Lazerdog: As they were descending in the the stall through 10,000 feet, the THS was trimmed up automatically."
Chris: All of us are occasionally running into problems of ambiguity, due to the inherent limitations of written language. That's why the FBW design engineers have to avoid it. I'm sure you don't mean to imply that the autotrim was still changing the THS trim position as AF447 was passing 10,000ft?
Lazerdog: "Would full forward side-stick have caused immediate stall recovery, or would the PF have to wait until the THS auto-trim caught up with nose-down trim?"
Chris -- Short answer is: don't know. But I think we can expect that the AoA would have started to reduce immediately. Unless the THS motor stalled, which would be unlikely at such a low airspeed (low loading), the THS would have started moving immediately. I don't know its maximum rate.
Chris, I think some of the ambiguity that has people concerned is that even with the THS being ~13 deg at apogee, other info from BEA based on FDR describes pilot nose down inputs at various times during the event, with apparently little or no influence on the THS position. (Ah, I see RetiredF4 has made an analysys that makes some sense to me).
Concern -- were control surfaces unable to respond (??).
Concern -- without creating an error message, (which a stalled THS motor would generate??) did properly operating functions (alt law speed stability, which you addressed earlier) or Abnormal Attitude law (at present conclusion is that it wasn't active) provide trim commands in opposition, or as a "correction," to the nose down commands? I would think it wouldn't, but if Airspeed sensing is out the window, what is speed stability using as a reference to direct an assist toward "better" nose pitch?
Since pilot can override the speed stability functions, Lazerdog's kinesthetic comments IIRC don't come into play with side stick forces, but can factor in to "seat of the pants."
(In unusual attitudes, in night instrument conditions, descending in stall, the "seat of the pants" fast becomes a false reference ...)
Idea: pilot is putting in nose down input, stability is either over helping (doubtful, as pilot overrides) or
sensing speed at the other extreme, so that as soon as pilot input stops, it helpfully moves THS in the wrong direction. That (if the THS isn't stalled) might be felt as turbulence, or not at all if there is already turbulent air as the environment.
But that idea may be nonsense.
There are still nose down commands from the sidestick of unknown duration. RetiredF4's post finally puts a finger on something I was trying to ask: were they at some point futile?
Or, were the pilots reverting to back stick inputs to get the aircraft
to respond at all. (Seen something similar to that in spin training with a pilot mentally behind the aircraft ... ) RetiredF4's post explores that nicely.
The skeletal nature of the reported timeline (needs a bit more meat on the bone, hopefully to come in time) leaves the question of "why didn't nose down commands (such as they were) change the THS position from the reported ~13 deg from apogee to the surface?"
If I am saying roughly what you are saying, my apologies for the repetition.
Back to one of our other posters, who described a while back how long it took for the nose to respond in stall recovery ... per lazerdog's kinesthetic comments. I will add to that thought the sense of tempopral distortion that frequently arises during disorienting events.
I've experienced it myself, and it ain't pretty.
By temporal distortion I mean a sense of it all happening in slow motion, where the sense of time passage is lost. This can influence actions and thoughts. Sample:
"I pushed the stick, nothing happened, I need to do something else" so another control input is made.
The decision/act cycle (or the OODA loop) happens in compressed time scales (fractions of a second) as compared to normal flying of a passenger jet, where smooth and deliberate is the normal pacing. (OT: That smooth and deliberate approach is much appreciated by the passengers, I can assure you!
)