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Comment by siwatanejo | Hacker News Reader

IIRC the two planes that crashed only had a single AOA sensor (the 2nd redundant one being only present in a premium add-on that those airlines didn't purchase), so this software fix would have not changed anything.

EDIT: alright thanks for the replies.

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From what I've gathered, all MAX planes (including the ones that crashed) have two AoA sensors, but MCAS just uses one. As far as I know there was never an option to have a redundant configuration. The premium add-on was the indication that they disagree.

No, all 737s have two AoA sensors. The one on the captain's side feeds the flight control computer on that side, and the one on the first officer's side feeds the flight control computer on that side. At any one time, one computer is in charge. They can compare data, but Boeing decided not to for MCAS.

All 737 MAX have two sensors. The Lion Air flight had sensors disagreeing by 20° right from the start. This made the stick shaker go off on one side right after departure (throughout the entire flight) and led to a multitude of other alarms (altitude disagree, unreliable airspeed).

> the 2nd redundant one

No, it was never redundant, in the "premium variant" only the "they don't match" signal would be displayed / sounded, but only one used still, and the pilots would have to turn MCAS off and fly with the plane which behaves differently than the one for which they are trained.

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