TCAS computation needs altitude to assess threats and should receive barometric and Radio Altimeter inputs! yes/ no?
TCAS depends on Range, Rate of Closure and Altitude Difference for Collision Avoidance, nothing more.
Range and Rate of Closure are determined by interrogating other aircraft's transponder. TCAS is like ground based ATC radar in that respect. Altitude Difference is found by subtracting other aircraft's reported altitude from own aircraft altitude.
TCAS receives Own Aircraft Altitude from the active ATC transponder, which in turn receives it from its associated Air Data Computer (ADR). This assures that the TCAS is calculating altitude difference from the same altitude that is transmitted to other aircraft TCAS.
Imperfect placement of the static ports on the side of the plane result in skewed static pressure at low airspeeds. The ADR corrects the static pressure based on airspeed when converting it to altitude for relay to the rest of the systems that use altitude.
The OZ A330 that had pitot icing in Aug 2009, indicated a sudden drop of 300 feet in measured altitude along with the airspeed decay to a low number, which is explained by the airspeed correction routine.
Why was the TCAS Fail reported on 447? BEA in their first release explained it was due to logic internal to the TCAS that would not accept the sudden drop in calculated altitude it was receiving.
Do you see the fallacy in that? If you don't want your TCAS working with bogus altitude, you sure don't want your ATC transponder working with it either. If there was such an altitude reasonableness check, it should be in the transponder, not the TCAS.
Maybe the TCAS Fail was like the Wiring Fail reported: the plane could have been getting the crap shaken out of it.
Cancel that last sentence. Found this from 16 April:
PJ2 said WRG means the fault is not correlated by another computer of the FWS.
I don't know why the TCAS reported Fail, but I'm certain it was not due to pitot error.