4 ms·

You only need two sensors to determine if one is faulty. You need three if you need the correct measurement. For this application, all that is required is a w

You only need two sensors to determine if one is faulty. You need three if you need the correct measurement. For this application, all that is required is a warning that the AoA sensors aren’t providing correct information.

mantap 7y ago
That's true but it puts the aircraft at a greater risk of stalling, because MCAS is supposed to be a safety feature to prevent stalls. Two sensors are sufficient to prevent false positives, but three or more are necessary to mitigate false negatives. If the MAX is really so easy to stall that it needs a computer system to prevent stalls, then that system should be robust enough to survive a sensor out.
- missosoup 7y ago
  There is no risk of stalling. There was never any risk of stalling. MCAS was added solely so that the 737 MAX 8 could share a type rating with the previous members of the 737 family. This is what allowed Airlines to put pilots on this plane without any significant new training. Please stop perpetuating urban myths. Here, listen to a guy who actually know what he's talking about describing the overall situation: https://www.youtube.com/watch?v=btZXVPfh-pE https://www.youtube.com/watch?v=btZXVPfh-pE
  - mantap 7y ago
    I don't think I'm perpetuating an urban myth. My understanding is that MCAS was necessary to correct a deficiency in the controls - that's the controls violated an FAA rule that the pitch up should not be superlinear relative to the control input (which clearly increases the risk of stall). And indeed after testing they had to increase the strength of MCAS because the tendency to pitch up was worse than previously anticipated. The desire for a common type rating is an explanation for why the FAA rule was violated without MCAS.
    - missosoup 7y ago
      This is incorrect. And this has been dispelled by multiple commercial pilots including Juan from the link above who is one of the most experienced pilots in the country. The origin of this noise is sensationalist news coverage and misinterpretation of FAA rules. I expect a higher standard on HN than perpetuating myths. You guys are like the flat earthers of aviation. https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Augmentation_System#Certification_inquiry_on_737_MAX https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Au... As Juan points out in either that or another video, the 767 has a stronger pitch-up characteristic and yet doesn't have MCAS and doesn't fall out of the sky from stalls. Another myth and piece of sensationalist news bullshit is that Boeing made a safety feature that would have prevented the accidents optional. The safety feature in question was AOE Disagree Indicator. The reason it was optional is because AOA doesn't mean anything to civilian pilots and the option only made sense for airlines who hire ex-militaray pilots who can actually read the AOA indicator and make sense of it.
      - piva00 7y ago
        So the whole point of MCAS is to basically create an emulated flight envelope more similar to how previous generations 737s flew just to avoid a type rating re-certification? People died because Boeing was playing with emulators in real life?
        missosoup 7y ago
        The shared type rating was a huge draw for airlines. Without it, the 737 MAX 8 would not have been nearly as popular in orders as it was. Boeing got very greedy and multiple failures have occurred along the way. MCAS on passenger planes is not unheard of, and has been implemented for various reasons before including shared type ratings. It was just never botched across the board this badly before. The biggest failure as parent comment correctly notes, is MCAS was given significantly more control authority than originally planned after flight testing showed it was ineffective as per the original design. But this change in control authority didn't trigger a review process which would have reclassified it from non-critical to critical system.
  - 7952 7y ago
    I always wondered if it makes sense to base anything like this on AOA alone. The aircraft has a ground speed of several hundred knots, a sensible air speed, is at a normal attitude, in normal wind conditions, no wind sheer warnings and with normal engine function. In that situation AOA sensor failure is far more likely than a stall.
CydeWeys 7y ago
But if they aren't providing correct information then MCAS can't work and now your plane has different flying characteristics than the older 737s, which is all your pilots are trained on because the whole point of MCAS is to prevent requiring recertification.

mantap 7y ago

That's true but it puts the aircraft at a greater risk of stalling, because MCAS is supposed to be a safety feature to prevent stalls. Two sensors are sufficient to prevent false positives, but three or more are necessary to mitigate false negatives. If the MAX is really so easy to stall that it needs a computer system to prevent stalls, then that system should be robust enough to survive a sensor out.

missosoup 7y ago
There is no risk of stalling. There was never any risk of stalling. MCAS was added solely so that the 737 MAX 8 could share a type rating with the previous members of the 737 family. This is what allowed Airlines to put pilots on this plane without any significant new training. Please stop perpetuating urban myths. Here, listen to a guy who actually know what he's talking about describing the overall situation: https://www.youtube.com/watch?v=btZXVPfh-pE https://www.youtube.com/watch?v=btZXVPfh-pE
- mantap 7y ago
  I don't think I'm perpetuating an urban myth. My understanding is that MCAS was necessary to correct a deficiency in the controls - that's the controls violated an FAA rule that the pitch up should not be superlinear relative to the control input (which clearly increases the risk of stall). And indeed after testing they had to increase the strength of MCAS because the tendency to pitch up was worse than previously anticipated. The desire for a common type rating is an explanation for why the FAA rule was violated without MCAS.
  - missosoup 7y ago
    This is incorrect. And this has been dispelled by multiple commercial pilots including Juan from the link above who is one of the most experienced pilots in the country. The origin of this noise is sensationalist news coverage and misinterpretation of FAA rules. I expect a higher standard on HN than perpetuating myths. You guys are like the flat earthers of aviation. https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Augmentation_System#Certification_inquiry_on_737_MAX https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Au... As Juan points out in either that or another video, the 767 has a stronger pitch-up characteristic and yet doesn't have MCAS and doesn't fall out of the sky from stalls. Another myth and piece of sensationalist news bullshit is that Boeing made a safety feature that would have prevented the accidents optional. The safety feature in question was AOE Disagree Indicator. The reason it was optional is because AOA doesn't mean anything to civilian pilots and the option only made sense for airlines who hire ex-militaray pilots who can actually read the AOA indicator and make sense of it.
    - piva00 7y ago
      So the whole point of MCAS is to basically create an emulated flight envelope more similar to how previous generations 737s flew just to avoid a type rating re-certification? People died because Boeing was playing with emulators in real life?
      - missosoup 7y ago
        The shared type rating was a huge draw for airlines. Without it, the 737 MAX 8 would not have been nearly as popular in orders as it was. Boeing got very greedy and multiple failures have occurred along the way. MCAS on passenger planes is not unheard of, and has been implemented for various reasons before including shared type ratings. It was just never botched across the board this badly before. The biggest failure as parent comment correctly notes, is MCAS was given significantly more control authority than originally planned after flight testing showed it was ineffective as per the original design. But this change in control authority didn't trigger a review process which would have reclassified it from non-critical to critical system.
- 7952 7y ago
  I always wondered if it makes sense to base anything like this on AOA alone. The aircraft has a ground speed of several hundred knots, a sensible air speed, is at a normal attitude, in normal wind conditions, no wind sheer warnings and with normal engine function. In that situation AOA sensor failure is far more likely than a stall.

CydeWeys 7y ago

But if they aren't providing correct information then MCAS can't work and now your plane has different flying characteristics than the older 737s, which is all your pilots are trained on because the whole point of MCAS is to prevent requiring recertification.