3 ms·

If the sensor fails, the plane fails I don't believe that's true - if the sensor gives an erroneous reading, it's up to the pilot to recognize uncommanded trim

If the sensor fails, the plane fails I don't believe that's true - if the sensor gives an erroneous reading, it's up to the pilot to recognize uncommanded trim and disable it by shutting off power to the system that moves the stabilizer. Really, flying by instrumentation is what you're saying is the problem and that's the truth Flying by faulty instruments is clearly bad, but flying by (working) instruments is much better than the alternative, every pilot going through instrument training learns very quickly that he needs to trust the instruments when flying in poor visibility, his senses don't work. They could at least have both sensors active as a failsafe in case one is acting up If you have two sensors and one is acting up, how do you know which one is true and which one is false?

yetihehe 8y ago
> If you have two sensors and one is acting up, how do you know which one is true and which one is false? Typically it is possible to determine this by looking at reading stability. If one sensor is constantly stuck or changes values too fast (0-100% several times per second) or too slow, you know it's faulty. Those sensors should be engineered so that you can know if it's faulty. If you can't detect faulty sensor, it's just bad engineering.
- Johnny555 8y ago
  If you have 2 sensors, how do you reliably detect that one of them is bent or installed incorrectly and gives an inaccurate, but stable, reading? If the sensor is completely malfunctioning it's easier to detect, but what about when it's just wrong?
  - yetihehe 8y ago
    > how do you reliably detect that one of them is bent or installed incorrectly During standard pre-launch or manufacturing tests. It should be verified by applying some change and checking that this change is measured correctly. Generally for critical sensors, you can add some circuitry or even mechanical means of checking (eg heater on temperature sensor). If mechanical side fails, whole sensor module is marked as failed. Critical sensors should be designed in a way that you know when it fails.
  - hanniabu 8y ago
    You can also have 3 sensors and use a simple 2 of 3 check. The likeliness of 2 failing at the same time would probably be pretty low.
  - chopin 8y ago
    For many sensors especially critical ones there are multiple independent ones (like indicated airspeed). If they deviate there are standard procedures to determine which one(s) are faulty. For IAS you basically set a determined thrust at a determined pitch. Then you have a table which gives you IAS for the altitude you are at. This will determine the faulty pitot tube. I think for other sensors there are similar procedures.
raverbashing 8y ago
> it's up to the pilot to recognize uncommanded trim and disable it by shutting off power to the system that moves the stabilizer. You have other things to do on that flight stage (right after flaps have been set to 0)
- Johnny555 8y ago
  Then you ought to react pretty quickly to disable the malfunctioning system that's going to force you into into a crash so you can continue flying the plane.
  - raverbashing 8y ago
    Yeah you have no idea of what you're talking about. An aircraft is not like your PC where you just click "ok" to some spurious popup and everything is fine Cognitive load is a factor in many accidents. You don't have the plane doing something stupid during a critical stage (like take-off) with the excuse that you can "just disable it". If a plane has an issue in keeping a stable flight but instead wants to point up or down beyond flight limits it is defective. Edit: https://twitter.com/SarahTaber_bww/status/1105256557154127872 https://twitter.com/SarahTaber_bww/status/110525655715412787...
    - Johnny555 8y ago
      Isn't handling unexpected conditions the entire reason for having a pilot onboard? If the pilot is not expected to detect and respond to something like a faulty sensor that causes an unwanted control surface movement, then why have the pilot onboard at all? Why not just let the plane fly itself?
      - ddalex 8y ago
        Unexpected conditions is not to mean "the aircraft software design is stupid and will try to kill you".
        8y ago

yetihehe 8y ago

> If you have two sensors and one is acting up, how do you know which one is true and which one is false? Typically it is possible to determine this by looking at reading stability. If one sensor is constantly stuck or changes values too fast (0-100% several times per second) or too slow, you know it's faulty. Those sensors should be engineered so that you can know if it's faulty. If you can't detect faulty sensor, it's just bad engineering.

Johnny555 8y ago
If you have 2 sensors, how do you reliably detect that one of them is bent or installed incorrectly and gives an inaccurate, but stable, reading? If the sensor is completely malfunctioning it's easier to detect, but what about when it's just wrong?
- yetihehe 8y ago
  > how do you reliably detect that one of them is bent or installed incorrectly During standard pre-launch or manufacturing tests. It should be verified by applying some change and checking that this change is measured correctly. Generally for critical sensors, you can add some circuitry or even mechanical means of checking (eg heater on temperature sensor). If mechanical side fails, whole sensor module is marked as failed. Critical sensors should be designed in a way that you know when it fails.
- hanniabu 8y ago
  You can also have 3 sensors and use a simple 2 of 3 check. The likeliness of 2 failing at the same time would probably be pretty low.
- chopin 8y ago
  For many sensors especially critical ones there are multiple independent ones (like indicated airspeed). If they deviate there are standard procedures to determine which one(s) are faulty. For IAS you basically set a determined thrust at a determined pitch. Then you have a table which gives you IAS for the altitude you are at. This will determine the faulty pitot tube. I think for other sensors there are similar procedures.

raverbashing 8y ago

> it's up to the pilot to recognize uncommanded trim and disable it by shutting off power to the system that moves the stabilizer. You have other things to do on that flight stage (right after flaps have been set to 0)

Johnny555 8y ago
Then you ought to react pretty quickly to disable the malfunctioning system that's going to force you into into a crash so you can continue flying the plane.
- raverbashing 8y ago
  Yeah you have no idea of what you're talking about. An aircraft is not like your PC where you just click "ok" to some spurious popup and everything is fine Cognitive load is a factor in many accidents. You don't have the plane doing something stupid during a critical stage (like take-off) with the excuse that you can "just disable it". If a plane has an issue in keeping a stable flight but instead wants to point up or down beyond flight limits it is defective. Edit: https://twitter.com/SarahTaber_bww/status/1105256557154127872 https://twitter.com/SarahTaber_bww/status/110525655715412787...
  - Johnny555 8y ago
    Isn't handling unexpected conditions the entire reason for having a pilot onboard? If the pilot is not expected to detect and respond to something like a faulty sensor that causes an unwanted control surface movement, then why have the pilot onboard at all? Why not just let the plane fly itself?
    - ddalex 8y ago
      Unexpected conditions is not to mean "the aircraft software design is stupid and will try to kill you".
      - 8y ago