FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 12. Aircraft Avionics Systems | 2. Ground Operational Checks for Avionics Equipment (Electrical) | 12-13. Automatic Direction Finder (ADF)
9/27/01
AC 43.13-1B CHG 1
transmission, squelch, operations using head
phones, speaker(s), and hand microphone. If a
receiver or transmitter is found to be defective,
it should be removed from the aircraft and re
paired.
12-11. VHF OMNI-DIRECTIONAL
RANGE (VOR). A VOR operates within the
108.0 to 111.85 MHz, and 112.0 to 117.95
MHz frequency bands. The display usually
consists of a deviation indicator and a
TO/FROM indicator. The controls consist of a
frequency selector for selecting the ground
station and an OBS, which is used for course
selection. An ON/OFF flag is used to deter
mine adequate field strength and presence of a
valid signal. There are numerous configura
tions when integrated into flight directors
and/or when using a slaved compass system,
which uses an additional indicator that points
continually to the selected omni station re
gardless of OBS selection. In order to deter
mine the accuracy specified in a functional
check, a ground test set must be used in accor
dance with the manufacturer’s specifications.
For the purpose of this inspection/maintenance
activity, the following operational check can
be accomplished to determine if the equipment
has the accuracy required for operation in in
strument flight rules (IFR) environment. Ver
ify audio identification, OBS operation, flag
operation, radio magnetic indicator (RMI) in
terface, and applicable navigation (NAV)
switching functions. The operational check is
also published in the AIM, section 1-1-4. This
check is required by 14 CFR part 91, sec
tion 91.171 before instrument flight opera
tions.
12-12. DISTANCE MEASURING EQUIP-
MENT (DME). The operation of DME con
sists of paired pulses at a specific spacing, sent
out from the aircraft (this is what is called in
terrogation), and are received by the ground
station, which then responds with paired pulses
at the specific spacing sent by the aircraft, but
at a different frequency. The aircraft unit
measures the time it takes to transmit and then
receive the signal, which then is translated into
distance. DME operates on frequencies from
962 MHz to 1213 MHz. Because of the cur
vature of earth, this line-of-sight signal is reli
able up to 199 nautical mile (NM) at the high
end of the controlled airspace with an accuracy
of 1/2 mile or 3 percent of the distance. DME
inspection/maintenance on the aircraft is most
commonly limited to a visual check of the in
stallation, and if there have been previously
reported problems, the antenna must be in
spected for proper bonding and the absence of
corrosion, both on the mounting surface, as
well as the coax connector. Accuracy can be
determined by evaluating performance during
flight operations, as well as with ground test
equipment. If a discrepancy is reported and
corrected, it is good practice to make the accu
racy determination before instrument flight.
Tune the DME to a local station, or use the
proper ground test equipment to check audio
identification, and DME hold function verify
correct display operation.
12-13. AUTOMATIC DIRECTION
FINDER (ADF). The ADF receivers are pri
marily designed to receive nondirectional bea
cons (NDB) in the 19 to 535 kHz amplitude
modulation (AM) broadcast low band. The
receivers will also operate in the commercial
AM band. The ADF display pointer will indi
cate the relative bearing to a selected AM band
transmitter that is in range. An ADF system
must be checked by tuning to an adequate
NDB or commercial AM station. Verify
proper bearing to station, audio identification
and tone/beat frequency oscillator (BFO), cor
rect operation in closed circuit (LOOP) and
sense modes. Note the orientation of the se
lected station to the aircraft using an appropri
ate chart. Observe the ADF relative bearing
reading, and compare to the chart. Slew the
needle and observe how fast (or slowly) it re
turns to the reading. ADF performance may
Par 12-10
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