EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
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A
747-400
MAINTENANCE MANUAL
(9)
The TCAS operates at the same transmit and receive frequencies as ground stations (1030 MHz transmit and 1090 MHz receive). The TCAS and ground stations operate at transmit and receive frequencies that are opposite to the ATC transponder transmit and receive frequencies as shown below.
~.................................................................... | SYSTEM | TRANSMIT FREQ | RECEIVE FREQ | ...................................................................... | TCAS | 1030 MHz | 1090 MHz | ...................................................................... | Ground Station | 1030 MHz | 1090 MHz | ...................................................................... | ATC transponders | 1090 MHz | 1030 MHz | 2.......................….........................…..................1
(10)
TCAS transmits 1030 MHz messages from the top and bottom TCAS antennas to interrogate ATC transponders in other airplanes. The TCAS receives 1090 MHz messages from ATC transponders through the top and bottom directional antenna.
B. TCAS Voice Alert
(1)
The TCAS system alerts the pilots with an audible caution or command during a traffic situation.
(2)
When an intruder airplanes projected path brings it close enough to be of concern (filled while diamond changing to filled yellow circle), a TRAFFIC TRAFFIC alert is sounded.
(3)
When a RA is encounter, the TCAS system will voice commands for the necessary corrective maneuvers. These voice commands are as follows:
Climb - climb - climb Climb, crossing climb - climb, crossing climb Descend - descend - descend Descend, crossing descend - descend, crossing decend Reduce climb - reduce climb Reduce descent - reduce descent Increase climb - increase climb Increase descent - increase descent Climb, climb now - climb, climb now Descend, descend now - descend, descend now
(4)
After an RA is resolved and the intruder airplane is no longer a threat, the TCAS system will announce "clear of conflict".
C. TCAS INHIBITS
(1) When a ground proximity or windshear alert occurs, the TCAS will be set to the TA-ONLY mode and all TCAS voice alert are inhibited.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
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MAINTENANCE MANUAL
(2)
All RAs and TA voice messages are inhibited when the airplane radio altitude is less than 1100 feet if the airplane is climbing.
(3)
All RAs and TA voice messages are inhibited when the airplane radio altitude is less than 500 feet if the airplane is descending.
(4)
No TCAS "Increase descent" commands are given when the airplane radio altitude is less than 1,450 feet.
(5)
No TCAS "Descend" commands are given when the airplane radio altitude is less than 1200 feet if the airplane is ascending, and 1000 feet if the airplane is descending.
(6)
TCAS Climb RA commands are inhibited above a barometer altitude of 48,000 feet.
D. BITE
(1)
The TCAS computer continuously runs BITE tests and monitors system functions when the microprocessor is not busy with system operations. The TCAS computer can detect any failure that would degrade the normal system operations. The TCAS computer also monitors the ATC system status. If a failure occurs in the ATC or TCAS systems these indications and system actions will occur in the TCAS:
(a)
TCAS FAIL will show on the ND
(b)
Normal TCAS display indications are stopped
(c)
Stops interrogations by your airplane TCAS
(d)
Sends TCAS FAIL or TCAS OFF status in the Mode S transmission when interrogations are received from other airplanes.
(2)
There are two ways to start the BITE test:
