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References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
Communication Systems
VHFHFACARS / AIRCOMSecal decodersSATCOM
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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).
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
Navigation Systems
VORADFILSLOCGSMarker beacons
Radio altimeters
DMEGPSTranspondersELT
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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)
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
Inspections for NAV/COMM Equipment
System inspections
Antenna inspections
Static discharge inspections
Operational checks or any additional
inspections required by the
manufacturer
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.
References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2
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.