User's Manual Part 2

T
2
CAS / Part No. 9000000
SYSTEM DESCRIPTION AND INSTALLATION MANUAL
34-43-20
15 Feb 2003
Use or disclosure of information on this page is subject to the restrictions in the proprietary notice of this document.
6--17
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 flightcrew 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
2
CAS CU, could result in the T
2
CAS CU
developing an intruder track file on its own associated transponder. Simply
performing a DC continuity test of the connection between the T
2
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
2
CAS CU and the non--selected transponder. With an
oscilloscope, monitor the signal at the T
2
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
2
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.
(h) Suppression Bus Clear Page
The Suppression Bus Clear page, Figure 6--11, 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.