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From memory; pitot tubes froze over and airspeed became unreliable. Autopilot disengaged and they had a stall warning. One pilot went full nose down, the other

From memory; pitot tubes froze over and airspeed became unreliable. Autopilot disengaged and they had a stall warning. One pilot went full nose down, the other wanted full nose up. The latter probably believed the flight envelope protections were still in place which would not let you stall even if you did full nose up. But they weren't because the flight computer switched to alternate law when airspeed was unreliable so they had full control of the airplane and (probably) didn't realize it. Additionally when presented with two different control stick inputs the flight computer just averaged them, and since there was no force feedback there is no tactile sense that you're arguing with the other pilot over what you should be doing. Also only one person is supposed to be in command. My memory is also that the senior captain was in the third seat and didn't have a full grasp of the situation either. I did read the air accident report quite a while ago so this might be wrong, but in summary, it's not exactly arguable that the aircraft did the wrong thing (it did as designed minus the freeze issue which is suboptimal but something that can happen) and the pilots didn't exactly do the wrong thing either since they may have little to no experience flying the plane in alternate law (certainly not at high altitude and speed), and it's not unreasonable to be fully aware that they had full control (as opposed to the flight computer mediating and not letting them do something stupid like stall it all the way down to the ocean). Lastly, when in cruise it's not completely trivial to fly like a Cessna at 1,000ft. At cruise on a big heavy jet you can't go much higher as the air is too thin to fly. You can't go much faster without braking the sound barrier. You can't go much slower as you'll stall. I believe it's called "coffin corner", and while commercial passenger planes do it every day it's not quite as simple as you might think.

garaetjjte 8y ago
> flight computer switched to alternate law when airspeed was unreliable so they had full control of the airplane Alternate law still enforces bank angle protection. With full control (direct law) it could have entered spin. (or maybe they could realized situation earlier) Stall warning was confusing because pulling up even more removed warning temporarily because extreme AoA was interpreted as sensor failure.
Johnny555 8y ago
it's not exactly arguable that the aircraft did the wrong thing I still think it's arguable that the "right thing" is for the plane to say "Hey, I don't know how to fly this thing anymore, so I'm giving up! Oh and since I'm so confused, the plane is in alternate law, so all of those nomal-law protections you usually have aren't there." and then handing over control to the pilot that hasn't been actively flying the plane and expecting him to suddenly figure out what's been happening and why the autopilot gave up. Since the pilots did pretty much the opposite of what they should have done, maybe the plane could have done better itself, even with the unreliable airspeed?
xenadu02 8y ago
There's no excuse for secretly averaging widely divergent inputs, especially in alternate law (which the plane wouldn't be in unless something is going wrong). It should have picked one and indicated to the other pilot that his/her input was being ignored. IIRC this isn't an issue on the Boeing design, only Airbus. One the contributing factors was that the stall warning cut out when the nose was pointed higher up, giving the copilot the impression his attempt to full nose up was the right decision. When the nose lowered the stall warning kicked back in. IIRC this was because the computer saw the full nose up as an "impossible" condition and decided not to issue the stall warning. As the nose lowered certain values came back in-range so it issued the warning. Without these two wildly incorrect behaviors the plane probably wouldn't have crashed.
- exidy 8y ago
  It didn't secretly average inputs. The plane gave alerts both visual and audible (DUAL INPUT) that the pilots were providing conflicting inputs. I agree that the force feedback of the Boeing FBW system is better, but the pilots should have understood the alerts provided, and either communicated or made use of their override switches. Solving the problem by ignoring one of the pilots would be an interesting engineering problem. How do you choose?
nasredin 8y ago
IIRC they hit the ocean so fast, that death must have been instantenous. Also IIRC the pilots didn't know what's going on until they hit the ocean.
thatswrong0 8y ago
> the pilots didn't exactly do the wrong thing Wasn't the one pilot pulling back fully on the stick and not communicating that he was doing that? And weren't the pilots aware that they were in a stall scenario? Which means that pulling back fully was the exact wrong thing to do? My impression is basically that it was almost entirely the fault of the pilot that was pulling back the whole time. Of course, it sounds like Airbus' controls could provide _a lot_ more feedback to pilots, especially when there are divergent inputs.
- hef19898 8y ago
  All cintrolls, invl. Boeing, are fly by wire now. And yes, pulling back was exactly the wrong thing. I would have to look up the rport again, but if I remember well pulling up silenced the stall warning. So nose down -> stall warning, nose up -> no stall warning. If memory serves me well, Air France revised their training afterwards to cover that exacz scenario, that pulling up silenced the stall warning was expected system behaviour. Complex systems require in depth system knowledge and quick reaction times. That is one of the points I took away from that incident.

garaetjjte 8y ago

> flight computer switched to alternate law when airspeed was unreliable so they had full control of the airplane Alternate law still enforces bank angle protection. With full control (direct law) it could have entered spin. (or maybe they could realized situation earlier) Stall warning was confusing because pulling up even more removed warning temporarily because extreme AoA was interpreted as sensor failure.

Johnny555 8y ago

it's not exactly arguable that the aircraft did the wrong thing I still think it's arguable that the "right thing" is for the plane to say "Hey, I don't know how to fly this thing anymore, so I'm giving up! Oh and since I'm so confused, the plane is in alternate law, so all of those nomal-law protections you usually have aren't there." and then handing over control to the pilot that hasn't been actively flying the plane and expecting him to suddenly figure out what's been happening and why the autopilot gave up. Since the pilots did pretty much the opposite of what they should have done, maybe the plane could have done better itself, even with the unreliable airspeed?

xenadu02 8y ago

There's no excuse for secretly averaging widely divergent inputs, especially in alternate law (which the plane wouldn't be in unless something is going wrong). It should have picked one and indicated to the other pilot that his/her input was being ignored. IIRC this isn't an issue on the Boeing design, only Airbus. One the contributing factors was that the stall warning cut out when the nose was pointed higher up, giving the copilot the impression his attempt to full nose up was the right decision. When the nose lowered the stall warning kicked back in. IIRC this was because the computer saw the full nose up as an "impossible" condition and decided not to issue the stall warning. As the nose lowered certain values came back in-range so it issued the warning. Without these two wildly incorrect behaviors the plane probably wouldn't have crashed.

exidy 8y ago
It didn't secretly average inputs. The plane gave alerts both visual and audible (DUAL INPUT) that the pilots were providing conflicting inputs. I agree that the force feedback of the Boeing FBW system is better, but the pilots should have understood the alerts provided, and either communicated or made use of their override switches. Solving the problem by ignoring one of the pilots would be an interesting engineering problem. How do you choose?

nasredin 8y ago

IIRC they hit the ocean so fast, that death must have been instantenous. Also IIRC the pilots didn't know what's going on until they hit the ocean.

thatswrong0 8y ago

> the pilots didn't exactly do the wrong thing Wasn't the one pilot pulling back fully on the stick and not communicating that he was doing that? And weren't the pilots aware that they were in a stall scenario? Which means that pulling back fully was the exact wrong thing to do? My impression is basically that it was almost entirely the fault of the pilot that was pulling back the whole time. Of course, it sounds like Airbus' controls could provide _a lot_ more feedback to pilots, especially when there are divergent inputs.

hef19898 8y ago
All cintrolls, invl. Boeing, are fly by wire now. And yes, pulling back was exactly the wrong thing. I would have to look up the rport again, but if I remember well pulling up silenced the stall warning. So nose down -> stall warning, nose up -> no stall warning. If memory serves me well, Air France revised their training afterwards to cover that exacz scenario, that pulling up silenced the stall warning was expected system behaviour. Complex systems require in depth system knowledge and quick reaction times. That is one of the points I took away from that incident.