Back in post #260 I made some assumptions about the THS and the AoA. The basic post is repeated below with a small addendum and should be self explanatory.
At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have
no valid indications". At that moment, the thrust levers were in the IDLE detent and the
engines’ N1’s were at 55% the angle of attack decreased, the speeds became valid again and the
stall warning sounded again.
My interpretation is that the aircraft was in a well established stall (deep stall?) and passing through FL250 with RoD about 10,000 feet/min, and even though both engines N1's were 55%, the pitch-down inputs decreased the AoA and the airspeed data became valid. However, that IAS was low and the stall warning activated again but ceased with further pitch-up commands as the data again became invalid.
Without AoA information, neither pilot had any idea in what part of the stall regime they were, and seemed to react as if a return of the SW was indicating Vmo, hence the continuing pitch-up command. So failure at this time to persist with the pitch-down command effectively left them doomed, as even then with the time taken for the THS to readjust (if it was going to
**) and for the wings to start flying, meant that the chance of reducing the RoD to zero before FL0 was marginal.
It strikes me that no-one on the flight deck realized that the AoA data was only valid when IAS was greater than 60KTS. Even though they went looking for the FPV, it seems it was only after the SW stopped at 2:11:40 plus a few seconds, and therefore to no avail - see ACARS FPV messages timed 0212z. Their final chance to grab the FPV page was missed shortly after 2:12:02 when the stall warning sounded again - meaning valid airspeed!
** The THS question?? As IAS had gone below 60KTS, the aircraft was no longer in Alternative 2 Law, but was now in
Abnormal Law which means that the THS must be manually trimmed. Even so, in the description given above, I believe that with the low airspeed the elevator was still capable of making an attitude change, provided it received a nose-down command.