I have to wonder if the initial thought of the PF was (after auto pilot, A/T disengage) to not let the aircraft increase its speed due to the anticipated turbulence upcoming. Remember there was a crew communication to the cabin about "it'll move about a bit more than at the moment" (2h06m04), along with the crew deciding to reduce speed from .82 to .80 a few minutes later (2h08m07) due to the anticipation of turbulence - "turbulence increases slightly". About 2 minutes later is when the A/P and A/T disconnect and the speed drops from 275kt to 60kt and a few seconds later the crew identified "so, we've lost the speeds". So now recognizing that they had invalid speeds, and knowing they needed to avoid penetrating the turbulence at too high of a speed, I wonder if the initial thought was to apply nose up inputs to ensure turbulence penetration speed was not exceeded. I also have to wonder with this being fresh on their mind, it might have been their initial concern when losing the speed indications, that we can't penetrate the weather at too fast a speed. Then while troubleshooting and dealing with everything going on and possibly being distracted, realized there was too much nose up input and went to nose down (7000ft/min to 700ft/min) You also have to wonder if through this whole ordeal, if that was something they were fighting if they were in IMC conditions and rough air for most of the 3 1/2 minutes.
Right or wrong, I just know that the weather and reducing speed was fresh on their mind. When the A/P and A/T disengaged, maybe there was zero panic and they were confident how to handle the situation and simply were going to wait for the speeds to come back. The other thing that caught my attention...was the crew briefing just before the captain left. The briefing from crew, was that they couldn't climb right now "we’re in the cloud layer unfortunately we can’t climb much
for the moment because the temperature is falling more slowly than forecast" - So I have to wonder if that is something they had discussed earlier about possibly trying to climb above the current cloud layer, but couldn't due to conditions and aircraft config at the time. When they lost the speeds, I wonder if there was a thought of trying to climb if they could to see if they could get to 1)smoother air and 2)out of the cloud layer to hopefully clear the pitot sensors.
I am probably reading between the lines, and CVR recordings would help to identify some of this. I just find it interesting that climbing was part of the crew briefing.
So did the PF try to pitch up slightly to keep the aircraft speed below .80 since they were now more than likely penetrating turbulent air? And was there a desire to see if they could get to a higher altitude (out of IMC) to help resolve the issue with the speed sensors? Again right or wrong from SOP, but it could point to one of the reasons of nose up initially. Once they entered a stall, that created a whole host of other challenges.
I haven't flown in a few years and only flew corporate jets for several years, but the mindset of the pilots will be very hard to decipher even with CVR recordings, which will help to paint a better picture of what they were thinking. I want to be able to give the pilots the benefit of the doubt and would like to think that there was some logic in the initial nose up and at other times nose up commands. As pilots, we need to be supportive of each other, and realize that many of us have been fortunate enough to not have to deal with a "hairy" cockpit in our careers. But for those that have, like this crew, we have no idea what was going through their heads.