Hello
disclaimer : this thread moved along too quickly for me to be able to cath all ; apologies if what follows was already discussed, I don't think so as a search on the word "abnormal" didn't return any match.
Since the publication of the note by the BEA (btw, it's not a report, semantics matters here), I was wondering why the THS would have stayed @ 13° pitch up, even when the PF made nose down inputs on its side stick.
2 answers were possible :
- it's normal (per specification, not meaning it's sensible in 447 case) ; but why ?
- it's not normal, and indicates a failure / bug in the THS or its command chain .
It now seem to me that "it's normal", i.e. the aircraft managed the THS as its conceptors wanted it to do (= no failure).
Indeed, we have :
- the ALT 2 LAW which is load factor pitch / direct roll / auto-trim / ...
- the ABNORMAL ATTITUDE LAW which is ~ the same as ALT 2 LAW with the exception of the auto-trim being unavailable.
The ABNORMAL ATTITUDE LAW is triggered if (non exclusive list):
- the [mesured I presume] speed is below 60kt
- the AoA is above 30°
Per the BEA note, at each time after the beginning of the final descent, one of these two conditions was met.
So the ABNORMAL ATTITUDE LAW should have triggered, meaning the auto-trim was lost, hence the THS stayed "stuck" at 13° value.
My question for those in the know : Does the ABNORMAL ATTITUDE LAW activation also trigger a message indicating to the crew that the auto-trim is unavailable ?
I know the DIRECT LAW does that ("USE MAN PITCH TRIM" on the PFD), but what about the ABNORMAL ATTITUDE LAW ?
Thanks.