User's Manual

SYSTEM DESCRIPTION AND INSTALLATION MANUAL
T
3
CAS/Part No.9005000
The flight crew may report a unique problem of an intruder displayed
which appears to be co-altitude, located on the own aircraft symbol. In
many of these cases, TCAS may issue a TA followed by an RA. After the
flight crew has initiated the advisory, the intruder may not appear to
change relative to the own aircraft symbol.
In this type of report, a failure in the mutual suppression bus, which
connects the own aircraft transponder to the T
3
CAS CU, could result in
the T
3
CAS CU developing an intruder track file on its own associated
transponder. Simply performing a dc continuity test of the connection
between the T
3
CAS CU and the transponders may not identify the
problem. In many cases, a connector termination or pushed back pin
may be the cause.
That is why it is very important to be monitoring the suppression signal
from the active source, on both ends. The following is one method to
monitor the signal. Remove the T
3
CAS CU and the non-selected
transponder. With an oscilloscope, monitor the signal at the T
3
CAS CU
rack rear connector for the Mode S transponder suppression signal
related to the squitter message sent every second by the selected
operational transponder.
Repeat the same test with the second transponder after removing the
first transponder. To test the T
3
CAS CU suppression pulse, install the
TCAS CU, remove the No.1 transponder and monitor the TCAS
suppression pulse during the time of the UF16 broadcast or the WSS
while in the air (if possible). This TCAS suppression signal should also
be present on the No.2 transponder.
(i) Suppression Bus Clear Page
The Suppression Bus Clear page, Figure 6-12, is displayed only when a
TCAS suppression bus failure is indicated and the 4096 Ident Code is
0510. This page briefly describes how to clear suppression bus failures
from the fault record by exiting the extended test mode with this page
displayed. When the TCAS extended test is exited, the failure indication
is cleared and a Suppression Bus Clear code is recorded in the current
flight leg.
Pub. No. 8600200-001, Revision 004
34-45-29
6-27
04 Nov2014
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