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Comment by steveBK123 | Hacker News Reader

The fly by wire as implemented by Airbus results in illogical states that are impossible in mechanically linked systems.

The most jaw dropping one is the stick input averaging.

https://www.reddit.com/r/NoStupidQuestions/comments/10w54e4/...

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The same thing happens on the 777 and 787: if too much opposite force is applied on both yokes, they lose their linkage and are averaged. There is no warning or priority button, unlike on Airbus planes.

Older Boeing planes also have a mechanism to unlink the controls if too much opposite force is applied. The left yoke would control the left side of the plane, the right yoke would control the right side.

Interestingly, the dual-input rate is roughly the same on Airbus and Boeing planes: 0.44 per 1000 flights and 0.4 per 1000 flights, respectively: https://bea.aero/fileadmin/user_upload/F-GSQJ_finalreport_EN... pages 45 and 47.

I don't really understand what's so jaw dropping about input averaging. Let's be clear - this is a fallback state that handles a situation that should never come up. Pilots aren't supposed to try to control the aircraft from both seats at the same time, both fly-by-wire and not. What we're talking about isn't a deficiency that can sporadically cause a dangerous situation, like the MAX, but a situation where the pilots have already made a massive mistake and the automation didn't bail them out. It's not like there's no workaround, either. Making conflicting commands results in the plane blaring a 'dual input' warning at you, and if one of the pilots desires exclusive control, they can press the side stick priority button. A further improvement of the system would be to add force feedback to the side sticks, to simulate the linked yokes of a non-fly-by-wire aircraft, but even without it, I feel like this issue is given way more publicity, and it's used as the scapegoat for the ultimate cause, pilot error. All incidents that involved this were ruled as being caused by pilot error - in the crash this article is about, the PF was literally holding his side stick full back until almost the very end. A force feedback system might've helped them realize it sooner, or it might not have - there's plenty of historical incidents where pilots managed to stall conventional aircraft out of nowhere in a similar fashion, but those were ruled to be their mistake only.

I struggle to think of a situation where "average the pilots' inputs when they disagree enough to sound the alarm" would ever be the expected or correct action to take, especially given the existence of the sidestick priority logic

Really seems to violate the "principle of least astonishment"

https://en.wikipedia.org/wiki/Side-stick#Handling_of_dual_in....

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