13.5 seconds. The accurate time difference is transmitted in the satellite broadcast.

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C/A CODE 1.023 MHZ

NAV/SYSTEM DATA 50 HZ

P CODE 10.23 MHZ

L1 Carrier 1575.42 MHz

L2 Carrier 1227.60 MHz

L1 SIGNAL

L2 SIGNAL

FREQUENCY AND CODING GPS satellites transmit on two frequencies:

L1 1575.42 MHz L1 transmits the Coarse/Acquisition (C/A) code, Precision (P) code, and system data message.

The C/A code is repeated every millisecond on a frequency of 1.023 MHz. The P code is repeated every 7 days on 10.23 MHz. The navigation and system data message is transmitted at 50 Hz. L2 1227.60 MHz Transmits the P code only This frequency determines ionospheric delay

New satellites will also have a capability for the inclusion of a new frequency (L5) upon which the calculations for automatic correction of ionospheric time delays will be based, although as yet the final frequency for L5 has yet to be decided. The frequency difference from L1 must be greater than 200 MHz in order to optimise the ionospheric corrections. Sufficient separation must also be allowed for other Radio Aids in the UHF band such as DME. These signals use Pseudo Random Noise (PRN) to carry messages. PRN uses binary mathematics generated in a predictable manner by the on-board clock. This is achieved by using Binary Phase Shift Keying (BPSK) in which the phase of the carrier wave is reversed when the PRN code changes.

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Since the on-board clock generates the PRN sequence, the start time of each sequence is precisely known and can be carried with the sequence. The PRN sequences also contain two codes known as:

Coarse/Acquisition code C/A Precision code P

Remember: L1 carries both C/A and P L2 carries only P

The P code is only available to authorised users. As a security measure, the military introduces a security feature that changes the coding of the P code, making it the Y code. This does not affect the C/A code which civilian aviation uses. NAVIGATION MESSAGE Superimposed on both C/A and P codes is a navigation message. (NAV-msg). This message contains five discrete sub-frames containing:

Clock data for the satellite being tracked Ephemeris (the satellite orbit) for the satellite being tracked Message – data on obtaining UTC and, for C/A users, ionospheric delay corrections Almanac data – information about all the satellites in the constellation.

TLM Telemetry HOW Handover word SV Space Vehicle (satellite)

Each sub-frame takes 6 seconds to transmit, the total frame time taking 30 seconds. The 4th subframe contains the ionospheric propagation data. Frame 5 transmits the current SV constellation data.

Frames 4 and 5 change in every message; a series of 25 frames is required to download the whole almanac. The almanac information takes 12.5 minutes to download, and is usually downloaded every hour and is valid for 4 hours to several months.

TLM HOW SV Clock Correction Data

TLM HOW SV Ephemeris Data (1)

TLM HOW SV Ephemeris Data (2)

TLM HOW Other Data

TLM HOW Almanac Data for all SVs

25 Pages of Subframes 4 & 5 take 12.5 minutes to download

1 2 3 4 5

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THE CONTROL SEGMENT This provides the control and support system for GPSI and consists of:

Master Control Station (MCS) Colorado Springs Monitoring Stations (MS) Ascension

Hawaii Kwajalein Diego Garcia Back up MCS Onizuka

ColoradoSprings

HawaiiKwajalein

Onizuka

AscensionDiegoGarcia

The Master station tracks, monitors, and manages the satellite constellation. It also provides an updating service for the Navigation Message. The monitor stations are precisely surveyed and consist of very accurate receivers that receive ranging data and navigation message from each GPS satellites in view. The satellite internally computed position and clock time are checked at least once every 12 hours. This data is transmitted to the master control station. The MCS establishes the satellite’s exact orbit and location, known as the satellite ephemeris, along with the actual and predicted clock parameters. The MCS then transmits the updated ephemeris and clock data to each satellite, to be included in its Navigation Message. THE USER SEGMENT Each GPS receiver decodes the space segment to determine position.

Multi-Channel Receiver This receiver is preferred for civil transport aeroplanes. This system monitors all satellites in view and selects the best four satellites in determining the position. Sequential Receiver This type of receiver scans the satellites in a sequential manner in order to determine the pseudo range. As a result, fixing can be quite slow.

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Multiplex Receiver The multiplex receiver is quicker than the sequential receiver. The system is still only single or twin channel.

Advantage can be gained by using more than four channels in an all in view system. Using five channels, it is possible to track all five satellites in view. If a satellite is temporarily obscured from the aerial, there are still four satellites in view and providing the full position, velocity, and time data. The satellite receiver includes:

Wide coverage aerials normally on the top of the aircraft fuselage Operating transmitters and receivers Quartz clocks

The satellite uses a combination of two caesium and two rubidium clocks to maintain atomic frequency standards. This gives a clock accuracy of 10-13 x 3, about 0.003 seconds every 1000 years.

GPS OPERATING PRINCIPLES Current satellite signals transmit on two frequencies. These are identified as L1 (1575.42 MHz) and L2 (1227.60 MHz). Each RF signal is modulated by Binary Phase Shift Keying (BPSK). This modulation provides Pseudo Random Noise (PRN) sequences that carry messages and make up two codes. These two codes are known as:

Coarse/Acquisition code (C/A) This code provides the Standard Position Service (SPS) and is available to all users. Precision code (P) A Precision Position Service (PPS) is provided. The availability of the P code is limited to users authorised by the US Department of Defense.

The satellite generates and transmits the PRN code. The code is not truly random but follows a strict mathematical process, so it is predictable, reproducible within the receiver, and referenced to GPS time. It is important to remember that the signal reproduced with the receiver is not transmitted. The GPS user unit receives satellite signals at the aerial and feeds them to the RF amplifier and the Phase Modulated receiver, where they are compared and matched with the appropriate PRN codes held in memory. This determines the identity of the satellite and the time at which the satellite transmitted the signal. During the time that the receiver is identifying the PRN code it is also downloading the navigation message, which is modulated onto the L1 carrier signal. This information provides the basis upon which to refine the initial range into an accurate value to provide the required accuracy for which GPS is certified.

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L-Band Antenna

PM Receiver

Data Processor

User Interface

Matching up the received signal and the reproduced signal determines a time of arrival. This TOA is the measured value of elapsed time between transmission and reception of the satellite signal. From this, it is possible to derive a range. This derived range takes no account of the fact that the receiver clock may be in error and is referred to as a Pseudo Range (PR). PSEUDO RANGE A Pseudo Range measurement is equal to the TOA value determined by the receiver. It contains:

Signal travel time errors The GPS receiver’s clock bias (error).

Pseudo Ranges (PR) feed from the receiver to the data processor. Within the data processor (sometimes called the navigation processor), each PR is corrected for:

Satellite clock errors (which are the difference between the satellite clock time and the GPS system time)

Atmospheric distortion of the radio signals Effects of relativity Receiver noise

The data for these corrections is determined from information that the processor collects from the satellite’s navigation message. This message is superimposed on both C/A and P code signals. The navigation message consists of 25 data frames. Each individual data frame contains 1500 bits of information, divided into five x 300 bit sub-frames. Each frame takes 30 seconds to transmit so that the entire 25 data frames repeat every 12.5 minutes.

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The navigation message contains:

GPS system time of transmission A hand-over signal for processors transferring from C/A to P code use Orbital position data for the satellite (its ephemeris) Clock data for the particular satellite being tracked Almanac data giving information about the operational status of all the satellites in

the constellation Coefficients for the calculation of UTC Coefficients for the determination of ionospheric propagation delay

The navigation message data is normally valid for up to four hours. It is monitored and maintained as part of the master control station’s task. Once the GPS receiver/processor has applied the corrections derived from the navigation message, it can now set out to resolve its own clock bias.

ActualPosition

4 Seconds(wrong time)

7 Seconds(wrong time)

9 Seconds(wrong time)

No Possible Point ofIntersection Using WrongTime Measurements

In the example above, a TOA system has determined three ranges in which all variable errors have been reduced to zero. If no clock bias existed, the three ranges would intersect at a single point. Clock bias affects all measured ranges equally. As a result, the actual position lies in the geometric centre of the shaded area.

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Adjusting the measured TOA values by equal amounts until the three ranges intersect at a point, determines the clock bias. This is what the receiver processor does in a mathematical solution but, instead of solving for a two-dimensional fix, it solves for four unknown quantities, namely:

The user’s x co-ordinate The user’s y co-ordinate The user’s z co-ordinate Time (t)

Position X1 Y1 Z1

PrimeMeridian

Equator

X

Z

Y

The same x, y, z co-ordinates are used in defining the positions of the satellites, referring to an origin located at the centre of the earth as shown above. Using the origin, the processor then converts the x, y, z co-ordinates into a fix referenced to the WGS – 84 ellipsoid. This conversion allows for the shape of the ellipsoid and results in a position in terms of latitude, longitude, and height. The GPS receiver/processor uses the information in the navigation message to compute the exact location of the satellite. The relative velocity of the satellite and the aeroplane does not affect the fix accuracy in any way. The time that it takes the GPS receiver to position the aircraft depends on the almanac currency and the position and time in the receiver. If these three parameters are correct, the fix is obtained within 30 seconds. If the almanac needs updating, or the position and time are wrong, obtaining a fix occurs only after transmission of all the subframes and updating the receiver. In this case, the time to fix is over 12.5 minutes. VELOCITY MEASUREMENT The processor generates a carrier signal at the same frequency as L1, which is compared to the frequency received from the satellite L1 signal. A difference exists due to Doppler shift. This relative motion between the receiver and the satellites is used to derive the aircraft velocity.

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The receiver can also derive an accurate UTC from the navigation message and display this to the user. The GPS receiver solves for the three elements:

Position Velocity Time

GPS RECEIVER A schematic diagram of a typical GPS avionics receiver is shown below. The receiver is fed from an aerial, generally mounted on the top of the fuselage.

The aerial is designed to provide uniform sensitivity for all signals from satellites above a specified angle of elevation (normally 5°). It is shielded from low elevation signals that are prone to multi-path signals, especially signals arriving from a low elevation satellite. Multi-path signals may occur from:

Reflections and refraction from the Earth Its environment

If received, multi-path signals would cause significant errors. The RF amplifier sets the receiver’s noise level and rejects interference from other RF sources that are not the satellite frequencies. The Reference Oscillator provides the receiver’s time and frequency reference. The output from the RO is fed to the Frequency Synthesiser, which converts the output to local oscillators. The frequency synthesiser also provides the essential clock information to the Signal Processor. The Signal Processor performs the following critical functions:

Splits the signal into multiple channels to allow parallel processing of the separate satellites in view of the aerial

Generates the reference PRN codes Acquires the signals from the individual satellites Tracks the code and carrier of the individual satellites De-modulates and reads the navigation message Extracts the pseudo range rate and pseudo range from the satellite signals Maintains the relationship between the receiver and GPS time

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This information is fed to the Navigation (data) Processor, which performs some or all of the following tasks:

Selects satellites to be acquired and tracked by the signal processor, and computes signal acquisition and tracking-aiding information for that function

Collects navigation data messages and measurements from the signal processor and maintains a database

Computes the positions, velocities, and time corrections for each satellite and corrects the measurements

Uses external navigation data to assist with navigation processing Determines position, velocity, and time

When switching any GPS receiver on, or if the GPS signal has been interrupted, the signal processor/ navigation processor must go through a search procedure in order to:

Detect and identify the visible satellites Carry out the tracking and information gathering functions Determine the position, velocity, and time

These processes, if not assisted, occupy a noticeable period of time, known as Time to First Fix. This can take up to 15 minutes on older systems. Pre-setting the receiver processor to the current position can reduce the time delay.

SYSTEM LIMITATIONS There are two levels of positioning service:

PPS, or Precision Positioning Service, is only available to authorized users at the time of this writing. SPS, or Standard Positioning Service, is carried on the C/A code, is available to all aircraft. This is the one of concern to pilots.

NUMBER OF USERS Since the pseudo ranges are determined from signals that are broadcast without specific address, the number of users that can be served at any instant is virtually limitless.

COVERAGE Of the 24 satellites in orbit, only 21 must be fully operational, with the remaining three considered as reserve satellites that can be rapidly re-deployed to replace other failed units. Current Minimum Operational Standard calls for a minimum of five satellites to be above a mask angle of 7.5°.

RELIABILITY/INTEGRITY Monitoring of the satellite is carried out by:

Internal systems within the satellite The five monitor stations The master control station of the ground segment

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These ensure the detection of signal performance degradation at an early stage and give GPS a similar reliability to most well-used navigation aids. It is possible that the satellite health message, a component of the satellite’s navigation message, may only be changed after a cycle of 25 frames transmission. So it is possible that a period of at least 12.5 minutes may elapse before a receiver/processor corrects the source message. ICAO does not accept this delay and GPS is not acceptable in precision approach landings. RECEIVER AUTONOMOUS INTEGRITY MONITORING (RAIM) RAIM is system integrity monitoring within the GPS unit. The receiver/processor evaluates the information from a minimum of five visible satellites. The position is determined. From the positions determined, the receiver looks to see if one of the satellites is providing an incorrect range and if so, removes it from the position calculation. For RAIM activity there must be:

Five satellites visible The receiver/processor must be capable of handling the extra data

The GPS receiver/processor can be integrated into on-board navigation systems, taking inputs from other navigational sources. This is known as receiver augmentation. If the navigation computer detects a sudden marked deviation of the GPS position, a satellite failure can be suspected. GPS INTEGRITY BROADCAST (GIB) GIB is a ground-based satellite monitoring system that is sited and surveyed accurately. These sites measure satellite range on a continuous basis and use the measured values to compute and broadcast range errors, via satellite, to all users. Modern equipment uses a combination of RAIM and GIB. COVERAGE PROBLEMS Transient holes in the coverage can interrupt or degrade GPS coverage. These holes can appear in certain areas on a regular basis lasting from a few minutes to a few days. Normally this weakens the GPS signal, causing a degradation of accuracy. In some cases, a total loss of the GPS service can occur. The cause of these problems can be the result of any of the following:

Other transmissions on the same frequency Multiples (harmonics) of other transmissions Inter-modulation which causes an effect similar to above Suppressing or blocking interference where the GPS receiver is swamped by strong

RF signals and is de-sensitised Deliberate jamming

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ACCURACY AND ERROR SOURCES ACCURACY FOR CIVIL USE The expected accuracy of the SPS 95% of the time is:

35 metres horizontally 75 metres vertically

In practice, the accuracy achieved is much greater. The reason for the discrepancy between the horizontal and vertical figures is due to geometry. The surface of the sphere around each satellite is predominantly in the vertical plane when perceived on or near the Earths’ surface. This gives rise to a stretching of the area of uncertainty in the vertical plane.

The derived velocity is accurate to within ± 0.2 metres/second. The time is accurate to 52 nanoseconds for GPS time and 340 nanoseconds for UTC. The PPS accuracies are:

5 metres horizontally 27.7 metres vertically

USER EQUIVALENT RANGE ERRORS User Equivalent Range Error (UERE) is the result of a number of sub elements as follows:

Errors in the content of the satellite navigation message Predictability of the satellite’s orbit, which may be disturbed by perturbations resulting

from: Asymmetry of the earth’s gravitational field Lunar and/or solar gravity Atmospheric drag Electro-magnetic forces Solar wind

Stability of the satellite’s clock The satellite clock is monitored and its general error trend established and extrapolated to form part of the navigation message. If the trend changes, this establishes an error source:

Precision of the PRN tracking in the GPS receiver. The heart of this is a stable clock. If the receiver clock drifts, it causes the tracking sequence to be in error.

Errors in the processor’s ionospheric model. If the ionosphere/troposphere creates different refractive indices from those used in the model, this causes errors.

Good satellite signal quality and good receiver/processor design minimise the UERE.

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DILUTION OF PRECISION (DOP) Like all position-determining systems that use lines of position, the geometry of the intersecting lines greatly affects the potential accuracy of any resultant fix. If the satellites in use, as viewed by the GPS receiver aerial, are close together, the surfaces of position have a poor angle of intersection and, consequently, there exists a significant loss of accuracy. This is referred to as a high dilution of precision. A high DOP causes any UERE to have a greater effect.

Small angle gives

less accurate

position

Large angle gives

better solution

DOP can be referred to as:

GDOP: Geometric DOP as just described VDOP: DOP in the vertical (altitude) HDOP: DOP in the horizontal PDOP: DOP of position (a combination of VDOP and HDOP) TDOP: DOP in time

ERROR PREDICTIONS Up to a point, both UERE and DOP error sources can be predicted for a specific receiver at a specific time in a specific place. Not all error sources are totally predictable, such as ionospheric refraction and solar wind. There is always the possibility of uncompensated errors.

DIFFERENTIAL GPS (DGPS) GPS provides a world-wide navigation capability with a high level of accuracy. At present, the system cannot be used for precision approaches unless using a differential system (ICAO requires a 2 second warning of failure for a precision approach and 8 seconds for a non-precision approach). Differential GPS involves the cooperation of two receivers:

An accurately surveyed stationary receiver A moving receiver that requires accurate position information

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DGPS PRINCIPLE OF OPERATION GPS receivers use timing signals from at least four satellites to establish a position. Each of those timing signals has some error or delay. If each timing signal has an error, the position calculation is going to be a compounding of the timing errors. The satellites are so far out in space that the short distances travelled on Earth appear insignificant. If two GPS receivers are close to each other, the signals that reach them will have travelled through the same portion of the atmosphere. This means that the same errors have affected both. By establishing these variable errors, they can be corrected. If a reference receiver is used to measure these errors, it can be used as a referencing system. This reference station receives the same GPS signals as the aircraft. By accurately knowing its own position, it calculates the time required for a satellite signal to reach the earth. Comparing the calculated to the actual time provides the error correction required for an accurate position. The receiver transmits this error correction to the aircraft, which then corrects its own messages. The reference receiver catalogues all visible satellites since it does not know which satellites the aircraft might be using. The aircraft receives the complete list of errors from the reference receiver and applies the corrections for the particular satellites it is using. The use of DGPS significantly improves the accuracy of GPS as illustrated:

SUMMARY OF GPS ERROR SOURCES Typical Error in Metres

Standard GPS Differential GPS Satellite Clocks 1.5 0 Ephemeris Errors 2.5 0 Ionosphere 5.0 0.4 Troposphere 0.5 0.2 Receiver Noise 0.3 0.3 Multipath Reception 0.6 0.6

Typical Position Accuracy Horizontal 29 1.3 Vertical 45 2.0

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PSEUDOLITE/DGPS Using a pseudolite (a pseudo-satellite) makes it possible to reduce the VDOP. Trials show that a reduction in VDOP to less than 1 m for a pseudolite-augmented DGPS is possible from 2.3 m for DGPS. The reference station is exactly the same as in DGPS. The pseudolite is set at a fixed location and accurately surveyed. The pseudolite generates a GPS style signal, which is capable of coding and serving as a ranging signal. The reference station monitors the transmission from the satellites in view and the pseudolite. Monitoring these signals allows derivation of differential corrections, which proceed to the pseudolite. The pseudolite broadcasts these corrections so that user equipment can use the broadcast to:

Determine the differential corrections Establish an additional ranging input

Pseudolite augmented DGPS provides a significant advance, especially in applications for precision-approach landing. In addition to the enhanced accuracy, a pseudolite provides the capability of overcoming multi-path effects. Additionally, their signals are unaffected by ionospheric and tropospheric delays. Because the range to the pseudolite changes rapidly, the receiver is subjected to a much greater variation in signal strength. If the pseudolite is set up on the approach path, its transmitter power may be set to provide a coverage of 20 nm. Approaching the pseudolite, the intensity of the received signal increases inversely with the square of the range from the pseudolite. At 0.1 miles, the signal is 40 000 times stronger, which could cause avionic saturation and swamp the satellite signal. Modifying the broadcast signal structure resolves this problem.

Aerial screening also poses a problem. The pseudolite is on the ground and the satellite navigation system receiver aerial is on top of the aeroplane. The fuselage can screen the aerial and prevent reception of the pseudolite signal. Using separate aerials solves this problem, with the satellite aerial on top of the fuselage and the pseudolite aerial below. This is not the ideal solution. Normally, the pseudolite position is offset from the approach path and, if possible, on an elevated site to overcome fuselage screening.

PSEUDOLITE SIGNAL DIFFERENTIAL CORRECTION→

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SATELLITE BASED AUGMENTATION SYSTEMS (SBAS) The pseudolite is capable of providing high accuracy in small areas. The accuracy deteriorates rapidly away from the pseudolite until 100 km. From this distance, there is little gain from its use. SBAS is being implemented to allow high accuracy at greater ranges. Three systems, all of which work on the same principle, are under development. These systems are:

Wide Area Augmentation System (WAAS), developed in the US European Geostationary Navigation Overlay System (EGNOS), developed in Europe Metsat Satellite Based Augmentation System (MSBAS), developed in Japan

All operate on the same basic principle and aim to provide accuracy sufficient to enable Category 1 precision approaches. SBAS uses:

A ground segment A space segment A user segment just like GPS

The ground segment consists of a number of precisely surveyed:

Wide Area Reference Stations (WARS) Wide Area Master Station (WAMS) A Ground Earth Station (GES)

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The WARS and WAMS stations are connected by communication data links. The network of reference stations (WARS) track the satellites and data link information to the WAMS. The WAMS:

Collates all the data Determines the differential corrections for each tracked satellite Organises the data Formats a data broadcast.

This is sent to the ground earth station (GES) and uplinked to geostationary satellite. In the American WAAS and the European EGNOS systems, the geostationary satellites used are from the INMARSAT 3 series of marine communications satellites. Up to 4 of these will be equipped with navigation packages. The Japanese system envisages the use of their meteorological satellites MTSAT 1 and MTSAT 2.

GROUND EARTH STATION (GES) Reference Station (WARS)

GPS SATELLITE Geostationary Satellite

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The geostationary satellite receives the data and transmits it to all users as a broadcast. The broadcast uses the GPS L1 frequency, modulated with a C/A code of the same category as the GPS C/A codes, and uses the same time basis. The signal also includes a ranging message so that the geostationary satellite can also serve as an extra positioning satellite. The message, broadcast by the geostationary satellite consists of:

An integrity message indicating the status of all GPS satellites in a use/don’t use format

Wide Area DGPS error corrections An ionospheric delay model Ephemeris and clock data for the geostationary satellite

At the aircraft, the broadcast from the geostationary satellite is decoded. Using a wide-area ionospheric delay almanac, the aircraft receiver determines the ionospheric delay for its position and applies the necessary corrections. No tropospheric delay correction data is included, so any correction calculation must come from the stored standard model.

RAIM IN THE WIDE AREA AUGMENTATION SYSTEM The Required Navigation Performance, as a sole means of navigation, makes it necessary to extend the role of Receiver Autonomous Integrity Monitoring. In a single navigation solution, RAIM has to detect, isolate, and exclude the failed source.

The RAIM specification for RNP must include:

Alarm Limits Alarm Response Time Limitations On Nuisance Alarms High detection probability

GLONASS GLONASS is the Russian-developed counterpart to GPS. BASIC CONCEPTS OF THE GLONASS SYSTEM The Russian Global Navigation Satellite System (GLONASS) is based on a constellation of active satellites similar to GPS Navstar. The planned space segment is:

A constellation of 24 satellites Arranged with 8 satellites in 3 orbital planes Satellites are identified by a slot number, which defines the orbital plane (1-8, 9-

16,17-24) and their locations within the plane The three orbital planes are separated by 120° of longitude at the equator and the

satellites within the same orbit plane by 45° of arc. GLONASS orbits are roughly circular with an inclination of about 64.8° The orbit is at 19 000 km with a period of 11 hrs 15 m 44 s.

The ground control segment of GLONASS is entirely located in Russia.

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The co-ordinate system definition of the GLONASS satellite orbits is in accordance with the PZ-90 system, formerly the Soviet Geodetic System 1985l1990. The time scale is defined as Russian UTC. One difference between GLONASS and GPS is that the GLONASS time system includes leap seconds. Satellites transmit simultaneously on two frequency bands, allowing the aircraft receiver to correct for ionospheric delays. Each satellite is allocated a particular frequency within the band, determined by the channel number of the satellite. Aircraft receivers identify each satellite by its frequency channel. Superimposed onto the carrier frequency, the GLONASS satellites modulate the navigation message. Two modulations can be used for ranging purposes, the Coarse Acquisition code, with a modulation length of 586.7 metres and the Precision code, of 58.67 metres. The satellites also transmit:

Orbital information An almanac of the entire constellation Correction parameters to the time scale

The ground control centre predicts the orbital values for a 24-hour period. The satellite transmits a new set of orbital data every 30 minutes. The almanac is updated once per day.

INTEGRATED NAVIGATION SYSTEMS The integration of the Navstar GPS and the GLONASS systems is a method of providing a truly Global Navigation Satellite System (GNSS). The system could provide for an essential high level of redundancy if the Required Navigation Performance (RNP) levels are to be achieved. Receivers are available that are designed to decode both GPS and GLONASS signals. Europe has announced that, in association with Russia, the GLONASS system will see further development. This would considerably enhance the reliability of the system and could bring GNSS close to meeting the needs of RNP. GNSS tends to be used:

As an integral part of a multi-sensor navigation system. As a secondary and supplemental system in which the GNSS and its augmentations

may be used, but another approved system must be available and useable at all times.

The integration of GNSS and an inertial reference system (IRS) is one means of achieving RNP today. This provides the levels of accuracy, integrity, availability, and continuity viewed as the essential elements of RNP. The advantage of this hybrid system is that the IRS continuously determines vector velocities to a very high degree of accuracy. Combining these with the positional accuracy derived from GNSS, results in navigation performance of a very high order.

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GNSS APPLICATIONS GNSS with suitable augmentation will provide for:

Accurate enroute navigation including area navigation capabilities Terminal area routing Precision approaches

In general, the navigation computer of the FMC processes the information and feeds it to the AFCS and to a display such as an EFIS or something similar. The Automatic Dependent Surveillance Broadcast (ADS-B) is also using GNSS. The system digitises the position information derived from the GNSS and broadcasts it as part of a data stream, which includes:

Aircraft identification/flight number Aircraft type Altitude Speed Heading Flight condition (climbing, turning levels, etc.)

This data renews several times a second.

If the data stream is linked to a communications satellite ATC will be given a continuous stream of real time data. Ideal for oceanic sectors, the same data stream transmitted through the transponder mode S could also be used by ATC for both short range ATC and, possibly, TCAS warnings.

Radio Navigation 19-1

INTRODUCTION In the early days of commercial air transport expansion, a system of air routes was developed to provide a safe means of control and separation of aircraft. These routes, which became known as airways, were defined by radio navigation facilities sited at strategic distances apart and at significant navigational points such as:

Airway intersections Turning points FIR boundaries

Following an airway provides an aircraft with a system of navigational checkpoints, and, by being enclosed (by ATC) in a clear box of airspace, separation from other known aircraft in the vicinity. For many years, the airway system has provided an adequate means of routing aircraft, in spite of the fact that navigation from departure aerodrome to destination is not normally the most direct route. In recent years however, a number of factors have led to a review of this situation. These include such elements as increasing congestion on the airways system, resulting in flow control and subsequent, frequently extensive, flight delays, and the need to conserve costs, which demands following the shortest route from departure to destination. The development of improved and enhanced navigation and communication systems permit an aeroplane’s position to be determined accurately and transmitted speedily to the responsible ATC unit. These enhanced ATC systems make it possible to provide aircraft with safe separation from other air traffic without the need to confine them to narrow corridors of airspace.

Hanley

StaveVOR

FaireVOR

Secon

Waypoint 1

Waypoint 2

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To respond to these problems and enhanced capabilities, a system known as Area Navigation (RNAV) is being introduced. This is a system of navigation that is not dependant upon routing between points coincident with the position of a radio facility. Instead, it is capable of providing navigational guidance along other non–airway routes marked by waypoints.

A waypoint is a predetermined geographic position defined in terms of latitude and longitude. Where appropriate, it may also be defined as a radial and range from VOR/DME beacons, which is known as rho/theta (ρ/θ). Waypoints may also be defined by ranges from two DME beacons, which is known as rho/rho (ρ/ρ). Subject to an aeroplane being properly equipped, area navigation is available as follows:

Fixed Published RNAV Routes These are usable in a flight plan only if the aeroplane has an approved RNAV capability. Contingency RNAV Routes These are published routes useable by suitably equipped aeroplanes during specified times. Random RNAV Routes These are unpublished routes and may be flight planned within designated areas

AREA NAVIGATION CONCEPTS JAR OPS 1 requires that an aeroplane’s navigation equipment should include “an Area Navigation System when area navigation is required for the route being flown”. There are three types of area navigation systems. Self-contained systems obtain their navigation data from onboard sensors and are therefore independent of external sources. Typical self-contained navigational systems use the outputs from inertial reference systems (IRS) or inertial navigation systems (INS). The difference between INS and IRS is covered later, but both provide navigation solutions without reference to external systems. They update the position of the aircraft by sensing its accelerations and integrating them with respect to time, establishing distance and direction of movement from the start position. An integral navigation computer carries out all related navigation calculations. Although they are extremely accurate from the initial position, the accuracy degrades with time. Externally referenced systems derive information from external sources in order to provide navigational guidance. Hybrid systems use information from a combination of self-contained and externally referenced navigation systems. Such systems are initially extremely accurate and maintain good accuracy

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over time because the long-term accuracy of external radio navigation aids such as VOR and DME counter the degradation of the self-contained system. Many commercial operators have been quick to realise the benefits of such a system and are not only specifying a suitable system for new aeroplanes but are, at considerable cost, actively retrofitting their older fleets with similar equipment. Most equipment installations on commercial aeroplanes form an integral part of a comprehensive avionics package and are capable of providing area navigation even when out of range of ground-based navigation facilities. Such systems are normally of the hybrid type. Most modern general aviation aeroplanes have a basic RNAV system (so called BRNAV) as the standard unit. These are generally based on the rho/theta or rho/rho system using inputs from VOR/DME. GNSS, the Global Navigation Satellite System, based on satellite navigation, is increasingly utilised as the prime source for the required navigation information. ACCURACY OF RNAV EQUIPMENT There are two types of RNAV:

Basic RNAV The lateral track-keeping accuracy of basic RNAV is ± 5 nm for 95% of the flight time. Precision RNAV The lateral track-keeping accuracy of precision RNAV is ± 1 nm for 95% of the flight time.

The track keeping accuracy is dependent on the navigation system error and Flight Technical Error. For obstacle clearance the Flight Technical Error is:

Departure ± 0.5 nm (at the DER a value of ± 0.1 nm is assumed) Initial and Intermediate Climb ± 1 nm Enroute 2 nm

BASIC RNAV VOR/DME based area navigation is a navigation and guidance system that uses basic signal inputs to compute track and distance to a waypoint. VOR bearings and DME slant ranging provide the required information. More sophisticated systems may also provide barometric altitude input. A block diagram of a simple navigation system appears below. The simple system, most commonly installed in general aviation aircraft, usually consists of a computer that defines each waypoint as a radial and range from a VOR/DME. Such waypoints are often called phantom or ghost stations. The computer’s memory is able to store a limited number of successive waypoints, normally a maximum of nine, which enables the pilot to enter the planned route before departure. A more sophisticated system utilises a navigational database stored either within the navigation computer or in an external storage unit. The navigational database contains all the necessary information regarding routes between airports, VOR/DME stations, and waypoints. It is obviously important that this database is kept up to date. It should be updated every 28 days.

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Memory

Computer

VOR / DME

GNSS

Air Data

Display

Pilot's CDU

Auto Pilot

The Control Display Unit (CDU) is used to enter information into the computer and to display navigation information. In a basic system, the navigation computer resolves the navigation problem. The computer receives a radial from the VOR receiver, DME distance from the DME interrogator, and altitude from the encoding altimeter. It uses these parameters to establish the aeroplane’s current position. It compares this to the position of the next waypoint and generates an error signal, which provides steering signals to a Course Deviation Indicator (CDI), Horizontal Situation Indicator (HSI) or other suitable display. It also derives a distance to go reading. In some aircraft installations, the computer may also send track correction signals (lateral steering commands) to the autopilot roll channel. Since the use of Area Navigation Systems permits waypoints to be accurately defined, determined and flown, this removes the need to follow the facility-determined structure of the airways and permits direct routing and more effective use of the available airspace. The aircraft equipment consists of the normal VOR/DME receivers, a navigation (course line) computer, and a simple interface display.

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USE OF BASIC RNAV When operating the course line computer, the pilot selects a VOR/DME station that is within the line of sight range of the desired waypoint. The radial and distance from the station to the desired waypoint is then manually entered. This can be repeated for a number of waypoints (if the equipment permits). Once the waypoint information is stored, the pilot can select the sector (waypoint from and to) and the course deviation indicator acts as if a VOR radial has been selected. Note that it is possible to select sectors that do not connect successive waypoints. This allows waypoints to be bypassed. Begin navigating in the same manner as when tracking a VOR station. Distance to go appears in the normal display. With area navigation, the amount of CDI needle deflection does not vary with distance to the waypoint as it would when tracking inbound to a VOR. It always represents a constant distance off track for a given deflection. On a 5 dot CDI, one dot deflection equals one mile of deviation, regardless of the distance to the waypoint. VOR/DME based RNAV has several applications:

The ability to file a RNAV route flight plan The opportunity of tracking a direct route (subject to ATC restrictions and

requirements) The ability to navigate directly to an intersection bypassing waypoints. The ability to set up a holding pattern when the ATC instructs the pilot to “hold at

present position” The ability to locate and approach an airfield that is not equipped with navigation aids

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The plate shown above is the Oklahoma City RNAV approach procedure, which gives all waypoints both in terms of radial/distance from the Oklahoma City VOR/DME, and latitude/longitude. The chart is for information purposes only. When using the RNAV approach mode, the system sensitivity is multiplied by 4. This means that each dot on the CDI represents a linear displacement of 1/4 of a nautical mile.

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RNAV LIMITATIONS The VOR/DME based BRNAV suffers the dependent limitations of VOR/DME equipment. If this signal is lost and the Nav warning flags appear on the CDI or HSI, the pilot must use an alternative method of navigation. A pilot may fly the area navigation route, using guidance signals to the waypoint, only as long as the aircraft is within the operational range of the appropriate VOR/DME station. The practical range limit is approximately 200 nm from the associated VOR/DME at the highest altitudes normally used for civil aviation. Remember that operational altitude makes the range limit for a light aeroplane normally considerably lower. The accuracy of the position information and any derived steering signals are affected by the same sources of error as the VOR/DME in use. Some systems use DME/DME navigation, with frequency-scanning DME interrogators. Such systems provide more accurate navigation. All other area navigation systems that depend on a single type of source, whether self-contained or facility-dependent are affected by the errors of that source. A hybrid system, in which the data from a number of sources is electronically compared and the best information used, tends to provide a higher and more consistent degree of accuracy.

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Radio Navigation 20-1

INTRODUCTION There is considerable pressure to make more effective use of the airspace in which pilots fly. As a result, the industry is increasingly adopting the Area Navigation philosophy, and the modern transport aeroplane is extremely well equipped to comply with the needs of an Area Navigation System. In simple terms, the fundamentals of navigation have not changed since ancient times. Pilots must know where they are (current position), and where they are going (the destination). If they cannot see their destination, they must be able to compute the direction and distance to that point and must continuously monitor their progress to ensure that they are following the correct path. The objective of navigation remains the same, but today the applicable tools to create a solution are powerful beyond the dreams of navigators of even 50 years ago. The heart of this power is the modern Flight Management System (FMS). This chapter is an introduction to the FMS.

THE ROLE OF FMS The FMS is an integrated automatic flight management system that provides, through precision control of engine power and flight path, optimum economy of flight. At the same time, the FMS reduces flight deck workload, which can considerably enhance safety. The diagram that follows illustrates the many tasks the FMS can perform. In such an integrated system, the FMS is interfaced with the Power Management Control System (PMCS) and the Automatic Flight Control System (AFCS) so that it manages both control of power and flight path (vertically and horizontally) against a pre-planned flight path. The FMS consists of two units:

The Command Display Unit (CDU) is the crew’s interface with the system. The Flight Management Computer (FMC) handles all the complex calculations and memory items required.

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The FMC has a data storage capacity, similar to the hard disk on a PC, which is in two broad sections. One section is dedicated to aircraft performance data for take-off, climb, cruise, descent, holding, go-around, and abnormal flight (e.g. engine-out) situations. This data has a comparatively long life. The second section, known as the Navigation database, stores all the data relevant to the airline’s route structure. This includes:

Navigation Facilities: Position, frequency, identification, type Waypoints: Latitude, longitude, type (enroute, etc.) Airports & Runways: Designations, elevations, locations, etc. Terminal Procedures: SIDs, STARs, holds, etc. Approach & Go-around Procedures Routes: Airway identifier, magnetic course Company Routes: Details of normal routings.

This data requires frequent updates, and must be renewed every 28 days. Using these two packages, along with the variable inputs (such as current position, wind velocity from the aeroplane’s navigation computer, and air traffic clearance), it is possible to generate, or modify, a flight plan to meet the current needs.

Introduction to the Flight Management System (FMS) Chapter 20

Radio Navigation 20-3

Since the FMC has all the data required, the activities associated with following a precision RNAV (PRNAV) route in three dimensions can be easily accommodated. All it requires is telling the system the route to follow, the preferred flight profile, and the ATC clearance, accomplished through the CDU. The aeroplane’s navigation sensors feed information to the FMC and, from those sensors, it becomes possible to derive the best position information and find a solution to the questions of how far to fly and in what direction. The navigation sensors normally consist of a combination of inputs from facilities selected by the FMC. A hybrid combination provides the necessary Required Navigation Performance to comply with the needs of a precision RNAV (PRNAV). These sensors may include some or all of the following:

VOR/DME ILS IRS LORAN GNSS

At this time, none of these sensors alone can dependably provide the reliability, integrity, and accuracy necessary.

VOR/DME units are limited in range ability and the position accuracy deteriorates with range from the facility.

IRS suffers from cumulative position errors. LORAN does not provide reliable coverage nor is it worldwide. GNSS still requires augmentation.

The FMC evaluates the data from the available sources to derive the best position. In addition, using inputs of altitude, airspeed, temperature, and Mach number from the air data computer, along with engine parameters and fuel data, complete control of the flight profile can be exercised. This ensures flight optimisation in terms of fuel efficiency.

USE OF FMS The FMS is now such a critical item of equipment that two are normally installed. Two units allows flexibility in usage:

Master/Slave Operation is the normal condition where one FMC is controlling and the other is monitoring. All data entered into the controlling FMC is shared with the other FMC. The computers talk to each other and, as well as sharing data, they compare each other’s outputs. Each FMC retains control of its associated AFCS, auto-throttle, and selection of radio navigation aids. Independent use occurs wherein the FMS units operate independently. This allows the pilots to operate with one unit displaying performance pages while the other displays navigation data. Alternatively, one may be used to revise or review activities without disrupting either the active flight plan or the commands of the other CDU. Single use occurs when only one FMS is operational.

Chapter 20 Introduction to the Flight Management System (FMS)

Radio Navigation 20-4

Back-up occurs when the FMC is suffering from some failure but a limited FMS function still exists.

Within those parameters, the crew must decide how much control to give to the FMS. The options are normally Managed Guidance, in which the FMS performs the task of maintaining the pre-planned route, speed, and altitude profiles, or to control some parameter, such as a heading or speed hold, through the use of the flight control panel. A typical CDU appears below. Through this unit, the flight crew can:

Construct a detailed flight plan Select data pages to view Respond to FMC requests for data entry Change displayed data

FMS design varies slightly from manufacturer to manufacturer but all have similar capabilities and systems.

At the top of the CDU is the data screen. This is a flat CRT, normally providing up to 14 lines of characters, each line providing space for up to 24 characters. Small sized characters are either default or predicted values. The crew can change these if the data originates from the computer. Large size characters show data entered by the crew. The bottom line of the data screen provides for three activities.

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The left-hand side is a scratch pad that shows data entered by the pilot. The FMS uses the next ten characters to pass messages to the crew, while the last two characters display up or down arrows to show the direction of any necessary scroll (movement) up or down the screen. At the end of each line on the CRT is a line key. When the FMC requires data, a question mark (?) appears at the relevant line. For example, the FMC needs to know the start position of the aeroplane in terms of gate number, so a question mark appears. The pilot can now type the gate number in, using the alpha-numeric keypad. The details typed appear on the scratch pad and, once verified, can be transferred to the correct line by pressing the adjacent line key. If an arrow appears against a line, it normally indicates an optional activity for the flight crew. This could be either functional (e.g. aligning the IRS, deselecting a GNSS satellite) or display (e.g. selecting another page of data). To choose the option, simply press the line key. Function keys are also located below the CRT.

OUTPUT INFORMATION Information derived from the FMS may be linked directly to the AFCS so that the aeroplane may be flown through or by the FMS. Information will normally be presented on the aeroplane’s EFIS system, with a map shown on the nav section showing planned route, active sector, waypoints, etc. Details of attitude, speed, vertical speed, etc., will appear on the PFD as normal. The Instruments section of this manual provides full details of EFIS. Information from the FMS may also be fed to the data transmission system for use in the ADS – B system, as covered in the next chapter.

Chapter 20 Introduction to the Flight Management System (FMS)

Radio Navigation 20-6

Radio Navigation 21-1

INTRODUCTION This chapter looks at trends in the Communication, Navigation, and Surveillance/Air Traffic Management (CNS/ATM, previously referred to as FANS) and provides an overview of each.

COMMUNICATIONS Current activity in Europe, as elsewhere in the world, shows a much greater sensitivity to the economic impact that ATM procedures have on aircraft operations. Much consideration is being given to creating new procedures (or modification of existing procedures) that will lead to more efficient fleet-wide operations. These services span oceanic, enroute, and terminal regimes. Most of the changes are dependent upon effective Data Link facilities rather than increased complexity of the FMS.

AIR TRAFFIC MANAGEMENT AND FANS 1 The integration of future Air Traffic Management ground systems with the Communication-Navigation-Surveillance functions in aircraft avionics will enhance the ability to provide concise scheduling, optimised time control, and well-defined, reduced air traffic separation. Aircraft equipped with ATM-compatible avionics will likely benefit by receiving clearances as filed for the scheduled landing time combined with minimising delays caused by weather and other aircraft. CNS-ATM is currently in the early stages of system definition. The first step in the airborne side of the equation (CNS) is the FANS 1 concept. Aircraft equipped with FANS 1 are already receiving benefits on specific routes. The avionics functions required for FANS 1 are:

Controller/Pilot Data Link Communication (CPDLC, also called TWDL or, offering easier comprehension of what is meant, ATC Comm Data Link)

Required Time of Arrival (RTA) GNSS input for time and position Required Navigation Performance (RNP) Automatic Dependent Surveillance (ADS)

These capabilities result in a fundamental change in airspace management today. The automatic transmission of ground-to-air and air-to-ground clearance messages, flight planning data, along with knowledge of the aircraft's intent, its scheduled arrival time and a negotiated RTA at the metering fix provide the ground ATM systems with an unprecedented amount of detailed information for each aircraft. This creates a better-managed airspace that makes the intervention of the manager an exception rather than the rule. It will not be controlled and will not require the intervention of the air traffic controller on a routine basis.

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Radio Navigation 21-2

Operators can realise the benefits associated with reduced aircraft separation as well as the ability to fly preferred (or direct) routings, provided their aircraft are properly equipped to meet the requisite RNAV level.

CONTROLLER/PILOT DATA LINK COMMUNICATION (CPDLC) The definition and design of Data Link systems for communications between aircraft and Air Traffic Control (ATC) agencies already exists in a very advanced state. To this end, manufacturers have worked extensively with regulatory authorities, airlines, and service providers to develop the Minimum Operational Performance Standards (MOPS) for airborne ATC implementations. Data Link communications systems are being designed to provide more efficient aircraft communications for ATC and Flight lnformation Services (FIS). Although these systems essentially replace normal voice radio communications, a voice radio backup is essential for ATC communications at this time. Flight plan data, including aircraft position and intent (in the form of future waypoints), arrival times, selected procedures, aircraft trajectory, destination airport, and alternates, will be transferred to the ground systems for traffic management. The data sent to the ground ATM system will aid in the process of predictions of where each aircraft will be at a given time. Conflict management becomes simpler for the ground equipment, based on the use of actual flight plan data, compared with making predictions on the ground. The ground system may decide that a re-clearance (e.g. new flight plan) is necessary for one of the aircraft in a predicted conflict situation. Through the utilisation of the RTA function on board the aircraft, a profile negotiation capability is possible based on the available RTA and the current flight plan.

FMS

Air Ops ATM

Voice Comm.

Data Links

The diagram above shows how Data Link messages are exchanged between aircraft and the ground ATM systems. Some operators may elect to use another link to their Airline Operations Centre (AOC), flight operations, or flight planning services. This additional link may be used for monitoring or intervention of flight planning route data, management of alternate airports, and weather data. All links are two-way and require no pilot intervention, except to monitor messages and to confirm and implement flight plan modifications. The monitoring may be accomplished via the MCDU.

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AERONAUTICAL TELECOMMUNICATIONS NETWORK (ATN) The Aeronautical Telecommunications Network (ATN) provides the means for world-wide data communication between ground and airborne host computers within the aeronautical community. It is a data communications network designed to allow interoperability between aircraft, airlines, and air traffic control facilities and authorities. ATN utilises satellite, VHF, Mode-S, and other specific sub-networks to transmit data from one end system to another, linked by a common working protocol. When fully completed, the ATN will allow any ATN host computer to communicate with any other ATN host computer without having a direct physical link between them. International agreements for the ATN are currently being documented in the International Civil Aviation Organisation (ICAO), with regard to Secondary Surveillance Radar improvements, Collision Avoidance Systems Panel, and Standards and Recommended Practices (SARPs). These will establish communications protocols, and will ensure international interoperability services and operational requirements are met. The ATN protocols are designed using existing international standards as a basis. The ATN will pave the way for major improvement in FAA/CAA Air Traffic Management services. The use of the bit-orientated, transparent ATN protocols allows any type of application data to be sent (including messages, graphics, and video). The aeronautical telecommunications industry is currently defining Air Traffic Services (ATS) applications to operate over the ATN. These applications provide a means for ATM facilities to communicate with the avionics and the flight crew on Data Link equipped aircraft.

NAVIGATION EUROCONTROL BRNAV AND PRNAV The Eurocontrol region recognises two forms (or levels) of RNAV namely basic RNAV (BRNAV) and Precision RNAV (PRNAV). BRNAV became mandatory in 1998 and PRNAV should be mandatory by 2005. The original BRNAV requirement of 99.999 percent availability has been removed. The existing VOR route structure and an operating onboard VOR receiver are now expected to provide this availability requirement. The use of RNP 1 is intended to meet PRNAV requirements. REQUIRED NAVIGATION PERFORMANCE (RNP) ICAO created the RNP concept defining a 95 percent confidence area of position. In the RNP concept, the equipment carried no longer defines the ability to fly in a particular airspace but rather the equipment’s ability to meet defined accuracy, integrity, and continuity of service requirements. TERMINAL AREA INITIATIVES For some time there has been a sustained effort to get more benefits from the existing FMS equipment on board EFIS equipped aircraft. This effort has resulted in the definition of FMS procedures for the terminal area airspace (often referred to as slant E procedures). A considerable effort has been made on the use of Baro VNAV to provide additional final approach benefits.

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Actual benefits received will typically be negotiated with the local authorities and may vary depending on the ability to highlight situational awareness, coupled with a flight control system and an auto throttle.

SURVEILLANCE AUTOMATIC DEPENDENT SURVEILLANCE (ADS) Automatic Dependent Surveillance (ADS) allows ground facilities to track aircraft current and predicted status with minimal crew interaction. Crew interaction consists of selecting ON, OFF, or EMERGENCY modes. All other operations are transparent to the crew. The general operation is for the ground application to request data, and the aircraft application to supply the requested data at the required interval. AUTOMATIC DEPENDENT SURVEILLANCE – BROADCAST (ADS-B) Automatic Dependent Surveillance - Broadcast, or ADS-B, is a system that transmits information about an aircraft's state and intent at a predefined interval for use by both ground-based air traffic control and other aircraft. This data is used for situational awareness and conflict resolution. The expectation is for this information to be transmitted using the Mode S transponder Data Link. All the information to be transmitted by ADS-B resides in the FMS function. MODE S DATA LINK This manual has already examined the principle of operation of the aeroplane’s transponder and looked at the introduction of Mode S transponders. Units are now available with a capacity to transfer such data as:

Traffic information service Graphical Weather information Differential GPS uplinks Windshear alerts TCAS traffic resolution

The next development will be to provide the capacity to communicate simultaneously with multiple ground stations while maintaining the capacity to conduct the TCAS function. Development will, no doubt, continue in these important subjects and, as a professional pilot, it will be your duty to remain up-to-date.

Radio Navigation 22-1

Reference: JAR 25 (Advisory Joint Material AMJ 25-11Electronic Display Systems)

GLOSSARY OF TERMS Abbreviation Decode Abbreviation Decode AC ACJ ADF ADI AFCS AFM AIR AMJ ARP AS CDI CRT DOT EADI ED EFIS EHSI EUROCAE

Advisory Circular (Published By The FAA) Advisory Circular Joint Automatic Direction Finder Automatic Direction Indicator Automatic Flight Control System Aeroplane Flight Manual Aerospace Information Report (SAE) Advisory Material Joint Aerospace Recommended Practice (SAE) Aerospace Standard (SAE) Course Deviation Indicator Cathode Ray Tube Department Of Transportation Electronic Attitude Director Indicator EUROCAE Document Electronic Flight Instrument System Electronic Horizontal Situation Indicator The European Organisation For Civil Aviation Equipment

FAA FAR HSI ILS INS JAA JAR JTSO MEL PFD RNAV ROM RTCA RTO SAE STC TSO VOR

Federal Aviation Administration Federal Aviation Regulations Horizontal Situation Indicator Instrument Landing System Inertial Navigation System Joint Aviation Authorities Joint Aviation Requirements Joint Technical Standing Order Minimum Equipment List Primary Flight Display Area Navigation Read Only Memory Radio Technical Commission For Aeronautics Rejected Take-off Society Of Automotive Engineers Supplemental Type Certificate Technical Standing Order VHF Omni-range Station

INTRODUCTION The contents of the reference provide guidance related to pilot displays and specifications for CRTs in the cockpit of public transport aircraft. This digest is intended as a reference document to supplement the FMS and EFIS notes found in the Instruments and General Navigation sections of the notes. This document has relevance to the exams and does provide the source for numerous questions in both examinations. The questions in the exams will refer to JAR 25 and to the Boeing 737-400.

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GENERAL The document covers general information on the following General Certification Considerations:

Display functions • Colour symbology • Coding • Clutter • Dimensions • Attention getting requirements

Display visual characteristics • Failure modes • Instrument display and formatting • Specified integrated display and mode considerations including:

Maps Propulsion parameters Warning and advisory checklist procedures Status displays

Initial electronic displays tended to follow the electromechanical display formats of the older style aircraft. Expect significant improvements as electronic displays evolve. The JAA allows for certification environments that will give flexibility yet still take into account flight safety.

GENERAL CERTIFICATION CONSIDERATIONS DISPLAY FUNCTION CRITICALITY New designs of electronic displays allow designers to integrate systems that are simpler to operate. The automation of navigation, thrust, aeroplane control, and related display systems has accompanied this integration. While the above statement is true regarding normal operations, does it apply during the failure of a system? Certainly, failure state evaluation and determination may become more complex. LOSS OF DISPLAY Criticality of flight and navigation data displayed is evaluated in accordance with JAR 25. Normally, pilot evaluation is used in determining the criticality of electronic displays. During test flying the test pilot will check:

The detectability of failure conditions The required subsequent actions That the actions taken are within a line pilot’s capabilities

Note: For the remainder of this document the word “improbable” means “remote”.

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The following are listed as critical functions, and the loss of information to both pilots must be improbable. Displaying hazardously misleading information must be extremely improbable.

Attitude Airspeed Barometric Altitude

As with the critical functions, loss of information to both pilots of the following essential functions must be improbable:

Vertical Speed Slip/Skid Indications Heading Navigation

The display of erroneous information to both pilots must also be improbable. Rate of turn information is a non-essential function. NAVIGATION INFORMATION Where there is a relationship between navigation information and communicated navigation information, a non-restorable loss must be extremely improbable. For navigation displays, hazardously misleading information on either pilot’s display must be improbable. The term hazardously misleading has to be agreed for certification purposes, and depends on the type of installation and flight phase. Generally, displaying both raw navigation and multi-sensor data ensures that the displays to both pilots are correct. PROPULSION SYSTEM PARAMETER DISPLAYS The failure of a system in one engine must not adversely affect the accuracy of any parameter for the remaining engines. No single fault shall result in the permanent loss of display of more than one propulsion unit.

CREW ALERTING DISPLAY The alerting display should be compatible with the safety objectives associated with the system function for which it provides an alert. FLIGHT CREW PROCEDURES The display of hazardously misleading flight crew procedures must be improbable. INFORMATION DISPLAY The Basic T is generally retained in the glass cockpit.

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INFORMATION DISPLAY COLOURS Display features should be colour coded as follows:

Display Colour Warnings Flight Envelope and System Limits Cautions, Abnormal Sources Earth Engaged Modes Sky ILS Deviation Bar Flight Director Bar

Red Red Amber/Yellow Tan/Brown Green Cyan/Blue Magenta Magenta/Green

Specified display features should be allocated colours from one of the following colour sets:

Colour Set 1 Colour Set 2 Fixed Reference Symbols Current Data, Values Armed Modes Selected Data, Values Selected Heading Active Route/Flight Plan

White White White Green Magenta** Magenta

Yellow* Green Cyan Cyan Cyan White

* The extensive use of the colour yellow for other than caution/abnormal

information is discouraged. ** In colour set 1, the intention is for magenta to be associated with those analogue

parameters that constitute fly to or keep centred type information.

Precipitation and turbulence areas should be coded as follows:

Precipitation Colour 0 – 1 mm/hr 1 – 4 mm/hr 4 – 12 mm/hr 12 – 50 mm/hr Above 50 mm/hr Turbulence

Black Green Amber/Yellow Red Magenta White or Magenta

Radio Navigation 23-1

INTRODUCTION The EFIS provides displays for most of the aircraft navigation systems. The system provides:

Colour displays of pitch and roll Navigational maps Weather Radio altitude and decision height Autopilot ADF/VOR bearings ILS data Stall warning information

SYSTEM ARCHITECTURE The system comprises the following components (See Diagram 1 — EFIS System Architecture):

Electronic Horizontal Situation Indicators (EHSI) — located directly in front of the captain and first officer

Electronic Attitude Director Indicators (EADI) — located directly in front of the captain and first officer

EFIS Symbol Generators (SG) EFIS Control Panels EFI Transfer Switch

Both the captain and the first officer have EFIS display units. Left and right SGs provide video signals to drive the respective display units. An EFI transfer switch determines whether:

The left and right SGs drive the captain’s and first officer’s EADIs and EHSIs respectively

One SG drives all four displays

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EFIS SYMBOL GENERATOR Two symbol generators receive inputs from various aircraft systems. The SGs respond to these inputs and then generate the proper visual displays for the respective EADI and EHSI. The EFIS control panel provides the system control.

Diagram 1 – EFIS System Architecture

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Radio Navigation 23-3

Navigation Systems Inputs Symbol Generator 1 Symbol Generator 2 VHF/NAV DME Flight Management Computer Air Data Computer Auto Throttle Inertial Reference System Digital Flight Control System Stall Warning Computer Automatic Direction Finder Weather Radar Radio Altimeter Ground Proximity Warning System

VOR 1 and 2 DME 1 and 2 LOC 1 and 2 ADF 1 and 2 SWC 1 ADC 1 LRRA 1 G/S 1 and 2 FCC A and B IRS L and R MCP A/T

VOR 1 and 2 DME 1 and 2 LOC 1 and 2 ADF 1 and 2 SWC 2 ADC 2 LRRA 2 G/S 1 and 2 FCC A and B IRS L and R MCP A/T

EFIS CONTROL PANEL The EFIS control panel controls:

Display modes Ranges on the EADI and EHSI Selection of Decision Height Weather Radar on/off control

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Diagram 2 – EFIS Control Panel EADI CONTROLS The left-hand side of the panel, shown in Diagram 2, controls the EADI.

BRT: Controls the brightness of the EADI display. DH REF: The LCD displays the selected decision height (DH). The DH also appears on

the EADI in the bottom right corner.

Underneath the DH REF display is the Decision Height Set Knob. This control has a range of -20 to +999 ft. The decision height defaults to 200 ft when power is applied. Turning the knob changes the DH.

RST: This manually resets the DH alert on the EADI. The radio altimeter display changes from yellow to white.

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EHSI CONTROLS As shown in Diagram 2, the EHSI controls are to the right of the EFIS control panel.

RANGE — This selects the range for the navigation (MAP, CTR MAP, and PLAN) and weather data display on the EHSI, the Flight Management Computer and Weather Radar. Mode Select Switch — This selects the mode of data to be displayed on the EHSI. BRT — Two concentric knobs consisting of the outer and inner controls: The Outer Control adjusts the brightness of the HSI display. The Inner Control adjusts the brightness of the weather radar display. WXR — This is the weather radar ON/OFF switch. When the switch is in the on position, weather radar information displays on the associated EHSI in the MAP, CTR MAP, and EXP VOR/ILS, but not in FULL NAV, FULL VOR/ILS, or PLAN modes. Map Mode Display Selector Switches — In the MAP, CTR MAP, or PLAN modes these switches activate the display of the symbols listed below. Any or all of the switches can be activated at the same time. When switched on, the switch illuminates (white). VOR/ADF — This displays VOR/ADF bearing data in the MAP and CTR MAP modes. When activated, this switch suppresses the MAP mode displayed ADF Bearing Pointer. NAV AID — Navigation Aid data is displayed for VOR, VORTAC, etc. The FMC database provides only the high altitude navigation aids when the 80 nm, 160 nm, or 320 nm range scales are selected. All navigation aids display when using any of the other range scales. ARPT — This displays all airports stored in the FMC database that are within the viewable map area of the EHSI. RTE DATA — This displays altitude constraints and the ETA for each active route waypoint.

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ELECTRONIC ATTITUDE DIRECTION INDICATOR The EADI has one basic display mode, which shows:

Aeroplane attitude Flight Director commands Various types of airspeed ILS Radio Altimeter

Across the top of the EADI, autothrottle and autopilot annunciations are provided when the autopilot is either armed or engaged. An inclinometer (slip indicator) at the bottom of the EADI provides turn and bank information.

20

20

10

10

10

10

1243

160

140

GS 250.765

V1128

THR HLD VNAV PTH HDG SEL FD

ALT

DH2001750

PITCH ROLL

AutothrottleModes

PitchIndication

PitchModes

RollModes

AutopilotModes

Roll Indication

Speed Tape

AttitudeComparison

Alert Localizer DeviationScale Inclinometer

RadioAltitude

FilledFlightDirectorCommand

AeroplaneSymbol

GlideslopeDeviationScale andPointer

H-Alert

DecisionHeight

Diagram 3 – Typical EADI

EADI GENERAL The EADI presents conventional EADI displays for:

Attitude • Pitch • Roll

Flight Director Commands Localiser and Glideslope deviation

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In addition, the EADI displays information relating to:

Autoflight systems mode annunciations Aeroplane speed (VMO/MMO) Minimum speeds CAS Pitch Limit Mach Number Groundspeed Decision Height Radio Altitude

ATTITUDE DISPLAY Attitude data is provided by the IRSs. The captain’s EADI uses the left IRS and the first officer’s EADI uses the right IRS. The IRSs pitch and roll attitude information is valid through 360° of rotation in each axis. MODE ANNUNCIATIONS Mode annunciations for the A/T and the AFDS appear at the top of the EADI displays. FLIGHT DIRECTOR (F/D) COMMANDS FD guidance commands from the selected FCC are displayed via split-axis flight director command bars. The pitch and roll commands appear independently. GLIDESLOPE (G/S) AND LOCALISER (LOC) DEVIATION DISPLAYS Glideslope and localiser deviation scales appear when a localiser frequency is tuned on the associated VHF NAV receiver. A valid signal is required before the deviation pointer is displayed. The normal localiser deviation scale is 1° per dot. When the course deviation is approximately 5/8 degree deviation (5/8 dot), and VOR/LOC is engaged, the scale automatically expands to indicate ½ degree deviation per dot. The scale remains expanded until:

After landing rollout Go-around with a radio altitude greater than 200 ft

On a backcourse approach, the symbol generator reverses the polarity of the localiser deviation pointer on the EADI. The reversal occurs when the aeroplane track differs from the selected MCP course by more than 90°. When the frontcourse is set in the MCP display, the EADI and EHSI course deviation display will agree on both a frontcourse and a backcourse approach. Additionally, the glideslope scale does not display for a backcourse approach.

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ILS DEVIATION WARNING ILS deviation monitoring alerts the flight crew of excessive LOC or G/S deviations. This alerting function is operative during single or dual A/P channel ILS approach. The alerting system is armed when the aeroplane descends below 1500 ft radio altitude (RA) with the LOC or G/S captured. If the captain’s or first officer’s LOC deviation exceeds ½ dot expanded scale or ¼ dot standard scale the respective LOC scale changes colour from white to yellow and the miniature runway stem flashes. If the captain’s or first officer’s G/S deviation exceeds 1 dot deviation, the respective G/S scale changes colour from white to yellow and the G/S pointer flashes. G/S deviation alerting does not initiate below 100 ft RA, but continues below this altitude if the alert was triggered prior to descent below 100 ft RA. Each pilot’s alerting system self-tests upon becoming armed at 1500 ft RA. This self-test generates a 2 second LOC and G/S deviation alerting display on each EADI. RISING RUNWAY SYMBOL The Rising Runway Symbol is an integral part of the LOC deviation display, and is positioned at the top of the LOC Deviation Pointer. The Rising Runway Symbol displays in addition to the RA display, giving an additional cue to the flight crew of the aircraft’s close proximity to the ground as the aeroplane descends below 200 ft RA. Full scale, vertical movement of the Rising Runway represents the last 200 ft of the radio altitude. Zero feet RA is indicated as the top of the Runway Symbol rises to the base of the aeroplane symbol. The requirements for display of the Rising Runway Symbol are as follows:

Valid ILS/LOC frequency selected Valid RA data RA less than 2500 ft

If any of the above conditions are not met, the Runway Symbol does not display. ATTITUDE COMPARATOR A yellow PITCH or ROLL alerting annunciation is displayed on both EADIs if either symbol generator detects a difference of more than 3° between the captain’s or first officer’s attitude displays. A short time delay is incorporated to minimise nuisance annunciations. DIGITAL RADIO ALTITUDE AND DECISION HEIGHT When RA is less than 2500 ft, a digital display of radio altitude shows in the lower right hand corner of the EADI. At all other times the digital RA display is blank. When a positive decision height has been selected on the respective EFIS Control Panel, the letters DH and the decision height are displayed just above the digital RA display of the associated EADI. When the aeroplane is below 1000 ft agl, an RA Dial is added to the radio altitude display and a magenta pointer located on the radio altitude dial replaces the digital DH display. When descending through the selected DH, a DH alert occurs. The RA dial, digital display, and the DH pointer change colour to yellow, flash momentarily, then remain steady yellow as the aeroplane continues to descend.

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The DH alert resets if any one of the following occurs:

The DH reset switch on the EFIS control panel is pressed The RA increases to DH + 75 ft The radio altitude is equal to zero feet (touchdown)

Following an electrical power interruption, the DH value defaults to 200 ft. MACH DISPLAY The current Mach number from the respective Air Data Computer (ADC) displays if the following are satisfied:

Accelerating Mach number is ƒ 0.40M Decelerating Mach number previously above 0.4M and is still > 0.38M

GROUNDSPEED DISPLAY There is a digital presentation of the current groundspeed. The groundspeed data comes from the FMC or IRS with the FMC being the primary source. The numeric range is from 0 to 999 kt. PITCH LIMIT SYMBOL The position of the Pitch Limit Symbol is a function of the stall warning computer. The Pitch Limit Symbol appears when the flaps are extended in any position. During take-off, the Pitch Limit Symbol is fixed at 15° pitch attitude until the stall warning computer commands a value greater than 15° (at approximately 100 kt). Above this speed, the position of the Pitch Limit Symbol is a function of the various inputs to the stall warning computer and is limited to a maximum of 30° of pitch. In general, the Pitch Limit Symbol is programmed so that stick shaker activation coincides with a pitch attitude equal to the Pitch Limit Symbol indication. In a rapid pull up, the pitch attitude may exceed the Pitch Limit Symbol indication for a brief period without initiating the stick shaker warning. With a lightweight aeroplane, the low speed limit logic of the stall warning computer may activate the stick shaker even with the Pitch Limit Symbol positioned slightly above the aeroplane symbol. SPEED TAPE SCALE The speed tape scale displays a range of approximately 84 kt. Numbers are placed on the tape at 20 kt intervals from 40 kt to 420 kt. The speed tape scrolls up and down and the digital readout indicates current airspeed. DIGITAL AIRSPEED READOUT A digital readout of the current calibrated airspeed appears within the fixed airspeed reference pointer. The units digit rolls continuously based on the current fractional unit value of the calibrated airspeed to emulate the rolling digit readout of a conventional electrical/mechanical airspeed indicator.

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AIRSPEED TREND ARROW The Airspeed Trend Arrow is a green arrow of variable length that points to the predicted airspeed the aeroplane will achieve within the next 10 seconds, based on the present airspeed and rate of acceleration. The Airspeed Trend Arrow does not display until its magnitude is greater than 4 kt, and it disappears when its magnitude drops below 3 kt.

COMMAND SPEED Command speed displays as a magenta, double-line cursor located on the speed tape scale if the command speed is within the currently displayed speed tape range. The display shows the numerical equivalent, above or below the speed tape scale, if the command speed is equivalent to the selected speed on the MCP or the FMC command speed, whichever is applicable.

MAX OPERATING SPEED (VMO/MMO OR GEAR/FLAP PLACARDS) A red and black barber pole represents the max operating speed. The position of the maximum operating speed symbol is a function of data supplied to the SG from the stall warning computer. The maximum operating speed is the lower of the:

Gear extended placard speed Flaps extended placard speed VMO/MMO

HIGH-SPEED BUFFET MARGIN The bottom of a hollow yellow bar that extends from the bottom of the VMO/MMO symbol at high altitude represents the high-speed buffet margin. As the aeroplane climbs to altitudes above 25 000 ft, the yellow bar begins to extend to give an indication of the speed that would provide a 0.3G to high-speed buffet margin. At lower altitudes, the VMO/MMO speed is more limiting and the high-speed buffet limit symbol is no longer visible. Since the stall warning computer uses FMC gross weight to calculate the high-speed buffet margin speed, this display is not available if the FMC is unable to compute gross weight.

NEXT FLAP PLACARD SPEED The same symbol is used to represent this speed as is used to represent the high-speed buffet margin. If the aeroplane is in the air and flaps are lowered, the hollow yellow bar extends from the high-speed end of the speed tape. The end of the hollow yellow bar represents the placard speed for the next normal flap position. Next flap placard speeds appear only for those flap positions normally used during an approach and landing. The next flap placard symbol appears blank when current flap position equals the selected landing flap configuration on the FMC/CDU APPROACH REF page or when the flaps are in the process of retracting.

FLAPS UP MANOEUVRING SPEED A small, green circle on the speed tape indicates the flaps up manoeuvring speed. This speed is an output of the stall warning computer and is based on the actual gross weight as computed by the FMC. It represents the best airspeed (climb or driftdown) for an aeroplane in the clean configuration. This function is not enabled until the flaps are up.

V1 (DECISION SPEED) Decision speed is depicted by a green -1 located opposite the V1 speed on the speed tape if the V1 speed is within the displayed range. If the selected V1 speed is not within the displayed range, a green V1 with the numeric value of the V1 speed appears at the high-speed end of the speed tape.

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Radio Navigation 23-11

Before the V1 speed displays on the speed tape, the pilot must first enter the correct speed in the scratch pad on the FMC/CDU TAKE-OFF page, and then line-select this speed to the V1 prompt line. VR (ROTATION SPEED) VR speed is depicted by a green -R located opposite the rotation speed if the rotation speed is within the displayed range. The symbol is blanked if the rotation speed is not within the displayed range. For VR to display on the speed tape, the pilot must first enter the correct speed in the scratch pad on the FMC/CDU TAKE-OFF page and then line-select this speed to the VR prompt line. VREF (REFERENCE SPEED) The -R symbol represents the VREF speed. The FMC/CDU APPROACH REF page displays VREF speed based on the current gross weight for three landing flap settings. The flight crew may select the FMC computed speed or manually enter another value into the field corresponding to the desired landing flap configuration. This speed then transmits via the FMC, causing the SG to display the -R symbol opposite that speed on the speed tape. The FMC updates the computed VREF speeds as fuel burns based on fuel totaliser inputs. A VREF value does not update once it has been selected for transmission to the speed tape. If the flight crew manually inserts a gross weight on the APPROACH REF page, the FMC computed VREF speeds will be based solely on the manually entered gross weight as long as the APPROACH REF page remains in view. A manually entered gross weight is not updated as fuel burns off. MINIMUM FLAP RETRACTION SPEED A green -F on the right side of the speed tape indicates minimum flap retraction speed. The stall warning computer computes this speed. It represents the speed that will provide the minimum manoeuvre speed (depicted by the end of the low speed yellow bar) for the next normal flap position (flap positions 5, 1, or UP only). The display will respond to the effects of extending the flight spoilers. MINIMUM MANOEUVRING SPEED The end of the low-speed hollow yellow bar represents the minimum manoeuvring speed. If the aeroplane is at low altitude and flies at this speed, it provides a 0.3G manoeuvre margin to stick shaker. This allows for a 40° bank turn while manoeuvring in level flight. If the aeroplane is at high altitude and flies at the minimum manoeuvring speed, it provides a 0.3G manoeuvre margin to low-speed buffet as opposed to a 0.3G manoeuvre margin to stick shaker margin. Since the stall warning computer uses the FMC gross weight to calculate the minimum manoeuvre speed at high altitudes, this symbol does not display at high altitude if the FMC gross weight is not available. The display reflects the effect of extending the flight spoilers. The hollow yellow bar is inhibited from take-off roll through the first flap retraction. Once the flaps are up, the display shows for the remainder of the flight, including subsequent flap extensions.

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STICK SHAKER SPEED The end of the low-speed, red and black striped barber pole represents the stick shaker speed. This speed represents the airspeed at which the angle of airflow vanes activates the stick shaker warning. The source of the stick shaker airspeed is the stall warning computer. The display reflects the effect of extending the flight spoilers. EADI SYMBOLS

Symbol Name Description

Aeroplane The EFIS SG provides a white

aeroplane attitude symbol

< Bank Indicator and Scale White

Sky/Ground/Horizon Line The sky is cyan (light blue) and the ground is yellow. The IRS data control the sky/ground movement and horizon line (white).

Pitch Scale A white scale (±90°) controlled by IRS data. 0° indicates the horizon line.

Flight Director Command A magenta symbol produced

by FCC data. Displays when the respective Flight Director (FD) switch is on and valid command steering is available, or during automatic operation of the FD. Blanks off when the FD switch is off or when command steering becomes invalid.

Localiser Pointer and Scale Expanded Localiser Scale and Pointer

A magenta pointer with a white scale and index that indicates the localiser position. The scale indicates the deviation. When LOC is engaged and the deviation is slightly more than ½ dot the scale expands. The pointer blanks when the ILS localiser signal is too weak to be usable.

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Radio Navigation 23-13

Symbol Name Description

Glideslope Scale and Pointer

A magenta pointer with a white scale and index that indicates the glideslope position and the scale deviation. The pointer does not display when the glideslope signal is unusable or when the track and the front course on the Main Control Panel (MCP) differ by more than 90° (Back Course).

ALT Height Alert A white display when Radio Altitude (RA) is between 500 and 1000 ft. Reset by the DH RST on the EFIS CP, or when RA is greater than the height alert value computed by the EFIS SG

DH 200 1750

Decision Height and Radio Altitude

The decision height displays in green. The DH is the one selected on the EFIS CP when the RA is above 1000 ft agl. Appears blank when the DH is negative Radio Altitude displays in white below 2500 ft agl. The display is blank above 2500 ft agl. The symbol colour changes to yellow when below the selected DH on descent. The symbol colour changes to white when passing DH +75 ft during a go-around, after touchdown, or after pressing the RST switch on the EFIS CP.

GS 250

Groundspeed The FMC/IRS values are displayed in knots and coloured white

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Radio Navigation 23-14

Symbol Name Description .765 Current Mach Number Displays when the Mach

increases above 0.4M. The Display is blank when the Mach Number decreases below 0.38M.

Pitch Limit Symbol A yellow symbol that indicates

the pitch attitude that activates the stick shaker.

Rising Runway A green symbol shaped like a runway at the bottom of the screen that displays when the localiser pointer is in view and the radio altitude is valid. The symbol rises toward the aeroplane symbol when radio altitude is below 200 ft agl.

RADIO ALTITUDE DIAL

Diagram 4 – Radio Altitude

The digital display of Radio Altitude (white) is replaced with the dial when the aircraft is at or below 1000 ft agl. A DH pointer (magenta) replaces the digital DH display.

At or below 1000 ft agl the circumference of the dial increases or decreases dependent on whether the aircraft is climbing or descending.

The display changes colour to yellow and flashes momentarily when the aircraft descends below DH.

The DH Alert is reset automatically if the aircraft climbs 75 ft or more above the selected DH or lands.

Pressing the RST switch on the EFIS Control Panel manually resets the DH Alert.

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Radio Navigation 23-15

SPEED TAPES

160

140

100

80

412

V1128

3

R

1 — V1 (decision speed) - Green

2 — FMC/MCP Command Speed - Magenta

3 — VR (rotation speed) - Green

4 — V1 (decision speed) - Green

5 — Speed Tape Scale - White

1. V1 Decision Speed

Displayed in green Displayed after manual entry on the FMC/CDU TAKEOFF REF page V1 is only displayed in this location during the initial take-off roll when the

speed is beyond the displayed range 2. FMC/MCP Command Speed

Displayed in magenta

3. VR Rotation Speed

Displayed in green Displayed after manual entry on the FMC/CDU TAKEOFF REF page

4. V1 Decision Speed

Displayed in green Replaces the digital display in the top right corner of the speed tape when V1

is within the displayed range 5. Speed Tape Scale

Displayed in white Scrolls up or down in response to the ADC calibrated airspeed Range 45 – 420 kt

5 – Speed Tape Scale - White

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Radio Navigation 23-16

160

140

180

315

2

F

6 — FMC/MCP Command Speed - Magenta

7 — Minimum Flap Retraction Speed - Green

8 — Minimum Manoeuvre Speed - Yellow

9 — Stick Shaker Speed - Red and Black

250250

120

6. FMC/MCP Command Speed

Displays in magenta Displays in this position when the FMC/MCP Command Speed is above the

displayed range 7. Minimum Flap Retraction Speed

Displays in green Displays on the speed tape during take-off or go-around

8. Minimum Manoeuvre Speed

Displays in yellow The top of the yellow bar indicates the minimum manoeuvre speed The display is inhibited from the take-off roll until first flap retraction

9. Stick Shaker Speed

Displays in red and black The top of the barber pole indicates the speed at which the stick shaker

activates

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Radio Navigation 23-17

180

160

200

318

2

10 — Flaps up Manoeuvering Speed - Green

11 — Rolling Digits Display - White

12 — Airspeed Trend Arrow - Green

13 — FMC/MCP Command Speed - Magenta134134140

220

10. Flaps up Manoeuvring Speed

Displayed in green Shown when the flaps are up

11. Rolling Digits Display

Displayed in white Indicates the current airspeed The position is fixed relative to the ADI position

12. Airspeed Trend Arrow

The tip of the arrow depicts the predicted airspeed in the next 10 seconds The prediction is based upon present airspeed and acceleration

13. FMC/MCP Command Speed

Displayed when the FMC/MCP Command speed is below the displayed range

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Radio Navigation 23-18

320

300

340

331

2

14 — Max Operating Speed - Red and Black

15 — High Speed Buffet Limit - Yellow

280

14. Max Operating Speed

Displayed in red and black Indicates VMO/MMO

15. High-Speed Buffet Limit

Displayed in yellow The bottom of the yellow bar indicates the speed that provides a 0.3G

manoeuvre margin to high-speed buffet at high altitudes

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Radio Navigation 23-19

160

140

180

315

2

R

16 — Placard Speed - Red and Black

17 — Next Flap Position Placard Speed - Yellow

18 — VREF Speed - Green

120

16. Placard Speed

Displayed in red and black Indicates gear extended placard speed Flap extended placard speed for the selected flap position

17. Next Flap Position Placard Speed

Displayed in yellow The bottom of the yellow bar indicates the flap extended placard speed for

the next normal flap position Displayed during flap extension

18. VREF Speed

Displayed in green Indicates the VREF speed for the landing flap configuration as selected on the

FMC/CDU APPROACH REF page

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Radio Navigation 23-20

EFIS – EADI FAULT DISPLAYS OPERATION If the specific input data to a symbol generator is identified as invalid data, the associated data or parameter value blanks. In some cases yellow fault flags are displayed. The location, orientation, and letter characters associated with each of these flags are shown below. The windshear warning annunciation is displayed in red.

Diagram 5 – EADI Fault Displays

EADI FAILURE FLAGS AND ANNUNCIATIONS 1. Selected Speed Annunciation: The command speed and displays are inoperative 2. V1 Inoperative Annunciation: V1 display is inoperative 3. Speed Flag: The speed tape is inoperative 4. Speed Limit Annunciation: The displays associated with the stick shaker and

maximum operating speeds have failed 5. Mach Flag: The Mach number display has failed 6. Pitch Comparator Annunciation: The captain’s and first officer’s pitch angle displays

differ by more than 3° 7. Attitude Comparator Function Flag: The comparator function has failed 8. Localiser Flag: The localiser deviation display on the EADI has

failed 9. Windshear Warning Annunciation: The ground proximity computer has detected a

windshear condition

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Radio Navigation 23-21

10. Roll Comparator Annunciation: The captain’s and first officer’s bank angle displays differ by more than 3°

11. Radio Altitude Flag: The radio altitude display has failed 12. Decision Height Flag: The selected decision height display has failed 13. Symbol Generator Fail Annunciation: The selected symbol generator has failed 14. Attitude Flag: The attitude display has failed 15. Flight Director Flag: The flight director has failed EFIS TYPICAL EHSI CENTRE MAP, MAP, AND PLAN DISPLAYS The EHSI can display selected FMC Data in three different selectable formats:

CTR Map Map Plan

The format displayed depends upon the mode selected on the EFIS Control Panel (Diagram 6).

HSI

BRT

VOR/ILS

VOR/ILS

NAV

NAV

EXP

FULL

PLAN

CTRMAP

MAP

Diagram 6 – EHSI Mode Selector GENERAL Each EHSI presents an electronically generated colour display of conventional HSI navigation data:

VOR/ILS Modes NAV Modes

Each EHSI is also capable of displaying the aeroplane’s flight progress on a plan view map:

Map Mode CTR Map Mode

Or the aeroplane’s flight plan on a plan view map orientated to True North:

Plan Mode Excluding operation in the FULL NAV, FULL VOR/ILS and PLAN Modes, each EHSI also serves as a weather radar display when the WXR Switch on the respective EFIS CP is on.

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Radio Navigation 23-22

During normal operation, each EHSI receives information from its own symbol generator. Each symbol generator receives data from a variety of aircraft systems to support the EHSI displays. EHSI DISPLAY ORIENTATION The various displays on the EHSI are orientated to aeroplane heading (heading up). With heading up orientation, all displayed data references the aircraft heading as shown at the 12 o’clock position on the compass rose. During normal operation, heading reference data is supplied to each EHSI from the respective IRS. The FMC supplies aeroplane track data. If the FMC track data should become unreliable, the respective IRS automatically supplies track data. PLAN MODE The PLAN mode is a map display which may be used to view an FMC flight plan route, either in total for a short route, or waypoint by waypoint for a longer route. Its primary use is to set up the flight plan conditions before flight. The upper part of the display describes the dynamic conditions of the aeroplane:

Track Selected and actual heading Distance ETA to the next waypoint

The lower part of the display is background data displaying the flight plan (Diagram 7).

Diagram 7 – PLAN Mode

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Radio Navigation 23-23

FEATURES OF PLAN MODE

PLAN is selected on the EFIS Mode Selector Switch. A static map is displayed, oriented to true north with only 70° of the compass rose

showing. The top of the EHSI is the same in MAP Mode. The pilot can review the planned route by using the FMC/CDU LEGS page CENTER

STEP line select key. Weather radar data is inhibited.

MAP AND CTR MAP MODES These modes display the aeroplane’s position with respect to the flight plan. The entire display is dynamic, rotating as the aircraft moves. A triangle in the centre of the display represents the aircraft. Waypoint and NAVAID symbols remain upright. Symbols which are rotated to maintain a proper orientation are:

ARPT (Airport) Holding pattern Procedural turn symbols

The displays are used to monitor the aeroplane’s position along the selected flight path.

Diagram 8 – Map Mode

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Radio Navigation 23-24

FEATURES OF MAP MODE

MAP is selected on the EFIS Mode Selector Switch The MAP mode display shows 70° of the compass rose

The aeroplane appears as a fixed symbol (⊇) at the bottom of the display superimposed on a moving map display

The basic map background includes • Origin/destination airports • Flight plan route • Display of navaids in use

Optional background data is selected by using the Map Mode Display Selectors on the EFIS Control Panel. This data includes: • Off-route navigation aids • Off-route airports • Off-route named waypoints • Tuned VOR/ADF radials • Flight plan route waypoints • ETAs • Altitude constraints

Weather radar returns are displayed when the WXR switch is ON

Diagram 9 – Centre Map Mode

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Radio Navigation 23-25

FEATURES OF CENTRE MAP MODE

CTR MAP is selected on the EFIS Mode Selector Switch The CENTRE MAP Mode includes a 360° compass rose Displays the same data and symbols as the MAP mode The aeroplane symbol displays in the centre of the display so that MAP information

appears behind the aircraft NAV MODE DISPLAYS Selected FMC data can be shown by using the NAV Modes display. The display is referenced to track and shows the aircraft position relative to:

The next waypoint The vertical and horizontal flight path The NAV modes can have 70° or 360° compass displays

Diagram 10 - Expanded Navigation Mode

FEATURES OF EXPANDED NAVIGATION MODE

EXP NAV is selected on the EFIS Control Panel Selector Switch The display shows lateral and vertical navigation guidance information similar to a

conventional HSI The FMC is the source of the navigation data Weather radar data is displayed when the WXR switch is on

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Radio Navigation 23-26

Diagram 11 – Full Navigation Mode

FEATURES OF FULL NAVIGATION MODE

FULL NAV is selected on the EFIS Control Panel Selector Switch Displays the same as EXP NAV except: • Weather radar displays are not available • The full compass rose is shown instead of the expanded compass rose • Alternate symbols are used for the aeroplane symbol and course pointers

VOR AND ILS DISPLAYS The VOR and ILS modes can be used with manually selected stations. The VOR mode is used enroute with VOR and DME station inputs. ILS is the landing mode, and uses ILS and DME station inputs. Appropriate deviations are displayed in both modes. The displayed heading is magnetic below 73° north and 60° south latitude. At higher latitudes, the heading automatically references to true north. The difference between the heading and track line indicate drift angle. For the VOR and ILS systems, the EHSI has two different types of displays which are selectable on the EFIS Control Panel. The FULL VOR/ILS displays include a 360° compass rose with the aeroplane symbol in the center, and so are unable to display weather radar data. The EXP VOR/ILS displays include only a 70° compass arc with the aeroplane symbol at the bottom center. This display makes it easier to read the aeroplane’s heading and track values. Additionally, these expanded displays can show the weather radar data. Whether the display presents VOR or ILS data depends upon the VOR or ILS frequency selection on the VHF NAV Control Panel.

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Radio Navigation 23-27

Except for the FULL and EXP display differences described above, the remainder of the navigational data shown is the same on both types of displays. A detailed description of all displayed symbols, parameters, and annunciations appears later in this chapter. EXPANDED VOR MODE

DD Diagram 12 – Expanded VOR Mode

VOR/ILS is selected on the EFIS Control Panel Selector Switch With a VOR frequency selected, VOR navigation data is displayed The navigation information is oriented to the aeroplane heading The source of the navigation data is displayed as VOR 1 or VOR 2 in the lower left

corner of the EHSI The TO/FROM annunciation and the navigation source frequency appear in the lower

right corner of the EHSI Weather radar return data and range arcs are displayed when the WXR switch is on

Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

Radio Navigation 23-28

FULL ROSE VOR MODE

Diagram 13 – Full Rose VOR Mode

FULL VOR/ILS is selected on the EFIS Control Panel Selector Switch The information displayed is the same as the expanded VOR mode with the following

exceptions Weather radar displays are not available A full compass rose shows instead of the expanded compass rose A drift angle pointer replaces the track line The TO/FROM pointer shows in addition to the TO/FROM annunciation Alternate symbols are used for aeroplane symbol and course pointer

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Radio Navigation 23-29

EXPANDED ILS MODE

Diagram 14 – Expanded ILS Mode

VOR/ILS is selected on the EFIS Control Panel Selector Switch With an ILS LOC frequency selected, ILS navigation data is displayed with the

aircraft heading at the top. The source of navigation data (ILS 1/ILS 2) is shown in the lower left corner of the

EHSI The frequency of the navigation source is shown in the lower right of the screen Weather radar return data and range arcs are displayed when the WXR switch is on

Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

Radio Navigation 23-30

FULL ROSE ILS MODE

Diagram 15 – Full Rose ILS Mode

FULL VOR/ILS is selected on the EFIS Control Panel Selector Switch The information displayed is the same as the expanded mode with the following

exceptions • Weather radar displays are not available • A full compass rose is shown instead of the expanded compass rose • A drift angle pointer replaces the track line • Alternate symbols are used for aeroplane symbol and course pointer

EHSI SYMBOLOGY Each EHSI may display the following symbols depending on the EFIS Control Panel selection. The colours used are as follows:

Green: Active or selected mode and/or dynamic conditions White: Present status situation and scales Magenta: Command information, pointers, symbols, fly-to conditions, and weather

radar turbulence Cyan: Non-active and background information Red: Warning Yellow: Cautionary information, faults, and flags Black: Blank areas and off conditions

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Radio Navigation 23-31

Data Name Colour

Applicable Modes

Remarks Symbol Data Source

Aeroplane Symbol White

FULL VOR/ILS FULL NAV

Aeroplane position is indicated by the centre of the symbol which is the centre of rotation and translation for all the background and dynamic symbols. Source: EFIS SG

Full Compass Rose Display Colour: White (Low intensity display)

FULL VOR/ILS FULL NAV

Displays 360° of IRS compass data. Source: IRS

Full Compass Rose Display Colour: White (Low intensity display)

CTR MAP Displays 360° of IRS compass data. Source: IRS

Expanded Compass Rose Colour: White

EXP VOR/ILS MAP EXP NAV

Heading is from IRS 360° is available only 70° is shown

Aeroplane Symbol Colour: White

EXP VOR/ILS MAP EXP NAV CTR MAP

The apex of the white triangle indicates aeroplane position. The apex of the aeroplane is the centre of rotation and translation for all the background and dynamic symbols.

Heading Annunciator Colour: Green Heading Readout and index Colour: White (Heading index low intensity) M/TRU Annunciator Colour: Green

EXP VOR/ILS EXP NAV MAP CTR MAP PLAN

The number under the low intensity index pointer is a heading. Readout displays actual heading. Compass is referenced to magnetic north between 73°N and 60°S. Above these latitudes the compass is referenced to true north. Source: IRS

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Radio Navigation 23-32

Data Name Colour

Applicable Modes

Remarks Symbol Data Source

Heading Annunciator Colour: Green Heading Readout and index Colour: White (Heading index low intensity) M/TRU Annunciator Colour: Green

FULL VOR/ILS FULL NAV

Indicates number under pointer is a heading. Box displays actual heading. Compass is referenced to magnetic north between 73°N and 60°S. Above these latitudes the compass is referenced to true north. Source: IRS

Magnetic Status Change Colour: Green Box around Green M annunciator

All Modes Box appears for 10 seconds at transition to magnetic reference display. Source: SG

True Enhancement Annunciator Colour: White box around Green TRU annunciator

All Modes Box surrounds TRU when display is referenced to true north unless yellow TRU annunciator (below) is displayed Source: SG

True Advisory Annunciator Colour: Yellow box around TRU annunciator

All Modes Yellow box surrounds TRU (Initially flashes for 10 seconds) when descent rate > 800 fpm for 2000 ft (landing phase) The yellow box remains until ascent rate > 500 fpm for 2000 ft (take-off phase) Then changes to the white enhancement annunciator above Source: SG

Selected Heading Marker and Line Colour: Magenta

All Modes Manually positioned by heading selector on the MCP. No dashed line on full displays Source: FCC Default: MCP

Drift Angle Pointer Colour: White

All Modes Indicates FMC/IRS computed drift angle Source: FMC Default: IRS

Present Track (Straight Trend Line) and Range Scale Colour: White

MAP NAV VOR ILS

Magnetic/true track which will result with present heading and winds. Displayed range is ½ the actual selected range.

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Radio Navigation 23-33

Data Name Colour

Applicable Modes

Remarks Symbol Data Source

CTR MAP Range marks are used in CTR MAP mode Range arcs (not shown) are used in the MAP mode and in the EXP VOR/ILS and EXP NAV modes with WX selected Track defaults to IRS for FMC not valid

Course Select Pointer and Vector Colour: Magenta

VOR Indicates selected VOR course when tuned to VOR source Source: FCC Default: MCP

Runway Heading Pointer Colour: Magenta White

ILS Indicates selected runway heading for front course when tuned to ILS source Source: FCC Default: MCP

Desired Track Pointer and Vector Colour: Magenta

NAV Indicates desired track angle from FMC or ANCDU

ALERT Course Change Annunciation Colour: Yellow

NAV Displayed 10 seconds before reaching waypoint. Removed at reaching waypoint Source: FMC or ANCDU

VOR Bearing Vectors and Identifiers Colour: Green

MAP CTR MAP

Displayed when VOR/ADF selector on EFIS CP is pushed, and associated DME not in agility mode Source: DAA

Course Deviation Scale Colour: Scale – White Bar - Magenta

VOR When VOR frequency tuned, VOR course deviation is displayed. One dot equals 5° deviation Computed in the SG Deviation = VOR Bearing minus selected course

Localiser Deviation Scale Colour: Scale – White Bar – Magenta

ILS When ILS frequency tuned, ILS course deviation is displayed. One dot is approximately 1° deviation Source: DAA

Cross Track Deviation Colour: Scale – White Bar - Magenta

NAV When NAV mode is selected, indicates deviation from desired track. One dot is equal to 2 nm Source: FMC

Glideslope Deviation ILS Displays glideslope deviation in

Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

Radio Navigation 23-34

Data Name Colour

Applicable Modes

Remarks Symbol Data Source

Scale Colour: Scale – White Bar - Magenta

ILS mode. One dot is approximately 0.35°. NCD in backcourse Source: VHF NAV Unit

ADF Bearing Vectors and Identifiers Colour: Green

MAP CTR MAP

Displayed when: VOR/ADF selector on EFIS CP is pushed, or In ADF mode Source: ADF RCVR

Left and Right ADF Pointers Colour: Green

Reciprocal Left and Right ADF Pointers Colour: Green

VOR ILS NAV PLAN

Displayed in ADF mode and if ON switch on ADF CP is on Source: ADF RCVR

DME 13.5 DME Distance Colour: White

VOR ILS

Displays distance to tuned DME station Two resolutions: Resolution 1: Whole nm if distance >100 nm Resolution 2: tenths of a nautical mile if distance < 100 nm Source: DAA

VOR 1 (2) VOR

ILS 1 (2)

Selected Radio Nav Source Colour: Green

ILS

Displays selected Radio Nav mode based on the EFIS CP mode selection or frequency from DAA Radio Nav source is based on source select programme pins on EFIS SG

NAV FMC Selected Colour: Green

NAV Display indicated source of NAV DATA. Source: FMC

110.10 ILS Frequency Display Colour: Green

ILS Displayed when a valid ILS frequency is being received Source: DAA

116.80 or AUTO

VOR Frequency Colour: Green

VOR The VOR frequency is displayed when a valid VOR frequency is manually tuned The word AUTO is displayed when the VOR frequency is automatically tuned by the FMC Source: DAA

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Radio Navigation 23-35

Data Name Colour

Applicable Modes

Remarks Symbol Data Source

TO (FROM) TO/FROM Annunciator Colour: White

VOR Indicates whether the selected course will take the aeroplane TO or FROM the selected VOR station Source: EFIS SG

Wind Direction and Speed Colour: White

MAP CTR MAP NAV VOR ILS

Indicates wind speed in knots Wind direction is with respect to the display reference (magnetic or true north) Displayed when wind speed is ƒ 6 kt Source: FMC Default: IRS

Waypoint and ID Colour: White

MAP CTR MAP PLAN

Identifier listed below and right of the standard waypoint Source: FMC

BUGLE

Active Waypoint Colour: Magenta

NAV Name of active waypoint Source: FMC

Route Colour: see right

MAP CTR MAP PLAN

The active route is displayed with continuous MAGENTA lines between waypoints Inactive routes in CYAN with long dashes between waypoints Changes to the active route are displayed in white dashes between waypoints When the route change is executed on the CDU, the short dashes are replaced with a continuous magenta line Source: FMC

Bearing to Waypoint and Vector Colour: Magenta

NAV Indicates bearing to active waypoint Source: FMC

27.5 NM Distance To Go (DTOGO) Colour: White

MAP CTR MAP PLAN NAV

Distance to an active waypoint: Resolution 1: Whole nm if DTOGO >100 nm Resolution 2: tenths of a nm if DTOGO < 100 nm Source: FMC

0834.4Z ETA Display Colour: White

MAP CTR MAP PLAN NAV

Indicates time of arrival at an active waypoint Source: FMC

FMC/IRU Position Difference Colour: White

MAP CTR MAP NAV

The SG computes the position difference between the FMC and each IRU

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Radio Navigation 23-36

Data Name Colour

Applicable Modes

Remarks Symbol Data Source

If either position difference > 12 nm, the SG displays the magnitude and direction of both position differences The position difference arrow points to the IRU position L or R indicates which IRS present position the displayed position difference corresponds to.

; KTEB Airport and ID Colour: Cyan

MAP CTR MAP PLAN

Non-flight plan airports are displayed when ARPT switch selected Source: FMC

Route Data Colour: same as waypoint symbol

MAP CTR MAP PLAN

ALT and ETA for active waypoints (with ID) displayed when route data switch on EFIS CP is on Source: FMC

Navaids and ID: VOR DME/TACAN VORTAC Colour: Untuned – Cyan Tuned - Green

MAP CTR MAP PLAN

Non-flight plan navaids displayed when NAV AID switch on EFIS CP on. Source: FMC Select course source: FCC or MCP

Tuned Navaid and Selected Course Colour: Green

MAP CTR MAP PLAN

When navaid is manually tuned Selected course and its reciprocal are displayed Source: FMC

Non-Flight Plan Waypoint and ID Colour: White

MAP CTR MAP PLAN

Non-flight plan waypoints displayed when WPT switch on Source: FMC

Airport, Runway and ID Colour: White

MAP CTR MAP PLAN

Selected on FMC CDU Displayed when EHSI range is 80 nm, 160 nm or 320 nm Source: FMC

Runway and ID Colour: White

MAP CTR MAP PLAN

Selected on FMC CDU Displayed when EHSI range is 10 nm, 20 nm, or 40 nm Source: FMC

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Radio Navigation 23-37

Data Name Colour

Applicable Modes

Remarks Symbol Data Source

Holding Pattern Colour: Inactive – Cyan Active – Magenta Modified - White

MAP CTR MAP PLAN

Displayed when a holding pattern is selected as part of the route Source: FMC

North Up Pointer Colour: Green

PLAN Display below track tape is referenced to True North Source: FMC

Vertical Deviation Scale and Pointer Colour: Scale – White Pointer - Magenta

MAP CTR MAP NAV

Displays vertical deviation from vertical profile during VNAV descent mode One dot equals 400 ft deviation For deviation greater than 440 ft pointer is at end of scale and, in addition, a digital readout appears below the scale if aeroplane is above flight path. If aeroplane is below flight path digital readout is above scale Source: FMC or ANCDU

Selected Reference Point (SRP) With ID and Radials Colour: Green

MAP CTR MAP PLAN

Displayed as a selected reference point (fix) via the FMC CDU Can be with any number of special map symbols (e.g. VOR, VORTAC, Airport, etc.). Source: FMC

Selected Reference Point (SRP) With ID and Distance Circle Circle: Green

MAP CTR MAP PLAN

Circle representing selected distance displayed around SRP Selected distance indicated below circle Source: FMC

Range to Altitude Arc Colour: Green

MAP CTR MAP

Curved arc represents the point where MCP selected altitude will be reached if current vertical and lateral flight path angles are maintained Source: FMC

; T/D ; S/C ; T/C ; E/D

Altitude Profile Points Colour: Green

MAP CTR MAP PLAN

Calculated by FMC T/D – Top of Descent S/C – Step Climb T/C – Top of Climb E/D – End of Descent Source : FMC

Curved Trend Vector Colour: White

MAP CTR MAP

Segmented curve predicts the directional trend It is calculated by the SG

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Radio Navigation 23-38

Data Name Colour

Applicable Modes

Remarks Symbol Data Source

Based on present position, groundspeed and cross track acceleration It shows the predicted position at the end of 30, 60, and 90 seconds The number of segments represented: Range > 20 nm - 3 segments Range 20 nm – 2 segments Range 10 nm – 1 segment

Weather Radar Returns Colour: As for AWR

MAP CTR MAP EXP NAV EXP VOR EXP ILS

Multi-coloured returns are presented when EFIS CP WXR ON switch is pushed Most intense areas are displayed in red, turbulence in magenta Source: WXR XCVR

VAR/WX VAR/WX + t VAR/MAP

TEST

Weather Radar Mode Colour: Green

MAP CTR MAP EXP NAV EXP VOR EXP ILS

Displayed when weather radar is turned on VAR/ is displayed when variable gain is selected Source: WXR XCVR

+ 12 Weather Radar Antenna Tilt Colour: Green

MAP CTR MAP EXP NAV EXP VOR EXP ILS

Displayed when weather radar is turned on Source: WXR XCVR

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Radio Navigation 23-39

EHSI SYSTEM FAILURE FLAGS AND ANNUNCIATION Whenever specific input data to a symbol generator is identified as invalid data, the associated symbol, or parameter value, goes blank. In all cases flags and annunciations are in yellow.

Diagram 16

HDG — This flag indicates that the heading data has failed RANGE DISAGREEMENT ANNUNCIATIONS Three sets of words can be used to show range disagreements:

WXR RANGE DISAGREE indicates that the selected range on the EFIS Control Panel is different from the WXR display (as above).

MAP RANGE DISAGREE indicates that the selected range on the EFIS Control

Panel is different from the MAP display range (see later diagrams).

WXR/MAP RANGE DISAGREE indicates that the selected range on the EFIS Control Panel is different from the MAP and WXR display range (see later diagrams).

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WEATHER ANNUNCIATIONS

WXR FAIL indicates weather radar has failed (no weather data displayed).

WXR WEAK indicates a weather radar calibration fault.

WXR ATT indicates loss of attitude stabilisation for antenna.

WXR STAB indicates weather radar stabilisation is off.

WXR DSPY indicates loss of Display Unit cooling or an overheat condition of the HSI. Weather Radar display is blanked

VTK (Vertical Track Flag) indicates a failure of the FMC vertical track data. VOR or LOC displays if the EXP VOR/ILS mode is selected. XTK (Cross track deviation flag) displays if the EXP NAV Mode is selected. XXXXX Possible annunciations are:

RT ANT CONT ATT WEAK STAB

Only when WXR TEST fails.

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Diagram 17

Diagram 18

MAP indicates selection of the MAP Mode.

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Diagram 19

VOR 1 (VOR Flag) indicates failure of a VOR Display on the EHSI. This function displays if the MAP or CTR MAP Mode is selected and the VOR/ADF map switch is on.

Diagram 20

EXCESS DATA indicates the refresh rate of the MAP Display has dropped below limits. The display may flicker at lower refresh rates.

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INSTRUMENT TRANSFER SWITCHING During normal operation, each pilot’s EFIS display utilises independent IRS and SG inputs. The EFI Transfer switch determines the SG source for both displays.

With the EFI transfer switch in the normal position the Number 1 SG provides display symbols for the captain’s EFIS displays, the Number 2 SG provides display symbols for the first officer’s EFIS displays.

If the EFI transfer switch is in the BOTH ON 1 position, both sets of displays utilise the Number 1 SG.

If the EFI transfer switch is in the BOTH ON 2 position, both sets of displays utilise the Number 2 SG.

The IRS transfer switch selects the IRS that supplies inputs to the respective SG as well as other aeroplane systems.

With the IRS transfer switch in the normal position, the left IRS provides inputs to the Number 1 SG and the right IRS provides inputs to the Number 2 SG

If the IRS transfer switch is positioned to BOTH ON L, the left IRS provides data to both SGs

If the IRS transfer switch is positioned to BOTH ON R, the right IRS provides data to both SGs

LIGHT SENSING AND BRIGHTNESS CONTROLS There are two sets of ambient light sensors that automatically adjust the brightness of the EADI and EHSI displays. The captain’s and first officer’s displays are adjusted independently. Two remote light sensors, located on the instrument glare shield, adjust the brightness of the associated EADI and EHSI as a function of the light coming through the forward windows. Two integral light sensors, located in the EADI and EHSI instrument bezels, work in parallel to adjust the brightness of the EADI and EHSI displays as a function of ambient light shining on the face of either display. Manual adjustment of the display brightness, above or below the brightness level set by the automatic system, is accomplished by adjusting the brightness controls on the associated EFIS Control Panel.

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Radio Navigation 24-1

GENERAL Four component systems comprise the Flight Management System (FMS):

Flight Management Computer System (FMCS) Autopilot/Flight Director System (AFDS) Autothrottle (A/T) Inertial Reference Systems (IRSs)

COMMANDS

FMC

COMPUTATIONS

V NAV L NAVON ON

PILOTS

AFDSIRSs

ACARS

A / T

INTEGRATED FMS OPERATIONINDEPENDENT OPERATIONACTIVEINACTIVE

FMS SCHEMATIC

CONDITION: L NAV AND V NAV ENGAGED

CDUs

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Each of these components is an independent system, usable individually or in various combinations. The term FMS refers to the concept of joining these independent components together into one integrated system that provides continuous:

Automatic navigation Guidance Performance management.

In essence, the FMS is capable of four-dimensional area navigation (Latitude, Longitude, Altitude, Time) while optimising performance to achieve the most economical flight possible. The integrated FMS provides centralised cockpit control of the aeroplane’s flight path and performance parameters. The Flight Management Computer, or FMC, is the heart of the system, performing navigational and performance computations and providing control and guidance commands. The automatic management features of the FMC eliminate many routine tasks and manual computations previously performed by the pilots. However, the pilots must still monitor the FMC to ensure compliance with the planned route of flight.

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OPERATION OVERVIEW The two Multi-Function Control Display Units (MCDUs) allow the crew to enter the desired flight plan routing and performance parameters into the FMC. FMC navigational and performance computations then display on the MCDUs for reference or monitoring. Related FMC commands for lateral and vertical navigation may be coupled to the AFDS and A/T through the Mode Control Panel (L NAV and V NAV). The IRSs and other aeroplane sensors provide additional required data. MCDUs also permit interface with the ACARS system. When radio updating is not available, the FMC uses the IRS position as a reference. This mode of navigation, referred to as IRS NAV ONLY, displays a message to warn the flight crew that navigation accuracy may be less than required. During IRS NAV ONLY operation, the FMC applies an automatic correction to the IRS position to determine the most probable FMC position. The FMC develops this correction factor by monitoring IRS performance during periods of radio updating to determine the IRS error. Flight crews should closely monitor FMC navigation during periods of IRS NAV ONLY operation especially when approaching the destination. The accuracy of the FMC navigation should be determined during the descent phase of flight by using radio nav aids and radar information if available. Inaccurate radio updating may cause the FMC to deviate from the desired track. The crew may select any degree of automation desired. This can mean simply using the CDU Data Displays for reference during manual flight, or using conventional autopilot functions, or selecting full FMS operation with automatic flight path guidance and performance control. Even with full FMS operation, management and operation of the aeroplane is always under the total control of the flight crew. Certain functions can only be implemented by the pilots, such as:

Thrust initiation Take-off Altitude selection ILS tuning Aeroplane configuration Landing rollout

The flight crew should monitor FMC navigation throughout the flight to ensure that the desired route of flight is being accurately followed by the automatic systems. The following schematic presents a simplified depiction of how the various FMS components interrelate. The Flight Management Computer System, with its Control Display Units (FMC/CDU), provides the pilots with a flight management tool which performs navigational and performance computations. Computations related to lateral navigation include items such as:

Courses to be flown ETAs Distance to go

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Radio Navigation 24-4

For vertical navigation, computations include items such as:

Fuel burn data Optimum speeds Recommended altitudes

When operating in the Required Time of Arrival (RTA) mode, the computations include:

Required speeds Take-off times Route progress information

In addition, the FMC also provides control and guidance commands that can be coupled to the AFDS and A/T. This allows integrated FMS operation with automatic lateral and vertical navigation from initial climb to final approach.

CDU FUNCTION CDU PAGE DISPLAY GENERAL

The page displays a single page of FMC data, as selected by a function and mode key or a line select key. The Ambient Light Sensor automatically adjusts the Display contrast for ambient light conditions. The Brightness Control adjusts the brightness of the display by rotating the knob.

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FUNCTION AND MODE KEYS

Pressing the Mode keys selects the appropriate page of FMC data for the display. The EXECute key executes the display data.

LINE SELECT KEYS There are 6 keys on either side of the screen (Left 1L – 6L, Right 1R – 6R). Each key is associated with its adjacent data line. (See diagram below).

Press — If the scratch pad is blank, pressing the line select key moves appropriate moveable data on the line into the scratch pad. If appropriate data already exists in the scratch pad, then that data transfers up the line (if modifiable) and replaces any previous data. If the line has the access prompt symbol < or > the display changes to the indicated new page, or the indicated function is accomplished. If the line is a procedure, the procedure is selected.

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KEYBOARD

SP key inserts a space into the scratch pad when pressed. ± key enters a minus sign(-) into the scratchpad that changes to a plus sign (+) with a second press. Delete Key causes the word DELETE to appear in the scratch pad (if previously blank). Subsequent line selection to a deletable line deletes that line (in some cases, execution is also required). CLR Key clears scratch pad data from this CDU only, or clears CDU Messages.

Momentary Press clears the last character keyed-in, or clears a message. Press and Hold clears all characters.

Slash (/) Key enters a / character in the scratch pad. This function serves to separate data entries for speed/altitude, etc. Main Keyboard enters the alpha-numeric characters into the scratch pad.

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CDU PAGE DISPLAY

PERF INIT: Page title 1/2 Top Right of Screen: The first digit identifies the page number (from

within a group of related pages) presently being displayed.

The second digit identifies the total number of related pages (if any) which are available for display using the PREV PAGE or NEXT PAGE keys.

Box Prompts: Identify a line requiring data entry for FMC

operation. Dash Prompts: Identify a line where is data entry optional. Such

entries help to optimise FMC computations. 2LData Line Title/ Data Line (line): When displayed, the title identifies the type of

data displayed on the line below. _ _ _ _ _ _ _ _ _ _ _ Display Division: Page data displays above the dashed line.

Various prompts and the scratch pad appear below the line.

Scratch Pad: The bottom line of the display. Displays CDU

messages, Keyboard entries, or data being transferred between lines or pages within the line select keys.

Selecting a new page does not affect scratch pad entries.

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PAGE STATUS

Page Status indicates the active or modified status of certain route or performance data (active route shown above). If the page data is inactive, Page status is blank. FUNCTION AND MODE KEYS

CLB: The Climb Mode Key displays various climb pages that allow evaluation and/or change of

the climb mode. CRZ: The Cruise Mode Key displays various cruise pages that allow evaluation and/or change

of the cruise mode. DES: The Descent Mode Key displays various descent pages that allow evaluation and/or

change of the descent mode. EXEC: The Execute Function Key is the FMC command key.

Illuminated (White) indicates that data entered on a page may now be activated. The data can consist of required entries, or be a proposed modification to the active route or performance data. If a modification, the original (unmodified) data is still active. Pressing the EXEC key activates the data or modification and extinguishes the light bar.

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PREV PAGE or NEXT PAGE:

The previous page or next page function keys. When pressed, the display changes to the next lower or next higher page number within a multiple page group of related pages.

N1 Limit Mode Key:

Displays a page with engine N1 limit values and allows the pilot to select thrust limits if automatic selection is not desired. The active limit is always available for display on the N1 indicators and for use by the autothrottle.

INIT REF: Initialisation/Reference Mode Key displays pages used for initialising the FMC

and IRSs, plus other pages containing various categories of reference data.

RTE: The route mode key displays pages used to enter or revise the origin,

destination, departure runway and each route segment of the flight plan route. Also displays procedures selected on the Departures/Arrivals pages. The route is entered manually or as a stored company route.

MENU: The Menu Key provides access to sub-systems such as FMC, ACARS, etc. DEP/ARR: The Departure/Arrival Mode Key displays the pages for listing terminal area

procedures for a selected airport and permits the selection of departure and arrival/approach procedures for entry into the flight plan route.

HOLD: The Hold Key displays the pages for any previously defined holding patterns, or

allows initial development of holding patterns for entry into the active route. It is also used to exit a holding pattern.

PROG: The Progress Mode Key, when pressed, displays pages with current dynamic

data concerning progress along the active route, including ETAs and fuel remaining estimates for the next two waypoints, destination, and the next altitude change point.

This also provides information on wind, temperature, TAS, Route Tracking, and the status of the IRSs and DME/VHF Nav Radios.

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It also allows access to the RTA PROGRESS page for the initialisation and monitoring of the RTE Mode.

LEGS: The Legs Mode Key displays pages containing lateral and vertical details for each leg of the flight plan route. It allows revision of individual waypoints and certain speed/altitude crossing restrictions.

FIX: The Fix Mode Key displays pages used for determining ETA at, distance to, and

altitude at the intersection of the active route and a radial or distance from any waypoint/fix. It also allows determination of present radial and distance from any waypoint/fix.

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LIGHTS

Menu Page — This page displays if the FMC fails. Message Light (Illuminated White) — The FMC contains an Alerting or Advisory Message for display in the scratch pad. If non-message data is presently displayed in the Scratch Pad, pressing the CLR Key displays the message. Pressing the CLR key clears the message and extinguishes the light.

Fail Light (Amber) — When illuminated, the FMC test is in progress. Call Light (White) — When illuminated, a user other than the FMCS is requesting control of the CDU. SYSTEM COMPONENTS The single FMC contains stored databases of navigation and in-flight performance information. This stored data is an electronic flight bag that contains information similar to (but more refined than) the pages of Operations Manual Performance Data and the navigation publications that are carried in a pilot’s flight bag.

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The two identical, independent CDUs provide the means for the FMC and flight crew to “talk” to each other in familiar Air Traffic Control language. The crew may enter data into the FMC using either CDU, although simultaneous entries should be avoided. The same FMC data and computations are available for display on both CDUs. However, each pilot has independent control over the information actually being displayed on an individual CDU. DATABASES Standard information stored in the permanent navigation database includes:

The location of and other facility information for selected airports Runways VHF navaids

Other data that may be stored (at the airline’s option) includes:

The company route structure Airways Waypoints SIDS, STARS, and approach procedures

This permanent navigation database contains two sets of time-sensitive data:

Active data that is applicable to an initial 28 day time period Alternate data that is applicable to the time periods below

During pre-flight, the pilots select the data to be used via the CDU IDENT page. Updates to the navigation database are performed by maintenance personnel using a magnetic tape cassette, and are normally accomplished on a 28 day cycle corresponding to the revision date of navigation publications. If the permanent database does not contain all of the required flight plan data, the crew can define additional airports, navaids, and waypoints and store them in either a supplemental or a temporary navigation database. Use of these additional databases provides world-wide navigational capability, with the crew manually entering desired data into the FMC via various CDU pages. Information in the supplemental nav database is stored indefinitely, requiring specific crew action for erasure. The temporary nav database is automatically erased at flight completion. The performance database contains information on:

Climb and cruise performance Thrust limits Maximum and minimum altitudes Maximum and minimum airspeeds for various configurations Drag characteristics

Maintenance personnel can refine the data by entry of correction factors for individual aeroplane drag and fuel flow characteristics.

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OPERATION The CDUs are used during preflight to manually initialise the IRSs and FMC with dispatch information such as:

Present position Flight plan routing Zero fuel weight Planned cruise altitude

These CDU entries and the databases then form the starting point for FMC computations. The FMC compares this planning information with actual data from a number of other sources (including required IRS inputs). These other inputs provide dynamic real-time information on:

Flight progress Aeroplane environment Systems status

The FMC then continuously computes:

Aeroplane position ETAs Thrust (N1) targets and Limits and optimum/required speeds Recommended altitude for the selected vertical profile

Computations are displayed on the CDUs, while associated outputs provide roll, pitch and airspeed commands to the AFDS (L NAV and V NAV modes) and thrust commands and limits to the A/T. FMC N1 Limits may be automatically displayed on the N1 Indicators. The N1 limit, or reduced mode, used by the A/T is annunciated on the Thrust Mode Annunciator. During V NAV operation, the FMC target airspeed may be automatically displayed on the Mach/Airspeed Indicators and EADI speed tapes. Also, lateral and vertical navigation data may be displayed for reference on the HSIs. With LNAV and V NAV engaged, the CDU displays allow the crew to monitor proper FMS operation and flight progress. With L NAV and V NAV disengaged, the displays provide a reference, allowing the crew to fly the selected route/profile either manually or with conventional autoflight modes. The CDUs also:

Provide “what if” previews of flight plan options Make revisions to the flight plan Provide reference data

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LATERAL NAVIGATION Lateral outputs from the FMC are normally referenced to a direct great circle course (either on or off airways), but can be referenced to a fixed heading or course when flying a published procedure. FMC navigational computations are based upon an FMC position established using radio inputs and/or IRS present position. The FMC position may be based upon IRS data only, but available DME inputs are normally used to refine and update the FMC position. Just prior to take-off, the crew may set the FMC position to a point on the departure runway via the CDU TAKEOFF REF page. Activation of the TO/GA button updates the IRS to this position. Note that radio updating does not occur on the ground. Consequently, navigation position error can accumulate in the FMC during transit or through flight stops. Fast realignment of the IRSs with a new present position removes the errors. The errors will also be removed after take-off when radio updating again becomes available. Also note that the FMC is not certified as a “sole source of navigation” system. It is certified to navigate accurately in conjunction with an accurate radio navaid environment. VERTICAL NAVIGATION Vertical outputs from the FMC are normally referenced to the best economy profile for:

Climb Cruise Descent and holding

Computation of optimum speeds for the economy profile is based upon a company specified Cost Index, which is the ratio of other operating costs compared to the cost of fuel. Changing the Cost Index changes the computed optimum speeds. If desired, the crew may manually select any speed profile other than economy.

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REQUIRED TIME OF ARRIVAL (RTA) NAVIGATION The RTA navigation mode is designed to assist the pilot in complying with a required time of arrival at a designated waypoint such as the final approach fix, holding fix, or airport. After inputting the appropriate waypoint and RTA to the FMC via the CDU, the FMC computes:

A recommended take-off time Speeds required to comply with the RTA Progress information as the flight takes place

Speeds are automatically adjusted for in-flight winds and route changes by the FMC adjusting the Cost Index. If the RTA is unobtainable under present routing and/or environmental conditions, the FMC so advises by displaying an appropriate message for the most economical operation. The pilot should try to meet the recommended take-off time, as a later take-off results in a higher cost index than originally planned. RADIO TUNING The dual frequency scanning DME radios are automatically tuned by the FMC. The stations to be tuned are selected based upon the best available signals (in terms of geometry and strength) for updating the FMC position, unless the flight plan requires a specific station. The intersection of two DME arcs determines radio position. If the DME radios fail, or if suitable DME stations are not available, FMC navigation is based upon IRS position information only. The FMC uses the two VHF NAV Radios for LOCALISER updating during an ILS approach and by the crew for navigation monitoring. The FMC automatically rejects unreliable navaid data during FMC position updating. However, in certain conditions, navaids that are in error may satisfy the reasonableness criteria and provide the FMC with an inaccurate radio position. One of the most vulnerable times is when a radio position update occurs just after take-off. This usually manifests in an abrupt heading correction after engaging LNAV. The position shift is visible on the EHSI map which shifts, the desired track and runway symbol to a position significantly different from that displayed during the ground roll. If the flight crew observes either of these indications, and an extended period of IRS NAV ONLY flight follows, the FMC position should be carefully monitored.

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AFDS

FCCsA / TCAPTCLOCK

MACHAIRSPEEDs

TOTALFUEL

AIR DATACOMPUTERS

DME RADIO

PNEUMATICSWITCH

POSITIONS

AIR-GROUNDSENSING

PMC ON / OFFLOGIC

FLAPPOSITION

IRSs

EFISCONTROLPANELS

N1s

EADIs

EHSIs

DMEAUTO TUNE

CAPTCDU

F/OCDU

THRUST MODEANNUNCIATOR

FMC

FMCS SCHEMATIC

NAVIGATIONDATA

BASES

PERMANENT

SUPPLEMENTALTEMPORARY

PERFORMANCEDATA BASE

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ELECTRICAL POWER The FMC and both CDUs are powered indirectly by transfer bus No. 1. If electrical power is lost for less than ten seconds:

LNAV and VNAV disengage The FMC retains all entered data When power is restored the FMC/CDU resumes normal operation

If power is lost for ten seconds or more:

On the Ground — All pre-flight procedures and entries must be repeated when power is restored. In-flight — LNAV and VNAV disengage and the FMC retains all entered data. When power is restored, the MOD RTE LEGS page displays with the Advisory Message SELECT ACTIVE WPT/LEG.

A Software Restart resulting from the FMC entering an impossible computational state, such as division by zero, may appear to the aircrew to be a temporary loss of electrical power. The CDU momentarily blanks and then displays “FMC”. The display of the MOD RTE LEGS page with box prompts in the Active Waypoint line quickly follows. The message SELECT ACTIVE WPT/LEG displays. In some cases, multiple Software Restarts inflight can result in FMC failure. The FMC may be reinitialised by removing AC power for more than 10 seconds after landing. TERMINOLOGY The FMC databases contain information from which the crew makes selections or modifications to their specific flight plan. The terminology below describes the status of this information and methods of crew interaction with the FMC/CDU. EXECUTING The term Executing refers to pressing the EXEC key when it is armed (Light Bar illuminated) and is often written as EXECuting. INACTIVE Inactive refers to route or performance information that the FMC is not actively tracking. Such information cannot be engaged to the AFDS or A/T. Inactive data is made active by EXECuting. ACTIVE Active refers to route or performance information that the FMC is actively tracking and that may be engaged to the AFDS (L NAV and/or V NAV) or Alt. This is often written as ACTive. Within the above general context, the term “active” may also specifically identify the current leg or route segment being flown, or the upcoming waypoint toward which the aircraft is flying, for example, when flying from ABC to DEF (the active Leg), the active waypoint is DEF.

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PAGE STATUS The Page Title line indicates whether certain route and performance pages are inactive, active, or modified. For example:

Inactive Title Active Title RTE ECON CLB

ACT RTE ACT ECON CLB

MODIFICATION Modification refers to proposed changes to active route or performance pages, as indicated by the Page Status. Modified pages again become ACTive after EXECuting, and are often written as MODified. For example:

Modified Title New Active Title MOD RTE MOD ECON CLB

ACT RTE ACT ECON CLB

INITIALISATION Initialisation is the process of checking the effective dates of the navigation database and entering preflight data into the FMC and IRSs via the CDU. LINE SELECT This is the act of pressing a Line Select Key. ENTER To enter data on a page, is to line select that data from the Scratch Pad up to the desired line. The data is initially entered in the Scratch Pad by a Keyboard entry or by copying existing page data into the Scratch Pad by Line selection. ACCESS To access a page is to cause that page to be displayed on the CDU. PROPAGATE Certain types of data (for example, cruise attitude) are used on more than one page. Generally, such data need only be entered one time. The FMC then automatically propagates (duplicates) the entry to other applicable pages.

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PAGE CONCEPTS GENERAL The FMC stores its navigation and performance information on electronic “pages”. These pages display on the CDU through use of the Mode Keys. Pressing a key provides access to all pages of data functionally related to that mode. This may be a single page, or multiple pages. Access Prompts on the displayed page serve as an index that provides access to other related pages (if any), or perhaps to a separate Index Page. Consider the following Display:

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ <INDEX TAKEOFF>

In this example, the complete index to other related pages is of such length it requires accessing a separate index listing by line selecting <INDEX. However, one of the related pages concerning take-off data is directly accessible by line selecting TAKEOFF. Occasionally, a page may be selected by pressing either the Mode Key or a Line Select Key. Consider the following display:

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ROUTE>

In this example, page 1 of route data can be accessed by either line selecting ROUTE, or by pressing the RTE Mode Key. Also, line selecting an Access Prompt may occasionally be used to perform a function rather than to select another page. Consider the following display:

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ACTIVATE> In this example, line-selecting ACTIVATE> arms the execution function, causing the Light Bar in the EXEC key to illuminate. PAGE SEQUENCE LOGIC Although the FMC contains many displayable pages, proper page selection and execution are not difficult. Automatic display of some pages by phase of flight, as well as access prompts on many displays, provide assistance with the proper sequence of steps to initialise, activate, and fly the desired flight plan. For example, the diagram on the next page shows how the FMC guides the crew through the required pages of a normal preflight. Upon initial power application, the IDENT page normally appears. If the IDENT page does not appear, it may be accessed via the INIT/REF INDEX page, as shown at the bottom of the diagram. After checking the displayed data, line select key 6R is pressed to display the next logical page, POS INIT. The crew continues with each page, checking and entering data as required, then line selecting 6R, until preflight is complete. If a Standard Instrument Departure (SID) must be entered into the route, press the DEP/ARR mode key for access to the DEPARTURES page. Following selection of the SID, line selection of 6R returns the display to the RTE page.

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Radio Navigation 24-20

When the EXEC key illuminates, it must be pressed before continuing in order to activate the entered data. The RTE page requires line selection of the ACTIVATE prompt before the EXEC key will illuminate. This two-step procedure protects the crew from inadvertent activation of unintended data.

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The FMC/CDU is designed to automatically preserve the most capable modes of navigation and guidance that can be maintained with the equipment and navigation aids available. If an error or system failure results in reduced capability (downmoding), then the FMC may generate a crew message for display in the CDU Scratch Pad. If other system inputs to the FMC should fail, affected CDU Displays are blanked to prevent the display of misleading or erroneous data. For example, loss of the total fuel input causes all performance-related data to be blank. The messages and FMC internal responses provide for an orderly transition from full FMC-guided flight to less automated capability, if required.

CDU MESSAGES There are two categories of CDU messages. Alerting Messages have the highest priority and identify a condition which must be acknowledged and corrected by the crew before further FMC-guided flight is advisable or possible. Advisory Messages have lower priority and inform the crew of CDU entry errors or system status. The generation of any message causes the white CDU MSG light to illuminate. Alerting Messages also illuminate the amber FMC Alert Light on each pilot’s instrument panel. Placing the test switch to position 1 or 2 also illuminates the lights. Pressing the switch extinguishes the light.

If the Scratch Pad is empty, any message is displayed immediately when generated. Some messages will displace an existing Scratch Pad entry and are also displayed immediately when generated. Other messages will not be displayed until the Scratch Pad has been cleared; however, the MSG Light will still be illuminated. A new entry in the Scratch Pad overrides any displayed message. Messages caused by CDU entry errors are displayed only on the associated CDU; other messages are displayed on both CDUs. When multiple messages have been generated, they are “stacked” for display in priority sequence, or in the order of their occurrence if of the same priority. As each message is cleared, the next message in the stack displays. The CLR key on the CDU clears most messages as does correcting the condition. Other messages are cleared by changing the displayed page, which will delete the entry which caused the message.

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WAYPOINT The term “Waypoint” may refer to either a specific waypoint name or, in a generic sense, to any of the below definitions. WAYPOINT IDENTIFIERS Flight crew may enter stored waypoint identifiers manually on either the RTE or RTE LEGS pages, or they may be entered automatically as part of a company route designation. The following are valid CDU entries for published waypoint identifiers stored in the permanent navigation database (five characters maximum):

Waypoint identifier (waypoint name) Navaid identifier Runway number Airport ICAO identifier

CREATED WAYPOINTS If the permanent nav database does not contain the desired stored waypoint(s), then the crew can define new (previously unstored) “Created Waypoints” on the RTE or RTE LEGS pages. Created Waypoints are keyed into the Scratch Pad as any of the following:

Place Bearing/Distance (for example, COV150/50) where the “place” is any identifier already stored in either the permanent, supplemental, or temporary nav databases. This Scratch Pad entry could also be a transfer from the FIX INFO page.

Place Bearing/Place Bearing (for example, COV080/TNT190) is the intersection of bearings from two different “places”.

Along-Track Displacement (for example, COV/-10) is the distance either side of an existing flight-plan waypoint.

Latitude and Longitude (for example, N5732.8W00410.3). When the Scratch Pad entry is line-selected into the route, the FMC assigns a sequential identifier number to Created Waypoints. For the first three types of waypoints, the FMC uses the first three letters of the reference waypoint, followed by the sequential number of times that reference has been used. For example, COV150/50 would be assigned the identifier COV01. Then COV080/TNT190 would receive the assignment COV02. Latitude/Longitude entries use WPT as the first three letters. The waypoints are automatically stored in the temporary nav database for one flight only. On the NAV DATA pages, entry of the FMC-assigned identifier on the WPT IDENT line provides a display of the parameters originally keyed-in to define that waypoint.

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Radio Navigation 24-23

Alternatively, Created Waypoints can also be initially defined using crew-assigned identifiers on either the SUPP NAV DATA or REF NAV DATA pages. This method allows waypoints to be defined in any of three FMC categories:

Waypoints Navaids Airports

Entries defined on the SUPP NAV DATA pages (accessible on the ground only) are automatically stored in the supplemental nav database until deleted by the crew. Entries defined on the REF NAV DATA pages are automatically stored in the temporary nav database for one flight only. The supplemental and temporary databases share storage capacity for:

40 Navaids 6 Airports

The entries being stored in either nav base on a “first come, first served” basis. For the Waypoint category, exclusive storage is reserved in the temporary database for 20 entries (including those created on the RTE or RTE LEGS pages). An additional 20 Waypoints (up to a maximum of 40) can be stored in either the temporary or supplemental data base on a “first come, first served” basis. CONDITIONAL WAYPOINTS The preceding waypoints all refer to geographically fixed positions. Waypoints that are not geographically fixed are called Conditional Waypoints, and are imbedded within stored procedures. They are displayed on the CDU in parenthesis. They cannot be entered manually. Conditional Waypoints are displayed as any of the following:

(1500) altitude condition (COV.100) VOR radial crossing condition (COV-l0) DME crossing condition (INTC) intercept course to next waypoint (VECTOR) maintain heading indefinitely

When (VECTOR) is the active leg, the FMC does not automatically sequence to the next waypoint. The next waypoint becomes active only upon EXECution of the procedures for proceeding direct to a waypoint or intercepting a leg to a Waypoint. The crew should delete entries that are no longer required when any storage category is full to make space for additional new entries. Created Waypoints cannot be stored in the database Runway Category.

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Radio Navigation 25-1

INERTIAL REFERENCE SYSTEM

1 2 3

4 5 6

7 8 9

EMT 0 CLR

ALIGN ON DC

FAULT DC FAIL

ALIGN ON DC

FAULT DC FAIL

DSPL SEL

IRS DISPLAY

SYS DSPL

WIND

TK / GS

PPOS

TEST

HDG / STS

RL

BR

N

W H

S

E

NAV

ATTOFF ATTOFF

L IRS R

ALIGN NAVALIGN

IRS MODE SELECTOR The IRS Mode controls the operating mode of the respective inertial reference system (left or right).

OFF: Alignment is lost. All electrical power is removed from the system after a 30-second shutdown cycle.

ALIGN: Used for initial alignment. The aircraft must be parked.

Moving the selector from OFF to ALIGN initiates the alignment cycle. The selector may be moved to NAV during the cycle. Moving the selector from NAV to ALIGN automatically updates alignment and zeroes groundspeed error (fast realignment). The aircraft’s present position should be manually updated, but is not required. Return the selector to NAV.

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NAV: Navigation is a detented position. The system enters the NAV mode after completion of the alignment cycle and entry of present position.

It provides full IRS data to aeroplane systems for normal operations.

ATT: Attitude is a back up mode. It provides only attitude and heading information.

Attitude Information is Invalid means the Attitude flag is in view until ALIGN

light is extinguished.

Heading Information is Invalid means the heading flag is in view until the actual magnetic heading is manually entered and the ALIGN light extinguished.

Position and groundspeed information is lost until after the IRS is aligned on the ground. The selector must be cycled through OFF before reselecting ALIGN or NAV.

ALIGN LIGHT (WHITE) Illuminated (Steady) The respective IRS is operating normally in either the:

ALIGN mode Initial ATT mode The shutdown cycle

Illuminated (Flashing) Completion of Alignment cannot be completed due to IRS

detection of one of the following errors:

Significant difference between previous and entered positions or an unreasonable present position entry

No present position entry

Extinguished IRS is not in the ALIGN mode:

Mode selector is in NAV and Alignment is completed. Full IRS data is available.

Mode selector is in ATT and Attitude information is available. Heading information is also available following entry of the initial magnetic heading.

FAULT LIGHT (AMBER)

Illuminated A system fault that affects the respective IRS ATT and/or NAV

modes has been detected.

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ON DC LIGHT (AMBER) Illuminated The respective IRS is operating on DC power from the switched

hot battery bus (AC power not normal).

If on the ground, the ground call horn in the nose wheel well sounds providing an alert that a battery drain condition may exist. Momentary illumination is normal during alignment self test (DC power normal).

DC FAIL LIGHT (AMBER) Illuminated DC power for the respective IRS is not normal.

If the other lights are extinguished the IRS is operating normally on AC power.

INERTIAL REFERENCE SYSTEM GENERAL Two independent Inertial Reference Systems (IRS) are installed consisting of:

Inertial Reference Units (IRU) Mode selectors IRS Display Unit

Each IRS has three sets of laser gyros and accelerometers that replace the conventional mechanical gyros and compass system. The IRSs are the aeroplane’s sole source of attitude and heading information, except for the standby attitude indicator and the standby magnetic compass. In their normal navigation mode, the IRSs provide:

Attitude True and magnetic heading Acceleration Vertical speed Groundspeed Track Present position Wind data

IRS outputs are independent of external navigation aids.

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ALIGNMENT ALIGNMENT ON THE GROUND An IRS must be aligned and initialised with the aeroplane’s present position before it can enter the NAV mode. The position is normally entered through the FMC CDU during alignment. If the position cannot be entered through the FMC CDU, it may be entered through the IRS Display Unit. The aeroplane must remain stationary during alignment. Normal alignment between 70°12’N and 70°12’S is initiated by rotating the IRS Mode Selector from OFF directly to NAV. The IRS performs a short DC power test, during which the ON DC Light illuminates. When the ON DC light extinguishes and the ALIGN light illuminates, the IRS has begun the alignment process. Aeroplane present position should be entered at this time. The IRS automatically enters the NAV mode after approximately 10 minutes, and the ALIGN light extinguishes. High latitude alignment, at latitudes between 70°12’ and 78°15’, require an extended alignment time. The mode selector must be left in the ALIGN position for 17 minutes, then rotated to the NAV position. The IRS then immediately enters the NAV mode. Magnetic variation between 73°N and 60°S is stored in each IRS memory. The data corresponding to the present position are combined with true heading to determine magnetic heading. If magnetic information is unavailable, special navigation equipment is required to provide true heading to the EHSIs. FAST REALIGNMENT ON THE GROUND During transit or through-flight stops with brief ground times, a 30-second realignment and zeroing of groundspeed error may be performed by selecting ALIGN from NAV while the aeroplane is parked. Present position should be simultaneously updated by manually entering latitude and longitude prior to reselecting NAV. Moving the aeroplane during alignment or fast realignment (ALIGN light illuminated) causes the IRSs to automatically begin the full 10 minute alignment process over again. LOSS OF ALIGNMENT If an IRS loses both AC and DC power, the alignment is lost. Moving the mode selector out of the NAV position causes the alignment to be lost as well. If alignment is lost during flight, the navigation mode (including present position and groundspeed outputs) is inoperative for the remainder of the flight. Selecting ATT allows the attitude mode to be used to re-level the system and provide ADI attitude. The attitude mode requires approximately 30 seconds of straight and level unaccelerated flight to complete the re-level process. Some attitude errors may occur during acceleration, but will be slowly removed after acceleration. The attitude mode can also provide heading information, but to establish compass synchronisation the crew must manually enter the initial magnetic heading. Thereafter, drift of the IRS heading will occur (up to 15° per hour). When in ATT mode, the crew must periodically cross check an operating compass system and enter an updated heading in the IRS as required.

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IRS DISPLAY UNIT

System Display Selector Displays the left (L) or right (R) IRS for the data displays. DISPLAY SELECTOR The Display Selector selects the desired function or data for the data displays. Displays are for the IRS selected with the System Display Selector.

TEST: The knob is spring loaded to return to TK/GS, and TEST is used only during alignment. All lights in the data displays and on the mode selector unit momentarily illuminate, followed by a 10-second internal self test.

Positioning the Master Lights Switch on the centre instrument panel to TEST illuminates all lights in the data displays and on the mode selector unit. TK/GS: When set to track and groundspeed, the left window displays present

true track (course), and the right window displays present in-flight wind speed (knots).

PPOS: The Present Position detent displays present latitude and longitude. WIND: In this position, the left window displays present in-flight true wind

direction, and the right window displays present in-flight wind speed (knots).

HDG/STS: In the Heading Status mode, the left window displays true heading. The

right window displays any applicable maintenance status codes (last two digits).

During IRS alignment, the right window also displays the minutes remaining until alignment is complete. The window displays 7 (at the third digit) until the time remaining reaches 6 minutes. The display then counts down in one minute intervals.

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BRIGHTNESS CONTROL Brightness control adjusts the brightness of the data displays and is located in the centre of the display selector.

DATA DISPLAYS Two windows display data for the IRS selected with the System Display Selector. The display selector normally determines the type of data displayed. Keyboard entry of present position or magnetic heading overrides the selected display. The last digit of each window is for a decimal place. ENTER KEY

Illuminated: The integral cue lights illuminate upon keying N, S, E, W, or H

entries. When keying is complete the key is pressed. Press: The cue lights extinguish and the keyed data is simultaneously entered

into each IRS following completion of a valid self-test for data sensibility. The data displays are again controlled by the display selector.

KEYBOARD

The keyboard provides for manual IRS entry of present position or magnetic heading. The keyboard functions independently from the display selector position and the L or R position of the System Display Selector.

Alpha Keys Press: The data displays are controlled by the keyboard when the N, S, E, or W

(latitude/longitude) or H (heading) key is pressed. Alpha keys arm the keyboard for numeric entries.

Numeric Keys Press: Permits manual entry of present position (latitude/longitude) when either ALIGN light is illuminated. Permits manual entry of present magnetic heading when either mode selector is in ATT.

Clear Key Illuminated: The integral cue lights illuminate following an ENT operation if the self test determines the data to be of an unreasonable value (entry not accepted by the IRSs). Press: Extinguishes the cue lights. If the cue lights are already extinguished,

pressing CLR clears the associated data display of data keyed in but not yet entered (or not accepted). The data displays are again controlled by the display selector.

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INSTRUMENT TRANSFER SWITCH/INSTRUMENT TRANSFER SWITCH LIGHT

IRS TRANSFER SWITCH Should either IRS fail, the crew uses the IRS Transfer Switch to switch the flight instruments attitude and heading source to the functioning IRS.

INSTRUMENT TRANSFER SWITCH LIGHT (AMBER) When illuminated, one or both of the Instrument Transfer Switches has been moved from the normal position.

DME SYSTEM A dual scanning DME is installed. This consists of two DME interrogators, each of which rapidly alternates between the manually tuned frequency (VOR/ILS) and an automatically tuned frequency for FMC use.

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RADIO DISTANCE MAGNETIC INDICATOR

1 DME Indicators 300 nm maximum search for all DME stations

Warning Flags:

Warning Flag – Electrical power lost

DME receiver powered, but not receiving a DME station, or during Agility-Tuning

2 Bearing Pointer Number 1 Warning Flag in View

VOR Mode: Power failure VHF NAV Signal unreliable ADF Mode: Power Failure

3 Heading Warning Flag In View Selected compass signal is invalid. Power failure 4 Bearing Pointer Number 2 Warning Flag in View

VOR Mode: Power failure VHF NAV Signal unreliable ADF Mode: Power Failure

5 Bearing Pointers Signals to the VOR Bearing Pointers are not affected by the VHF NAV Transfer Switch.

Narrow Pointer : Uses signals from the VHF NAV receiver Number 1, or ADF receiver number 1 Wide Pointer: Uses signals from the VHF NAV receiver Number 2, or ADF receiver number 2

6 ADF/VOR Bearing Pointer Switches When pressed, selects the ADF or VOR for the bearing pointer.

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VOR/ILS NAVIGATION Two navigation receivers and control panels are installed. The panels are used to tune related VOR and ILS frequencies. VOR/ILS information is displayed on the RDMI and the EHSI VOR/ILS mode. The VHF NAV Transfer Switch is used to switch the EHSI to a functioning receiver in the event of a failure of the number one or the number two navigation radio, or the loss of navigation information to an EFIS display.

VOR Test Switch: With a VOR frequency tuned and a course of 000 selected:

Press: The course deviation bar centres VOR Bearing Pointer indicates 180° TO-FROM Ambiguity Indicator shows a FROM indication

ILS Test Switch: With an ILS frequency tuned, pressing switches provides test indications. Frequency Selector: Manually selects the desired frequency Frequency Indicator: Indicates the frequency selected by the frequency selector or by the automatic tuning system

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Mode Selector Switch: Selects between automatic and manual tuning of the frequencies Marker Beacons: Each pilot has a set of marker beacon lights that show outer, middle, and

airways beacon passage. One marker beacon receiver operates both sets of lights.

The high-low switch adjusts the sensitivity of the receiver.

Airways (White): Illuminates over an inner or airways marker beacon Middle (Amber): Illuminates over a middle marker beacon Outer (Blue): Illuminates over an outer marker beacon MARKER BEACON SWITCH

High: High sensitivity of the receiver Low: Low sensitivity of the receiver

ADF NAVIGATION Two ADF receivers are installed. The ADF bearing signals are sent to the pointers on the EHSI and RDMI. The audio is heard by using the ADF Receiver Control on an audio selector panel. An automatic direction finding (ADF) system enables automatic determination of magnetic and relative bearings to selected facilities. If heading or track information is lost or invalid, EHSI ADF bearing pointers do not display, and RDMI ADF bearing pointers do not display correct magnetic bearings. Relative bearings indicated by pointers may be correct, if the receiver is operating.

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Radio Navigation 25-11

Frequency Indicators: Two windows showing the frequency selected for ADF 1 and ADF 2 ADF Mode Selector: Two selectors for each ADF

OFF: No electrical power to the receiver ANT: Audio reception optimised. No ADF bearing sent to the RDMI. ADF: Audio reception is possible. ADF bearing sent to RDMI TEST: Bearing pointer indicates 45° left of lubber line for a valid test

ADF Gain Control: Adjusts the receiver gain of the respective ADF Tone Switch: Position 1 or 2 adds tone to the respective ADF receiver

Central position disables tone

SSR TRANSPONDER SELECTIONS Two ATC Transponders are installed and controlled by a single control panel. The ATC Transponder System transmits a coded radio signal when interrogated by ATC ground radar. The system also provides altitude reporting capability, allowing altitude information from a selected ADC to be transmitted to the ATC radar facility.

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ATC Identification Code Selectors: Select the ATC code ATC Code Indicator: Displays the code selected by the code selectors “F” appears if a fault in the transponder system is detected Altitude Reporting Switch: Enables altitude reporting Identification Pushbutton: Transmits the identification signal Transponder Select Switch:

STBY: Transponder mode disabled L or R: System connected to Number 1 or Number 2 ADC AUTO: Some systems have an AUTO system that activates the transponder when an air/ground switch in the main landing gear shows the aircraft to be airborne. The transponder is deactivated when the aircraft is shown to be on the ground.

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Radio Navigation 25-13

WEATHER RADAR The weather radar is an X band colour radar system used for:

Weather detection and analysis Ground mapping

The system detects and locates various types of precipitation bearing clouds along the flight path of the aircraft, and gives the pilot a visual indication of their intensity by using colour contrast. The radar indicates the clouds rainfall intensity against a black background.

Areas of heaviest rainfall appear in red The next level in yellow The least rainfall in green

In map mode, the radar displays surfaces in red, yellow and green (most reflective to least reflective). These displays enable identification of:

Coastlines Hilly or mountainous regions Cities or large structures

Ground mapping mode can be useful in areas where ground-based navigation aids are limited. The WX/T mode displays normal precipitation and precipitation associated with turbulence. When the radar detects a horizontal flow of precipitation, with velocities of 5 or more metres per second, toward or away from the radar antenna, that target display also becomes magenta. This magenta area is associated with heavy turbulence. The detection of turbulence is automatically limited to 50 nm range regardless of the selected range. The IDNT mode activates the ground clutter reduction circuits. Signals determined to have a high probability of originating from ground returns are automatically removed from the display. Some portions of weather targets may be removed as well. The IDNT mode is provided for analysis by the pilot and is not for continuous use.

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EFIS Control Panel – Top Right Section

Range Selector: Selects the desired range in nautical miles for:

HSI MAP Plan, and Weather radar displays

Weather Radar Switch: Press to activate the weather radar display

TFR: Activates the radar display on the left or right HSI WX/T: Activates display of detected precipitation and turbulence within 50 nm WX: Activates display of detected precipitation MAP: Activates display of detected ground returns IDNT: Activates ground clutter suppression in WX mode, normal operation position

would be off TEST: Displays maintenance test pattern

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GAIN: Rotating gain control. Manually sets receiver sensitivity to enhance

Ground WX WX/T MAP

TILT: Manually controls antenna tilt position from 15° up to 15° down. GAIN UCAL: Illuminates when gain is improperly set. RADIO ALTIMETERS The low range radio altimeters provide indication of aeroplane height above the ground up to 2500 ft absolute altitude. Each pilot’s EADI indicates the radio altitude. When the Captain’s RA is inoperative:

All modes of the GPWS are inoperative Autopilot A channel should not be selected for approach Autothrottle automatic retard during landing flare is inoperative

When the First Officer’s RA is inoperative:

Autopilot B channel should not be selected for approach

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