Honeywell CAS-100 Maintenance Manual page 45

Table 1.
Equipment Type
TRA-67 Transponder Subsystem (cont)
TRA-67A Mode S
Transponder (cont)
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MAINTENANCE MANUAL
CAS-100 COLLISION AVOIDANCE SYSTEM
TCAS System Components (Honeywell Supplied) (cont)
Honeywell
Part Number
066-01127
Description
Once for each second of time, Mode S
transponders automatically transmit a squitter
message that contains its aircraft address
identification. These squitter messages tell other
TCAS equipped aircraft and ground stations that the
Mode S equipped aircraft is present.
The Mode S transponder in TCAS equipped aircraft
is connected to the TCAS processor with a
two-direction ARINC 429 data link. Many data link
communications between the TCAS processor and
Mode S transponder are continuously interchanged.
The CTA-81( ) Control Unit gives on-board control
for manually selecting Mode S transponder and
TCAS operating modes. Mode control data from
the control unit is connected into the Mode S
transponder and moved to the TCAS processor
through ARINC 429 data links.
A change to TCAS operating modes (i.e. sensitivity
levels) can be requested from future Mode S ground
stations through the messages received by the
Mode S transponder. The Mode S transponder
moves this mode control request data to the TCAS
processor through the ARINC 429 data link. The
TCAS processor routinely moves operating mode
status data to the Mode S transponder. When a
request from a ground station is made, the
operating mode status data is put in(to) a message
transmitted from the Mode S transponder.
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1 Dec 2003