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Comment by throwaway313373 | Hacker News Reader

I always wondered who even decided that averaging the input is a good idea.

It sounds like it makes sense at first glance, but if you think about it a little bit more it actually doesn't make any sense.

The average of two inputs is basically garbage, it doesn't do what either of the pilots want to do and it breaks feedback for both of the pilots.

After watching tons of Mentour Pilot videos (who, by the way, covered [0] this incident) I am convinced that this feature shouldn't exist at all.

And no, I don't think that I'm smarter than people who originally designed this system. I just think that this particular feature was not designed at all. It seems like an afterthought. Like, "hey, there is this corner case that we haven't thought about, what should we do if both pilots input something on the controls? - well, let's just average it, kinda makes sense, right?"

[0] https://www.youtube.com/watch?v=6tIVu0Dpc2o

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> After watching tons of Mentour Pilot videos (who, by the way, covered [0] this incident) I am convinced that this feature shouldn't exist at all.

There is some selection bias at play here. We don't know how many situations happened where averaging the input was the right thing to do and avoided an accident, as Mentour Pilot does not make videos about those.

I'm not saying averaging is good. I have no idea. But a number of videos about crashes (which I watch and think are awesome) are not a good reason to form beliefs.

> I don't think that I'm smarter than people who originally designed this system.

This sentence says one thing, the other sentences in your comment say the opposite. It certainly reads like you think you're smarter than those people. Which as far as I know could be true, no idea. My point is a disclaimer does nothing if you actually do the mistake you know you should avoid.

> The average of two inputs is basically garbage, it doesn't do what either of the pilots want to do and it breaks feedback for both of the pilots.

I think it's done in case one of the sticks has a bit of drift. If there was an alarm for dual input it would constantly be going off in that case.

There is an alarm on dual inputs.

Except when there's not ... In this case, it was superseded by "more pressing" alarms, namely "pull up"/"you're too low".

Yeah, that's a good point though, of course in most situations it is more urgent so this choice makes sense. BUT in this case not being aware of the dual input made the GPWS worse. So in this paricular case it was not.

Personally I would do a different type of alarm for dual input, like a big red light somewhere. Or just not allowing dual input somehow (always requiring the use of the takeover button).

I mean, what choice, besides averaging, would make sense? Completely disregarding one pilots input seems worse, and averaging is what happens in a mechanically connected system. The crucial difference is that in that case the pilots can feel that this is happening. I don't know what sort of force feedback the Airbus sidesticks provide, but this lack of feedback seems to me to be the real root of the problem, not the averaging itself.

Disregarding one pilot input seems better: one pilot can correctly fly the plane while the other does nothing vs two pilots getting confused and flying planes into the ground. Even better would be a system that somehow follows the "I have the stick" procedure, although I don't know if that is possible.

You are right though that either way force feedback make sense. You could even just do a buzzing if there's dual inputs, like when you take your hand off a lane-controlled vehicle.

Say one of the pilots is suicidal, or had a heart attack and is unconsciously while holding the stick in the wrong direction, how does the airplane know which input to ignore?

> I don't know what sort of force feedback the Airbus sidesticks provide,

None.

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