What is stall?
How a pilot should react in front of a stall situation?
The worldwide air transport fleet has recently encountered a number of stall events, which indicate that this phenomenon may not be properly understood and managed in the aviation community. As a consequence, the main aircraft manufacturers have agreed together to amend their stall procedures and to reinforce the training. A working group gathering Authorities and aircraft manufacturers will publish recommendations for harmonized procedures and appropriate training. This article aims at reminding the aerodynamic phenomenon associated with the stall, and the recently published new procedures.
In summary:
FIRST: The AoA MUST BE REDUCED. If anything, release the back pressure on the stick or column and apply a nose-down pitch input until out of the stall (no longer have stall indications). In certain cases, an action in the same direction on the longitudinal trim may be needed. Don’t forget that thrust has an adverse effect on AoA for aircraft with engines below the wings. SECOND: When the stall clues have disappeared, increase the speed if needed. Progressively increase the thrust with care, due to the thrust pitch effect. In practice, in straight flight without stick input, the first reaction when the SW is triggered should be to gently push on the stick so as to decrease the pitch attitude by about two or three degrees in order to decrease the AoA below the AoA SW. During maneuvers, the reduction of the AoA is generally obtained just by releasing the backpressure on the stick; applying a progressive forward stick input ensures a quicker reduction of the AoA. If the SW situation occurs with high thrust, in addition to the stick reaction, reducing the thrust may be necessary.
by Jacques ROSAY VP Chief Test Pilot
Generic Stall Warning or Aerodynamic Stall Recovery Procedure
Immediately do the following at the first indication of stall (buffet, stick shaker, stick pusher, or aural or visual indication) during any flight phases except at liftoff.
1. Autopilot and autothrottle............................. Disconnect
Rationale: While maintaining the attitude of the aircraft, disconnect the autopilot and autothrottle. Ensure the pitch attitude does not change adversely when disconnecting the autopilot. This may be very important in mis-trim situations. Manual control is essential to recovery in all situations. Leaving one or the other connected may result in inadvertent changes or adjustments that may not be easily recognized or appropriate, especially during high workload situations.
2. a) Nose down pitch control… Apply until out of the stall (no longer have stall indications)
b) Nose down pitch trim.................................. As needed
Rationale:
a) The priority is reducing the angle of attack. There have been numerous situations where flight crews did not prioritize this and instead prioritized power and maintaining altitude. This will also address autopilot-induced full back trim.
b) If the control column does not provide the needed response, stabilizer trim may be necessary. However, excessive use of trim can aggravate the condition or may result in loss of control or in high structural loads.
3. Bank...............................................................Wings Level
Rationale: This orientates the lift vector for recovery.
4. Thrust...............................................................As Needed
Rationale: During a stall recovery, many times maximum power is not needed. When stalling, the thrust can be at idle or at high thrust, typically at high altitude. Therefore, the thrust is to be adjusted accordingly during the recovery. For engines installed below the wing, applying maximum thrust can create a strong nose up pitching moment, if speed is low. For aircraft with engines mounted above the wings, thrust application creates a helpful pitch-down tendency. For propeller-driven aircraft, thrust application energizes the airflow around the wing, assisting in stall recovery.
5. Speed Brakes.........................................................Retract
Rationale: This will improve lift and stall margin.
6. Bank...............................................................Wings Level
Rationale: Apply gentle action for recovery to avoid secondary stalls then return to the desired flight path.
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