Salute,
Originally Posted by Graybeard
This is illogical. Why would the TCAS have a credibility filter on altitude data from the transponder? It would be just as important for the transponder to have the same credibility filter, as it transmits own ship altitude to ATC and other aircraft. If there were such a filter, it should be in the ADIRU, or even the Air Data Module, whichever unit contains the correction factor for airspeed.
Well, considering that the purpose of a TCAS (Traffic Collision Avoidance System) is to predict a safe flight vector, it seems someway quite
logical that its own "prediction" function would be compared to any computed air data received from any sensor source. What is obviously discussed, here by the BEA, is the way that this TCAS function will be shut down to inop, they are not discussing the relevance of the whole architecture of the air data computations in relation with other systems -transponder and/or ADIRU- failures.
Originally Posted by Graybeard
Again, when the ADM or ADIRU detects a fault, Fail Warn is transmitted on the data bus to the transponder. The transponder reverts to responding with Mode C, no altitude, which it also relays to the TCAS. The TCAS then stops, and annunciates OFF to the pilots. This is not a TCAS Fail.
Nowhere the BEA said that the TCAS "failed". In fact, the opposite is said: it is inoperative because of those "wrong data" from external sources (ADR1-2) were detected by its built in function.
Originally Posted by Graybeard
Think about it: ACARS maintenance messages are transmitted to the destination. You don't want the mechanic to change a TCAS processor when it's a source that's faulted.
But, be sure they won't change anything as the CFR (Code Failure Received) is pointing at an
external source and there is only one possibility (external) for this message, as duly mentioned by the BEA.
Originally Posted by Graybeard
I'm sure BEA is mistaken. There was another reason for the TCAS Fail.
Sure, the BEA is always mistaken each time it doesn't fit with your own theories (vertical stab, systems, attitude, etc.)
S~
Olivier