E. Coordination The avoidance maneuvers initiated by the TCAS could create a conflict situation if directed at another TCAS-equipped aircraft as this aircraft may also take similar evasive action, resulting in an unchanged situation. To avoid this situation, a communication link between the two aircraft is established via the transponders, exchanging coordination messages. The first aircraft to detect the other one initiates the communication procedure, indicates the maneuvers it intends to perform and communicates orders to the other aircraft requesting it to maintain its trajectory. This necessarily involves the use of Mode S transponders, the only equipment of this type possessing the LINK function required for data exchange. The Mode S transponders provide the capability to transmit a unique address (24 bits) assigned to each aircraft, permitting them to reply individually to other TCAS-equipped aircraft. It can respond to ground station interrogations in Mode A and Mode C and also in Mode S if the stations are suitably equipped. With respect to aircraft equipped with Mode A transponders only, the TCAS cannot generate resolution advisories as these transponders do not communicate aircraft altitude. The aircraft are however displayed on the ND, enabling their location in range and bearing, but with no altitude indications. The ground stations can modify the TCAS operating mode via the transponder link so as to inhibit resolution advisories in certain conditions.
2. Component Location
__________________
**ON A/C 001-049, 101-105, 151-199,
(Ref. Fig. 002)
**ON A/C 051-099,
(Ref. Fig. 002A)
R **ON A/C 106-149, 201-299, 301-399, 401-499,
(Ref. Fig. 002B)
1EFF : ALL 1 34-43-00Page 8 1 1 Aug 01/05 1 1 1CES 1
TCAS - Component Location
Figure 002
R 1EFF : 001-049, 101-105, 151-199, 1 34-43-00Page 9 1 1 May 01/05 1 1 1CES 1
R TCAS - Component Location
R Figure 002A
R 1EFF : 051-099, 1 34-43-00 Page 10
1 1 May 01/05
1 1
1CES 1
TCAS - Component Location
Figure 002B
R 1EFF : 106-149, 201-299, 301-399, 401-499, 1 34-43-00Page 11 1 1 Aug 01/05 1 1 1CES 1
R **ON A/C ALL
(Ref. Fig. 003)
-------------------------------------------------------------------------------FIN | FUNCTIONAL DESIGNATION | PANEL|ZONE|ACCESS | ATA | | | | DOOR | REF.
-------------------------------------------------------------------------------3SH CTL UNIT-ATC/TCAS 11VU 211 831 34-52-12 1SG CMPTR-TCAS 82VU 128 824 34-43-34 7SG1 ANTENNA-TCAS, TOP 230 34-43-11 7SG2 ANTENNA-TCAS, BOTTOM 130 34-43-11
3. System Description__________________ (Ref. Fig. 003, 004) The TCAS environment is composed of items closely associated with its operation, such as the transponders and the EFIS display units and peripherals supplying parameters or with maintenance functions.
A. TCAS Computer The TCAS computer is the heart of the TCAS II system. It complies with the dimensional standard in ARINC 600 for 6 MCU form factor. It is compatible with ARINC 600 forced air cooling. It ensures two main functions:
-
a radio-electric transmission reception function in the L-band frequency for intruder acquisition
-
a processing function ensuring total operation control: digital, discrete and analog-type interfaces, intruder trajectory computation and tracking, visual and aural alert commands.
B. Directional Antennas The TCAS has two antennas, one located on the top of the aircraft and the other on the underside of the fuselage. These antennas, of the transmit/receive type, provide azimuth information on aircraft located within the TCAS surveillance range. They consist of four independent elements. In reception, the amplitude of the signals received by each element depends on the direction of the signal source, which permits the relative bearing of the transmitting aircraft to be determined.
C. ATC/TCAS Control Unit The ATC/TCAS control unit common to the ATC transponders and the TCAS, enables the operating modes of these two items of equipment to be selected. Information intended for the TCAS is transmitted via an ARINC 429 bus to the transponders which in turn transmit it to the TCAS computer.
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