Table of Contents

Chapters (Excerpts)

Index

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Contents

Section 1 Systems

Chapter 1. The Meaning of “Avionics” .......................................... .1First Instrument Panel .......................................................................... 1“Blind Flying” ........................................................................................ 2All-Glass Cockpit .................................................................................. 4

Chapter 2. A Brief History ............................................................... 6Sperry Gyroscope ................................................................................ 7Turn and Bank ..................................................................................... 8Morse, Bell and Hertz ........................................................................... 9First Aircraft Radio ................................................................................ 10Lighted Airways .................................................................................... 11Jimmy Doolittle; Beginning of Instrument Flight ..................................... 12

Chapter 3. VHF Com (Very High Frequency Communications) .... 16Acceptable VHF Com Radios ............................................................... 17VDR (data radio) .................................................................................. 17Navcom Connections ........................................................................... 18VHF System......................................................................................... 19Com Control Panel ............................................................................... 20Com LRU ............................................................................................. 20Splitting VHF Channels ........................................................................ 21

Chapter 4. HF Com (High Frequency Communications) ............. 23HF Control-Display ............................................................................... 23HF System ........................................................................................... 24SSB (Single Sideband)......................................................................... 24Line Replaceable Units ........................................................................ 25HF Datalink .......................................................................................... 25Control Panel (Airline) .......................................................................... 26HF Transceiver..................................................................................... 26Antenna Coupler .................................................................................. 27HF Antenna Mounting .......................................................................... 27

Chapter 5. Satcom (Satellite Communications) ............................ 29Inmarsat............................................................................................... 29Aero System ........................................................................................ 31Space Segment .................................................................................... 32Cell Phones ......................................................................................... 33Ground Earth Station (GES) ................................................................. 34Aircraft Earth Station (AES) .................................................................. 35Satcom Antennas for Aircraft ................................................................ 36Steered Antennas ................................................................................. 37High Speed Data .................................................................................. 38Aero Services ...................................................................................... 39

Chapter 6. ACARS (Aircraft Communication Addressing and ....... 41 Reporting System)In the Cockpit ....................................................................................... 41ACARS System.................................................................................... 42

Preface

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Messages and Format ......................................................................... 43ACARS Bands and Frequencies .......................................................... 45

Chapter 7. Selcal (Selective Calling) ............................................... 46Controller, Decoder .............................................................................. 46How Selcal Code is Generated ............................................................. 47Ground Network ................................................................................... 47Selcal Airborne System ........................................................................ 48

Chapter 8. ELT (Emergency Locator Transmitter) ......................... 50Search and Rescue ............................................................................. 51ELT Components ................................................................................. 52406 MHz .............................................................................................. 52406 ELT System ................................................................................... 53Fleet Operation .................................................................................... 54Cospas-Sarsat ..................................................................................... 55

Chapter 9. VOR (VHF Omnidirectional Range ............................... 57Coverage ............................................................................................. 58VOR Phase.......................................................................................... 59VOR Signal Structure ........................................................................... 60Subcarrier ............................................................................................ 61VOR Receiver ...................................................................................... 62Navigation ............................................................................................ 63Horizontal Situation Indicator (HSI) ...................................................... 64Radio Magnetic Indicator (RMI) ............................................................ 64Nav Control-Display ............................................................................. 65

Chapter 10. ILS (Instrument Landing System ................................ 67ILS System .......................................................................................... 68ILS Components and Categories.......................................................... 68Approach Lighting ................................................................................ 69Flight Inspection and Monitoring ........................................................... 70ILS Signals ........................................................................................... 71Glideslope ............................................................................................ 72Glideslope Receiver ............................................................................. 73Marker Beacon Receiver ...................................................................... 74Marker Beacon Ground Station ............................................................ 74

Chapter 11. MLS (Microwave Landing System .............................. 76Azimuth Beam ..................................................................................... 77Elevation Beam .................................................................................... 78Time Reference ................................................................................... 79Multimode Receiver ............................................................................. 79

Chapter 12. ADF (Automatic Direction Finder) ............................. 81Radio Magnetic Indicator ...................................................................... 82Sense .................................................................................................. 82ADF System......................................................................................... 83NDB (Non-Directional Radio Beacon) ................................................... 83Control-Display (Airline)........................................................................ 84Line-Replaceable Unit (Airline) ............................................................. 84Limitations ............................................................................................ 85Digital ADF ........................................................................................... 85EFIS Display ........................................................................................ 86

Chapter 13. DME (Distance Measuring Equipment) ....................... 88Obtaining Distance ............................................................................... 89DME “Jitter” for Identification ................................................................ 89EFIS Display of DME ............................................................................ 90Airborne and Ground Stations .............................................................. 91

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Channels X and Y ................................................................................ 92

Chapter 14. Transponder ................................................................ 94Control-Display .................................................................................... 94Transponder Interrogator...................................................................... 95Panel-Mount ........................................................................................ 96ATCRBS and Mode S .......................................................................... 96Transponder System ............................................................................ 97Airline Control-Display .......................................................................... 98Line-Replaceable Unit .......................................................................... 98Mode S Interrogations and Replies ....................................................... 98

Chapter 15. Radar Altimeter ........................................................... 104Antennas ............................................................................................. 105Operation ............................................................................................. 106

Chapter 16. GPS/Satnav (Satellite Navigation) .............................. 108GPS Constellation ................................................................................ 109Frequencies ......................................................................................... 110Satnav Services ................................................................................... 111Panel-Mount Receiver .......................................................................... 111Time Difference Measurement.............................................................. 111Finding Position ................................................................................... 112The Satellite Signal .............................................................................. 113GPS Segments .................................................................................... 114WAAS: Wide Area Augmentation System ............................................. 114Second Frequency for Civil Aviation...................................................... 112LAAS: Local Area Augmentation System .............................................. 116RAIM: Receiver Autonomous Integrity Monitoring ................................. 117Galileo Constellation ............................................................................ 118

Chapter 17. EFIS (Electronic Flight Instrument System) ............... 120Electromechanical to EFIS ................................................................... 122Three-Screen EFIS .............................................................................. 123EFIS Architecture ................................................................................. 124Multifunction Display (MFD) .................................................................. 125EFIS on the B-747................................................................................ 126Airbus A-320 Flight Deck ...................................................................... 127

Chapter 18. Cockpit Voice and Flight Data Recorders.................... 129CVR Basics.......................................................................................... 129Underwater Locating Device (ULD) ...................................................... 131CVR Interconnect ................................................................................. 132Flight Data Recorder: Solid State .......................................................... 134Flight Data Recorder: Stored Information .............................................. 135

Chapter 19. Weather Detection ...................................................... 136Radar Color-Coding ............................................................................. 137Multifunction Display ............................................................................ 137Types of Detection ............................................................................... 138Radar Transmitter-Receiver ................................................................. 139Weather Radar Control Panel ............................................................... 140Lightning Detection .............................................................................. 140Radar Antenna ..................................................................................... 141Datalink ................................................................................................ 141Radomes ............................................................................................. 142Radome Boot ....................................................................................... 142Windshear ........................................................................................... 143Lightning Detection .............................................................................. 145Windshear Computer ........................................................................... 144

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Satellite Datalink .................................................................................. 145

Chapter 20. TCAS (Traffic Alert and Collision Avoidance System)............... 147

Basic Operation ................................................................................... 148Traffic and Resolution Advisories (TA, RA) ............................................ 150TCAS System ...................................................................................... 150TCAS I and II ....................................................................................... 150Coordinating Climb and Descend ......................................................... 150TCAS Components .............................................................................. 150Whisper-Shout ..................................................................................... 151Directional Interrogation ....................................................................... 151Non-TCAS Airplanes ............................................................................ 152TCAS III ............................................................................................... 152Voice Warnings .................................................................................... 152

Section 2 InstallationInstallatio

Chapter 21. Planning the Installation ............................................. 154Replacing “Steam Gauges” .................................................................. 155Required Instruments and Radios ........................................................ 156Flight Instrument Layout ....................................................................... 157Basic T ................................................................................................. 157Large Aircraft EFIS ............................................................................... 158Flat Panel Integrated ............................................................................ 159Avionics Planning Worksheet ............................................................... 160Manuals and Diagrams ........................................................................ 161Installation Drawing .............................................................................. 162Connectors and Pin Numbers .............................................................. 162Pin Assignments .................................................................................. 163Schematic Symbols.............................................................................. 164Viewing Angle ...................................................................................... 165Survey Airplane .................................................................................... 165Navcom Connections, Typical .............................................................. 166

Chapter 22. Electrical Systems ...................................................... 168AC and DC Power................................................................................ 168DC System .......................................................................................... 169Airline Electrical System ....................................................................... 171Switches .............................................................................................. 172Lighted Pushbutton .............................................................................. 174Circuit Breakers/Fuses ......................................................................... 173

Chapter 23. Mounting Avionics ....................................................... 178New or Old Installation? ....................................................................... 179Hostile Areas ........................................................................................ 179Selecting Metal .................................................................................... 179Cutting Holes ....................................................................................... 180Structures ............................................................................................ 181Avionics Bay ........................................................................................ 182Airlines (ARINC) MCU Case Sizes ....................................................... 183ATR Case Sizes ................................................................................... 184Electrostatic Discharge......................................................................... 185Cooling ................................................................................................ 186Cooling for Airline Avionics ................................................................... 187Locking Radios in Racks ...................................................................... 188

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Panel-Mounted Radios......................................................................... 188Remote-Mounted Radios (Corporate) ................................................... 190Airline Mounting ................................................................................... 191Locking Systems (Airline) ..................................................................... 192Indexing Pins ....................................................................................... 193Integrated Modular Avionics ................................................................. 194Instrument Mounting ............................................................................ 195Round Instruments: 2- and 3-inch ......................................................... 196Airline Instrument Mounting ................................................................. 197

Chapter 24. Connectors ................................................................. 199Typical Connectors............................................................................... 200RF Connectors..................................................................................... 200How to Identify Connector Contacts ...................................................... 201Contact Selection ................................................................................. 201Identify Mil-Spec Part Numbers ............................................................ 202Coaxial Connectors, Typical ................................................................. 203ARINC Connectors .............................................................................. 203Crimping Contacts ................................................................................ 205Releasing Connector Pins .................................................................... 207Heat Gun for Shrink Tubing .................................................................. 207Safety Wiring Connectors ..................................................................... 208Attaching Coaxial Connectors .............................................................. 204

Chapter 25. Wiring the Airplane ..................................................... 210Swamp ................................................................................................ 210High Risk Areas ................................................................................... 211Selecting Wire ...................................................................................... 213High-Grade Aircraft Wire ...................................................................... 213Wire Sizes ........................................................................................... 214Wire and Cable Types .......................................................................... 215Wire Stripping ....................................................................................... 216Nicked or Broken Wires........................................................................ 217Precut Cables` ..................................................................................... 217Splicing Wires ...................................................................................... 217Location of Splices ............................................................................... 218Ring Terminals ..................................................................................... 219Terminal Strip (Block) ........................................................................... 219Marking Wires ...................................................................................... 220Harnessing the Wire Bundle ................................................................. 222Tie Wraps ............................................................................................ 223Problems: Chafing and Abrasion .......................................................... 224Clamping ............................................................................................. 224Grounding to Airframe .......................................................................... 227Bending Coaxial Cable ......................................................................... 228Service Loops ...................................................................................... 229

Chapter 26. Aviation Bands and Frequencies ................................ 230Radio Frequency Bands ....................................................................... 231Higher Bands (Microwave, Millimeter) ................................................... 232Low Frequencies.................................................................................. 232Skipping through Ionosphere ................................................................ 233High Frequencies ................................................................................. 233Very High Frequencies ......................................................................... 234L-Band ................................................................................................. 234From Hertz (Hz) to Gigahertz (GHz) ..................................................... 234Line of Sight Communications .............................................................. 235Control and Display of Bands and Frequencies .................................... 236

Chapter 27. Antenna Installation .................................................... 239Antennas for Airline, Corporate and Military Aircraft ............................... 240

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How to Read an Antenna Spec Sheet ................................................... 241Antennas for Light Aircraft ................................................................... 242Airline Antenna Locations ..................................................................... 243Antenna Types ..................................................................................... 244Location ............................................................................................... 245Bonding the Antenna to the Airframe .................................................... 248Antenna Mounting ................................................................................ 249Antenna Couplers ................................................................................ 251Base Station and Mobile Antennas ....................................................... 252GPS Antennas ..................................................................................... 251

Chapter 28. Panel Labels and Abbreviations ................................. 254Silk Screen, Engraving, Tape ................................................................ 254Panel Abbreviations ............................................................................. 255

Section 3

Chapter 29. Test and Troubleshooting ........................................... 261ADF ..................................................................................................... 262Antennas ............................................................................................. 263Antenna VSWR .................................................................................... 263Autopilots ............................................................................................. 264Com Transceivers ................................................................................ 264DME .................................................................................................... 265ELT-Emergency Locator Transmitter..................................................... 266Glideslope Receiver ............................................................................. 266Lightning Strikes ................................................................................... 266Software Loading ................................................................................. 267Transponder ........................................................................................ 267VOR .................................................................................................... 268Wiring and Connectors ......................................................................... 270Fault Detection Device (Wiring) ............................................................ 271Precipitation (P) Static .......................................................................... 273Avionics Checklist ................................................................................ 274

About the Author ............................................................................. 275

Index

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VHF-Com System

A com radio typically found in airliners andlarge aircraft. The pilot operates the VHFControl Panel, while the main unit of the VHFtransceiver is in a remote electronics bay. Two frequencies may be selected at onetime; the active channel sends and receives,the stored channel remains inactive. Whenthe transfer button is pressed, the two chan-nels exchange places. The Audio Panel connects pilot micro-phone and headset or loudspeaker. “PTT”is the push-to-talk button that switches the

radio between transmit and receive. Thebutton is on the microphone or the con-trol yoke. The transceiver also provides an audiooutput to the Cockpit Voice Recorder toretain radio messages in the event of asafety investigation. There are usually three VHF com radiosaboard an airliner. One radio, however, isoperated in the ACARS system, as de-scribed below.

Third Com RadioThis is the same as the other two com ra-dios, except for modifications to operate onACARS (Aircraft Communication and Report-ing System) described in a later chapter.Thereis no pilot control panel because the fre-quency is pre-set to an assigned ACARSchannel. ACARS automatically receives andtransmits messages about company opera-tions. A pilot may also use voice on this radiothrough the mic and receiver audio connec-tion. VHF com radios in large aircraft typicallyoperate from a 28 VDC power source. Thetransmitter is often rated at 25 watts of radiofrequency output power.

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Located in the electronics bay, the VHF transceiver isremotely tuned by the control head in the instrumentpanel. This LRU (line replaceable unit) has several testfeatures built in. The indicator at the top shows trans-mitter power in the forward direction (toward the antenna)or power reflected back to the transmitter. If reflected

power is high, there’s a problem in the antenna or cable.This is covered in the chapter on test and troubleshoot-ing. The jacks at the bottom enable the technician totalk and listen while testing in the electronics bay. .

VHF-Com Control Panel

Typical airline control headfor one VHF transmitter-re-ceiver (transceiver). The pilotis communicating on the leftdisplay; the frequency trans-fer switch is pointing left. Hehas stored the next frequencyon the right side. A flip of thetransfer switch activates thenext frequency. This panel-mounted unit controls a re-mote transceiver in the elec-tronics bay. The “Com Test” button atthe bottom disables the auto-matic squelch. This allowsatmospheric noise to beheard, which is an approxi-mate test of whether the ra-dio is operating.

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Chapter 4

HF ComHigh Frequency Communications

When an airplane leaves the coastline for a tran-soceanic flight, moves into a polar region or venturesover a remote area, it loses VHF communications. VHFsignals are line of sight and cannot curve over the ho-rizon. For long-range flight, the airplane switches toHF---high frequency---communications.

In a band from 2-30 MHz, HF radio travels2000-6000 miles by “skipping” through the ionosphere,an electrical mirror that reflects radio waves back toearth.

HF has never been a pilot’s favorite radio. Earlymodels didn’t have the reliability of VHF becausethe ionosphere is always changing---between day andnight and season to season. It is struck by magneticstorms from the sun which repeat over an 11-yearsunspot cycle, interrupting communications for hours,even days.

The cure is the eventual elimination of HF radioby satellite communications. Nevertheless, thousandsof aircraft will continue to fly with HF for decadesbefore the transition is complete. Fortunately, HF hasenjoyed several improvements.

Early HF radios were difficult to operate. Mostantennas for aircraft measure from inches to severalfeet long. The length tunes the antenna to one-quarter

Bendix/King

Control-Display for an HF radio for General Aviation. Withoutput power of 150 watts (Single Sideband, or SSB) ittunes 280,000 channels. An antenna coupler (remotely lo-cated with the receiver and transmitter) ) automaticallytunes the antenna when the microphone button is pressed.Some models, like this one, have a “Clarifier” control (lowerleft) to fine tune the incoming voice. The radio also solves the problem of hunting for a work-able frequency under changing ionospheric conditions.With circuit called “automatic link establishment” itsearches for the best available channel. This model is theBendix/King HF-950. Weighing about 20 lbs, it is also usedby helicopters, which often fly in remote areas beyond VHFcommunicating range.

HF Control-Display

wavelength, which is standard for aircraft. A VHF an-tenna at 120 MHz, for example, has a quarter-wave-length of only two feet, easy enough to mount as asmall whip or blade on the airframe. But as operatingfrequency goes lower, wavelength grows longer. A

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quarter-wave HF antenna on 2 MHz would have to runover 100 feet long!

Radio pioneers solved this with a “trailing wire”antenna----reeling it out to float behind the airplane. Ifradio conditions changed, they hunted for a new fre-quency and changed antenna length. They also had tomanually adjust an antenna tuner.

A breakthrough happened when Arthur Collins(founder of a company that produces air transport avi-onics) came up with an improvement called“Autotune.” It is a tuning unit that matches a short,fixed antenna on the airplane to the wavelength of anyHF frequency. It’s done automatically when the pilotselects a channel.

The concept of automatic antenna tuning is basedon “reflected power.” If an antenna and antenna tunerare adjusted for, say, an operating frequency of 12 MHzand the pilot changes to 5 MHz, there will be a largeelectrical mismatch between the antenna and feedlinefrom the transmitter. This causes radio frequencypower to reflect back from the antenna and be lost.The Autotune system measures the reflected power andoperates tuning elements in the antenna coupler to re-duce the reflection to the lowest possible value. (Theconcept of reflected power reappears in the chapter ontest and troubleshooting, where it’s called VSWR, forvoltage standing wave ratio.)

In today’s HF radios, changing frequencies and

HF System

When the pilot keys the transmitter on a new channel, a 1000 Hz (audio)tone is modulated onto the radio wave and sent to the antenna coupler.This enables the coupler to match the antenna to any HF frequency. Atone is used because, unlike voice, it produces a steady radio-frequencyoutput for the coupler to measure. Antenna tuning usually takes lessthan four seconds.

retuning the antenna can occur in less than a secondfrom the time the pilot turns the channel selector.

Automatic HF antenna tuning, which greatly re-duced pilot workload, was followed by a developmentthat improved HF radio’s ability to avoid fading sig-nals and poor radio conditions caused by variations inthe ionosphere.

SSB HF radio originally transmitted in the AM(amplitude modulation) mode, the same as AM broad-cast radio today. An AM transmitter generates threecomponents; a radio-frequency (RF) carrier, an uppersideband and lower sideband. The audio (or voice) isfound only in the sidebands. This was discovered inthe 1920’s, along with the observation that the RF car-rier served only to create the sidebands inside the trans-mitter. The carrier doesn’t “carry” the sidebands. Side-bands travel just as well with or without a carrier. Be-cause the sidebands lie just above and below the car-rier frequency, they are termed USB and LSB (for up-per and lower).

In regular amplitude modulation, more than two-thirds of the transmitter power is lost in the carrier.What’s more, the upper and lower sidebands carry theidentical information. So all that’s required for trans-mitting the voice is a “single sideband.”

It took several decades for the electronics indus-try to develop stable transmitters and receivers and

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sharp filtering to make “SSB” practical. As a result,today’s HF-SSB transceiver places nearly all trans-mitter power into a single sideband, producing a pow-erful signal that punches through worsening iono-spheric conditions.

HF Datalink. Despite the improvement of SSB,pilots were not yet completely satisfied; HF still didn’tprovide the solid reliability of VHF communications.In seeking further improvement, the avionics industryconsidered digital communications to handle routinemessages. The first experiments failed as researchersdiscovered that digital signals barely survived the tur-bulent ride through the ionosphere. Too many digitalbits were lost in transmission.

At about this time, the first communications sat-ellites were rising in orbit, offering solid long rangecommunications to the aeronautical industry. Thisthreatened to kill further development in HF, but theairline industry wasn’t ready for “satcom.” Satelliteinstallations at the time proved too expensive for manycarriers, which motivated researchers to design a work-able HF datalink.

Today, HF datalink is a reality. The new radiosperform ”soundings”---listening for short bursts of datafrom ground stations around the world. A link is estab-lished to the best one for communications. If condi-tions deteriorate, the radio automatically searches for,and switches to, a better channel. If there are errors intransmission, the ground station senses them and auto-matically calls for repeats until the data is correct.

Remote Line Replaceable Units (HF)

HoneywellThree remote-mount boxes for an HF radio installed on business aircraft.They are controlled by the pilot on the flight deck. The radio tunes 280,000 channels and stores 99 user-programmable fre-quencies (for quick retrieval). For sending distress calls, the internationalmaritime distress frequency on 2.182 MHz is pre-programmed. The modelshown here, the Primus HF-1050, is upgradeable for HF datalink.

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Pilot’s HF control panel. Frequency is selected by two outer knobs. RF SENSEadjusts receiver sensitivity. The knob at bottom---OFF - USB - AM---selects modeof operation. Most HF communications for aircraft are on USB (Upper Sideband).Lower sideband is not permitted in aeronautical service. The AM knob selectsold-type Amplitude Modulation, which is much less effective than SSB, but en-ables pilot to talk to ground stations not equipped for SSB,

HF Control Panel: Airline

HF Transceiver

Mounted in an electronics bay, the HF transceiveris operated from the pilot’s HF control panel. It hasseveral provisions for testing. Three lights showsystem status (the red lamp is indicating “LRUFAIL,” meaning this transceiver, a line-replaceableunit. The button ”SQL/LAMP” is pressed for twotests; all lamps should light, and the squelch isdisabled. During a disabled squelch, the techni-cian should hear atmospheric noise, which is anapproximate test that the receiver is working. Hecan also plug a microphone into the “MIC” jackand talk on the radio during troubleshooting. The transmitter in airline service is usually ratedat 400 watts of radio frequency power duringsingle-sideband (SSB) transmission; 125 watts inthe AM mode.

Advantages of HF Datalink•Lower Pilot Workload•Shorter Message Transmission Time (lessthan 3 seconds vs more than 1 minute)•Channel Access Time (less than 60seconds vs up to 10 minutes)•Less Operational Training for Flight Crew•Data Relieves Congestion on VoiceFrequencies•Automatic Selection of Frequency and DataRates•Voice Is Prone To Human Error andInterpretation•Data Detects Errors and AutomaticallyRetransmits•Data Extracts Signals in NoisierEnvironments (3dB/10dB)•Increased HF Traffic Capability•Assured Communication LinkAutomatic Air/Ground HF linkage With Less Acquisition and Message Cost(Compared to Satcom)•Improved Voice/Data Quality•Data Link Messages Are Not Written or Sensitive to Verbal Language

(The above list is based on a Honeywell report)

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HF Antenna Mounting

The HF antenna on a typical airliner is located in the vertical tail fin. The radiating an-tenna is inside a U-shaped fiberglass leading edge. The antenna coupler is just below,inside the rudder fin. The coupler matches any HF frequency (2 - 30 MHz) and sends itthrough a feedline to the antenna.

Mounted below antenna in rudder fin, HFantenna coupler tunes antenna to the fre-quency in less than 4 seconds after pilotselects a channel. Pressure Nozzle at the bottom pressur-izes the coupler enclosure. Otherwise, lowair pressure at altitude would cause highvoltage in tuning coils to arc over andshort.

HF Antenna Coupler

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SatcomSatellite Communications

A Ground Earth Station communicates with orbitingInmarsat satellites, which relay messages to and fromaircraft. The Ground Earth Station receives andsends those messages through telephone compa-nies and other telecommunications services through-out the world.

(Inmarsat)

Satcom provides communications between aircraftand ground through most of the world. Free from at-mospheric interference and limited bandwidth, it is thereplacement for High Frequency (HF) as the band forlong-range communications. Satcom signals penetratethe ionosphere without bending or reflecting and areunaffected by electrical noise or weather. As satcomavionics build through aircraft fleets, they will even-tually replace VHF com, as well. The signals of sat-com are digital, not only for data communications,but voice, as well. This means voice messages can beencrypted for security.

Satcom is also the foundation for the next genera-tion of air traffic control. After a half-century of air-craft confined to narrow routes and tracks, achangeover is beginning to a new architecture knownas FANS, for Future Air Navigation Systems. Moreairplanes will fly safely within the same airspace un-der a concept known as “Free Flight.” Satcom makesit possible, as well as providing information, enter-tainment and other services for passengers in the cabin.

InmarsatThe London-based organization providing satel-

lites and ground support is Inmarsat (International Mari-time Satellite). Consisting of more than 60 member

Chapter 5

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Generations of Inmarsat SpacecraftInmarsat - 2 (called I-2) was launched in 1991after the first generation raised the demandin aviation for more satellite services. I-2provides four times more capacity than I-1.The constellation consists of four active sat-ellites, with four spares in orbit to assure con-tinuous service. All satellites are monitored by control cen-ters on the ground. As gravity causes a sat-ellite to drift from orbit, the vehicle’s attitudeand orbit are adjusted by a control station.When the satellite moves into the dark sideof the earth at night, its solar cells areeclipsed. Batteries provide power in the dark.Controllers monitor the battery backup to besure satellite power is sufficient.

Inmarsat-3 has ten times the capacity of I-2.Each of the four spacecraft has one globalbeam which covers a wide area of the earth.Each also has 7 spot beams which concen-trate power over a narrower area (usuallywhere demand is high, along heavily traveledroutes). Backup for I -3 is the previous gen-eration of I-2 spacecraft. The next constellation is I-4, designed tobe 100 times more powerful and have tentimes the communications capacity.

countries, it provides the space segment known as “In-marsat Aero. Using four satellites, it provides two-way voice and data (fax, Internet, e-mail, ATC) overmost of the world. Because the satellites hover overthe equator, their beams cannot extend into the Northand South Pole regions. Future systems will add polarorbits to fill in these limited areas. The four Inmarsatsatellites:

Pacific Ocean Region (POR)Indian Ocean Region (IOR)Atlantic Ocean Region West (AOR-W)Atlantic Ocean Region East (AOR-E)

Each satellite is backed up with a spare orbitingin same vicinity. The other two major components ofthe satcom system are:

Ground Earth Station (GES). These radio sta-tions around the world operate large dishes for com-municating with satellites. They receive messages sentto a satellite by an aircraft, then pass them to a tele-communications company for relaying them to any tele-phone or data terminal in the world.

If the message is intended for an aircraft in flight,

the ground earth station receives it through telecommu-nications networks and beams it up to a satellite for re-lay to the airplane.

Aircraft Earth Station. This is the avionics sys-tem aboard the aircraft for communicating with satel-lites. It must conform to Inmarsat standards and thespecification for ARINC 741.

Satcom antennas. A component of the airbornesystem is the antenna, which must always aim directlyat the satellite (to receive all of its services). AlthoughInmarsat satellites appear never to move (they are ingeostationary orbit), the airplane often cruises over 500mph, rapidly changing position. This is solved by abeam steering unit on the airplane that operates amotor-driven antenna or an electronic system known asa “phased array.” Consider the satcom antenna catego-ries:

Low Gain. Various communications via satelliterequire a different amount of power. A message con-sisting only letters and numbers moving at a slow rate(300-1200 bits per second) uses relatively little powerand can operate on a “low gain” antenna on the air-plane. The antennas is simple, little more than a blade,and picks up signals from any direction.

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Ground Earth Station (GES)

Inmarsat

Ten ground stations like this one are locatedaround the world for communicating with air-craft via satellite. The ground station connectsto international telecommunications networksto route calls and messages to any telephone,fax machine or data terminal in the world. The station’s dish antenna is typically 10meters in diameter and operates in the sat-

com band between 4 and 6 GHz. Voice sent via satellite uses “codec,” for digital voicecoding and decoding. Digitizing the voice reduces errorin transmission and speech is high in quality. The various blocks seen at the bottom of the illustra-tion reveal a wide range of satellite services for aircraft,including air traffic control, passenger telephone, airlineoperations and data.

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Low and High Gain Satcom Antennas for Aircraft

Low-gain model has conformal an-tenna mounted on fuselage. Becauseof its simplicity it operates only on ser-vices with slow data rates (600 bits persecond) such as air traffic control andairline operational messages. Suchdata may be a stream of characters(letters and numbers) displayed on ascreen. Low in cost, the low gain sys-tem operates in the “Aero L” service.

Low Gain Antenna

High Gain Antenna

The high gain satcom antenna supportsservices with higher rates, such as “Swift64,” which handles multichannel voice,data, fax and Internet connectivity. Thetransmission rate is 64K bits per second. High gain is achieved by an array ofantenna elements formed into a beamthat focuses on the satellite.

Although the satellite is stationary, theairplane is moving. The antenna, therefore.needs the “beam steering unit,” whichkeeps the beam aimed at the satellite. Steer-ing information is obtained from theairplane’s navigation system.

AlliedSignal

37

High gain satcom antenna, the “Airlink” by Ball,measures 32-in x 16-in, with a depth of only .29-in. It is a conformal antenna, sufficiently flexibleto curve to the aircraft body. It is attached by fas-teners around the edges of the antenna. Fre-quency range is 1530-1559 MHz and 1626.5-1660.5 MHz, for communicating with Inmarsatsatellites. Antenna circuits inside the housing usemicrostrip technology, with no active electroniccomponents. The outer assembly is fiberlasslaminate.

Conformal antenna locationfor a B-747. Antenna is posi-tioned so mounting holesalong edges and two holesfor the RF cables do not in-terfere with structure of theairplane.

Honeywell/Thales

Two steerable satcom antennasmounted in a rudder cap. They oper-ate electromechanically, under controlof a beam steering unit. The antennasare aimed toward the satellite, regard-less of aircraft position on earth, andprovide high gain performance.

Electronically Steered Conformal Antenna

ElectromechanicallySteered Antenna

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Chapter 7

SelcalSelective Calling

During oceanic flights, aircraft monitor a HF (highfrequency) radio for clearances from a ground control-ler. Because HF reception is often noisy, and manymessages are intended for other airplanes, a pilot pre-fers to turn down the audio He will not miss callsintended for him however, because of Selcal---selec-tive calling. The ground controller sends a special codethat sounds a chime or illuminates a light to warn thepilot of an incoming message and to turn the volumeup. Because it’s selective, Selcal “awakens” only theHF receiver with the appropriate code.

This Selcal controller, located on the instrumentpanel, monitors two radios simultaneously (VHF orHF). An incoming tone code lights a green lampand sounds an aural warning (chime). The pilotturns up the audio volume on the radio. Pressingthe RESET button arms the system to receive thenext call.

Selcal decoder is an LRU (line replaceable unit) locatedremotely in the airplane’s electronic bay. The four-lettercode assigned to that airplane is programmed manuallyby four thumb wheels (code selector switches). The four-letter code (EG-KL, for example) is drawn fromthe letters A through S (I, N and O are excluded). Some aircraft have two decoders, one to receive Selcaltones for up to four radios (2 VHF and 2 HF). The sameassigned letters, however, are entered into the decoders.

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TONE FREQUENCY (HZ)

A 312.6B 346.7C 384.6D 426.6E 473.2F 524.8G 582.1H 645.7J 716.1K 794.3L 881.0M 977.2P 1083.9Q 1202.3R 1333.5S 1479.1

How Selcal Code is Generated

A Selcal code consists of four tones taken from the 16audio frequencies shown at the left. In this example, thecode is AB-CD. As seen in the diagram, they are sent intwo pairs. A and B are mixed together (312.6 and 346.7 Hz)and transmitted for one second. After a .2-second interval

the second pair is sent; C and D, or 384.6 and 426.6 Hz.(The technique is similar to touch-tone dialing for tele-phones.) Because the tone signals are audio in the voicerange, they can be detected by a conventional VHF or HFcommunications transceiver.

Selcal Ground Network

When Selcal must operate on VHF, where maximum rangeis about 200 miles, it is done through a network of re-mote ground stations. The airplane, always within rangeof some ground station, transmits and receives Selcalmessages through an ARINC control station (in the U.S.).ARINC relays the message to the airline company. The

link between stations is usually through telephone lines. Selcal over oceanic routes is done on HF, where rangefrom airplane to ground may be several thousand miles.The future of Selcal will be satcom; the airplane will com-municate with satellites for relay to the ground.

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VHF. Selcal also operates with VHF radios, usedby aircraft flying within a country or continent. Notonly does Selcal reduce pilot workload, but extendsthe communication distance of VHF. If an airlinecompany in Denver, for example, wants to talk to oneof its airplanes in flight over Chicago, this is far be-yond the range of VHF. Instead, the message is sent,through a telephone line to a network of ground sta-tions. A VHF groiund station near the aircraft trans-mits to the airplane, and the pilot is signalled. He re-plies on VHF to the ground station and the messagereaches the airline company through the network.

Coding. Selcal is based audio tones, as shown inthe illustration. Each airplane has a code of four lettersset into the Selcal decoding unit aboard the airplane.

The code is entered into the flight plan to controllerscan address it.

Although there are nearly 10,000 possible four-letter codes, they are in short supply. The demand isso high that more than one aircraft may be assignedthe same Selcal code. To avoid answering a call in-tended for another airplane, identical codes are assignedin widely separated parts of the world. There is alsoan attempt to assign the same code to airplanes withdifferent HF channel assignments.

It is important to warn pilots that it’s possible toreceive a Selcal alert not intended for them. This canbe corrected by the pilot by clearly identifying his flightto the ground station.

Selcal Airborne System

Block diagram of Selcal system. Signals are received andfrom ground stations through the aircraft HF and VHF trans-ceiver. They are processed by the Remote Electronics Unitand sent to the Selcal decoder for delivery to the pilot (ona screen or printer).

An incoming signal with the correct code illuminates agreen panel light in the Selcal Control Panel and sounds achime (aural alert). A single system is shown here, but many aircraft havedual Selcal installations.

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Airport Systems Int’l

Chapter 10

ILS

An array of antennas launches the localizer signal near the end of an ILS runway. Thebeams are beamed toward an airport runway at the right and reach out to about 50 miles.

The ILS is responsible for the ability of airlinersand other aircraft to reach their destination more than95 percent of time in bad weather. The system im-proves safety to such a degree that most airlines willnot operate into airports without an ILS. In the busi-ness world, many corporations will not base their air-planes at airports without an ILS.

The ILS isn’t only for bad weather. While descend-ing into an airport at night at a brightly lighted city,pilots see a “black hole” where the runway surfaceshould be. But a descent along an ILS glideslope clearsall obstacles brings the airplane safely within feet of

the touchdown zone. That guidance is also neededon bright summer days when an airport is hidden inhaze.

Another benefit of ILS is that it provides a“straight in” approach. As airplanes become heavierand faster, there is more danger in maneuvering closeto the ground at low airspeed. A 70-ton airliner can-not nimbly bank and turn through the right angles ofan airport traffic pattern. But flying the ILS, the air-plane “stabilizes” on the approach 30 or 40 miles fromthe airport and flies straight “down the slot.”

Instrument Landing System

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ILS System

A three-dimensional path leads an airplane to the runwaythreshold at upper left. After intercepting the localizer(right), the airplane receives left-right guidance. At the outer

marker the airplane begins a descent on the glideslope. Atthe middle marker the pilot decides whether there is suffi-cient visibility to land, or perform a missed approach.

ILS ComponentsThe ILS consists of more than a half-dozen sys-

tems, both aboard the airplane and on the ground. EachILS fits in a category, depending how low the airplanemay fly---known as “minimums”--- before seeing therunway and deciding to land. Even a few dozen feethave great impact on airline operations. If the ceiling,for example, is 150 feet and ILS minimums require adescent no lower than 200 feet, the airplane may haveto fly to an alternate airport, deal with hundreds of un-happy passengers, miss connecting flights and disruptschedules over the country. Similar problems face theovernight express industry (Fed Ex, Airborne, etc.). Butwith sufficient investment in avionics, training, main-tenance and ground facilities, airplanes are unable toland at their destination only four or five days a year!(In the US, this usually happens when a low pressurearea with clouds, fog and rain cover the East Coast.

ILS CategoriesBecause avionics in the airplane and ground

stations must be equal to the ILS to be flown, considerthe major divisions. The categories are based on ceil-ing and visibility at the airport when the airplane ar-rives. For ILS operations they are known as “Deci-sion Height” (DH) and RVR (Runway Visual Range).

Decision Height. When the airplane descends todecision height (shown on an instrument approachchart) the pilot must decide whether to continue andland, declare a missed approach or go to an alternateairport. To continue the approach, he must be in a po-sition to land (without excessive maneuvering) and seethe approach lights or other visual component on thesurface.

RVR (Runway Visual Range). Visibility is usu-ally estimated by a weather observer and stated in miles.But the person may be more than mile from where the

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The localizer antenna focuses the radio carrier into twonarrow lobes, shown here as blue and yellow. The bluelobe is modulated with a 150 Hz tone; the yellow lobeby a 90 Hz tone. If the airplane flies along the center ofthe overlapping (green) area, the pilot sees a centeredILS pointer. An ILS receiver does not measure the difference instrength of the two radio lobes. Rather, the receivercompares the difference in strength between the twoaudio tones. This is known as “DDM,” for difference indepth of modulation. Many localizer antennas also launch signals off theirback end (to the right in this illustration) and form a “backcourse.” This can be used for limited guidance, but insimple localizer receivers, the needle indications are re-

versed; the pilots flies away from the needle to getback on course (known as “reverse sensing”). Becausethis is confusing to the pilot, most localizer receivershave a back course switch (“BC”)” to keep the samesensing as on the front course. Back courses are present at all localizers, but shouldnever be flown unless there is a published procedure.Also, there is no glideslope with a back course ap-proach. Many localizer displays use the blue and yellow col-ors shown in the above illustration. The trend, how-ever, is not to use these colors on an instrument be-cause they don’t provide useful information. The needleprovides all the guidance.

ILS: Two Audio Tones on a Carrier

Localizer Indications

The localizer needle indicates “flyleft” to intercept the centerline ofthe localizer course. When tuned toa localizer frequency, the OBS(omnibearing selector) is disabled.Most pilots, however, set it to thelocalizer course as a reminder. Thisexample is Runway 36 (the same as0 or 360 degrees).

WIth the needle centered, the airplaneis on an extended centerline of therunway. The same indicator is usedfor VOR navigation, but when a local-izer frequency is selected, the needlebecome four times more sensitive. Thisachieves the higher accuracy requiredfor an ILS approach.

The needle indicates “fly right” to geton the localizer course. The overall width of a localizercourse is usually 5 degrees. Thus, aneedle deflecting full right or full leftindicates the airplane is 2.5 degreesoff the centerline.

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A transponder (“transmitter-responder”) receivesa signal from a ground station (an “interrogation”) andautomatically transmits a reply. Transponders were de-veloped for the military at a time when radar couldlocate airplanes but couldn’t tell the friendlies fromthe enemy. The reply of a transponder provides thatinformation; the airplane’s ID, altitude and other data.

When first introduced, transponders were called=“IFF,” for Identification, Friend Or Foe.” The term isstill used, but mostly by the military. In civil aviation,it is in a system called SSR, for “Secondary Surveil-lance Radar.” It is secondary because primary radarsimply sends a signal from the ground that reflectsfrom the metal surface of the airplane and receives anecho called a “skin return.”

In the airline world the transponder is labeled“ATC, ” referring to Air Traffic Control.

. Squawk. When a pilot is instructed by ATC toset his transponder to a code (say, 1234), the control-ler says:

“Squawk 1234.”The pilot selects the code on the control panel that

causes his airplane’s ID to appear on the radarscope.Sometimes a controller may need to verify the ID, inwhich case he asks the pilot to “Ident.” The pilot re-sponds by pressing an ID button on the transponder,which causes his target on the ground radar to “bloom,”creating a circle of light that clearly indicates the loca-tion of the airplane.

The word “squawk” goes back to World War IIwhen the British, to keep their new transponder secret,

Chapter 14

Transponder

Control-Display Unit

Transponder control head. The transponder is “squawk-ing” an identification code of “1045, ” which is the ModeA function. Also transmitted is altitude, the Mode Cfunction. The ident button is pressed only when re-quested by the controller. The standby (STBY) positionkeeps the transponder hot, but prevents replies. Thisreduces clutter on the radar screen while the airplanetaxis on the ground at an airport. As the airplane lifts off,the pilot turns the knob to Mode C (which activates IDand altitude replies). Note “ATC” at the upper right. This term is used forthe transponder in large and airline aircraft.

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The aircraft transponder sends to, and receives from, the top section ofa surveillance radar known as a “beacon interrogator.” The larger antenna below it is the older primary radar, which sendsout a pulse and picks up the signal reflected from the skin of the air-craft. Because skin returns are weak, difficult to see and carry no infor-mation other than the range and bearing of the aircraft, they are usedonly as a back-up. The beacon interrogator on top, on the other, hand, picks up a signalthat’s strengthened thousands of times by the aircraft transponder.Besides a bright display, the image on the radar screen carries datasuch as aircraft ID, transponder code and ground speed. The surveillance radar shown above is an ASR---airport surveillanceradar---that covers up to about 60 miles from the airport. To the pilot,this is “approach control” or “Tracon” (terminal radar approach con-trol). During cross-country flight, airplanes receive longer range coveragefrom “en route” radars of larger size and power.

(Westinghouse)

Transponder Interrogator

called it “Parrot.” It survives to this day in the mili-tary; when a (British) controller wants a pilot to turnoff his transponder, he says, “Strangle your parrot!”

The word “parrot” also explains why controllerstoday ask the pilot to “Squawk” a transponder code.

Grand Canyon. Transponders came into wide-spread use after a mid-air collision between two air-liners over the Grand Canyon in 1956. A DC-7 and aConstellation requested permission from ATC to flyoff course so passengers could enjoy the view. Fly-ing outside controlled airspace (on a sunny day) the

airplanes collided with the loss of 128 lives. The disas-ter began an overhaul of the ATC system (and createdthe FAA). With an ability to put strong targets andflight data on the radar screen, transponders became akey component in the air traffic system.

Two Systems: ATCRBS and Mode SATCRBS. The transponder improved air traffic

control for a half-century, operating under the name,ATCRBS, for Air Traffic Control Radiobeacon Sys-tem.” But it began showing its age as the aircraft popu-

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Panel- Mount Transponder (Mode S)

A Mode S transponder for General Aviation, the Bendix/King KT-73. Its controls and displays include:

IDENT BUTTON. The pilot presses the button when airtraffic control requests “Ident.” The reply light (R) illumi-nates for several seconds while the reply transmits. The same Reply Light also blinks when the transpon-der answers interrogations from the ground.

FLIGHT LEVEL. The altitude of the airplane, as reportedby the transponder in hundreds of feet. Thus, “072” onthe display is 7200 feet (add two zeroes).

ID CODE. The squawk code assigned by ATC underthe older transponder system (ATCRBS). It is dialed in byfour knobs along the bottom of the panel.

FUNCTION SELECTOR. This turns the transponder on,displays the flight ID code and tests all lighted segmentsof the display. The Ground position disables most tran-sponder functions because they are not needed on theground. A large number of airplanes on the airport sur-face would clutter radar displays. The pilot switches,shortly after take-off to Alt (altitude) to resume normaltransponder operation. The Alt position reports ID and al-titude. The “VFR” button at the bottom right automatically setsthe transponder to 1200. This code is selected when theairplane is not on an instrument flight plan and is flyingunder visual flight rules (VFR).

lation grew and more airplanes operated out of fewerairports.

There are several limitations on ATCRBS. First,it wastes space in the radio spectrum. When the radarinterrogator on the ground sweeps around, it interro-gates all airplanes within range---and all airplanes re-ply. The controller cannot obtain a reply only from theairplane it needs to contact.

Also, when radar sends a beam, it sweeps acrossthe airplane, making 20 or more interrogations in onepass. Only one interrogation and reply are required;additional replies only limit the capacity of the sys-tem.

Another shortcoming is “synchronous garble,”which is two replies happening at the same time. Let’ssay two airplanes are on the same line north of the ra-dar site; one at 20 miles, the other at 30 miles. Becausethey are both struck by the same radar interrogation,they reply nearly at the same time. The two replies

move along the same line back to the radar antennaand interfere with each other. To the controller, the tar-gets appear confused or “garbled.”

Another limit for the ATCRBS transponder is inthe collision avoidance system (TCAS). As describedin the chapter on TCAS, two aircraft approachingeach other must fly an escape maneuver that keeps themapart; for example, to avoid a collision, one flies up,the other flies down. That maneuver must be coordi-nated by the transponder, but ATCRBS cannot providethis function.

Mode S. The answer to these problems came asa completely new transponder known as Mode S (Sfor Select). It means “selective addressing,” whichenables a controller to request a specific airplane toreply, not the whole fleet. This greatly reduces thenumber of unnecessary signals filling the air.

A requirement of Mode S is that it does not rap-idly obsolete the ATCRBS transponder. The two must

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Transponder

The transponder is a transmitter-receiver with these ma-jor building blocks:

RECEIVERInterrogations from the ground station are picked up bythe antenna on a frequency of 1030 MHz. The pulses areapplied to the decoder.DECODERMeasuring incoming pulses, the decoder identifies thetype of interrogation. If they are recognized they arepassed on to the encoder.ENCODERThe encoder creates the pulse train which contains thereply.ENCODING ALTIMETERAfter converting barometric pressure (based on 29.92inches of mercury) to electrical signals, the encoding al-timeter sends altitude information to the encoder for theMode C repy.CODE SELECTORThe pilot dials in the 4-digit transponder code, which issent to the encoder.

MODULATORPulses that form the reply are amplified in the modulatorand applied to the TRANSMITTER for transmission on 1090MHz.SIDE LOBE SUPPRESSIONThe radar signal from the ground contains a main lobeand several side lobes. If the transponder replies to aside lobe, the radar operator will see the airplane at thewrong position. The side lobe suppression circuit pre-vents the transponder from replying if it senses receptionof a side lobe.SUPPRESSIONThere is a chance that other transmitters aboard the air-plane might interfere with the transponder. This usuallycaused by the DME. which operates close in frequency.To avoid interaction, the transponder receiver is sup-pressed when the DME transmits. The DME receiver isalso suppressed when the transponder is transmitting.

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Ch 16

A typical GPS satellite weighs nearly 1800 pounds and ispowered by a combination of solar panels (in the light)and ni-cad batteries (in the dark). Because precise timeis essential, each satellite carries four atomic clocks thatkeep time accurate to one second in 80,000 years. Theoverall width of the satellite, including solar panels, isabout 19 feet. The satellite continuously broadcasts the GPS signalthrough 12 rod-like (helical) antennas, shown in the illus-tration as pointing “To Earth.”

Rockwell

GPS/Satnav

Satnav---satellite navigation---will replace nearlyevery other form of radionavigation. It meets or exceedsthe accuracy, reliability and global coverage of land-based systems. Satnav is also supported by world avia-tion agencies to eliminate the high cost of servicingthousands of VOR, ILS, NDB and other ground sta-tions.

The benefits of satnav will multiply as GPS, aU.S. system, is joined in coming years by Europe’sGalileo. To avoid obsoleting the huge avionics invest-ment in old aircraft, however, today’s land-based sta-tions will continue to operate well into the 21st Cen-tury.

Satnav. In the 1980’s, the captain of a trans-atlanticflight between Sweden and New York walked back to

the passenger cabin. He was approached by a man whosaid, “Captain, I believe we are 10 miles off course.”

The captain looked at him and replied, “You’reprobably right.” He had noticed the man holding aportable GPS. The airliner was navigating by the mostadvanced system known; the ring laser gyro. (Threeof them, in fact, for redundancy.) The laser gyro isguaranteed not to exceed an error of 1 mile per hour-

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GPS Constellation: “Space Segment”

Number of satellites in orbit..........24 (21 active and 3 spares)Height above earth...........11,000 n milesOrbital planes...................................6Time to complete one orbit.......12 hours (circles the earth twice a day)

There are six paths, or “planes,” around theearth, each with six satellites. To an observeron earth, they appear to rise at the horizon,cross the equator, then descend below the op-posite horizon. Over most of the earth, at leastfive or more satellites are available for naviga-tion at any time.

Launch Vehicle

GPS satellite is launched by Delta II rocket at CapeKennedy. Although satellites are usually rated for alife of 7.5 years, many have operated 11 years.

--meaning that after a 4-hour flight across an ocean,the airplane would be no more than 4 miles off eitherside of its assigned track. That passenger’s pocketGPS not only knew the aircraft position within lessthan 100 meters, but held that accuracy throughout thetrip (updating once per second).

Radionavigation for nearly 100 years sent outsignals to be detected by an airborne receiver. But bythe 1960’s the microcomputer introduced digital sig-nal processing. Instead of transmitting simple tones ortiming pulses, a satellite could encode large amountsof data and broadcast it over the earth’s surface. Thisdata could then control the accuracy and performanceof even the most inexpensive GPS receiver.

This places the costliest components---like preci-sion timing generators---aboard the satellites, not inthe receiver. Each GPS satellite carries at least twoatomic clocks, which measure time by the motion inatomic particles of the elements rubidium or cesium.When the Galileo satellites appear, they will add yetanother technology; the “maser,” a cousin to the laser.In the maser, radio waves are driven to a high state ofenergy, then allowed to fall to a lower level. Duringthe fallback, they produce oscillations which are ex-tremely accurate timing references.

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Panel-Mount GPS Receiver

A GPS receiver used in IFR (instrument flight rules), like this Bendix-King KLN-94,must update its navigation database regularly. This can be done in two ways. Adatabase card is inserted into the slot, or the dataloader jack connected to a PC.Updates may be obtained over the Internet.

1. The signal from the satellite is trans-mitted as a pulse code. Each satellitesends a unique identification, as rep-resented by red, green and bluepulses.

2. The receiver in the airplane alreadyknows the code patterns sent by ev-ery satellite. It searches until it locatesa satellite signal that matches a storedpattern. The satellite message also tells thereceiver the time the signal was trans-mitted. By comparing this time withthe time of arrival at the receiver, a timedifference is calculated. This is multi-plied by the speed of light and the an-swer is distance.

CODE TRANSMITTED BY SATELLITE

CODE STORED BY GPS RECEIVER

Airplane Measures Time to Compute Distance to Satellite

two after being turned on. With a 12-channel parallelsystem, the receiver performs a quick “sky search”.

Satnav Terms and ServiceSome major terms and acronyms to describe sat-

nav systems:

GNSS: Global Navigation Satellite System. Theinternational term to describe navigation based on sat-ellites. When GNSS describes a precision instrumentapproach, it is called GLS (the LS meaning landing

system).

SA: Selective Availability. Because GPS beganas a system for the U.S. Dept. of Defense, the highestaccuracy was reserved for the military. The signal avail-able to civil users was degraded by “SA,” which lim-ited receivers to about 100-meter accuracy.

In the year 2000, Selective Availability was turnedoff and accuracy improved by about five times.

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Finding Position

When only one signal is received, theairplane may be located anywhere onthe surface of a sphere (or “bubble”),with the satellite (SV1) at its center. Af-ter receiving a second satellite (SV2)the spheres intersect and narrow theposition. With SV3, the position is fur-ther refined. It takes a fourth satelliteto obtain latitude, longitude and alti-tude, which is a 3-dimensional fix. Receiving a fourth satellite is re-quired for correcting the clock in theGPS receiver. That enables a low-costclock to keep sufficiently accurate timefor the distance-solving problem.

SPS: Standard Positioning Service This ser-vice is intended for civil users and is located on L1,one of two existing GPS channels. More channels willbe added in the future.

C/A Code: Coarse/Acquisition Code. This isthe code transmitted on the civil channel, L1. It is“coarse” because it has the least accuracy.

PPS: Precise Positioning Service. Provides thegreatest accuracy for military users and operates onthe two existing GPS channels, L1 (shared with civil)and L2 (military only). It uses the “P Code,” which isencrypted and available only to qualified users.

Propagation Corrections. The advantage oftwo channels, L1 and L2, is reducing propagation er-ror. As satellite signals move toward earth, they passthrough the ionosphere, which lies from about 60 milesto 200 miles above earth. Although radio signals moveat close to the speed of light, higher frequencies movefaster through the ionosphere, which introduces error.By measuring different GPS frequencies, L1 and L2,the receiver computes the “propagation” error and re-moves it.

The military removes the error because it isable to receive both L1 and L2. However, future satel-lites will add a civil code to L2, enabling any civilreceiver to solve the error. Later, civil aviation will re-ceive a third civil frequency, L5.

PRN CodeEach satellite transmits a unique identity known

as a “pseudorandom” code. The term “pseudo” usu-ally means “false” but in GPS it means “uncorrected.It is called “random” because the GPS signal resemblesrandom noise.

The atomic clocks aboard satellites are extremelyprecise, however, they do drift in time. The error ismeasured by ground stations, but this is not used tocorrect satellite time. Atomic clocks are not easilyreset while in orbit. It is more practical to develop atime correction factor based on the error and send it tothe GPS receiver. The receiver stores the correctionfactors for all satellites in orbit and applies them whiledeveloping a position fix. For maximum timing accu-racy, at least four satellites should be received.

Position-fixing. Determining aircraft position issimilar to “triangulation.” The receiver draws lines ofposition from several satellites, and locates the air-plane where they intersect. One way to visualize thisis to imagine each satellite surrounded by a largebubble. When the airplane measures distance from asatellite, the receiver places the airplane somewhereon the surface of the bubble. For example, if the rangeis 15,000 miles, the airplane may be anywhere on thebubble and still be at 15,000 miles.

Next, assume the receiver measures 18,000 milesto another satellite, placing the airplane on the surface

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Chapter 17

EFISElectronic Flight Instrument System

Along with digital electronics and GPS naviga-tion, the Electronic Flight Instrument System changedthe face of the flight deck. The term EFIS originallydescribed an airline system (that first rolled out withthe Boeing 767 in 1981) but today it identifies elec-tronic instruments for aircraft of all sizes.

EFIS is often called the “glass cockpit” becauseTV screens replace mechanical and electromechani-cal instruments. Dozens of old “steam gauges” are nowreplaced by an EFIS display that is rapidly changingfrom about a half-dozen separate screens to “wall-to-wall” glass.

Six large EFIS screens span across themain instrument panel. This is the flightdeck of a B-757, first airlinerto adopt electronic flight instruments.Although these displays are CRT’s,newer aircraft use LCD flat panels

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Transition from Electromechanical to EFISThis EFIS screen is a “Primary FlightDisplay” and combines many earlyinstruments into a single screen. Thetop half was once the artificial hori-zon. One of the first improvementswas the addition of “command” bars---the V-shape near the middle of thescreen. Driven by the flight controlsystem (autopilot), the bars helpedguide the pilot fly manually or enabledhim to observe commands of theautopilot. At this stage, the instru-ment was called an “ADI,” for attitudedirector indicator. When EFIS appeared, all the samefunctions were pictured on a videoscreen. This called for a new name,EADI, for electronic attitude directorindicator. At the same time, severalother instruments were added to theimage; air speed indicator, altimeter,vertical speed indicator and others.

The lower half of the screen was oncethe horizontal situation indicator(HSI). When the electromechanicalinstrument is shown on an EFISscreen it is known as an EHSI, the “E”is for electronic.

When the two major flight instru-ments---ADI and HSI---are placed oneabove the other and connected to theautopilot, they are known as a “flightdirector.”

The trend in EFIS, however, is to com-bine those instruments onto onescreen, as shown here, and call it a“Primary Flight Display.”

The system in the illustration is theHoneywell Primus EPIC, a flat panelmeasuring 8-in by 10-in.

ing system) by keeping two needles centered; one forthe localizer to remain on the runway centerline, theother a glideslope for vertical guidance. In a series ofexperiments by NASA, the “highway in the sky” wasdeveloped. The pilot aims the airplane at a rectangle(or hoop) on the screen and flies through it. Additionalhoops appear in the distance; if the pilot keeps flyingthrough them (like threading a needle), the airplaneremains on the localizer, glideslope or other 3-dimen-sional path.

The original technology for EFIS was the heavyglass cathode ray tube. Flat panel LCD’s of the 1970’s

were not ready for aviation; they were monochrome,had narrow viewing angles and low resolution. Drivenby the large market in portable PC’s, the technologyadvanced rapidly and all new EFIS systems are flatpanel.

There is much retrofitting of old aircraft to re-place their electromechanical instruments with EFIS.It’s happened in most major transport aircraft in “de-rivative” models, usually shown by a “dash number;”for example; the Boeing 737-100 first rolled out in1967 with conventional instruments. It is now up to737-900, with recent generations equipped with EFIS.

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Three-Screen EFIS

The future of instrument panels is shownin this “Smartdeck” by L3 Communica-tions. It is “wall-to-wall” glass, with three10.5-inch panels that display informationonce required by three separate instru-ments. Panels like these are usually inter-changeable, with their function determinedby how their software is programmed. Thispermits “reversionary modes,” meaningthat any display on one panel can beswitched over to another. The panels are arranged as PrimaryFlight Displays for captain (left) and firstofficer (right). In the center is the multi-function display. Because the multifunc-tion display typically displays engine in-struments and warnings it is also calledEICAS, for engine instrument and crewadvisory system. The Primary Flight Display is mainly forcontrolling the attitude of the airplane andfor navigating.

L3 Communications

Primary Flight DisplayAttitude Engine PowerHeading Selected HeadingAltitude Selected CourseAirspeed Autopilot/Flight DirectorVertical Speed NavigationLateral/Vertical Path Timer

Multifunction DisplayRadio Management ChartsAircraft Systems Runway DiagramsEngine Instruments Wind Direction/SpeedChecklists Ground TrackMoving Map Caution/WarningFlight Plan Geographic OverlaysTerrain Lightning/WeatherDatalink (Traffic/Weather) Traffic Information

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Chapter 20

TCASTraffic Alert and Collision Avoidance System

Honeywell

Keeping aircraft safely separated had been thetask of air traffic control since the 1930’s when pilotsradio’ed position reports by voice. This was followedprimary surveillance based on radar “skin returns,” thensecondary surveillance using transponder interrogationand reply. But as airplanes began cruising near Mach1 and air traffic multiplied, so did the threat of the“mid-air.”

The search for a workable anti-collision systempersisted for 50 years. Early experimental systems re-quired costly atomic clocks, complex antennas andtechniques borrowed from electronic warfare. Progresswas slow until, in 1956, two airliners collided over theGrand Canyon on a sunny day. Closing at about 900miles per hour, the pilots would have to see the otherairplane at four miles, decide on the correct response,then maneuver off the collision course. All this wouldhave to happen in 15 seconds. As a resultof the acci-dent, the U.S. Congress brought pressure on the FAAto develop an anti-collision system, and for airlines toinstall it at an early date.

During the 1960’s, the transponder was spread-ing through aviation and researchers decided to aban-don earlier technology and adopt the transponder as abuilding block in a new anti-collision system. Aftertrying several variations, the TCAS system (TrafficAlert and Collision Avoidance System) was chosen asa world standard and it’s now in widespread use ev-erywhere, with scaled-down versions for business andlight aircraft. In Europe the system is known as ACAS,for Airborne Collision Avoidance System, but all sys-tems follow the standard adopted the International CivilAviation Organization (ICAO).

While the transponder is a major component, thefoundation is the TCAS processor. It performs one ofthe most intensive and rapid computations aboard theaircraft, executing software for collision logic. It mustacquire, track and evaluate dozens of aircraft up toabout 40 miles away---then issue commands on howto avoid a collision---all within seconds.

The road to TCAS was not entirely smooth. As

148

TCAS Symbols on a Radar Display

Bendix-King

If an airplane has an EFIS or radar display, it can showTCAS information. The weather radar control panel is atthe top, with a button at top left for activating the TCASdisplay. Besides TCAS symbols on the display, there are voice

announcements. If a threat advisory (TA) appears on thedisplay, the voice says, “Traffic, Traffic.” If it turns into aresolution advisory (RA), the voice gives a command toclimb or descend.

the first systems were fitted to aircraft, pilots com-plained about false alarms (and shut them off). It mostlyhappened near crowded terminals and at low altitude.The technical committee responsible for TCAS re-sponded with software upgrades (“Changes”) that ad-dress each complaint. The performance of TCAS is nowso effective, the FAA ruled that if a pilot receives aclearance from a controller that conflicts with TCAS,the pilot must obey the TCAS. In 2002 a pilot ig-nored that procedure and caused a mid-air collision35,000 feet over Europe between an airliner and a cargoplane. Air traffic control had instructed the pilot to

descend, while TCAS advised him to climb. All 69people perished in the collision. Both aircraft had fullyfunctioning TCAS.

Basic OperationOnce every second, the transponder of TCAS air-

plane automatically transmits an interrogation. This issimilar to the interrogations sent out by air traffic sur-veillance radar and the frequencies are the same.

If another airplane is within range, its transpon-der replies to the interrogation. The first airplane mea-sures the time between interrogation and reply to de-

150

TCAS System

Honeywell

Major functions of a TCAS II system. It requires aMode S transponder to enable two closing aircraftto communicate and determine which direction tofly (up or down) to avoid a collision. The transpon-der often uses a top and bottom antenna on the air-craft to assure full coverage above and below.

The computer processes large amounts of infor-mation; transponder replies of other aircraft, tar-get tracking, threat assessment, visual and auraladvisories, escape maneuvers and coordinatingmaneuvers between closing aircraft.

Traffic and Resolution AdvisoriesIf a collision is possible, TCAS delivers two kinds

of warnings

•Threat Advisory (TA). This is the less seriousof the two. It means another aircraft might be 45 sec-onds from the closest point of approach (CPA). Thepilot sees the TA on a display (shown in the illustra-tion) and becomes aware of the threat.

•Resolution Advisory (RA) With this warning theconflict is rapidly growing more serious. The threataircraft could now be 30 seconds from closest pointof approach. TCAS issues a Resolution Advisory,which commands the pilot to climb, descend, remainlevel or observe a vertical restriction, as shown.

TCAS I and TCAS IIThere are two versions of TCAS, for large and

small aircraft. The full system, TCAS II, is requiredaboard airliners and large transports with 31 or moreseats. In TCAS II, the full collision logic is providedto generate the two types of warnings; TA (threat advi-

sory) and RA (resolution advisory).

TCAS I is a scaled-down system that issues onlyTA’s (threat advisories). Otherwise, everything is muchthe same as TCAS II; the symbols, warnings and dis-plays. Lower in cost, TCAS I is designed for corpo-rate, business and light aircraft.

The added complexity of TCAS II is in the colli-sion logic for developing the evasive commands, a moreelaborate antenna system, the need for a Mode S tran-sponder and a method of air-to-air communicationknown as “datalink.”

Coordinating Climb and DescendWhen TCAS issues a Resolution Advisory (RA)

it instructs the pilot how to avoid a collision by flyingup or down. Obviously, if both aircraft fly toward eachother and perform the same =escape maneuver (bothfly up, for example) they would collide. This is pre-vented by “coordination interrogations” transmitted byeach aircraft once per second. These are regular tran-sponder signals on 1030 and 1090 MHz, but now usedas a datalink to exchange information between aircraft.

193

Indexing Pins Prevent Error

Different avionic LRU’s (line replaceable units) are often housed in cabinets of the samesize---which could cause installation error. To prevent it, a connector has an indexingpin at an angle that matches only one LRU. Unless all pins line up with connectorholes, the radio cannot be pushed in. To prevent damage, however, avoid forcing aradio into the rack.

ARINC trays are designed with variations to accom-modate different cooling, connector and radio sizes.The black knobs, which lock in the equipment, have amechanism which cannot be overtightened and dam-age the connectors.

Several ARINC trays are often mounted to-gether to form a “rack” (sometimes calledan “equipment cabinet”).

BarryUS Technical

195

Instrument Mounting

Instruments like this 3-inch rectangular are often held by a mounting clamp be-hind the panel. The clamp is slid over the case and two sets of screws areadjusted. Two screws have large heads labelled “Clamp Adjustment”. They tightenthe clamp around the case. The other pair, labelled “Clamp Mounting,” hold theclamp to the back of the instrument panel. Round instruments are installed in similar fashion with a round clamp. How-ever, there are only two screws; one to tighten the clamp on the instrument, theother to hold the clamp to the panel. Some instruments have tapped holes on their cases and need no clamps.Check the manufacturer’s literature on using the correct screws. If too long, theycan penetrate the case and damage the instrument, Instrument screws are often made of brass, especially when mounting a mag-netic compass. As a non-magnetic metal, brass will not cause deviation in thecompass.

Some instrument cases are fitted withmounting studs, as in this DynonEFIS display. Four holes are drilledin the instrument panel according tothe template (below) supplied by themanufacturer. The large hole re-ceives the instrument case.

FRONT

REAR

196

Round Instruments: 2- and 3-inch

Many flight instruments in GeneralAviation mount in round holes. Thetwo main sizes are 2- and 3-inch di-ameters (actually 2-1/4 and 3-1/8-inches). An example of each is shown inthis Mooney panel; a 2-inch chro-nometer and a 3-inch airspeed indi-cator. The instruments are held to thepanel by four screws, as seenaround the instrument face. Thescrews are held behind the panel bythreaded fasteners (“grasshoppernuts”). Because the fasteners areeasily lost during installation, thereare mounting kits like the one shownbelow to simplify the job.

Instrument Mounting Kit

“Nut rings” make the installation job easier.They come instandard 2- and 3-inch sizes. There are two versions ofthe 3-inch; note the one in the center, “ALT/VSI” whichhas a cut-out at the lower right. This allows space for thealtimeter knob after the instrument is installed. ALT is foraltimeter, which has a knob adjusted by the pilot (for ba-rometer setting). VSI (vertical speed indicator) has a smallscrew adjustment for zero’ing the needle.

Edmo

A nut plate is installed by sliding it onto the back of theinstrument. To make it match holes in the panel with holesin the nut plate, the installer inserts an alignment toolthrough one hole, as shown. It’s removed when all holesline up, and mounting screws can be inserted.

239

Chapter 27

A light aircraft that occasionally flies on instru-ments (“light” IFR) typically has these antennas:

Com 1 DMECom 2 GPSVOR ADF Loop/Localizer ADF senseGlideslope Marker BeaconTransponder Emergency Locator

For low IFR (low ceilings, extended flight inclouds) a well-equipped General Aviation airplane mayadd antennas for:

Weather detection (Stormscope)Traffic detection (TCAS I)Datalink for weather (XM radio, WSI)Antenna for emergency handie-talkie

Airliners and corporate aircraft carry most of theabove, plus antennas for:

Weather radarTCAS II (collision avoidance)Satcom (satellite communication)Radar altimeterPassenger telephone and entertainment

Not mentioned above is Loran, a popular naviga-

Antenna Installation

tion system that rapidly declined with the arrival ofGPS. Loran does not cover the world and suffers in-terference from precipitation. Loran, however, is stillaboard many light aircraft---which means there is aneed for replacement antennas. The installation of aLoran antenna is the same as that described for a VHFcom.

In 1971, a system known as Omega providedworld-wide long-range navigation. But with the riseof GPS, Omega lasted only until 1997, when its eightglobal stations were taken off the air. Omega antennaswere difficult to install because the airplane had to be“skin-mapped”---tested all over to find an electrically

Antennas by HR Smith for high-performance aircraft areencased in thermosplastic composite material to resist rainerosion, impact, chemicals and temperature changes.

240

Sensor Systems

Antennas for Airline,Corporate and Military Aircraft

VHF Com, will operateat 100 watts. Has in-ternal duct for hot airde-icing. Used onBoeing, Lockheedand Douglas.

VHF Com with lowprofile. Has filter to pre-vent VHF interference toGPS receiving antenna.

Glideslope antennarated for Cat III (instru-ment) landing. Usedon Gulfstream, Re-gional Jet, others.

UHF com antenna formilitary aircraft covers180-400 MHz. Rated to70,000 ft and 35 G’s

TCAS (collision avoidance)antenna determines directionof target. Arrow shows an-tenna mountng direction.

Directional antennas for TCAD (colli-sion avoidance) system. Mounts ontop and bottom of fuselage.

GPS models may look thesame but some have built inpreamplifiers to overcomelosses in long cable runs

This amplified GPS antennais aboard Boeing aircraft forGPS reception in multimodereceivers.

Satcom antenna for operating inAero-L and Aero-C bands ofINMARSAT satellite. It is a low-gainantenna for moving data on 1.5-1.6GHz.

Outside and underside views of ra-dio altimeter antenna. Operatingon 4200-4400 MHz, it is flush-mounted on belly of aircraft.

Antennas for passenger radiotelephoneservice operating on 830-900 MHz.

VHF-FM com antenna for140-180 MHz (outside theaviation bands). Providescommunications with non-aviation services.

Two different marker beacon anten-nas (75 MHz). Top one is a flush-mount used on the Boeing 747.Bottom one is low-profile, used onthe Boeing 737 and Pilatus.

ADF antenna contains bothloop and sense antennas forautomatic direction finder. Ap-plications include severalBoeing, Douglas and Airbusairliners.

Two blades, known as a “bal-anced loop,” mount on rudderfin to provide VOR, localizer andglideslope reception.

241

quiet place that would not interfere with the Omegasignal.

Hostile environment. Aircraft antennas operateunder the worst conditions. Sitting on the ramp in Ari-zona on a summer day, they bake in over 100 degreesF. After the airplane takes off and reaches altitude 15minutes later, antennas are chilled to 50 degrees Fbelow zero and buffeted by winds over 500 kts. If theairplane flies in clouds at or near the freezing level,ice may form on the antenna. And it’s not the weightof the ice, but the change in antenna shape that causes

How to Read an Antenna Spec Sheet

First, consider the type of aircraft. Catalogs of-ten divide them into such categories as General Avia-tion, Commercial (business jets), air transport (airline)and military. These categories are divided into type ofservice; communications, navigation, transponder,DME and others.

In the example shown here, we are seeking a com-munication antenna for a business jet. Looking downthe list of specifications (see numbers in red);

1. Frequency. The aviation “com” band extendsfrom 118 to 137 MHz. The band is also called “VHF”or “VHF com.”

2. VSWR. Meaning “Voltage Standing Wave Ra-tio,” VSWR indicates antenna efficiency. The lowerthe first number (2), the higher the efficiency. Manu-facturers produce antennas with a VSWR usually lessthan 3.0:1.

3. Polarization. VHF com antennas operate with“vertical” polarization, which helps concentrate sig-nals toward the horizon, rather than angling up to space.

4. Radiation Pattern. “Omnidirectional” sendssignals in every direction, a requirement because theground station may be anywhere.

5. Impedance. The AC electrical load of the an-tenna. 50 ohms is standard in aviation. The cable feed-ing the antenna is also 50 ohms, which produces a cor-rect match to the antenna.

6. Power. The amount of radio-frequency powerthat can be handled by the antenna. Light aircraft trans-mitters generate about 5 to 10 watts. A transmitter foran airliner or business jet may run 25 watts.

7. Connector. Many antenna connectors are the“BNC” (bayonet) type, but be sure the coaxial cable isalso fitted with a BNC connector. TNC is also used.

8. Altitude. Rated to 50,000 feet, this antennacan operate at altitudes flown by a business jet. (Thehighest altitude for air traffic control is 60,000 feet.)

9. Air speed. The antenna can operate at 600knots at 25,000 feet. This is accomplished by the“blade” design, which is stronger than narrow whips

or rods for slower aircraft. Any requirement above 600knots would be for military, or aircraft flying at super-sonic speeds

10,11 Certifications. These ratings mean theantenna will meet environmental and performance stan-dards for this application.

12. BNC The antenna accepts the common BNCconnector used on most coaxial antenna cables.

Comant

“flutter,” a vibration that can break the structure. As ifthat weren’t enough, the antenna is mounted on an alu-minum fuselage which flexes as the airplane pressur-izes. Add such hazards as fluid sprayed on the air-plane for de-icing or hydraulic oil in the belly andyou can see why antennas require rugged constructionand follow-up maintenance.

What goes wrong? Despite the hostile environ-ment, most problems (antenna-makers say) result frompoor installation. Materials used by every reputableantenna maker are tested and well-proven. It’s the

243

Airline Antenna Locations

=

Shown above is a Boeing 737. Antennas divide into threecategories, often known as CNI, for Communication, Navi-gation and Interrogation. Navigation antennas are shownin red, communications in blue. The two interrogationantennas (green) are for ATC, which is the airline term for“transponder.” Most antennas are dual installations because safetyrequires two or more radios for each function. Where pos-sible, they are placed at top and bottom of the fuselage forgreatest reliability. The two radar altimeters must be at the bottom becausethey measure the few feet between the airplane belly andrunway during a low-visibility landing (Category 2 ILS and

higher). In the nose are three antennas protected againstweather by a plastic radome. The glideslope antenna insmall aircraft is usually on the tail (as part of the VOR an-tenna). In large aircraft, however, the glideslope antennais usually in the nose. During an approach, large aircraftpitch up at a high angle of attack, which could cause itswings and fuselage to block glideslope signals arrivingfrom the ground. Putting the glideslope in the nose elimi-nates that problem. New airline models add several more antennas; GPSfor navigation and satellite (for voice and data).

installer’s responsibility to provide a good location, asecure mounting, a seal against weather and a low-resistance electrical ground to the airframe---all fac-tors covered in this chapter.

Selecting an AntennaCatalogs on antennas are filled with engineering

terms; isotropic radiator, dB gain, VSWR, impedance,and more. It is not difficult, however, to choose theright antenna for the job, so long as you select a modelfrom a reputable antenna manufacturer---for example,Comant, Dorne & Margolin, Sensor Systems, RAMIand HR Smith---the antenna should perform as de-scribed for its category (airline, military, general avia-

tion, etc.). An explanation of important antenna termsis shown in the table.

An antenna with a “TSO” (Technical StandardOrder) assures the antenna was tested to the limit ofits specifications. The TSO is not a legal requirementfor many installations, but antenna makers obtain thiscertification as a mark of quality. Business and airlineoperators usually require it.

Major specifications to know are shown in thetable, “How to Read an Antenna Spec Sheet.” Con-sider other details in selecting an antenna:

Speed. A dividing line between antennas dependson the speed of the aircraft. For General Aviation look

261

Chapter 29

Test and Troubleshooting

The first step in troubleshooting an avionics prob-lem is when the pilot describes the complaint to thetechnician, or fills out a squawk sheet. The quality ofthese reports often means the difference between aquick fix or wasted hours looking for trouble.

The typical pilot squawk is often brief, such as“My number 1 com doesn’t work.” This gives fewclues and is only the starting point to ask questions tonarrow the problem. The pilot knows much more thanhe thinks---if the technician asks well-placed questions.

Here are suggestions to make the diagnosis gofaster. Frame your questions to learn the conditions sur-rounding the failure (we’ll use the com as an example):

Does the problem affect both transmit and receive?Does the problem happen in all directions?Does it occur over both high and low terrain?If there are two navcoms, are both transmitters

affected?Is communicating distance affected by the

weather?Is the problem worse during taxi and takeoff, then

improves while cruising? Have you tried a different microphone? When was the most recent repair to any avionics

equipment?Answers to specific questions like these can nar-

row down the faulty area.

Technical TermsBe certain you and the pilot are talking about the

same thing. For example, one pilot said “My speakerdoesn’t work,”---but pointed to his microphone. To

TCAS Ramp Testing

Tests to verify and certify a TCAS (Traffic Alert and Colli-sion Avoidance System) can be done outside the airplane.The ramp tester, an IFR Systems TCAS-201, communicateswith the airplane via radio signals and simulates differentcollision conditions. Without connecting directly into air-plane systems it measures signal power, frequency, inter-rogations and replies. The tester is programmable to per-form ten different collision scenarios.

276

IndexAACARS 41

bands and frequencies 45cockpit display 41message format 43messages 43OOOI 42system 42

ADF (Automatic Direction Finder) 81broadcast stations 85coastal effect 86compass card, fixed 81control-display, airline 84digital ADF receiver 85display, EFIS 86loop 82NDB station 83night effect 86quadrantal error 86receiver, airline LRU 84receiver, analog 82RMI (Radio Magnetic Indicator) 82sense 82system diagram 83

Aircraft earth station 35Airways, lighted 11altitude reporting: mode C 100Antenna Installation 239

ADF 246airline antenna locations 243altitude 244antenna types 240, 244antennas for light aircraft 242base station, mobile 252bonding 248

to airframe 249coaxial cable 250combination antenna 253connectors 251couplers 251doubler plate 247duplexers 251gaskets 250GPS antennas 251HF (high frequency) 245hidden structure 246high-performance antennas 239hostile environment 241location 245mark and drill 248mounting 249selecting an antenna 243spec sheet, how to read 241typical antennas 239VOR blade 245

ARINC 183structures 183

Aviation Bands and Frequencies 230control and display 236frequency assignments 237future bands 234ground wave transmission 238hertz to gigahertz 234high frequencies 233Higher bands 232L-band 234line-of-sight 235microwave 235Radio frequencies (RF) 230radio signal 230skipping through ionosphere 233vhf band 234

Avionicsdefinition of 1

Avionics master switch 173

BBarany chair 7Beam steering unit (BSU) 35Bell, Alexander Graham 9Blind flying

first flight 2

CCalibration 264Cell Phones 33Channels

splitting 16Clear air turbulence (CAT) 136CNS: Communication, Navigation,Surveillance 4Cockpit Voice and Flight Data Record-ers 129

cable assembly 133cockpit area mike 130, 131CVR basics 129CVR channels 130Flight data recorder 133

parameters 135solid state 134

flight data recorders 131inertial switch 130interconnect, CVR 132LRU: line replaceable unit 130tape drive 132temperature test 130underwater locating device 131

tester 132Connectors 199

Amphenol 206application 201crimp tool 206crimping 202d-subminiature 206heat gun 207how to identify contacts 201Molex 206radio frequency 200reading pin connections 199releasing pins 207

safety wiring 208solder cups 206soldering 202trends 202typical 200

Cooling 186

DDME (Distance Measuring Equip-ment) 88

airborne system diagram 91chanelling 88, 90EFIS display 90ground speed 88ground station 91jitter 89, 90obtaining distance 89pulse spacing 92reply frequencies 92scanning and agile 89slant range 89X and Y channels 92

EEFIS: electronic flight instrumentsystem 120

Airbus A-320 127archictecture 124electromechanical to EFIS 122flight deck 120glass cockpit 120MFD: multifunction display 125on B-747-400 126pictorial display 121replacing old instruments 121three-screen 123

Electrical Systems 168115 volt system 17028 volt DC 170AC and DC power 168APU (Auxiliary Power Unit) 170battery charge, percentage 168circuit breakers 173

recessed button 176DC system 169fuses 176ram air turbine (RATS) 172switches 172

avionics master 173llighted pushbutton 175pushbutton 174switch guards 175types 173

Electrostatic discharge 185ELT 50ELT (Emergency Locator Transmitter

406 MHz ELT 51406 system 53components 52controls and connections 54Cospas-Sarsat satellites 51, 55direction of fllight 50dongle 54

277

fleet operation 54ground stations 51Leosars, Geosars 52registration 53, 55

ELT (Emergency Locator Transmitter)266

test in aircraft 266

GGalileo 118Glideslope 73GPS/Satnav (Satellite Navigation) 108

clock 110constellation 109EGNOS 116frequencies 110Galileo 118GNSS 111LAAS: local area augmentation

system 116ground station 117

launch vehicle 109LNAV-RNAV 116LPV 116multimode receiver 117position finding 112PPS: precise positioning service 112PRN code 112propagation corrections 112RAIM: receiver autonomous integrity

monitoring 117SA: selective availability 111satellite signal 113satellite, typical 108SBAS 116second civil frequency 116segments 114space segment 109SPS: standard positioning service 112WAAS: wide area augmentation

system 114system 115

Ground earth station 34

HHertz, Heinrich 9HF (High Frequency)

antenna coupler 27antenna mounting 27control panel 26control-display 23datalink 25, 26LRU (line replaceable unit) 25SSB (single sideband) 24system diagram 24transceiver 26

HSI (Horiz. Situation Indicator) 64

IILS (Instrument Landing System) 67

90 Hz, 150 Hz audio tones 71approach lighting system 69categories 68

Category I 69Category II 69Category III 69compass locator 72components 68decision height 68glideslope 70glideslope indications 72glideslope, pictorial 72glideslope receiver 73glideslope station 73localizer 70localizer array 70localizer indications 71marker beacon 72marker beacon ground station 74marker beacon receiver 74RVR (Runway Visual Range) 68system; pictorial view 68

Inmarsat Aero System 31Instrument panel

first 2interference 85

LLightning detection 140Lindbergh, Charles 2Low frequencies 232

MMarconi, G 6Marker beacon receiver 74MLS: Microwave Landing System 76

azimuth beam, diagram 77elevation antenna 78elevation beam 78multimode receiver 79space shuttle 76time reference scanning beam 79transmitting azimuth signal 77

Morse, Samuel 9Mounting avionics 178

airline mounting 191ARINC structures 183ATR case sizes (ARINC 404) 184avionics bay, corporate jet 182Case sizes, MCU (ARINC) 183cooling 186

airline 187fans 187

cutting holes 180electrostatic discharge 185indexing pins 193instruments 195instruments, airline 197integrated modular avionics (IMA)

194locking radios in racks 188locking systems, airline 192new or old installation 179panel-mounted radios 188rack, equipment cabinet 193radio stack 181

releasing radio 188remote-mountiing, corporate 190round iinstruments 196structures 181tray 190tray preparation 189

Multimode receiver 117

NNDB (Non-Directional Beacon) 83

PPanel labels and abbreviations 254

abbreviations 256engraving 254preprinted 254silk screen 254tape 254terms on labels 254

Planning the Installation 154:"steam gauges" 1554-inch EFIS 155basic T instrument layout 157connectors and pin numbers 162EFIS, turbine aircraft 158flat panel 159grounds 164installation drawings 161instruments and radios 156manuals and diagrams 161navcom connections, typical 166non-certified airplanes 154pin assignments 163schematic symbols 163schematics 162STC: Supplemental Type Certificate

154TC: Type Certificate 154type of flying 155typical avionics equippage 160viewing angle 165wiring diagram, reading 163

RRadar Altimeter 104

altitude trips 107antennas 105carrier wave 106components 105decision height 105display 104display, analog 107gear warning 107operation 106

Radio management system 21RAIM: receiver autonomous integritymonitoring 117RMI (Radio Magnetic Indicator)64, 82

SSatcom (Satellite Communications)

aircraft earth station 30, 35antennas 30

278

conformal 31, 37high gain 30, 31, 36intermediate gain 33low gain 30

beam steering unit (BSU) 35data system 38ground earth station 29, 34Inmarsat 29Inmarsat Aero System 39radio frequency unit 35satellite data unit (SDU) 35space segment 32

Selcalairborne system 48codes 47, 48controller 46decoder 46ground network 47

silk screen 254Sperry, Elmer 7SSB (single sideband) 24Swift64 33

TTCAS (Traffic Alert Collision Avoid-ance System 147

basic operation 148components 151coordinating climb and descent 150directional interrogation 151non-TCAS airplanes 152RA: Resolution Advisory 150, 152Symbols on radar display 148TA: Threat Advisory 150, 152tau 149TCAS I, TCAS II 150TCAS III 152voice warnings 152whisper-shout 151

Terminals 219block 219ring 219

Test and Troubleshooting 261ADF antenna 262air data test set 265antennas 263

doubler 263rf wattmeter 264

audio quality 263automatic test station 265autopilot 264

cable tension 264porpoising 264

checklist 274coaxial cable 263com transceiver 264

no receive 264no transmit 265squelch 264

enclosures 270fault detection device 271glideslope 269glideslope receiver 266

ILS (Cat III) tester 267in-flight interference 263lightning strike 266loading software 267

dataloader 268navcom ramp tester 272P (precipitation) static 273

static wicks 273Portable maintenance aid 272reporting trouble 261RF signal generator 266selective call 262servo 263switchology 262TCAS ramp test 261technical terms 261transponder 267VOR checkpoint 268VOR receiver 268

course bends 269VOR test facility (VOT) 268VSWR 263wiring and connectors 270

Transponder 94aircraft address 98ATCRBS and Mode S 95code selection 101control-display 94control-display (airline) 98ID code 101interrogator, ground 95LRU (line replaceable unit) 98mode A interrogation 99mode C interrogation 99mode S 96mode S: all call 102mode S: interrogations and replies

102mode S: selective address 102panel-mounted 96reserved codes 101squawk 94System diagram 97

Turn and Bank 8

VVDR: VHF Data Radio 16VHF Com 16

acceptable radios 17basic connections 18control panel 20line replaceable unit 20radio management system 21splitting channels 21system diagram 19

VOR 57course indicator 63coverage 58HSI (Horizontal Situation Indicator)

64Nav control-display 65navigation 63principles 59

receiver diagram 62reference and variable phase 61RMI (Radio Magnetic Indicator) 64service volume 58signal components 59signal structure 60VOR-DME station 57

WWeather detection 136

clear air turbulence 136datalink 141, 145lightning detection 140sensors 138Stormscope 141, 143weather radar

color coding display 137control panel 140radome 142receiver-transmitter 139system components 139thunderstorms 138, 139

windshear 143computer 144

Weather radar 137antenna 141

Wind shear 143Wiring the Airplane 210

Adel clamp 222bending coaxial cable 228chafing and abrasion 224clamping 223, 226conduit 225corrosive chemicals 225ducts 225electromagnetic interference 222grounding 227Harnessing 222high grade wire 213high risk area 211high temperature 225intervals 220lacing 223length 216marking 220methods 221moisture 225nicked and broken wires 217precut 217PVC 212selecting 213service loops 229splicing 217

knife 218location of splices 218

stranded vs. solid 216stripping 216SWAMP area 210tie wraps (cable ties) 223wire and cable types 215

Wright Brothers 1, 6