Honeywell CAS-100 Maintenance Manual page 78

CAS-100 COLLISION AVOIDANCE SYSTEM
(c) The TCAS processor starts to interrogate the intruder if a correct Mode S squitter
message is sensed. The Mode S equipped intruder is put into the track if an
interrogated Mode S equipped aircraft is in TCAS Mode S tracking range and
altitude. The mode S track changes are then done. These changes include the
TCAS processor formatting and transmitting 1030 MHz Mode S interrogation
messages on the directional antenna and/or the omni antenna. The processor also
receives 1090 MHz Mode S reply messages on the directional antenna and/or the
omni antenna. The TCAS processor sets one directional antenna beam to use for
directional message transmission and reception.
(d) The TCAS processor does ATCRBS search, track initialization, and track changes.
The ATCRBS equipped intruder is put into the track if an ATCRBS equipped aircraft
is in TCAS ATCRBS tracking range and altitude. ATCRBS search, track
initialization, and track update operations include the TCAS processor formatting
and then transmitting 1030 MHz ATCRBS interrogations, and receiving 1090 MHz
ATCRBS replies on the directional antenna and/or the omni antenna. The TCAS
processor sets one directional antenna beam to use for ATCRBS directional
message transmission and reception.
NOTE: Mode S and ATCRBS interrogation and reply message formats are shown
in Figures 5 and 6.
(e) The TCAS processor does functions that find the range, bearing, and altitude of
intruder aircraft from the data calculated from or contained in the reply messages.
The bearing can be found for the intruder replies received on the directional
antenna. The altitude can be found if the intruder is reporting altitude in its
transponder reply message.
(f) Based on the data extracted or calculated from the reply, the TCAS processor
examines the threat potential of the intruder by calculating the intruder closing rate
and position related to own aircraft. From this analysis, the TCAS processor
categorizes the intruder as a nonthreat, proximity, traffic advisory, or resolution
advisory.
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MAINTENANCE MANUAL
34-45-47
Page 45
1 Dec 2003