User's Manual

SYSTEM DESCRIPTION AND INSTALLATION MANUAL
TCAS 3000 Traffic Alert and Collision Avoidance System
34−43−23
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Page 6−17
15 Dec 2005
(8) Suppression Bus Fail Page
The Suppression Bus Fail page, Figure 6−10, is displayed only when a TCAS
suppression bus failure is indicated and the 4096 Ident Code is 0010. This page
displays information about detected suppression bus failures. It briefly describes the
problem and instructs maintenance personnel to change the 4096 Ident Code to
display the Suppression Bus Clear page for clearing instructions. If there is no
suppression bus failure, the main menu (0000) is displayed.
AD−53901,SH9@
Figure 6−10. Suppression Bus Fail Page
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 TCAS CU, could result in the TCAS CU developing an
intruder track file on its own associated transponder. Simply performing a DC
continuity test of the connection between the TCAS 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 TCAS CU and the non−selected transponder. With an oscilloscope,
monitor the signal at the TCAS 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 TCAS 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.