Dozy:
Aside from the pitots, nothing was wrong with that aircraft.
Not quite so. There was the matter of a few pitot tubes going AWOL for a bit that was trigger to this event. Absent that, no UAS, and no issues with hand flying way up there where the air is thin, and a bit bumpy. Granted, that is a malfunction, and there are procedures for it, but there was something wrong with the aircraft. Something fundamental.
Ian, please don't hate me for what follows:
First note: if the two pilots were both aware of them being in condition UAS, what is the likelihood that they were skeptical of stall warning, knowing that airspeed is a component of stall AoA calculations? That might explain in part the apparent "ignore" of the stall warning.
Second note:
From the latest release, the aircraft went into a condition of unreliable airspeed. What leaped out at BEA was that (if I read this rightly) the crew didn't progress to the unreliable airspeed checklist/procedure as was standard practice at the time. (If I misunderstand that, my apologies).
The information released shows me a PNF who had to focus on flying problems rather abruptly. His requirement to assist (rather than take over from??) the PF, to include the switch to (F/O 3 on the ATT select?? takata's illustration informs this) indicates to me that he felt that the PF was having difficulty with his PFD. Given the number of things going wrong on displays, and the PF being unclear on what he was seeing (from PNF perspective) giving the PF a better inertial unit to run his would be a helpful copilot (role) assisting PF. (If this guess is off, apologies).
In the meantime, hand flying at altitude with UAS in Alt 2: is this trained for?
If not, the PF was playing catch up.
A human factors question arises that may be answered by AF SOPs or habits, or it may not have an answer.
With what appears to be the senior pilot between the two recognizing a pilot who was fighting the aircraft a bit, or chasing it, his initial "talk him back into the scan/situation" is what most of us would do as good copilots ( in terms of our role at the time.)
At what point should/would it have been "I have the controls" when the PF kept chasing the attitude and the PNF kept having to prompt him to go in a different direction? (Aside: Isn't that the question every Captain must have a clear answer to before takeoff, or an instinct for, in terms of his threshold of "that's enough, I have controls" when his copilot is flying?) If the PNF made a number of inputs on the SS but didn't take controls, I know a few CRM people who'd be aghast, as the preference is that one pilot is on controls, the other isn't. (We could probably spend all day debating the intricacies of what's behind that.) WIth a SS, his inputs won't be felt by the PF, so the "summing" function may have less than the desired effect, as opposed to conventional controls where the PF would have felt what PNF was doing. <== Is this a shortcoming of SS, or an advantage? I can see it both ways. (Anyone whose instructor "rode the controls" while you were learning probably sees the issue here).
The SOS call to the Captain was a good idea. I am unclear on the problem that seems to have delayed the Captain's return ... maybe it wasn't delayed, but PNF was in a mild case of temporal distortion -- time was slowing down or speeding up for him.
If the PF was unable to get level, you can argue that PNF can't get to the next logical task: procedure for airspeed indications being unreliable, and announced in the cockpit, acknowledged, and subsequently they follow the step by step UAS procedure.
The PF's flying occupied most of his attention.
Why PF couldn't get to straight and level is a question AF has to answer.
If the aircraft can enter a given mode, (degrade into ALT Law 1 or 2 or direct) then the pilot must be trained to fly it in that mode. Likewise direct law. Not just initial training, but proficiency, and/or refresher.
You never know when you'll need it.