4 ms·

The pitot tubes had iced-over and it wasn't the first time: https://en.wikipedia.org/wiki/Air_France_Flight_447#Pitot_tubes https://en.wikipedia.org/wiki/Air_F

by js2 6y ago

The pitot tubes had iced-over and it wasn't the first time: https://en.wikipedia.org/wiki/Air_France_Flight_447#Pitot_tubes https://en.wikipedia.org/wiki/Air_France_Flight_447#Pitot_tu... But that's not what made me nervous about Airbus. Rather, that's when I learned that Airbuses are flown by side-sticks that aren't mechanically linked while Boeings are flown by yokes which are. https://en.wikipedia.org/wiki/Air_France_Flight_447#Side-stick_control_issue https://en.wikipedia.org/wiki/Air_France_Flight_447#Side-sti... The idea that two pilots can provide conflicting inputs without realizing it bothers me from a design standpoint.

pirocks 6y ago
Pitot tubes icing over is common on all planes not just Airbus planes. It's more or less expected and planned for.
- js2 6y ago
  I’m not a pilot. I’ve just read the Wikipedia page on this crash and the final report. I don’t know what is common or expected and planned for but I take your characterization to mean that you think that it’s not a significant problem. There’s three pitot tubes. There were ADs issued over them icing over. Airbus replaced them multiple times with tubes from different vendors. In the final report, the first major issue is “Temporary inconsistency between the measured speeds, likely as a result of the obstruction of the pitot tubes by ice crystals, caused autopilot disconnection and reconfiguration to alternate law.” Icing over of pitot tubes seems more significant to me than I think you’re making it out to be.
  - temp667 6y ago
    It really highlights how terribly trained the pilots involved are - temporary inconsistency in measured speeds (there are still plenty of reasonable speed sources) in almost all other planes does not result in the plane crashing. Heck, my GPS can do groundspeed easily enough and you have basic pitch and power settings. How did they not notice their altitude was climbing as they pulled the plane up - they got into a CLIMB rate of 7,000 feet per minute - that's STUPID! WHY climb like that? This has nothing to do with airspeed. The stall alarm goes off 75 times! They reduce power to idle for a bit?? It's total nonsense, anyone who has flown a single engine cessna for 200 hours or more would have been able to get out of this easily just based on stall buffet and stall alarms.
    - dxdm 6y ago
      Or you underestimate the complexity of the situation and overestimate how a 200-hour Cessna pilot would have performed in that cockpit that night.
    - imtringued 6y ago
      I'm not sure what accident you are talking about but the MCAS in the 737 Max overrode pilot input. The real problem was that pilots did not know that the MCAS existed, nor did they know how to disable it.
      - markus92 6y ago
        He's talking about AF447, which involved an Airbus.
- knaq 6y ago
  No, large aircraft have pitot tube heaters. Flying in non-visual conditions without working pitot tubes would be crazy. There are aircraft, for example the B-2, that can't fly at all without working pitot tubes.
dingaling 6y ago
> while Boeings are flown by yokes which are [mechanically linked] They can still be disconnected with sufficient opposite force, there's a shearable torque tube between them.
- FabHK 6y ago
  Indeed, but you'd definitely notice (unlike on the Airbus). Furthermore, if I'm not mistaken, you'd then have a split elevator (one side up, one side down), while the Airbus just averages the two inputs and sets the elevator there, conceptually.
getpost 6y ago
The advantages of fly-by-wire are too good to pass up, so that leaves the question of how to design an FBW system. A high school teacher of mine in the 1970s predicted an accident like AF447. He framed it this way: the 'American' approach is to implement FBW to always do what the pilot inputs indicate, whereas the 'French' approach is to do the right thing, and override the pilot if the FBW 'knows' better. That's an interesting cultural cultural consistency as well! So, the 'American' approach is better if the sensors are not working as expected, and it makes the software simpler. The 'French' approach is better if the pilot is wrong, but both the sensors and the software must be working perfectly. Everyone makes mistakes, and all software has bugs. What to do? (In reality, some 'judgement' is needed by the software, even in the American approach.) EDIT: That said, some of the design choices in the Airbus FBW are baffling, such as making the control input the average of two different inputs. I like to think AF447 is less likely to have happened in a Boeing ship, although the ulitimate cause of the crash was a pilot making what amounts to a beginner mistake. Don't miss William Langewiesche's article! https://www.vanityfair.com/news/business/2014/10/air-france-flight-447-crash https://www.vanityfair.com/news/business/2014/10/air-france-...
- js2 6y ago
  > although the ulitimate cause of the crash was a pilot making what amounts to a beginner mistake. But it was only one of the pilots, the right-side pilot, who continued to hold the stick back and and retained command. The left-side pilot didn't realize that was occurring until it was too late.
- stouset 6y ago
  None of this is relevant to the actual issue raised by the GP: the yokes of the pilot and co-pilot are not mechanically linked. They can be mechanically linked even with a FBW system. And personally, as someone with a bit of flying experience myself, I can't comprehend why you'd want them to not be mechanically linked. The opportunity for confusion with conflicting inputs is too damn high.
  - getpost 6y ago
    Mechanically linking is heavier than fbw/electrical/fiber optic linking, and what's the point if there's no mechanical linkage to the control surfaces? With the fbw system, the software makes the choice on how to interpret the control movement, use one or both? If one, which one? EDIT: Maybe you mean that a mechanical linkage would provide a feedback mechanism, so that one pilot would know if the other pilot was attempting an input? I don't know if there's force feedback on Airbus flight controls.

by js2 6y ago

pirocks 6y ago

Pitot tubes icing over is common on all planes not just Airbus planes. It's more or less expected and planned for.

js2 6y ago
I’m not a pilot. I’ve just read the Wikipedia page on this crash and the final report. I don’t know what is common or expected and planned for but I take your characterization to mean that you think that it’s not a significant problem. There’s three pitot tubes. There were ADs issued over them icing over. Airbus replaced them multiple times with tubes from different vendors. In the final report, the first major issue is “Temporary inconsistency between the measured speeds, likely as a result of the obstruction of the pitot tubes by ice crystals, caused autopilot disconnection and reconfiguration to alternate law.” Icing over of pitot tubes seems more significant to me than I think you’re making it out to be.
- temp667 6y ago
  It really highlights how terribly trained the pilots involved are - temporary inconsistency in measured speeds (there are still plenty of reasonable speed sources) in almost all other planes does not result in the plane crashing. Heck, my GPS can do groundspeed easily enough and you have basic pitch and power settings. How did they not notice their altitude was climbing as they pulled the plane up - they got into a CLIMB rate of 7,000 feet per minute - that's STUPID! WHY climb like that? This has nothing to do with airspeed. The stall alarm goes off 75 times! They reduce power to idle for a bit?? It's total nonsense, anyone who has flown a single engine cessna for 200 hours or more would have been able to get out of this easily just based on stall buffet and stall alarms.
  - dxdm 6y ago
    Or you underestimate the complexity of the situation and overestimate how a 200-hour Cessna pilot would have performed in that cockpit that night.
  - imtringued 6y ago
    I'm not sure what accident you are talking about but the MCAS in the 737 Max overrode pilot input. The real problem was that pilots did not know that the MCAS existed, nor did they know how to disable it.
    - markus92 6y ago
      He's talking about AF447, which involved an Airbus.
knaq 6y ago
No, large aircraft have pitot tube heaters. Flying in non-visual conditions without working pitot tubes would be crazy. There are aircraft, for example the B-2, that can't fly at all without working pitot tubes.

dingaling 6y ago

> while Boeings are flown by yokes which are [mechanically linked] They can still be disconnected with sufficient opposite force, there's a shearable torque tube between them.

FabHK 6y ago
Indeed, but you'd definitely notice (unlike on the Airbus). Furthermore, if I'm not mistaken, you'd then have a split elevator (one side up, one side down), while the Airbus just averages the two inputs and sets the elevator there, conceptually.

getpost 6y ago

The advantages of fly-by-wire are too good to pass up, so that leaves the question of how to design an FBW system. A high school teacher of mine in the 1970s predicted an accident like AF447. He framed it this way: the 'American' approach is to implement FBW to always do what the pilot inputs indicate, whereas the 'French' approach is to do the right thing, and override the pilot if the FBW 'knows' better. That's an interesting cultural cultural consistency as well! So, the 'American' approach is better if the sensors are not working as expected, and it makes the software simpler. The 'French' approach is better if the pilot is wrong, but both the sensors and the software must be working perfectly. Everyone makes mistakes, and all software has bugs. What to do? (In reality, some 'judgement' is needed by the software, even in the American approach.) EDIT: That said, some of the design choices in the Airbus FBW are baffling, such as making the control input the average of two different inputs. I like to think AF447 is less likely to have happened in a Boeing ship, although the ulitimate cause of the crash was a pilot making what amounts to a beginner mistake. Don't miss William Langewiesche's article! https://www.vanityfair.com/news/business/2014/10/air-france-flight-447-crash https://www.vanityfair.com/news/business/2014/10/air-france-...

js2 6y ago
> although the ulitimate cause of the crash was a pilot making what amounts to a beginner mistake. But it was only one of the pilots, the right-side pilot, who continued to hold the stick back and and retained command. The left-side pilot didn't realize that was occurring until it was too late.
stouset 6y ago
None of this is relevant to the actual issue raised by the GP: the yokes of the pilot and co-pilot are not mechanically linked. They can be mechanically linked even with a FBW system. And personally, as someone with a bit of flying experience myself, I can't comprehend why you'd want them to not be mechanically linked. The opportunity for confusion with conflicting inputs is too damn high.
- getpost 6y ago
  Mechanically linking is heavier than fbw/electrical/fiber optic linking, and what's the point if there's no mechanical linkage to the control surfaces? With the fbw system, the software makes the choice on how to interpret the control movement, use one or both? If one, which one? EDIT: Maybe you mean that a mechanical linkage would provide a feedback mechanism, so that one pilot would know if the other pilot was attempting an input? I don't know if there's force feedback on Airbus flight controls.