High altitude stall recovery B737
We know that if a high altitude stall occurs for whatever reason, the initial action is to level the wings and lower the nose; thus reducing the angle of attack. Simultaneously thrust is applied. For 20,000 lbs thrust CFM 56 engines at 37,000 ft the thrust available is about one quarter of that at sea level and the pitch up from thrust application is easily countered. Different of course during a go around at sea level
Once recovery from the stall is made (almost instantaneously if the angle of attack if reduced sufficiently and promptly) the question arises what minimum safe airspeed should be attained before the pilot eventually aims to level out? To quick a level out after stall recovery at high altitude invites secondary stalls as evidenced by continued buffeting. The Boeing FCTM does not address this clearly, especially as the pilot may be tempted to prematurely initiate levelling out for minimum height loss.
One clue may be found in the FCTM under Chapter 4, Climb, Cruise, Descent and Holding where in part, it states the following:
"Recommended holding speeds can be approximated by using the following guidance until more accurate speeds are obtained from the QRH.
Above FL250, use VREF 40 +100 knots to provide at least a 0.3 g margin to initial buffet (full maneuver ability)"
This suggests that once the airspeed reaches approximately 230 knots (depending on weight of course) during the course of recovery after lowering the nose, it would be safe to stop further descent and review the situation from there. It follows that if the stall was the result of mishandling due to severe turbulence and this severe turbulence was still present during the recovery process, the recovery to level flight should be delayed until reaching severe turbulence optimum penetration speed.
This recovery technique when used in the simulator results in a height loss of approximately 3500 feet. If using optimum severe turbulence penetration speed as the aiming point before recovery to level flight, then a height loss of approximately 5000 ft is needed.
Constructive comments welcomed.