4 ms·

This was exactly the problem in the Airbus crash shown above; reconciling the inputs is hard. One pilot kept holding one stick back, unbeknownst to the other. T

This was exactly the problem in the Airbus crash shown above; reconciling the inputs is hard. One pilot kept holding one stick back, unbeknownst to the other. This plane averages them by default, and therefore the plane stalled. That couldn't happen on a Boeing because the yokes are yokes (inputs on one are easily visible to both pilots) and physically linked. (Supposedly the plane is supposed to loudly complain if the inputs diverge. I'm not sure if this happened.)

theoh 10y ago
The Airbus did make the expected warnings ("DUAL INPUT") when the control inputs conflicted, at least according to this Vanity Fair article: http://www.vanityfair.com/news/business/2014/10/air-france-flight-447-crash http://www.vanityfair.com/news/business/2014/10/air-france-f...
- saint_fiasco 10y ago
  "DUAL INPUT" is only marginally better than "PC LOAD LETTER"
  - schoen 10y ago
    On the other hand, typical Airbus A330 operators probably have a lot better training about what diagnostic messages mean than typical HP LaserJet operators do.
    - ceejayoz 10y ago
      On the other other hand, two pilots issuing opposite control inputs generally has a bit more impact than an empty printer tray. Boeing's relatively low-tech solution of making the two controls physically interlinked seems like a common-sense solution to a potentially immense issue.
    - snowwrestler 10y ago
      But obviously the training did not suffice in the Air France case, because those were experienced Airbus pilots and they did not detect and resolve the contrary inputs.
    - lallysingh 10y ago
      Something easy to ignore when you're freaking out over a plane going straight into the ocean.
  - ceejayoz 10y ago
    Yeah. In an emergency with a frazzled brain it's entirely possible someone'd read that and say "No shit, of course we're both trying to pull up..."
    - caf 10y ago
      Pulling up being exactly the wrong action in this case!
- engi_nerd 10y ago
  As others point out, just because the warning is displayed as expected, does not make it a good warning. In flight testing, whenever we encounter situations like this (the aircraft does not react as the pilot expects for a given input), we don't necessarily blame the pilot. Especially if multiple pilots get into the same mess. Then we know it's time to change how the aircraft behaves and bring it in line with what the pilots expect.
- mikeash 10y ago
  A little blinkenlight among the masses is easy to miss. Having your controls physically fight you because the other pilot is doing something is impossible to miss.
  - theoh 10y ago
    It was actually a voice alert. I'm not making any judgement about its appropriateness. In fact by the time it arose, the aircraft may already have been in an unrecoverable dive (or whatever the word is for rapid descent while stalled), I don't remember. So it's not a primary cause of the accident.
    - mikeash 10y ago
      A voice alert in a cockpit where people are probably frantically shouting at each other is just as ridiculous. There's no substitute for physical feedback. It's instantaneous and impossible to miss. It's completely beyond my comprehension that Airbus eliminated it. As I recall, the one pilot held full back stick all the way down, while the other pilot tried and failed to recover. Releasing the back stick and executing a normal stall recovery would have saved the airplane at just about any time.
      - theoh 10y ago
        I understand the Boeing approach of physical linkage to be the best idea, rather than any kind of indirect force feedback which is possible to misinterpret. As for your last point, I'm not an expert, and I'm not as incredulous about this scenario as you seem to be. (As a teenager I did fly a lot in PC flight simulators, though.) The non-technical Vanity Fair article I referred to claims that the accident investigators estimated the last point at which the aircraft could have recovered from the dive was around the time it passed 13,000 feet: "Though precise modeling was never pursued, the investigators later estimated that this was the last moment, as the airplane dropped through 13,000 feet, when a recovery would theoretically have been possible. The maneuver would have required a perfect pilot to lower the nose at least 30 degrees below the horizon and dive into the descent, accepting a huge altitude loss in order to accelerate to a flying angle of attack, and then rounding out of the dive just above the waves, pulling up with sufficient vigor to keep from exceeding the airplane’s speed limit, yet not so violently as to cause a structural failure. There are perhaps a handful of pilots in the world who might have succeeded, but this Air France crew was not among them. There is an old truth in aviation that the reasons you get into trouble become the reasons you don’t get out of it."
mattkrause 10y ago
I don't understand why you'd want this averaging behavior at all. When trying to get the plane onto the center of the runway, both pilots' actions are probably pretty correlated, and averaging could remove any noise (e.g., twitches). But in many other circumstances, it seems like it would be downright dangerous. Something's in front of the plane. One pilot goes to the left, the other pulls to the right, and the system averages the commands and smashes straight into it. The benefits of a marginally straighter landing don't seem like they would outweigh the potential of a massive catastrophe.

theoh 10y ago

The Airbus did make the expected warnings ("DUAL INPUT") when the control inputs conflicted, at least according to this Vanity Fair article: http://www.vanityfair.com/news/business/2014/10/air-france-flight-447-crash http://www.vanityfair.com/news/business/2014/10/air-france-f...

saint_fiasco 10y ago
"DUAL INPUT" is only marginally better than "PC LOAD LETTER"
- schoen 10y ago
  On the other hand, typical Airbus A330 operators probably have a lot better training about what diagnostic messages mean than typical HP LaserJet operators do.
  - ceejayoz 10y ago
    On the other other hand, two pilots issuing opposite control inputs generally has a bit more impact than an empty printer tray. Boeing's relatively low-tech solution of making the two controls physically interlinked seems like a common-sense solution to a potentially immense issue.
  - snowwrestler 10y ago
    But obviously the training did not suffice in the Air France case, because those were experienced Airbus pilots and they did not detect and resolve the contrary inputs.
  - lallysingh 10y ago
    Something easy to ignore when you're freaking out over a plane going straight into the ocean.
- ceejayoz 10y ago
  Yeah. In an emergency with a frazzled brain it's entirely possible someone'd read that and say "No shit, of course we're both trying to pull up..."
  - caf 10y ago
    Pulling up being exactly the wrong action in this case!
engi_nerd 10y ago
As others point out, just because the warning is displayed as expected, does not make it a good warning. In flight testing, whenever we encounter situations like this (the aircraft does not react as the pilot expects for a given input), we don't necessarily blame the pilot. Especially if multiple pilots get into the same mess. Then we know it's time to change how the aircraft behaves and bring it in line with what the pilots expect.
mikeash 10y ago
A little blinkenlight among the masses is easy to miss. Having your controls physically fight you because the other pilot is doing something is impossible to miss.
- theoh 10y ago
  It was actually a voice alert. I'm not making any judgement about its appropriateness. In fact by the time it arose, the aircraft may already have been in an unrecoverable dive (or whatever the word is for rapid descent while stalled), I don't remember. So it's not a primary cause of the accident.
  - mikeash 10y ago
    A voice alert in a cockpit where people are probably frantically shouting at each other is just as ridiculous. There's no substitute for physical feedback. It's instantaneous and impossible to miss. It's completely beyond my comprehension that Airbus eliminated it. As I recall, the one pilot held full back stick all the way down, while the other pilot tried and failed to recover. Releasing the back stick and executing a normal stall recovery would have saved the airplane at just about any time.
    - theoh 10y ago
      I understand the Boeing approach of physical linkage to be the best idea, rather than any kind of indirect force feedback which is possible to misinterpret. As for your last point, I'm not an expert, and I'm not as incredulous about this scenario as you seem to be. (As a teenager I did fly a lot in PC flight simulators, though.) The non-technical Vanity Fair article I referred to claims that the accident investigators estimated the last point at which the aircraft could have recovered from the dive was around the time it passed 13,000 feet: "Though precise modeling was never pursued, the investigators later estimated that this was the last moment, as the airplane dropped through 13,000 feet, when a recovery would theoretically have been possible. The maneuver would have required a perfect pilot to lower the nose at least 30 degrees below the horizon and dive into the descent, accepting a huge altitude loss in order to accelerate to a flying angle of attack, and then rounding out of the dive just above the waves, pulling up with sufficient vigor to keep from exceeding the airplane’s speed limit, yet not so violently as to cause a structural failure. There are perhaps a handful of pilots in the world who might have succeeded, but this Air France crew was not among them. There is an old truth in aviation that the reasons you get into trouble become the reasons you don’t get out of it."

mattkrause 10y ago

I don't understand why you'd want this averaging behavior at all. When trying to get the plane onto the center of the runway, both pilots' actions are probably pretty correlated, and averaging could remove any noise (e.g., twitches). But in many other circumstances, it seems like it would be downright dangerous. Something's in front of the plane. One pilot goes to the left, the other pulls to the right, and the system averages the commands and smashes straight into it. The benefits of a marginally straighter landing don't seem like they would outweigh the potential of a massive catastrophe.