Boeing 737 MAX runaway trim scenario in a sim

“Ethiopian MAX Crash Simulator Scenario Stuns Pilots” (Aviation Week) describes an American crew given a comparatively trivial challenge. They were put into a sim and advised in advance that the MCAS system would go haywire. They started from a 10,000′ moderate speed (250 knots) cruise.

This is analogous to the crews that were given the “Skiles and Sully” US Air 1549 scenario and were able to do a 180-degree turn and land back at LaGuardia on a dry runway.

Piece of cake, right?

What the U.S. crew found was eye-opening. Keeping the aircraft level required significant aft-column pressure by the captain, and aerodynamic forces prevented the first officer from moving the trim wheel a full turn. They resorted to a little-known procedure to regain control. The crew repeatedly executed a three-step process known as the roller coaster. First, let the aircraft’s nose drop, removing elevator nose-down force. Second, crank the trim wheel, inputting nose-up stabilizer, as the aircraft descends. Third, pull back on the yokes to raise the nose and slow the descent. The excessive descent rates during the first two steps meant the crew got as low as 2,000 ft. during the recovery.

(i.e., they would have crashed if they hadn’t started with at least 8,000′ of altitude above the ground)


5 thoughts on “Boeing 737 MAX runaway trim scenario in a sim

  1. I have no comment on the story itself, only the fact that anyone is surprised. It has been discussed at length on various aviation forums, and reproduced in full detail in a public YT video. Only once a US based crew redproduced it, does it become a news story…

  2. Has Boeing (or anyone else) developed documentation of how many crashes were avoided by the AOA sensor and stick pusher? We know of two aircraft that crashed because of it, but were any aircraft saved by it? …or more prosaically, does anyone have data as to how often is this system operated? For each 1000 flights, does it kick in once or twice, or hundreds of times?

    • I think that the lack of data recording activations without crashes is another indication of a flawed system design. You would think that every activation, since Boeing did not expect such activations to be common, would result in a flagged log entry and an (or similar) message.

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