navigation and communication systems prepared by: lindsay v. oczak fall 2000

Navigation and Communication Systems

Prepared by:

Lindsay V. Oczak

Fall 2000

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

Communication Systems

VHFHFACARS / AIRCOMSecal decodersSATCOM


COMM Radios 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


VHF & HF Systems 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).


ACARS (ARINC Communication Addressing and Reporting System)

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


Secal Decoder

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


SATCOM 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


Navigation Systems

VORADFILSLOCGSMarker beacons

Radio altimeters

DMEGPSTranspondersELT


VOR (VHF omni-directional range) 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 Operation

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.


ADF (automatic direction finder)

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.


ILS (instrument landing system) 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


LOC (localizer) 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.


GS (glide slope) 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 Beacons 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.


Radio Altimeters 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.


DME (distance measuring equipment) 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.


GPS(global positioning system) 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.


Transponders 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


Transponder operationThree 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)


ELT (emergency locator transmitter) 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


ELT Testing 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


ELT Servicing 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


Inspections for NAV/COMM Equipment

System inspections

Antenna inspections

Static discharge inspections

Operational checks or any additional

inspections required by the

manufacturer


Inspection of NAV/COMM Systems 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.


Inspection of NAV/COMM Systems 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.


Inspection of NAV/COMM SystemsCheck 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.


Antenna Inspection

Check for: broken or missing antenna insulation

lead through insulators

Safety wires

Cracked antenna housing

Missing or poor sealant at base of antenna


Antenna Inspection

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, maximum


Inspection of Static Dischargers/WicksCheck 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.


Inspection of Static Dischargers/Wicks

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.


Additional InspectionsTransponder

Per FAR 14 Part 91.411 and 91.413ELT

Per FAR Part 91.52Functional checks of all other COMM

and NAV systems per the manufacturer’s instructions

navigation and communication systems prepared by: lindsay v. oczak fall 2000

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