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Comment by andy_ppp | Hacker News Reader

I mean just to give an anecdote that is slightly worrying; I was about to land in Grenoble and it was quite rocky the turbulence and incredibly windy, you could tell we were coming in too fast and the pilot decided to back out of the landing and take off again with the wheels nearly on the runway.

Suffice to say the angle of attack was extreme and the power produced by the engines quite impressive/terrifying. I would say anything that decided to change the express wishes of the pilot in that situation would have been hugely dangerous.

Can someone explain why ever overriding the pilot rather than warning them would be a good thing?

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I can't find a source right now but I remember reading that there had been a few cases where there had been an emergency situation and pilots had ignored stall warnings, resulting in the plane stalling and crashing. This was why Boeing had elected to make the system on the 737 Max 8 override the pilots inputs.

I think having an emergency system that overrides the pilot is fine, but it is crucial that the pilot can easily and quickly disable such a system when they know the plane is doing the wrong thing.

> a few cases where there had been an emergency situation and pilots had ignored stall warnings

I remember that being about pilots' becoming over-sensitized to visual (red lights) over audio ("stall warning" audio) warnings during a crisis, often ignoring the audio inadvertently (i.e. not hearing it).

You say that «the angle of attack was extreme», but are you sure about that? Bear in mind that AoA is not equal to pitch. As the engines were producing a lot of thrust, the AoA might as well have been relatively low once positive climb was established.

From the diagrams I see online [1] it's difficult to know either way because the wind direction plays a part in the AoA. It could have been more or could have been less than I felt it was, but for certain the pitch was much higher than normal flying.

[1] https://en.wikipedia.org/wiki/Angle_of_attack

On the MAX, this case ("take off/go around power") seems like it is one of the cases that MCAS should have an interest in protecting against. The risk from the high/forward engines causing lift and inducing a stall seems like it would be high here.

I've read conflicting information about whether MCAS would activate during TO/GA. But regardless, if you're saying that you don't want MCAS to activate, it seems like you're also saying that you want the pilot in control during a moment where the plane is so liable to stall that they invented a system to try to safeguard against it happening.

(Not a pilot.)

My local airport (Halifax YHZ) has notoriously bad landing conditions, and around a year ago I was in a 767 that aborted its landing and went back around. Turns out (at least as far as I've been able to tell from Wikipedia etc.) that the entire aborted landing sequence is activated in one step by the pilot and the plane does all the multiple complicated things it needs to do (change thrust, trim, flaps, etc.) mostly by itself. How that would work with bad sensors is a separate question - although presumably by this point in a flight you'd know what's up with your sensors one way or another.

I agree with what you are saying in principle. However, the MCAS system apparently is designed to not kick in when the flaps are extended. In your situation, since you were descending to land, the flaps would have been extended and MCAS wouldn't be activated. The pilot would have kept the flaps that way until the aircraft reaches a certain altitude.

For what it's worth, I'm not sure that this is true. I think there is a conjunction involved -- MCAS is activated when [a] or [when flaps are up and b]. I'm not sure whether [a] covers the take off/go around case, but it seems like it might since that case produces high AoA due to the extra lift generated by the engine placement at high load.

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