Originally Posted by
CONF iture
You simply cannot obtain a similar trajectory with an identical stickforce with 2 scenarios as different as one with a THS set at 3 deg and another one with a THS moving from 3 to 13 deg.
That flys in the face of everything published about Airbus C* control law. It is supposed to be path stable, make an input and then the path will be held until you change it. If you point it up and don't have enough thrust then it will continue to pitch up to try and do what you asked, even to stall. The BEA make exactly that point in the report.
Sidestick force is not relevant because you could have let it return to neutral and it would do the same.
THS is not relevant either, until you reach elevator limit, because the control feedback loops will simply command elevator deflection to achieve the path. If the THS helps then they will use less elevator, if not then they will use more. None of that changes sidestick force as there is no feedback.
A simulator experiment would clearly point the difference.
How are you programming in a 3deg THS limit in your sim when there is not one on the a/c - are you using a THS-failure setup of some sort or are you physically holding the trim wheel to override the autotrim or what ?
Trimming in a stall is an unknown procedure. It is dangerous stuff.
Stall is part of a procedure (outside test flights) ?
Trimming in stall
recovery (if that's what you mean) damn well should be part of the procedure (if it's got to the point that pilots need a SOP for stall recovery
) and definitely should
not be unknown. Failure to trim in stall (and approach to) recovery has killed or nearly killed a lot of people, on bus and other types.
We need to ask Airbus why they think differently.
As the BEA avoids asking the tough questions, we need to do it.
BEA doesn't ask because they have excluded autotrim as not relevant to this accident. I can see why: elevators alone would have got them stalled, kept them stalled (see OG and HN39 posts here, but BEA will have access to similar data), and autotrim did not hinder recovery because stall was never diagnosed (BEA conclusion) so no recovery was even started (BEA conclusion).
If BEA find something relevant but then fail to ask the tough questions of the mfr / regulator then you might validly criticise [actually I think they have on at least one point, but no ones really picked up on it here yet...].
You might also disagree with their conclusions, just as some think that their conclusion that the fin stayed attached is wrong (or at least not sufficiently investigated).
But what you are doing is the same as criticising BEA for not asking hard questions about the composite fin and its attachments - there might well be hard and interesting questions still to be asked in that area, but they aren't for this report because they didn't cause this accident.