6 ms·

The fact that airbus AVERAGES the control inputs, with no indication of conflicting inputs, when one pilot is pulling back and one pilot is pushing down is just

The fact that airbus AVERAGES the control inputs, with no indication of conflicting inputs, when one pilot is pulling back and one pilot is pushing down is just a perfect example that even at the most critical points, where the stakes are the highest, we as engineers and designers fail to think through the implications of bad design.

cjrp 14y ago
But would adding an extra caution light / sound to the already-stressful situation have helped? I agree that averaging the inputs seems like an imperfect solution, but what would the alternative be... ignore both or ignore just the Captain/First Officer's inputs? edit: Re: physically-linked controls (à la Boeing), with one pilot pulling back as hard as he can Vs. the other pushing fwd, isn't the result still (approximately) an average of the two inputs? Obviously they'd feel that the controls weren't moving, but that could be attributed to a number of factors (e.g. icing of the control surfaces).
- rubyrescue 14y ago
  an alternative would be to move the sticks together, the way non-fly-by-wire planes work.
  - rogerbinns 14y ago
    They could also make the sticks move together even on fly by wire planes (Boeing does it) using force feedback. That is one thing that Airbus really should have done instead of providing no physical feedback. The expectation is that you would use your eyes instead, but the visual channel is already heavily loaded.
- yesimahuman 14y ago
  Well the alternative is what planes with yokes were doing before: they move together. However, I feel this behavior would be odd on a joystick...
simias 14y ago
I've read about this problem several times already but nobody ever explained what was the rationale behind this strange behaviour. Maybe there's a case where that's useful? I can't imagine any engineer would just say "Mmh, what happens if both pilots move the commands in different directions? Oh well, let's just take the average". I'm sure there's more to it.
- s_baby 14y ago
  I don't know the answer but this is "mission critical" code. Averaging inputs is more testable than having a process for passing control and managing edge cases. Every branch in mission critical code is tested for all possible permutations. Averaging is simpler from a verification standpoint. Theoretically...
snippyhollow 14y ago
Agreed, the design was not good at all. Indeed, they now added a compulsory formation in the pilots curriculum for this kind of situation (degraded control mode). However, the pilots took a very big risk when they said "On ne va pas se laisser emmerder par des cunimbs." (We won't be pissed off by cumulonimbi!) and got straight into the storm while others were all rerouting around. Ego kills.
pinko 14y ago
Maybe in the non-pathological case (two pilots performing the same actions almost in sync--which would include many moments of minor conflict as one transitions before the other) it results in a slightly smoother result? Even if so, a terrible design choice to improve the common case at the expense of the rarer but much more critical case.

cjrp 14y ago

But would adding an extra caution light / sound to the already-stressful situation have helped? I agree that averaging the inputs seems like an imperfect solution, but what would the alternative be... ignore both or ignore just the Captain/First Officer's inputs? edit: Re: physically-linked controls (à la Boeing), with one pilot pulling back as hard as he can Vs. the other pushing fwd, isn't the result still (approximately) an average of the two inputs? Obviously they'd feel that the controls weren't moving, but that could be attributed to a number of factors (e.g. icing of the control surfaces).

rubyrescue 14y ago
an alternative would be to move the sticks together, the way non-fly-by-wire planes work.
- rogerbinns 14y ago
  They could also make the sticks move together even on fly by wire planes (Boeing does it) using force feedback. That is one thing that Airbus really should have done instead of providing no physical feedback. The expectation is that you would use your eyes instead, but the visual channel is already heavily loaded.
yesimahuman 14y ago
Well the alternative is what planes with yokes were doing before: they move together. However, I feel this behavior would be odd on a joystick...

simias 14y ago

I've read about this problem several times already but nobody ever explained what was the rationale behind this strange behaviour. Maybe there's a case where that's useful? I can't imagine any engineer would just say "Mmh, what happens if both pilots move the commands in different directions? Oh well, let's just take the average". I'm sure there's more to it.

s_baby 14y ago
I don't know the answer but this is "mission critical" code. Averaging inputs is more testable than having a process for passing control and managing edge cases. Every branch in mission critical code is tested for all possible permutations. Averaging is simpler from a verification standpoint. Theoretically...

snippyhollow 14y ago

Agreed, the design was not good at all. Indeed, they now added a compulsory formation in the pilots curriculum for this kind of situation (degraded control mode). However, the pilots took a very big risk when they said "On ne va pas se laisser emmerder par des cunimbs." (We won't be pissed off by cumulonimbi!) and got straight into the storm while others were all rerouting around. Ego kills.

pinko 14y ago

Maybe in the non-pathological case (two pilots performing the same actions almost in sync--which would include many moments of minor conflict as one transitions before the other) it results in a slightly smoother result? Even if so, a terrible design choice to improve the common case at the expense of the rarer but much more critical case.