Thanks for posting several articles that provide very useful information about flying an A/C of this kind.
...I've always doubted the notion that the airplane was slow and 'slushy' to respond to the stick at altitude and that a bit of PIO or inadvertent backstick while controlling roll resulted in an "accidental" climb that continued to 38,000ft but I'm outa ideas!
PJ2
One element that drew my attention in the last article you've posted was the mentioning that the A/C reaction to pitch and roll commands is amplified at high altitude.
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Regarding the climb from FL350 to FL380, there are several elements in the BEA text (marked in italic, and/or color) that attracted my attention, and perhaps are worth mentioning:
Sometime
between 1:59:32 and 2:01:46, the PF said, “…turbulence that you just saw…. We’re in the cloud layer unfortunately we can’t climb much… because the temperature is falling more slowly than forecast… and the logon with Dakar failed”.
The text marked in blue can be considered as implying that going to a higher flight level, above FL350, was considered as a possible solution, had the air temperature and the Dakar logon been OK.
At 2:08:07 PNF said “you can maybe go… to the left” airplane ….
change ….about 12 degrees possibly because the increasing turbulence …
. The level of turbulence increased … the crew reduce the speed to about Mach 0.8.
At the moment the A/P and A/THR disconnected, at 2:10:05, the A/C needed a correction command, and I think it is also possible that the PF thought, that it is worth trying to go at a higher flight level - we don't know if the air temperature may have decreased?
The BEA text indicates that the
A/C climbed (from FL 350 and speed 275 kt) while rolling left and right
between 12 and 10 degrees to FL 375, at which time the speed on the Left indicator increased (came back) to 215 kt, Mach 0.68, and the AoA was of 4 degrees (with stall warning stopped).
Based on the vertical speed of 7000ft/min mentioned by the BEA's text, the A/C climbed the 2500 ft to FL 375 in about 20 seconds, which left about another 20 seconds of flying approximately at this FL375 and A0A of 4 degrees, before the stall warning was triggered again at 2:10:51.
Note the left speed indicator seems to have been back OK right before the stall warning was triggered again at 2:10:51.
Did the PF, at this moment of stall warning again, decide to go a bit further up, as gaining altitude seemed to him to help with the turbulence, but also be a help with the coming back of the speed indicator? We don't know what he saw through the windshield - ice? - that may have been another contributor to the decision.
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Recently, on a cross continental flight, as passenger, during the heavy storm season, at about ½ way into the flight, at cruise altitude, and clouds way bellow, out of nowhere, the A/C entered a high altitude cloud, and hit heavy turbulence. After a couple of seconds in the cloud and turbulence, the plane climbed, and I could tell, as soon as it came out of the cloud, after not too long, that it was at least several hundred feet higher.