TCAS Fail comes on when #1 ATC selected, Ok with #2 ATC selected. 737-6/7/8/900

Fleet Type: 700
Applicable Reference:
SDS AMM part 1, 34-53-00-008, AMM 34-53-00/501, SSM 34-53-21
TCAS Fail comes on when #1 ATC selected, Ok with #2 ATC selected. Both systems BITE tests good
Possible Fix:
Correct program pins at failed ATC transponder.
Using ground test equipment, compare information transmitted by each ATC and look for large differences of
In this case the common pin at the Dip switchs for the #1 ATC transponder was open. This resulted in a aircraft ID of
all O’s when the #1 ATC was selected.
The ATC’s do not fail themselves when they do not have a valid aircraft ID progamed. But in order for the TCAS to
operate correctly it must have a valid aircraft Mode S ID to coordinate with other TCAS capable aircraft. This resulted in a TCAS fail when TCAS was placed in a operational mode. But the passed self test when the TCAS and the ATC were tested individually.


Thanks to Tom S. for his input.

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