Originally Posted by
Hyperveloce
Is the nearly saturated THS nose up angle of 13° a consequence of the autotrim and of the (integrated/lagged) repeated nose up orders ?
That is at least consistent with the way Auto- Trim is supposed to behave under normal conditions and therefore a likely scenario.
- 13° THS nose up angle: were the pilots informed of this ? If so, a manual trimming back to lower angles would have been their only hope then ? (related SOP ?)
At least before probably entering into Abnormal Law when the AoA exceeded 30°, a normal continuous Nose down command by pushing the stick forward should have also reduced THS angle accordingly.
Therefore it is likely that a manual use of the Trim wheel would only have been required when deep in the stall, long after starting the descent.
That point would have been reached somewhere around 2:11:30.
And even after that point Auto Trim could have been regained if continuous Nose Down combined with reduced thrust would have reduced the AoA below 30°.
In that case auto Trim would have been available again.
The fact that a brief Nose Down and Thrust reduction brought back the speed readings indicates that very likely a continuos full Nose Down command would have saved the day, probably even after exceeding 35° AoA.
Unfortunately it seems that was never really attempted, at least not persistently enough.
Sad.
The question remains Why !?
Let's hope the CVR will shed some light on that.
Edit:
Graybeard:
The THS and elevator would not work in a normal manner.
Even at these angles the deflection of THS and elevator will have significant influence on the behaviour, especially in combination.
The combination produces camber which even under high AoA will change the drag coefficient significantly.
That is one advantage compared to the all moving tailplanes on an F-16 for recovery in such a situation.
The other advantage of the 'Bus' is the fact that it is by far more longitudinally stable than the F-16 which was even slightly unstable in the A- Version. It had a negative stability coefficient (albeit very little).
The 'Bus' has definitely a positive longitudinal stability margin even with max aft CG.
Therefore it surely needed the 13° THS (potentially plus Nose Up elevator) to keep it in the deep stall.