TCAS question

[fellman]

1. The ICAO recommendation is that ALL RAs should be followed. TCAS II uses the radio altimeter to estimate the aircraft's height above the ground. All RAs are inhibited below 1,000 ft AGL. Descend RAs are inhibited below 1,100 ft AGL. The cockpit avionics give priority to wind-shear and GPWS warnings over TCAS RAs.
2. TCAS II is required to be able to track at least 30 targets, and to be able to display at least 8 targets on the traffic display. TCAS II has specific algorithms to resolve conflicts with multiple threats.
3. TCAS II detects Mode C aircraft, Mode S aircraft, and other TCAS II aircraft (which are necessarily Mode S equipped). If the other aircraft's transponder is reporting altitude then an RA can be issued. If the other aircraft's transponder is not reporting altitude then only a TA can be issued. TCAS II can not detect aircraft with only a Mode A transponder.
The vertical sense of RAs in encounters between two TCAS II aircraft are coordinated.

TCAS is specified in ICAO SARPS (Annex 10, Vol. 4) and RTCA MOPS (DO-185B, also published as EUROCAE ED-143). A useful introduction is the EUROCONTROL ACAS II Guide, available at
http://www.eurocontrol.int/msa/public/standard_page/ACAS_Training.html