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In many aircraft hard elevation will overpower even a faulty horizontal stabilizer In the 737 you can get into situations where the elevator has insufficient
by inferiorhuman 8y ago
In many aircraft hard elevation will overpower even a faulty horizontal stabilizer
In the 737 you can get into situations where the elevator has insufficient authority to overcome a stabilizer. Excessive pitch up (leading to a potential stall) that you can't counter by pushing on the yoke is exactly what MCAS is designed to prevent.
There was a mechanical failure, the AoA sensor.
A fixed offset from reality is an interesting failure mode, especially in two separate sensors (Lion Air replaced the alpha vane before flight 610), and even more interesting as it's the same alpha vane used in the 737 NG. The left alpha vane was being interpreted as almost exactly twenty degrees higher than the right.
- 6nf 8y agoThe left alpha vane was being interpreted as almost exactly twenty degrees higher than the right. Is that because the plane was in a banking maneuver at the time maybe? I dont know anything about planes but I heard that when you're turning the two sensors will disagree by some amount
- inferiorhuman 8y agoIs that because the plane was in a banking maneuver at the time maybe? I dont know anything about planes but I heard that when you're turning the two sensors will disagree by some amount The difference in angle of attack was consistent throughout the entire flight (well up until the crash where the values began to converge). The threshold for the optional 'angle-of-attack disagree' warning is, I think, ten degrees. It seems very unlikely that the plane had a twenty degree bank angle for two entire flights.
- cjbprime 8y agoI think it's been disclosed that in Lion Air the sensors were twenty degrees apart even when sitting on the runway before the flight. It is shocking that nothing checked for disagreement or communicated it to the pilots.