OwainG;
Great post, thank you - it is taking me some time to absorb and think it through. I would like to offer what I can by way of response.
I will bow to any pilot opinion that differs, but it seems to me to be perhaps expecting too much for a pilot to distinguish a change in frequency content of cockpit motion when he has been experiencing turbulence and was expecting more severe turbulence to come shortly. I note that the AI Chief Test Pilot has said that it is very difficult, even for experienced test pilots, to distinguish the transition into stall.
Yes, I think that is a very good point. I think it is probably expecting too much to distinguish between the character of turbulence and buffet under the circumstances described. Confirmation bias may play a role in this, for as you say, "more turbulence" was expected. I have asked and I think simulators, even D-Level, do not replicate turbulence and either high or low speed buffet differently. Perhaps that will be one of many changes that will emerge in the learning.
If there is no pitch break and the buffet is difficult to interpret, he would have been thrown back on symptoms that do not appear in the JAR description of stalls – high attitude and inability to arrest the rate of descent – but over to pilots to evaluate those.
Again yes, I think that is a good place to start the change in the teaching/checking of stalls in all conditions. Despite the fact that simulators do not currently replicate the aerodynamics of the actual stall, (once past the approach to the stall), they could certainly replicate these two symptoms and training stall recovery techniques as per the revised "
Stall Warning or Aerodynamic Stall Recover Procedure" (Airbus, Boeing, Bombardier, Embraer document), revised published procedures could be scripted in recurrent training. In fact, I would expect such training and checking are already being implemented as is the UAS procedure (including clarifications on how to do the drill and checklist).
I'm sure that the various regulatory authorities are examining all this and will change their PPC (Pilot Proficiency Check) mandatory requirements concerning the approach to the stall from "minimum loss of altitude" to the current wisdom. Currently in Canada even teaching/checking the approach to the stall, and the stall itself, are not required if the PPC is for FBW aircraft, (not sure if this includes the B777 or not - anyone?).
One other thing that is hardly rocket science either but will probably surprise many people is the THS behaviour. THS AOA is just the body AOA less downwash and THS setting. The downwash is usually expressed as a value at zero AOA plus a downwash gradient relating downwash and AOA. I have used 1deg and 0.4 if anyone cares.
The aircraft first went into the final stall at about 02:11:55 at which time the AOA was around 10 deg and the THS at -3.4. Downwash was 5 deg, so the THS angle of attack was 1.6 degrees positive. The THS arrived at -13.6 at 02:12:27, when the AOA was over 40 deg. With the above assumptions the downwash would have been 17 deg and the THS angle of attack 9.5 deg positive. There are arguments to suggest that this is an overestimate of downwash behind a stalled wing, so the THS AOA would have been at least this positive value.
For virtually the whole of the event, and certainly for the whole time the aircraft was stalled, the THS had a positive AOA so that it was generating upwards lift and a nose down pitching moment despite the fact that it was set at -13.5 degrees!. This is consistent with it being a stable aeroplane as shown by that pitching moment curve.
The one question I have on this then, is about the elevator which clearly had aerodynamic authority all the way down. If, after the stall was fully-developed and even with the THS at -13.5deg, if the SS had been placed in the full ND position and held there, depending upon when this was done, (earlier the better of course!), and given the ND pitching moment afforded by the THS, would such elevator position be sufficient to eventually get the nose down or would it partially/fully stall given the already-positive AoA of the THS, and lose all effectiveness thereby?
Fascinating post, thank you sir.