aircraft radio navigation communication systems

Air Waves in Aviation

Radio transmission is an electromagnetic wave with the same characteristics as light or heat.

Wavelength is the linear measurement of the wave.

Cycle is the interval in which the wave rises and falls between its crest and trough.

Frequency is the number of cycles/second.

Amplitude is the strength of the signal.

3 kHz to 30 kHz Very Low Frequencies (VLF)

30 kHz to 300 kHz Low Frequencies (LF)

300 kHz to 3,000 kHz Medium Frequencies (MF)

3,000 kHz to 30,000 kHz High Frequencies (HF)

30,000 kHz to 300,000 kHz Very High Frequencies (VHF)

300,000 kHz to 3,000,000 kHz Ultra High Frequencies (UHF)

RADIO FREQUENCY BANDS

T3-6

Propagation: How Signals Travel Propagation On The HF Bands

Ground-wave Propagation Sky-wave Propagation HF Scatter Propagation

VHF/UHF Propagation Characteristics Line-of-sight Propagation Tropospheric Bending and Ducting VHF/UHF Signals Through The Ionosphere

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Radio waves travel to their destination in four ways:

1. Line of Sight Directly from one point to another.

2. Ground-Wave Along the ground, bending slightly to follow the

Earth’s curvature.3. Tropospheric Bending and Ducting

In the lower layer of the Earth’s atmosphere.4. Sky-Wave

Refracted or bent back to the Earth’s surface by ionized layers in the ionosphere.

Both the VHF and HF system utilize transmitters, receivers and antennas. Transceivers are units that include both the transmitter

and receiver in one unit. VHF and HF systems are completely independent of each

other and utilize their own transmitters, receivers and antennas.

VHF systems are found in any aircraft capable of two way radio communication and are largely used for controlling traffic.

HF systems are found in large transport category aircraft that may need to communicate over large distances (overseas).

References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

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Line Of Sight (LOS) Tropospheric Bending Tropospheric Ducting VHF/UHF Signals Through The Ionosphere

Sporadic “E”

Anytime radio waves are used to follow a path over the ground.

Types VORs NDB/ADF GPS

Uses Guidance during times of reduced

visibility Establish orientation Enhance Situational Awareness

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Region Height

Notes

Troposphere

7 miles Region where all weather occurs

Stratosphere

6 to 30 miles

Region where atmospheric gases “spread out” horizontally. The high speed jet stream travels in the stratosphere.

Ionosphere 30 to 400 miles

Region where solar radiation from the sun creates ions. Major influence on HF radio wave propagation.

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Ground-Wave Propagation Sky-wave Propagation HF Scatter Mode

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Results from a radio wave diffraction along the Earth’s surface.

Primarily affects longer wavelength radio waves that have vertical polarization (electric field is oriented vertically).

Most noticeable on AM broadcast band and the 160 meter and 80 meter amateur bands.

Communication distances often extend to 120 miles or more.

Most useful during the day at 1.8 MHz and 3.5 MHz when the D-Region absorption makes sky-wave propagation impossible.

T3-19

The curved surface of the Earth horizon can diffract long-wavelength(low frequency) radio waves. The waves can follow the curvature of theEarth for as much as several hundred miles.

T3-20

Ionization levels in the Earth’s ionosphere can refract (bend) radio waves to return to the surface. Ions in the Earth’s upper atmosphere are formed when

ultraviolet (UV) radiation and other radiation from the sun knocks electrons from gas atoms.

The ionization regions in the Earth’s ionosphere is affected the sunspots on the sun’s surface. The sunspots vary in number and size over a 11 year cycle.

Sky-wave propagation is determined by radio wave frequency and level of ionization in the ionosphere.

T3-21

Communication distances of 2500 miles are possible with one skip off the ionosphere. Skip propagation has both minimum and

maximum ranges. The area between the maximum ground wave

distance and the minimum skip distance is called the skip zone.

World-wide communications is possible using several skips (or multi-hops)

The highest frequency that a radio wave transmitted straight up is reflected back to Earth is called the critical frequency.

T3-22

The maximum usable frequency (MUF) is the highest frequency at which the ionosphere bends radio waves back to a desired location on earth. MUF is dependant on level of solar

radiation strength and time of day. The maximum usable frequency (MUF)

tends to be higher during periods of high sunspots.

T3-24

The Earth’s ionosphere contains several regions of charged particles which affect radio signal propagation.

The ionization regions change from day to night periods. Region Height Above Surface

D Region 30-60 miles

E Region 60-70 miles

F Region 100-310 miles

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D Region Height about 35 to 60 miles above Earth. Maximum ionization at or near noon. Ionization disappears by sunset. Absorbs energy from radio waves. Absorption on

lower frequencies is greater than higher frequencies.

Radio wave absorption is most pronounced at mid-day.

Responsible for short daytime communication ranges on lower-frequency HF bands (160, 80 and 40 meters).

T3-26

E Region Height about 50 to 70 miles above Earth. Ionization useful for bending radio waves

when in sunlight. Reaches maximum ionization level

around mid-day. Ionization reaches a minimum level just

prior to sunrise. Radio wave propagation up to about 1250

miles in a single skip hop.

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F Region Height ranges from 100 to 310 miles above Earth. Ionization reaches a maximum about noon and

tapers off gradually toward sunset. Minimum ionization is reached just prior to sunrise.

F region splits into two parts (F1 and F2) during the day and recombine at night.▪ F1 region forms about 140 miles above Earth▪ F2 region forms about 200 miles above Earth

F2 region is responsible for long distance HF band communication with distances of about 2500 miles.

T3-28

All electromagnetic wave propagation is subject to scattering influences from the Earth’s atmosphere, ionospheric regions and objects in radio path.

Scattered signals may be received in sky-wave propagation skip zone.

Scatter signals are generally weak and subject to echoes and distortion.

Most common when operating near the MUF. Under ideal conditions, scatter propagation

is possible over 3000 miles or more.

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Back Scatter Propagation

T3-30

Radio signals travel in a straight line from a transmitting antenna to the receiving antenna.

Provides VHF/UHF communications within a 100 miles or so.

Signals can be reflected by buildings, hills, airplanes, etc.

Reflections vary the propagation path causing signal cancellation and reinforcement. This results in a rapid fluttering sound called picket fencing.

T3-32

Slight bending of radio waves occur in the troposphere close to the Earth’s surface. There is always a radio signal loss as radio

waves travel through the troposphere▪ Radio signal loss increases as the frequency increases

The radio path horizon is generally 15 percent farther away than the visible horizon (typically 8 to 9 miles).▪ Communication distances can be increased by

increasing the antenna height above the terrain

Tropospheric bending propagation is most useful at 144 Mhz and higher frequencies

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The farthest point to which radio waves will travel directly.

The structure of the atmosphere near the Earth’s surface causes the radio waves to bend in a curved path.

The radio horizon exceeds the geometric horizon by approximately 15%.

T3-34

The distance D to the radio horizon is greater from a higherantenna. The maximum distance over which two stations maycommunicate by space wave is equal to the sum of theirdistances to the horizon.

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0.05.0

10.015.020.025.030.035.040.045.050.0

1.0 10.0 100.0 1000.0

Height(ft)

Dis

tanc

e(m

iles)

Chart shows theoretical communication distance (in miles) to the radio horizon for various transmitter antenna heights above terrain (in feet).

HxD 415.1

T3-36

Radio signals can also be trapped in the troposphere, traveling a long distance before returning to the Earth’s surface.

Results when a “duct” is formed by a temperature inversion level (warm air over cold air) over land or water. Adjacent tropospheric regions having different

densities will bend radio waves passing through the regions

Most useful at VHF/UHF frequencies. Most frequent during spring, summer and fall. Can provide contacts of 950 miles or more

over land and up to 2500 miles over ocean

T3-37

When a cool air mass is overrun by a mass of warmer air, a “duct” may be formed, allowing VHF and UHF radio signals to travel great distances with little attenuation or signal loss.

T3-38

Sporadic E A type of sky-wave propagation that allows long

distance communication on the VHF bands (6 meters, 2 meters and 220 Mhz) through the E region of the atmosphere.

Occurs only sporadically during certain times of the year.

Most common type of VHF atmospheric propagation.

The 6 meter band is most likely experience sporadic-E propagation during the summer months ... even during periods of low sunspot activity.

VHFHFACARS / AIRCOMSecal decodersSATCOM


Two types commonly used for communication: VHF

▪ VHF (very high frequency) is used by air traffic control and operates in the VHF band between 118 and 136.975 MHz

▪ Range is 30 miles at 1000 feet and approximately 135 miles at 10,000 feet

HF▪ HF (high frequency) used for extended

range communication operates between 2.0 and 29.999 MHz


Transmits short messages from aircraft systems to central facility in Chicago

Two modes used Demand mode – Flight crew transmits Polled mode – Ground station transmits

Note: AIRCOM is the European and Australian equivalent


Used to “filter” messages on COMM radio receivers

Aircraft are assigned a tone combination for secal unit to monitor.

Secal unit alerts the crew to an incoming radio transmission


Utilizes satellites for transcontinental flight communications

More reliable the HF communication Range is between latitudes 75º N and 75º S Uses three sub-systems

Ground earth station Aircraft earth station Satellite system

Capable of of transmitting information from many different sources AIRCOM, ACARS, flight-crew communications, passenger

telephone, telex and fax


NDB/ADF

Ground Equipment– NDB: Non – Directional Beacon

• Refers to the actual station of ground

Airborne Equipment– ADF: Automatic Direction Finder

• Refers to instrument found in the airplane

Nondirectional Radio Beacon (NDB) Transmits same signal in all directions

Directional/Loop Antenna Rotates to find the most powerful signal

Sense Antenna Receives equal signal throughout

System uses both antennas to figure out where you are in relation to the station

ADF Receives NDB Signals in (190-535)kHz AM Broadcast Low Band

Relative Bearing What is read from the Indicator Degrees from nose of aircraft to the station

Magnetic Heading What is read from the Heading Indicator Degrees from North to nose of aircraft

Magnetic Bearing Where you are in relation to the station Degrees from north to the station

RB + MH = MB

53

Tracking Tracking InboundInboundTracking Tracking InboundInbound

010

Wind

000

350

010

350

Wind

54

Tracking Tracking OutboundOutboundTracking Tracking

OutboundOutbound

350

000

340

340

015

Wind Wind

55

Navigation ProceduresNavigation Procedures

• Homing– Keep the nose of the aircraft always

pointing to the station– Needle always be aligned– Does not take into account wind

WHEATON 326 ETH

1. Where is the station in relation to me?

look at the ADF needle - Relative bearing

2. What direction am I going? look at heading indicator - Magnetic

heading

1. Where is the station in relation to me?

look at the ADF needle - Relative bearing

2. What direction am I going? look at heading indicator - Magnetic

heading

3. Where am I in relation to the station?

North, South, East, or West?

4. What course would I fly to get to the station?

3. Where am I in relation to the station?

North, South, East, or West?

4. What course would I fly to get to the station?

Homing Keep the nose of the aircraft always

pointing to the station Needle always be aligned Does not take into account wind

Ground EquipmentAirborne EquipmentPrinciple : Bearing measurement

by “PHASE DIFFERENCE”

Very High Frequency Range 108.0-117.95

Transmits two signals Reference Phase

▪ Same all the way around Variable Phase

▪ Rotates at 1800 RPM Measures Phase Difference

360 different radials, that can each be flown in 2 directions

Is not heading sensitive

Altitude Class of facility Terrain

off flag appears Morse Code no longer heard Inoperative CDI

Corrective Actions ADF GPS Radar vectors (flight assist)

Omnibearing Selector (OBS)Course Deviation Indicator (CDI)To-From Indicator

Parts of a VOR systemParts of a VOR systemParts of a VOR systemParts of a VOR systemReceiver

Course Deviation Indicator (CDI)

To/From ind.

Receiver

Course Deviation Indicator (CDI)

To/From ind.

Omni bearing selector


KX 155 TSO COMM NAV

118.00 136.97 USE STBY

108.00 117.95

BENDEX / KING

PULL TEST OFF

PULL IDENT

USE STBY

•VHF ANTENNA

•VHF RECEIVER

Identifying the Station Interpreting the VOR Indications Reverse Sensing Off Indications Tracking Intercepting a Course Cross Checking Position

Must do prior to using the VOR Ensure correct station is selected Ensure station is working

Morse code identification

Turn the OBS so that the CDI is aligned Make sure that it has a FROM indication Draw out where you are in relation to the

station

090

KING

OBS

0

90180

270

30

60120

160210

240

300

330

KING

OBS

0

90180

270

30

60120

160210

240

300

330

Selected Course:360o

From Envelope

OFF OFF

To Envelope

Selected Course

Crossbar

OFF

FROM

FROM

OFF

TO

TO TO

TFROM

VHF OmnirangeVHF OmnirangeVHF OmnirangeVHF Omnirange

Where are you in relation to the station?

KING

OBS

0

90

180

270

30

60120

160210

240

300

330 0

Where are you in relation to the station?

KING

OBS

0

90

180

270

30

60120

160210

240

300

330180

If wrong course is set in… Needle will move farther away when

correcting Make sure that OBS course matches

Aircraft Heading If you want to head TO the station line

up TO indication If you want to head FROM the station

line up FROM Indication

Reasons for OFF indications Cone of Confusion Out of Range/Unreliable 90° from selected course

KING

OBS

0

90

180

27

0

30

60120

160210

240

300

330

KING

OBS

0

90

180

27

0

30

60120

160210

240

300

330

Cone of Confusion Zone of Ambiguity

Only "B" signal

received

Only "A" signal

received

"A" and "B" signal

received

Neither "A" or "B" received

VOR station "A"

VOR station "B"

Fly from one point to the other keeping the CDI centered

Bracket by keeping a stabilized crosswind correction

Draw out which way you need to turn to intercept

Turn to heading and set OBS to desired radial

Track inbound on new radial

Use two VORs to find your exact position Center both VORs with a from

indication Draw out the radials Where they cross is where you are at

Advantages Concise form of

Navigation Easy to interpret

position Not heading

sensitive Provides multiple

courses TO/FROM the station

Limitations Line of Sight Range

Advantages Not limited to

Line of Sight Simple form of

Navigation

Limitations Errors

▪ Quadrantal error▪ Night effect▪ Terrain effect▪ Precipitation static

Heading sensitive

Combination of several systems to provide pilot with the ability to land in conditions with poor visibility.

Localizer – indicates alignment w/ runway

Glideslope – indicates correct descent path

Outer Marker – Final Approach Fix

Middle Marker – Missed Approach Point

Needle indicates direction of runway.

Centered Needle = Correct Alignment

Needle indicates above/below glidepath.

Centered Needle = Correct Glidepath

Runway

Correct Glidepath

Descent Cone

OM – Denotes beginning of final approach segment (Final Approach Fix).

MM – Denotes Missed Approach Point (MAP) Usually placed at decision height on

glidepath. “If you can’t see the runway yet, go

around.”

Represented by indicator lights with accompanying aural tone in cockpit.

When glideslope is unavailable, pilots may still make a localizer-only approach.

VORADFILSLOCGSMarker

beacons

Radio altimeters

DMEGPSTranspondersELT


VOR’s operate between 108.0 to 117.9 MHz frequency band

System includes VOR ground station or transmitter VOR receiver in aircraft

▪ In light aircraft this is often combined with the comm radio

Aircraft display ▪ CDI course deviation indicator▪ TO/FROM indicator▪ OBS omni-bearing selector or course selector▪ ON/OFF flag to determine field strength

Antenna


VOR station continually transmits an infinite number of radials.

The VOR receiver in the aircraft receives the signal and operates the visual indicator.

The pilot determines the bearings of VOR station with respect to the aircraft.


Operation The ADF receives NDB (non-directional

beacon) signals in the 19 to 535 kHz AM broadcast low band.

The ADF display pointer (RMI or radio magnetic indicator) will indicate the relative bearing to the selected AM band in that range.


Combination of several systems to provide pilot with the ability to land in conditions with poor visibility.

Components LOC (localizer)

▪ Horizontal reference GS (glide slope)

▪ Vertical reference Marker beacon

▪ Distance from runway Radio altimeter

▪ Very accurate altitude measurement DME (distance measuring equipment)

▪ Very accurate distance measurement


Combined with the VOR system Utilizes 1 of 40 ILS channels between

108.10 to 111.95 MHz. Operation

The ground transmitter is located at the far end of the runway and provides a valid signal up to 18 NM

The CDI (course deviation indicator) gives full fly left/right deviation of 700 feet at the runway threshold.


Utilizes 1 of 40 channels between 329.15 to 335.00 MHz.

Operates on the same principles as the LOC. The GS transmitter is located between 750 and

1250 ft. from the approach end of the runway and is offset 250 to 650 ft.

The indicator is either an ADI (attitude-director indicator) or HSI (horizontal-situation indicator).▪ Both indicators combine other indications for ease of

use.


Marker beacon receivers operate at 75 MHz and sense the audio signature of 3 types of beacons. Blue outer marker (5 miles from end of runway)

▪ Modulated with 400 Hz Amber middle marker (2/3 mile from end of runway)

▪ Modulated with 1300 Hz White inner marker (1500 feet from end of runway)

▪ Modulated with 3000 Hz Operation

As the aircraft flies over each maker the appropriate light will flash and an audible sound may be heard.


The radio altimeter provides better accuracy then the pressure sensitive altimeters.

Operation The transmitter sends out a VHF signal

downward then receives the reflected signal. The transmitter-receiver unit calculates the

time needed for the signal to transmit and return to obtain AGL (above ground level) altitude.

DH (decision height) used for instrument landings may be incorporated in this system.


Range is up to 199 NM at the high end of controlled airspace based on line of sight with accuracy of ½ mile or 3% of the distance.

DME operates on frequencies from 962 to 1213 MHz.

Operation The aircraft transmitter sends out paired pulses at

specific spacing. The ground station receives the pulses and then

responds with paired pulses at the same spacing but a different frequency.

The aircraft receiver measures the time it takes to transmit and receive the signal which is transmitted into distance.


Utilizes a 24 hour satellite system that is accurate within 100 meters and is unaffected by weather.

Has 3 independent segments Space segment – satellites Control segment – ground based monitoring User segment – aircraft

Database updating and antenna maintenance are the primary concerns to the GPS user.

Will be the most widely used system in the near future.


An automatic receiver and transmitter that can receive a signal (be interrogated) from a ground station and send a reply back to the station.

Used to identify aircraft on radar Identification or squawk is 1200 for VFR flight Squawk assigned by ATC for IFR flight Used for emergency transmissions


Three modes of operation Mode A

▪ Location only, non-altitude reporting Mode C

▪ Location and altitude reporting Mode S

▪ Can do Mode A and C and also responds to TCAS (traffic collision avoidance systems)


Required on all aircraft to provide a signal on crash landings that will enable search aircraft or ground stations to locate the aircraft.

Consists of a dual frequency radio transmitter and battery power supply with a whip antenna.

Transmits on international distress signals of 121.5 (civil) and 243.0 (military) MHz. Activated by impacts of 5g or more or manually. Transmits up to 100 miles at receiver altitude of 10,000

ft for 50 continuous hours. Located in an area of the aircraft where impact

damage will be minimal. Tail cone area Aft top of cabin


Three switch positions: AUTO, OFF and ON Testing may be done under the following

conditions: Tune VHF COMM receiver to 121.5 MHz Only within the first 5 minutes of an hour Only three pulses should be activated Listen for an audible signal when switched to

ON position


The battery pack must be changed in accordance with the date stamped on the unit.

The battery pack must also be replaced or recharged when it has been in use for more than one cumulative hour, or when 50% of the useful life or charge has expired.

Testing should be performed regularly. Inspections must be made every 12 calendar

months. Regulations FAR Part 91.52


System inspections Antenna inspections Static discharge inspections Operational checks or any additional

inspections required by the manufacturer


Inspect the condition and security of equipment including wiring bundles.

Check for any indications of overheating in the equipment or wiring.

Check for poor electrical bonding Requirements are specified by the manufacturer. Cables should be kept as short as possible, except

antenna cable which have a specific length determined in installation.

Proper bonding on the order of .003 ohms is important to the performance of avionics equipment.


Check instruments and radios for secure attachment to the instrument panel.

Check that all avionics are free of dust or contaminates.

Equipment ventilation openings must not be obstructed.

Check all plugs, connectors, switches, controls for operation and condition.


Check all instruments for placards as needed.

Check all instrument lighting and annunciator lights for operation.

Check circuit breaker panel for placards labeling each circuit breaker installed.


Check for:

broken or missing antenna insulation

lead through insulators

Safety wires

Cracked antenna housing

Missing or poor sealant at base of antenna


Check for:

Correct installation

Signs of corrosion

Condition of paint/bonding and grounding

Bonding of each antenna from mounting base to the aircraft skin.

▪ Tolerance 1 ohm, maximumReferences: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

Check for: Physical security of mounting

attachments, wear or abrasion of wicks, missing wicks, etc.

Assurance that one inch of the inner braid of flexible vinyl cover wicks extends beyond the vinyl covering.

Assurance that all dischargers are present and securely mounted to their base.


Check for: Assurance that all bases are securely

bonded to the skin of the aircraft. Any sign of excessive corrosion or

deterioration of the discharger tip. Any lighting damage shown by pitting

of the metal base. The ohm value of the static wick itself

per manufacturer’s instructions.


Transponder Per FAR 14 Part 91.411 and 91.413

ELT Per FAR Part 91.52

Functional checks of all other COMM and NAV systems per the manufacturer’s instructions


Ground station oriented to magnetic north, transmitting directional information to aircraft

Benefits More accurate, precise flying Reliable Not susceptible to interference Voice Capable

Errors/Negatives Costly to maintain Line-of-sight

Omnidirectional reference signal

Directional signal from antenna rotating @ 1800 rpm

Receiver uses phase discrimination

Navigation in polar coordinates (rho-theta)

Distance Measuring Equipment (DME) & often Tacan are colocated with VOR

Distance Measuring Equipment (DME) & often Tacan are colocated with VOR

VHF – 108.0-117.95mhz Line of sight

1 LOP at a time 2 receivers give 2 LOPs (fix) VOR + DME = LOP & Arc (fix)

Not sensitive to aircraft heading Fly to or from a VOR or intercept a radial

Radial – courses oriented FROM the station

High 1,000 – 14,500; 40NM 14,500 – 18,000; 100NM 18,000 – 45,000; 130NM 45,000 – 60,000; 100NM

Low 1,000 – 18,000; 40NM

Terminal 1,000 – 12,000; 25NM

* All altitudes AGL

090

045

135

180

225

270

315

360

VOR receiver gives 1 LOP called a RadialVOR receiver gives 1 LOP called a Radial

Magnetic North

135º

ReceiverCourse

Deviation Indicator (CDI)

To/From ind.

ReceiverCourse

Deviation Indicator (CDI)

To/From ind.



Initial Tracking Tune, Identify, Twist Turn OBS to center needle and figure out

position (use FROM) Note heading on top of card

▪ If flying FROM station (radial), then turn to that heading

▪ If flying TO station, put reciprocal heading on top and center, then turn to that heading

Wind Correction Further away, more correction is needed

to get back on track▪ At 60NM from station, 1° = 1NM

Generally, when within 20NM, 20-30° in direction of needle works

Once needle centers, turn back towards original heading, but add wind correction of 5°

Station Passage CDI will become very sensitive, and then

begin to oscillate Flag will switch from TO/OFF/FROM

Switching Radials During station passage, turn OBS to new

course to fly

Intercepting If needle is alive, then turn towards it as if you

were tracking it If full deflection, first center needle to find what

radial you are on Twist OBS back to desired course Parallel that course Turn 30-60 in direction of needle, depending on

distance from station Once needle is alive, turn back in direction of

desired course Follow tracking procedures

Radio signal sent out from aircraft to ground station. Ground station interprets this signal and sends back. Equipment in aircraft measures time and converts to nautical miles.

Errors Diagonal (slant-line) distance from station to

aircraft – not lateral▪ Becomes greater the closer you get to the station▪ Greatest when directly over station at high altitudes▪ Limited number of queries

Uses▪ Intersections/Fixes▪ IAP▪ Groundspeed

Pilotage Dead Reckoning Radio Navigation

ADF VOR/DME/RNAV

Electronic Navigation Loran GPS Inertial

Celestial

Generic name for a system that permits point-to-point flight Onboard computer that computes a

position, track, and groundspeed VOR/DME Loran GPS Inertial

Collection of antennas throughout the United States transmit signals

Aircraft receiver calculates position based on intersection of multiple signals

GPS = Global Positioning System A space based, all-weather, jam

resistant, continuous operation, worldwide radio navigation system.

Provides extremely accurate 3D location data as well as velocity and time.

System of 24 satellites, 4/5 of which are in view at all times

Receiver uses 4 of these to determine position of aircraft

Each satellite transmits code, which contains satellite position and GPS time

Receiver, knowing how fast signal was sent and at what time, calculates position

RAIM – Receiver Autonomous Integrity Monitoring Determines if satellites are providing correct data

WAAS – Wide Area Augmentation System Collection of ground receivers take satellite data

and correct it for atmospheric conditions Works based on known position of ground

stations LAAS – Local Area Augmentation System

Same as WAAS, but on a smaller, more precise scale

For terminal area around airport

Single range can lie anywhere on a sphere

R1R1

Courtesy of Leica GeosystemsCourtesy of Leica Geosystems

Two ranges will intersect on a line, defined by the intersection of two spheres


Three spheres intersect at a point

Three ranges needed to resolve lat/long/altitude


Civilian Uses Marine Navigation Air Navigation Surveying Search and Rescue Collision

avoidance Agriculture

Military Uses Marine

Navigation Air Navigation Rendezvous Close Air Support Mine Warfare Unmanned Aerial

Vehicles (UAVs)

Dead-Reckoning Self-contained source of:

Position, groundspeed, & heading Does not even need a receiver

Cannot be jammed Gets better with use

Applies a calibration correction after each flight

Acceleration is vectorially summed in x, y, & z.

Output is compensated movement of the platform & for curvature & rotation of the earth.

Acceleration is vectorially summed in x, y, & z.

Output is compensated movement of the platform & for curvature & rotation of the earth.

2)()( dttats

Early systems required precise mechanical parts Bigger is more accurate

Modern systems can be: Mechanical (platform)

Simple gyrosAccurate

Electronic (strap-down)Few moving partsSmaller Cheaper

Modern systems can be: Mechanical (platform)

Simple gyrosAccurate

Electronic (strap-down)Few moving partsSmaller Cheaper

Aircraft systems use Pendulum accelerometers or MEMS

▪ Micro-electromechanical sensors Ring laser gyros

▪ To measure angular change INS complements GPS

Mechanical

Ring Laser Gyro

Pilotage Dead Reckoning Radio Navigation

ADF VOR/DME/RNAV

Electronic Navigation Loran GPS Inertial

Celestial

Advantages No power required Self contained Cannot be jammed Available

everywhere

Disadvantages Dusk & dawn only Clear weather only Slow for aircraft Needs the art of nav.

Navigator’s skill Requires

computation At least data entry

Circle of Equal AltitudeCircle of Equal Altitude

DeRemer & McLean Global Navigation

Error increases with distance VOR/DME, ADF

Error increases with time DR, Inertial

Reliability Concerns GPS, Loran, Celestial

Human error

1. Pilotage2. Dead Reckoning 3. Radio Navigation

ADF VOR/DME/RNAV

4. Celestial5. Electronic Navigation

LoranGPSInertial

Be suspicious. Check and recheck. If you cannot tell your passengers your

ETA at the destination, you are not navigating.

Assume you’re near your DR position Do not assume a huge wind just came up

Use your VOR/DME or 2 VORs Look on the chart for landmarks

Especially those that are shown small If you miss a checkpoint, hold your

heading & look for the next one Do not guess where you are! If all else

fails, CALL ATC (after all, YOU are paying for it)

Frequency Band: Airborne: 1025 MHz – 1150 MHz Ground : 63 MHz below Tx frequency 1025 – 1087

MHz63 MHz above Tx frequency 1088 –

1150 MHz This gives 126 channels but two codings are used (X

and Y) which doubles the capacity

As the name implies , DME provides information on the distance from the aircraft to the ground station

Used to establish position along an airway and also to establish hold points

Frequency Band: Airborne: 1025 MHz – 1150 MHz (L band) Ground : 63 MHz below Tx frequency 1025 – 1087 MHz

63 MHz above Tx frequency 1088 – 1150 MHz

This gives 126 channels but two codings are used (X and Y) which doubles the capacity

General Principle: Airborne transceiver transmits a pair of pulses (spaced at 12μs for mode X and 30μs for mode Y)

Ground transmitter receives the pulses, waits 50μs and then transmits another pair of pulses back to the aircraft

Airborne transceiver measures the time between transmission and reception, subtracts the 50μs, multiplies by the speed of light and divides by 2.

This is very simple but gets more complicated when we want to service more than one aircraft

We need a method of distinguishing among the signals from up to 100 aircraft.

This is done essentially by generating a random set of pulses and correlating with the replies to determine the correct ones.

•Distance

•Speed

•Time to StationNotes:

1. The last two are valid only if the aircraft is going

directly towards or away from the ground station.

2. The DME measures SLANT RANGE to the station.

DME Distance (Slant Range)

Ground Range

Altitude

The ground station simply receives a pulse pair, inserts the 50 μs delay and retransmits it.

To reduce the effects of reflections it will not reply to another interrogation for about 60 μs (dead time)

The ground station transmits 2700 pulse pairs per second regardless of the number of aircraft interrogating.

The extra pulse pairs are called “squitter”

If there are not enough interrogations to make up 2700 pulse pairs, the ground receiver increases its sensitivity until noise pulses trigger enough replies to make up the difference

If there are too many interrogations, the receiver decreases its sensitivity so that the weakest interrogations get ignored

Using squitter has the following advantages:

• The transmitter average output power is constant

•The receiver AGC has a constant average signal to work with

•The ground receiver sensitivity is maintained at the optimum level

•In the case of overload, the aircraft farthest from the station are dropped off first.

Accuracy:The ICAO specification for DME is 0.5NM or 3% of distance

Tests done on Canadian DMEs show that their errors are less than 30m.

IntegrityDME ground stations are equipped with monitors which can detect erroneous delays and out-of-tolerance power output levels. These shut the system down if and error is detected

Availability:

As with most systems there is a standby transmitter which takes over when the main one fails.

availability is well above 99.9%

Non-precision approaches supply the pilot with horizontal guidance only. (VOR, NDB, Localizer, Loc. B/C, GPS without VNAV)

Precision approaches supply the pilot with horizontal and vertical guidance. (ILS, MLS, PAR, GPS with VNAV)

ILS is the primary international precision approach system approved by ICAO and protected until 2010.

ILS provides an aircraft with precision horizontal and vertical guidance to the runway.

Localizers operate in the VHF range and provide horizontal course guidance to runway centerline. Transmitters are located on the centerline at the opposite end of the runway from the approach threshold.

The signal transmitted consists of two fan shaped patterns that overlap at the centre. The overlap area provides the on-track signal.

The angular width of the beam is between 3°and 6°. Normally width is 5°, resulting in full scale deflection at 2.5°. The width of the beam is adjusted to be 700 feet wide at runway threshold.

The localizer may be offset from runway centerline by up to 3°. Localizers offset more than 3° will have an identifier beginning with X, aligned localizer identifiers begin with I.

A cautionary note will be published in the CAP whenever localizer is offset more than 3°.

Normal reliable coverage of localizers is 18nm within 10° of either side of course centerline and 10nm within 35°.

Localizer installations provide back course information, and non-precision localizer back course approaches may be published. (ignore all glide path information on back course) Normally glide path will flag off.

Caution: a localizer signal is transmitted differently than a VOR radial. Aircraft receivers are not supplied with azimuth information relative to magnetic or true north. It is simply a beam aligned with the runway centerline. For this reason CDIs will display normal sensing characteristics when flying in the same direction as front course alignment, but reverse sensing when traveling in the direction of back course alignment. (HSI will normal sense anytime front course direction is set on head of track bar.)

Glide path information is paired with the associated localizer frequency.

The glide path is normally adjusted to an angle of 3° (may be adjusted 2° to 4.5°) and a beam width of 1.4°(0.7° for full scale deflection).

The antenna array is located approx. 1000ft from the approach end of the runway and offset approx. 400ft. (if glide path is followed to the pavement touchdown point will be at the 1000ft markers)

In installations with an ILS serving both ends of a runway the systems are interlocked so only one can operate at a time.

Note: on a standard 3° glide path 320ft/1nm can be used to verify.

Typical final approach fixes are NDBs in Canada, but can also be identified by DME or VOR radial and DME as published.

Fan Markers are commonly used in the US as a means of identifying aircraft location along a localizer. As the marker is reached a fan marker light will illuminate in the flight deck (if equipped).

CAT I: operation down to a minimum of 200ft DH and RVR2600 or ½ sm ground visibility when RVR not available.

CAT II: operation down to a minimum of 100ft DH and RVR 1200ft.

CAT III: minimums will be prescribed in the carrier’s operating specifications, carriers operations manual, or the CAP. (minimums are further broken down into A,B, or C with a CAT IIIC minimums being zero-zero).

Requirements: CAT II/III approaches require specific aircraft and airport capabilities. (ex: airport lighting, aircraft autoland)

Note: when CAT II/III approaches are being conducted the CAT II or CAT III hold line must be adhered to.

The following must be fully serviceable to meet CAT II/III standards:

Airport lighting: approach lights runway threshold lights touchdown zone lights centerline lights runway edge lights runway end lights all stop bars and lead-on lights essential taxiway lights

ILS components: localizer glide path

RVR equipment: CAT II- two transmissometers- approach end,

mid-field CAT III- three transmissometers- approach end,

mid-field, departure end Power source:

Airport emergency power as primary power source for all essential system elements.

Commercial power available within one second as a backup.

aircraft radio navigation communication systems

Documents

precision

full scale

radio waves

omni bearing

constant average

distance measuring

maximum usable

altitude reporting