The A/THR involuntary disconnection in this case was not "faulty". It was due to a failure condition, but one that is handled in the software. After that, A/THR is simply disengaged and disarmed, with a thrust lock situation, as if it had been disconnected with the FCU pushbutton.
I haved described the complete behaviour in case of the thrust lever angle sensor problems in an earlier post, but here are the relevant bits:
- With TLA (at time of failure) below FLEX/MCT, on the ground or in flight with slats extended, FADEC commands idle power, regardless of autothrust engagement status.
Bsieker,
Excuse me about the "faulty". I just wanted to mean an involuntary disconnection of the A/THR (in this case by a difference between target EPR's)
You are right about the TLA disagree. FADEC sets even the TLA reading itself to idle in this case.
But it is also true that we are dealing with general statements from the FCOM here. Complete logic diagrams like that of the warning previously discussed might help us to be sure about the applicability of the TLA disagrement procedures to this specific case of A/THR disconnection.
Anyway one thing would certainly rule out the hypothesis of a software caused failure: The independent SEC reading of the TLA position !
If the SECs read a distinct set of sensors (pots) then the fact that ground spoilers were not deployed proves beyond reasonable doubt that the TL was actually left by the crew at CLIMB detent.
That if the TRA (resolver) readings are not queried simultaneously to the pots readings by the SEC's spoiler deployment logic.
