mm43:
Yesterday when posting the FDR traces for the Jetstar A330 incident, I mulled over the static port problem, then looked at the ECAM messages and realized that the sequence of events was very similar to AF447. So, getting back to the TCAS fail message, I'm starting to feel that the ALT supplied to the Transponder changed at a rapid rate, i.e. the speed correction value changed, and the TCAS determined the rate of change wasn't valid and shut-up shop.
Do you think that could fit the bill?
Thanks for the question, MM. Jetstar did not get a TCAS Fail, did it?
The companies that build the TCAS also build the ATC Transponders. Like I wrote before, if you're going to insert such a reasonableness filter into the ATC/TCAS system, you would put it in the transponder, as it's just as important to report correct altitude to other aircraft as it is to have your TCAS using correct altitude.
Besides, failed altitude input should cause TCAS to report OFF, not Fail, but I'm not 100% sure of that at the moment. Selecting ALT to OFF on the ATC/TCAS control panel will for sure result in TCAS OFF.