In this incident, as with Air France flight 447, pilot and co-pilot were holding the controls in opposite directions, and the software averages the input. In this case the warning that the controls were mismatched was not of sufficiently high priority to be issued (other warnings were taking precedence: You're about to crash). This user interface just continues to appall me.
With mechanically joined controls, it is impossible to have this happen. I think if I were designing a modern aircraft, I might retain physical linkage for just the reason.
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?"
Mechanically joined flight controls typically have a linkage designed to break when sufficient force is applied. This can cause equally disastrous results when the two pilots are putting in different control inputs.
My dad taught instrument flying in fighter jets. He'd ride in the back seat, with the student in the front. The controls were linked together.
Against regulations, he carried with him a length of steel pipe. The problem was sometimes a student would freeze and hang onto the controls with all his might. The pipe was so my dad could beat him on the head until he let go, and save both their lives.
Fortunately, he was never forced to do this. But he said "I'll be damned if I let any student kill me!"
P.S. the thing about instrument flying is your senses lie to you, and you need to rely on the instruments. A green student is at risk of panicking and believing the lies his inner ear is telling him (spacial disorientation). When JFK jr crashed in the mist at sunset, my dad passed by the TV when they reported it, and said "spacial disorientation". It's killed a lot of pilots.
A major part of learning to fly instrument is to learn to ignore your body screaming at you that you're flying upside down.
And the reason they have this, is so that pilots can overcome a jam by breaking that linkage. Only half the plane will then be responding to the controls, but that's much better than none.
The rationale for this (I did some work on this system at Boeing) was that the pilots would not be fighting each other for control, they would be fighting a jam.
Flight controls at the time were not designed for dealing with a crazy or malicious pilot.
With mechanically joined controls, it is impossible to have this happen. I think if I were designing a modern aircraft, I might retain physical linkage for just the reason.