Why stalls happen — and how to control them

Q: Did you ever practice actual ( not simulated) stall recoveries while an active captain?

— Bob Dienes, Tampa

A: Yes, I did some flight test work on the Fokker F- 28 and B737. In both airplanes, we did full stalls. This is not usual, and many pilots have not fully stalled a transport jet. Fully stalling the actual airplane is usually left to test pilots.

Q: If you are flying into the wind just a bit above stall speed and then make a sharp turn to downwind, will you stall?

— David Soom, Sparks, Nev.

A: It is possible that you will. If you make a very sharp turn downwind, allowing the airflow to slow, then a stall could result. If the wind suddenly shifts from a headwind to a tailwind, a stall can occur ( this would be a wind shear condition).

The determining factor is whether the airflow detaches from the wing. If the turn is slow enough that the air remains attached, then it will not stall.

Q: You have said that stalls are not related to engine power. If that’s so, why couldn’t Capt. Chesley Sullenberger’s plane make it back to LaGuardia or another airfield?

— Brian, Monument, Colo.

A: Speed is related to lift, and insufficient speed results in a stall. Stalls are not related to engine power. The engines provide thrust, making it possible to fly in level or climbing flight. Without thrust, the only means to keep air flowing over the wing is to trade altitude for airspeed ( potential energy into kinetic energy).

In the 2009 case of US Airways 1549, when the engines failed, Sullenberger had to trade altitude to maintain the necessary airflow. He would have run out of altitude before reaching LaGuardia Airport; the best option was the Hudson River landing.