B737
MAINTENANCE MANUAL
EFFECTIVITY
Post ELT STC ST03081AT
23-24-00
PAGE 101
JAN 02/07
EMERGENCY LOCATOR TRANSMITTER SYSTEM
FAULT ISOLATION
1. General
A.
Before proceeding with testing, carry out the applicable Maintenance Practice depicted in this
maintenance manual supplement. Any obvious damage should be rectified before proceeding.
2. System Tests
A.
The system test is an operational test used to test the basic functionality of the ELT system. This
test does not give specific levels of performance for any of the functions of the ELT but it does
indicate that the system is functioning in a satisfactory manner. The system test is detailed
below:
(1) Always perform the test within the first 5 minutes of the hour (UTC) as required by AC
43.13-1B, 12-21 and 12-22 Note 3. Be sure to notify any nearby control tower of your
intentions.
WARNING: DO NOT ALLOW TEST DURATION TO EXCEED 5 SECONDS. The ELT will
transmit a 406.025 MHz signal after the ELT is active approximately 47 seconds, the
satellite system considers the transmission to be a valid signal.
(2)
Ensure ELT system circuit breakers are closed.
(3)
Tune a VHF receiver to 121.5 MHz.
(4) Turn the ELT remote switch panel to ON, wait for 3 sweeps of the receiver, which takes
about 12 second, and then turn the switch back to ARM (OFF) position while paying
attention to the LED activity upon entering the ARM (OFF) condition.
3. Fault Isolation
A.
The microprocessor in the ELT checks the G-switch (automatic activation switch) latching circuit,
pins 5 and 6 on the 12-pin connector of the ELT; the 406.025 MHz transmitter for proper RF
output; presence of valid navigation data (ELT/NAV Interface and navigation system must be
active) and a battery check. If the ELT is working properly, the sequence following entry to the
ARMED (OFF) condition will result in the panel LED staying ON for approximately 1 second then
extinguishing.
B.
If a problem is detected, the LED provides a coded signal following the initial 1 second pulse.
The coded signal and related problem are as follows (the LED will flash in order of importance
with approximately a 0.5 to 1 second pulse between each error code if multiple errors are
present):
(1)
1 flash indicates a G-switch loop open failure.
(2) 3 flashes indicates a 406.025 MHz transmitter problem (i.e. bad or unconnected coax, an
antenna problem, low power output or a programming error).
(3) 5 flashes indicates there is no navigation data present. This is most likely due to improper
wiring between the system interface connections, improper programming, invalid
navigation data (navigation system not powered up) or an ELT/NAV Interface Unit (453-
6500) is not being utilized.
(4)
7 flashes indicates a battery problem (i.e. battery usage time over an hour).
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