Originally Posted by Lazerdog
As they were descending in the the stall through 10,000 feet, the THS was trimmed up automatically. Would full forward side-stick have caused immediate stall recovery, or would the PF have to wait until the THS auto-trim caught up with nose-down trim? (How long would that take if so?)
I don’t think that stall recovery could have been immediate. With the aircraft “deep” into the stall (AoA >40 degrees ?) it must be pitched down over a considerable arc: 10, 20 or 30 degrees, would that take 5, 10, or 15 seconds? I don’t know, but I believe one should think in terms of those delays.
Perhaps the graphs posted earlier would help to answer questions about AoA and pitch.
The green line in
Figure 1 shows the total energy (expressed as the equivalent FL) at five instants at which the BEA update provided altitude and airspeed. Total energy is the sum of:
Potential energy = m*g*h, and
Kinetic energy = 0.5*m*TAS^2,
where m=mass, g=acceleration of gravity, and h=height.
The red line shows the vertical acceleration assumed to calculate the actual FL (shown in blue), by integrating vertical acceleration to obtain vertical speed, and integrating that again.
Figure 2 shows the vertical speed and altitude, and also the airspeed calculated from the kinetic energy, i.e. from the difference between altitude and total energy FL shown in figure 1.
Figure 3 shows the air-based flight path angle calculated from TAS and vertical speed, and the AoA that corresponds to the lift force that would produce the vertical acceleration at the calculated CAS. The pitch angle is then the sum of FPA and AoA. The two red nearly parallel lines show the alpha-max for the Mach-number at each instant (full line), and the stall warning threshold (dotted line).
How does one recover from a stall without reliable airspeed and without AoA display?
AP and A/THR disconnected when one or more pitots iced up at 2h10min05 at FL350 and M=0.8. Less than one minute later the airplane’s climb peaked at FL380. The airplane stalled some seconds earlier, and the PF apparently made only a half-hearted attempt to prevent that. His pitch-down input reduced the pitch to about 7 degrees up, and the v/s from 7000 to 700 fpm. Maybe if he had stopped the rate of climb, and reduced pitch to below 5 degrees, that would have been enough to prevent stalling. Given the inadequate control commands in that first minute it is perhaps unlikely that, even if the PF had been aware that the was in a fully developed stall, he would have made the more agressive commands that were needed for recovery from “deep” into the stall.
The inconsistency between speeds 1 and 3 lasted less than one minute in this case, but in one documented cases of UAS as much as 3 minutes and twenty seconds. So I asked myself: how does one recover from a stall without reliable airspeed and without AoA? I would think that the proper action would be a determined nose-down push, maintained until the stall warning stops, and then trying to maintain an AoA on the edge of s/w, gently allowing the nose to raise until s/w occurs, then a small nose-down correction to silence it, etc., until back in approximately level flight at a reasonable pitch attitude.
EDIT:: Can anyone be expected to do that succesfully without being trained for that eventuality?