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) | 12-20. Transponders
AC 43.13-1B CHG 1
9/27/01
reading on the altimeter instrument. The dif
ference must not exceed 125 feet.
12-20. TRANSPONDERS. There are three
modes (types) of transponders that can be used
on various aircraft. Mode A provides a
(non altitude-reporting) four-digit coded reply;
Mode C provides a code reply identical to
Mode A with an altitude-reporting signal; and
Mode S has the same capabilities as Mode A
and Mode C and responds to traffic alert and
collision avoidance system (TCAS)-Equipped
Aircraft.
a. Ground ramp equipment must be
used to demonstrate proper operation. Enough
codes must be selected so that each switchpo
sition is checked at least once. Low and high
sensitivity operation must be checked. Identi
fication operation must be checked. Altitude
reporting mode must be demonstrated. Dem
onstrate that the transponder system does not
interfere with other systems aboard the aircraft,
and that other equipment does not interfere
with transponder operation. Special consid
eration must be given to other pulse equip
ment, such as DME and weather radar.
b. All transponders must be tested every
24-calendar months, or during an annual in
spection, if requested by the owner. The test
must be conducted by an authorized avionics
repair facility.
12-21. EMERGENCY LOCATOR
TRANS- MITTERS (ELT). The ELT must
be evaluated in accordance with TSO-C91a,
TSO-C126 for 406 MHz ELT’s, or later TSO’s
issued for ELT’s. ELT installations must be
examined for potential operational problems at
least once a year (section 91.207(d)). There
have been numerous instances of interaction
between ELT and other VHF installations.
Antenna location should be as far as possible
from other antennas to prevent efficiency
losses. Check ELT antenna installations in
close proximity to other VHF antennas for
suspected interference. Antenna patterns of
previously installed VHF antennas could be
measured after an ELT installation. Tests
should be conducted during the first 5 minutes
after any hour. If operational tests must be
made outside of this time frame, they should
be coordinated with the nearest FAA Control
Tower or FSS. Tests should be no longer than
three audible sweeps.
12-22. INSPECTION OF ELT. An in
spection of the following must be accom
plished by a properly certified person or repair
station within 12-calendar months after the last
inspection:
a. Proper Installation.
(1) Remove all interconnections to the
ELT unit and ELT antenna. Visually inspect
and confirm proper seating of all connector
pins. Special attention should be given to co
axial center conductor pins, which are prone to
retracting into the connector housing.
(2) Remove the ELT from the mount
and inspect the mounting hardware for proper
installation and security.
(3) Reinstall the ELT into its mount and
verify the proper direction for crash activation.
Reconnect all cables. They should have some
slack at each end and should be properly se
cured to the airplane structure for support and
protection.
b. Battery Corrosion. Gain access to the
ELT battery and inspect. No corrosion should
be detectable. Verify the ELT battery is ap
proved and check its expiration date.
c. Operation of the Controls and Crash
Sensor. Activate the ELT using an applied
force. Consult the ELT manufacturer’s in
structions before activation. The direction for
mounting and force activation is indicated on
Page 12-8
Par 12-20