TCAS Fail
Re-thinking the TCAS Fail report, and inputs that could have caused it:
Airspeed: airspeed has no input to the TCAS, so possible clogged pitot is unrelated.
Altitude input fail: Altitude data goes to the transponder, not the TCAS processor. Transponder would report Altitude Fail, but that is redundant with the ADIRU air data fail message, so may be suppressed. Transponder would revert to Mode A, making the TCAS inoperative, which would trigger a TCAS message. It's hard to tell from the ACARS reports if the Altitude function of the ADIRU was inoperative as well as airspeed.
Attitude Fail: Pitch & Roll are fed to TCAS, so IRU Fail would trigger the message.
Heading Fail: used only for smoothing target movements, so not worthy of a TCAS report.
Radio Altimeter: unlikely that both could fail at this time, although they can lock onto really heavy rain, but not at FL 350.
Antennas: A TCAS antenna fail would trigger TCAS Fail. Hate to say it, but one cause could be lightning.
GB