Back to your post 4435 on 21 Sep, Belgique:
The ADMs, Air Data Modules, used in the A330 can be pretty dumb sensors, equivalent to the blind encoders that came out 25 years ago: just an absolute pressure transducer and a digital output. I'm not intimate with the A330, but here's a logical way to build a pitot/static system with modern devices:
Each ADM for static pressure puts out a 429 word labeled, ALT, which is fed to its companion ADR with minimal monitoring. The ADR passes the ALT on to the using devices, such as pilot displays, AP and transponder. The using devices receive ALT from two or three ADR for redundancy and/or voting.
No airspeed input is needed or used in the altitude calculation.
For airspeed measurement, we use an identical ADM, but connected to a pitot probe, and its output word coded for impact pressure. The ADR merely subtracts ALT from impact pressure to calculate IAS, which is then forwarded on. There is no reason for the ADR to report ALT Fail if it can't compute IAS. Each output from an ADIRU stands on its own.
So, I come back to my original premise: blocked pitot tubes do not cause TCAS Fail to be reported. There must be another cause of the TCAS Fail that was reported by the ACARS.
Beyond that, if there were ALT Fail out of the ADR it would have caused the transponder to revert to Mode A,
thereby causing the TCAS to report TCAS OFF to the ACARS, and not TCAS Fail. There is no direct connection between the ADR and the TCAS processor.
TCAS Fail is reported in case of:
TCAS processor computation fail
TCAS directional antenna fail
Loss of valid data from transponder
The first ACARS reports mentioned a TCAS Antenna Fail, which should have been coded in the report.
Again, I agree with the BEA report: the TCAS Fail is unexplained. It may be a symptom of an event that was otherwise unreported.
GB