5 ms·

It means one was trying to increase pitch angle (trying to climb?) and one was trying to do the exact opposite. They were canceling each other’s inputs.

by eknkc 3y ago

gambiting 3y ago
it's an "interesting" difference between Airbus and Boeing - on Boeings the input is averaged between both pilots. So if one is giving it maximum tilt left, the other maximum tilt right, the airplane doesn't move. On an Airbus both sticks have to mave in unison, they are physically linked. Edit: Actually, I'm completely wrong, ignore me
- andruby 3y ago
  Could it be that you mean the opposite: Airbus is averaged, Boeing is physically linked? That is my understanding of both systems at least
  - fhars 3y ago
    Wasn't the problem here that Boeing is only linked if no great force is applied and also switches to the average it the force difference is large enough, and that it didn't really document that behaviour?
    - masklinn 3y ago
      IIUC the possibility of breakout is documented, but pilots > often only associated it with a jammed control I assume in no small part because > the description of the system in the [flight crew operating manual] was limited to an explanation about the risk of a control jamming And it seems likely the precise behaviour of the system in case of breakout is not documented either.
- Symbiote 3y ago
  I thought it was the other way around, which is what led to the AF447 flight crashing — the other pilots didn't realize what the one in control was doing? > The inputs cancelled each other out and triggered an audible "dual input" warning. https://en.wikipedia.org/wiki/Air_France_Flight_447 https://en.wikipedia.org/wiki/Air_France_Flight_447
- mazugrin2 3y ago
  I think you're getting your aircraft manufacturers mixed up. On all modern Airbus airliners, there is no physical link between the two pilots' controls at all. On Boeing aircraft, the controls are physically linked and both move even when one pilot is making inputs. On the 777-300ER, if both pilots are making inputs, and those inputs differ enough, then the physical link can be disabled and then the inputs are considered "desynchronized" and only then to the inputs become averaged.
  - cesarb 3y ago
    > then the physical link can be disabled and then the inputs are considered "desynchronized" and only then to the inputs become averaged. My understanding is that it always averages the input, even when they're not desynchronized (but obviously, since the inputs are equal in that case, the average ends up being equal to the inputs themselves).
- verandaguy 3y ago
  No, it's the opposite. Airbus does not use active side sticks; you get no haptic feedback from the other pilot. You do get an aural warning, "dual input," if split control inputs are detected, and each stick has an override button against the other side. See here[0]. Boeing's control columns are mechanically linked, but given (iirc) 50 lbs of force, they will mechanically desynchronize. If memory serves, they will snap back into sync once the force is released. I don't recall there being an aural warning for this. The issues with Airbus's approach are that (a) in high-stress environments, aural warnings are the first ones to be unconsciously ignored, and (b) you get no haptic feedback, either from the other pilot's side stick, or from the control surfaces (since modern Airbuses are FBW, though you could still do electronic feedback via an active side stick). There's some talk of Airbus moving to active side sticks in the future to mitigate this issue. The issue with Boeing's approach is that in a high-stress, tunnel-visioned situation, you can't tell another pilot's input feedback apart from something like jammed flight controls, a runaway stabiliser, or any other trim or autopilot malfunction, to name a few. There's also some talk of Boeing moving to active side sticks in the future to mitigate this issue. [0] https://aircrafttechnic.com/wp-content/uploads/2020/10/Ads%C4%B1z-4.png
  - masklinn 3y ago
    Note that here a breakout is exactly what happened and the behaviour of the controls in case of breakout is similar to Airbus’s: > in the event of antagonistic inputs exceeding the breakout mechanism’s activation threshold, the controls would be desynchronised and the control surface would react according to the mean control position. The breakout threshold is 50lbs, but it’s the combined thresholds, so sudden opposite force applied by two pilots (as apparently happened here) can unexpectedly trigger it. The report confirms there is no warning of breakout situation whether visual or aural.
    - spangry 3y ago
      What a horribly confusing control mechanism. It could become very hard to distinguish between (1) desynchronization (2) your copilot yielding control to you and (3) a control jam being overcome. They would all feel exactly the same. Not the sort of ambiguity you would want in an emergency situation!
- AnimalMuppet 3y ago
  > On an Airbus both sticks have to mave in unison, they are physically linked. Is that true? I seem to recall that Airbus gave "priority" to one side or the other (with the side being switchable on demand, not fixed).
  - masklinn 3y ago
    They are incorrect, but you are as well - airbus controls are not mechanically linked, save possibly on the A300 (which has a yoke not side-stick), but there’s less than 200 of these still flying - airbus sticks have a priority / takeover button, but by default dual inputs are averaged (this is also what happens in Boeings when you trigger a breakout apparently) - Airbus has a “dual input” aural alarm
- barrkel 3y ago
  https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/dual-side-stick-inputs.pdf https://safetyfirst.airbus.com/app/themes/mh_newsdesk/docume... Side sticks are not mechanically linked.

It means one was trying to increase pitch angle (trying to climb?) and one was trying to do the exact opposite. They were canceling each other’s inputs.

by eknkc 3y ago

It means one was trying to increase pitch angle (trying to climb?) and one was trying to do the exact opposite. They were canceling each other’s inputs.

gambiting 3y ago

it's an "interesting" difference between Airbus and Boeing - on Boeings the input is averaged between both pilots. So if one is giving it maximum tilt left, the other maximum tilt right, the airplane doesn't move. On an Airbus both sticks have to mave in unison, they are physically linked. Edit: Actually, I'm completely wrong, ignore me

andruby 3y ago
Could it be that you mean the opposite: Airbus is averaged, Boeing is physically linked? That is my understanding of both systems at least
- fhars 3y ago
  Wasn't the problem here that Boeing is only linked if no great force is applied and also switches to the average it the force difference is large enough, and that it didn't really document that behaviour?
  - masklinn 3y ago
    IIUC the possibility of breakout is documented, but pilots > often only associated it with a jammed control I assume in no small part because > the description of the system in the [flight crew operating manual] was limited to an explanation about the risk of a control jamming And it seems likely the precise behaviour of the system in case of breakout is not documented either.
Symbiote 3y ago
I thought it was the other way around, which is what led to the AF447 flight crashing — the other pilots didn't realize what the one in control was doing? > The inputs cancelled each other out and triggered an audible "dual input" warning. https://en.wikipedia.org/wiki/Air_France_Flight_447 https://en.wikipedia.org/wiki/Air_France_Flight_447
mazugrin2 3y ago
I think you're getting your aircraft manufacturers mixed up. On all modern Airbus airliners, there is no physical link between the two pilots' controls at all. On Boeing aircraft, the controls are physically linked and both move even when one pilot is making inputs. On the 777-300ER, if both pilots are making inputs, and those inputs differ enough, then the physical link can be disabled and then the inputs are considered "desynchronized" and only then to the inputs become averaged.
- cesarb 3y ago
  > then the physical link can be disabled and then the inputs are considered "desynchronized" and only then to the inputs become averaged. My understanding is that it always averages the input, even when they're not desynchronized (but obviously, since the inputs are equal in that case, the average ends up being equal to the inputs themselves).
verandaguy 3y ago
No, it's the opposite. Airbus does not use active side sticks; you get no haptic feedback from the other pilot. You do get an aural warning, "dual input," if split control inputs are detected, and each stick has an override button against the other side. See here[0]. Boeing's control columns are mechanically linked, but given (iirc) 50 lbs of force, they will mechanically desynchronize. If memory serves, they will snap back into sync once the force is released. I don't recall there being an aural warning for this. The issues with Airbus's approach are that (a) in high-stress environments, aural warnings are the first ones to be unconsciously ignored, and (b) you get no haptic feedback, either from the other pilot's side stick, or from the control surfaces (since modern Airbuses are FBW, though you could still do electronic feedback via an active side stick). There's some talk of Airbus moving to active side sticks in the future to mitigate this issue. The issue with Boeing's approach is that in a high-stress, tunnel-visioned situation, you can't tell another pilot's input feedback apart from something like jammed flight controls, a runaway stabiliser, or any other trim or autopilot malfunction, to name a few. There's also some talk of Boeing moving to active side sticks in the future to mitigate this issue. [0] https://aircrafttechnic.com/wp-content/uploads/2020/10/Ads%C4%B1z-4.png
- masklinn 3y ago
  Note that here a breakout is exactly what happened and the behaviour of the controls in case of breakout is similar to Airbus’s: > in the event of antagonistic inputs exceeding the breakout mechanism’s activation threshold, the controls would be desynchronised and the control surface would react according to the mean control position. The breakout threshold is 50lbs, but it’s the combined thresholds, so sudden opposite force applied by two pilots (as apparently happened here) can unexpectedly trigger it. The report confirms there is no warning of breakout situation whether visual or aural.
  - spangry 3y ago
    What a horribly confusing control mechanism. It could become very hard to distinguish between (1) desynchronization (2) your copilot yielding control to you and (3) a control jam being overcome. They would all feel exactly the same. Not the sort of ambiguity you would want in an emergency situation!
AnimalMuppet 3y ago
> On an Airbus both sticks have to mave in unison, they are physically linked. Is that true? I seem to recall that Airbus gave "priority" to one side or the other (with the side being switchable on demand, not fixed).
- masklinn 3y ago
  They are incorrect, but you are as well - airbus controls are not mechanically linked, save possibly on the A300 (which has a yoke not side-stick), but there’s less than 200 of these still flying - airbus sticks have a priority / takeover button, but by default dual inputs are averaged (this is also what happens in Boeings when you trigger a breakout apparently) - Airbus has a “dual input” aural alarm
barrkel 3y ago
https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/dual-side-stick-inputs.pdf https://safetyfirst.airbus.com/app/themes/mh_newsdesk/docume... Side sticks are not mechanically linked.