User's Manual
SYSTEM DESCRIPTION AND INSTALLATION MANUAL
TCAS 3000 Traffic Alert and Collision Avoidance System
34−43−23
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Page 6−23
15 Dec 2005
F. Directional Antenna Test / Fault Isolation Procedure
NOTE: These procedures are recommended only if a TCAS computer bite or extended
test failure of the top or bottom directional antenna has occurred.
(1) Review extended maintenance or flight leg BITE data to determine which antenna
has failed.
(2) Remove TCAS computer unit from mounting tray. Visually examine all antenna coax
cable connectors at the mounting tray side as well as the LRU connectors. Remove
any foreign material discovered and reinstall the LRU.
(3) Do a system self−test to determine if the fault has cleared. If the failure continues,
remove the TCAS computer unit and proceed.
(4) Do a continuity test at the LRU end of each antenna cable. The resistance values
should be as specified in Table 6−5.
(5) If an open circuit, short circuit, or unacceptable resistance measurement is detected
on the directional antenna path, a failure has occurred in the connector, coax cable,
or directional antenna.
(6) Locate the directional antenna that has a suspected failure. Remove the coax cable
from the antenna port that is suspected to have failed. Isolate which section of the
antenna system is at fault by a process of elimination. The resistance values of the
antenna ports should be as specified in Table 6−5.
(7) Remove and replace the appropriate failed component in accordance with approved
Aircraft Maintenance Manual procedures.
Table 6−5. Antenna Wiring Resistance
Antenna
Connector
Section
Pin DC Resistance
Top Directional Antenna LTP 1
2
3
4
1000 ± 100 Ohms
8060 ± 800 Ohms
4020 ± 400 Ohms
2000 ± 200 Ohms
Bottom Directional Antenna LMP 1
2
3
4
1000 ± 100 Ohms
8060 ± 800 Ohms
4020 ± 400 Ohms
2000 ± 200 Ohms
Optional Bottom
Omnidirectional Antenna
LMP 1
2
3
4
0 to 50 Ohms (50 Ohms maximum)
Infinite (>50K Ohms)
Infinite (>50K Ohms)
Infinite (>50K Ohms)