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That they didn't add a third AoA sensor does not fill me with confidence that they've done all they can to fix this fatal issue that's already claimed over 300

That they didn't add a third AoA sensor does not fill me with confidence that they've done all they can to fix this fatal issue that's already claimed over 300 lives. I'm skeptical that a software-only fix is good enough. Airbus planes, by contrast, have three AoA sensors. How can Boeing justify doing fewer given how critically important these sensors are for preventing crashes?

consp 8y ago
> How can Boeing justify doing fewer given how critically important these sensors are for preventing crashes? Money, as adding a third would likely require recertification as has been mentioned in some articles about the sensors in the past few months.
- CydeWeys 8y ago
  If the FAA had any balls they'd say that the 737 MAX is a new type anyway, thus allowing necessary safety improvements to be made.
  - CaptainZapp 8y ago
    Let's wait and see what other regulatory agencies have to say on the issue. I see a political thunderstorm brewing in the not very far future.
    - milesvp 8y ago
      Lol! The engine placement on the Maxx so fundamentally alters the physics of the plane, that it’s a totally different beast. Even if it flew the same in common flight scenarios (aka passed all it’s unit and integration tests) it will perform very differently in uncommon situations. It’s the uncommon situations that require pilots anyways, since so much otherwise is automated for safety. There will need to be retraining and hopefully recertification involved. Even then, I think the plane is fundamentally unsafe for passenger flight and cannot be fixed without massive redesign. As I now reread your comment, I’m no longer convinced you meant it in the contrary way I read it. I agree there’s a thuderstorm coming, and I hope all regulators involved can have the conviction to stand up to the pressures from both sides and rule based on the design merits of the plane (even if they are able to conclude differently from my armchair engineer opinion).
Someone1234 8y ago
Airbus aircraft require three AoA sensors because they're considered safety critical. On the 737 Max they weren't safety critical right up until they added MCAS, at which point that changed, and the regulators should have required it but failed to (in part because Boeing mislead regulators about how much MCAS could adjust the deflection in the horizontal stabilizer, doubling it after regulators had already sign off on it[0]). The fact that Boeing is able to skate by with two and a software off-switch if they disagree, while Airbus continues to be required to have triple redundancy says a lot about their respective regulators (EASA Vs FAA). I'm sure "cost" was discussed given the 350+ aircraft already produced and how impractical it is to add a third AoA sensor, but that's literally putting cost over safety. [0] See "Inaccurate limit": https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/ https://www.seattletimes.com/business/boeing-aerospace/faile...
- CaptainZapp 8y ago
  but that's literally putting cost over safety. Which seems to be fully in line with Boeing's business model and their behavior after the Lion Air crash. Even after the Ethiopian crash they did just about everything to deflect, blame and obfuscate until this behavior was just no more maintainable based on the known facts. Switching then to a "We apologise if your dead" marketing shtick. I find it hard to believe, based on all the evidence, that this company put lifes before profit.
- carlmr 8y ago
  >The fact that Boeing is able to skate by with two and a software off-switch if they disagree, while Airbus continues to be required to have triple redundancy says a lot about their respective regulators (EASA Vs FAA). I'm sure "cost" was discussed given the 350+ aircraft already produced and how impractical it is to add a third AoA sensor, but that's literally putting cost over safety. Looking at this image here: https://qz.com/1461400/pilots-werent-informed-of-risks-of-boeing-737-maxs-new-feature/ https://qz.com/1461400/pilots-werent-informed-of-risks-of-bo... My biggest doubt is regarding the symmetrical left-right placement of the AoA vanes. Isn't it realistic that they may freeze in the same position, thus not disagreeing, but still wrong? I'm not in aviation, so I'm not sure about this, but without deeper knowledge this seems like a realistic reason to ask for a 3rd sensor with a different placement at least.
deleted 8y ago
[deleted]
penagwin 8y ago
In these crashes though removing the sensor would have prevented them. The entire issue is that the plane could override pilot controls without pilots knowing and/or not knowing or being able to turn it off.
mikeash 8y ago
This sensor isn’t that important. You can fly the plane fine without it. The problem is when the sensor gives a bad reading and the system trusts it. Two sensors are enough to overcome that. If they disagree, ignore them both. The problem wasn’t that they only had two sensors, it was that they didn’t use them both simultaneously and ignore them when they disagreed.
- kalleboo 8y ago
  The question is if MCAS is safety critical or not. To me it looks like there are two options: 1. Keep claiming the MAX has the same flight characteristics as previous 737 models, keep the type certification (=minimal pilot retraining) and classify MCAS as safety-critical and require a third AoA vane 2. Classify MCAS as not safety-critical, disengage it on a disagree between left and right, and require pilots take simulator training on MCAS failure modes and how to fly the plane without MCAS (in situations where it differs from previous 737 models) My guess is they'll take the 2 tack. At this point 1 might not even be an option - regulators would probably require MCAS training no matter what.
  - salawat 8y ago
    There's still a potential failure mode where both vanes get stuck at the same anomalous reading, so therefore still feed bad data to MCAS. There's more likely a threshold of equality rather than exact equality in measurement going on I'd imagine, but I'd have to see their code to know for sure what their definition of "equal" is.

consp 8y ago

> How can Boeing justify doing fewer given how critically important these sensors are for preventing crashes? Money, as adding a third would likely require recertification as has been mentioned in some articles about the sensors in the past few months.

CydeWeys 8y ago
If the FAA had any balls they'd say that the 737 MAX is a new type anyway, thus allowing necessary safety improvements to be made.
- CaptainZapp 8y ago
  Let's wait and see what other regulatory agencies have to say on the issue. I see a political thunderstorm brewing in the not very far future.
  - milesvp 8y ago
    Lol! The engine placement on the Maxx so fundamentally alters the physics of the plane, that it’s a totally different beast. Even if it flew the same in common flight scenarios (aka passed all it’s unit and integration tests) it will perform very differently in uncommon situations. It’s the uncommon situations that require pilots anyways, since so much otherwise is automated for safety. There will need to be retraining and hopefully recertification involved. Even then, I think the plane is fundamentally unsafe for passenger flight and cannot be fixed without massive redesign. As I now reread your comment, I’m no longer convinced you meant it in the contrary way I read it. I agree there’s a thuderstorm coming, and I hope all regulators involved can have the conviction to stand up to the pressures from both sides and rule based on the design merits of the plane (even if they are able to conclude differently from my armchair engineer opinion).

Someone1234 8y ago

Airbus aircraft require three AoA sensors because they're considered safety critical. On the 737 Max they weren't safety critical right up until they added MCAS, at which point that changed, and the regulators should have required it but failed to (in part because Boeing mislead regulators about how much MCAS could adjust the deflection in the horizontal stabilizer, doubling it after regulators had already sign off on it[0]). The fact that Boeing is able to skate by with two and a software off-switch if they disagree, while Airbus continues to be required to have triple redundancy says a lot about their respective regulators (EASA Vs FAA). I'm sure "cost" was discussed given the 350+ aircraft already produced and how impractical it is to add a third AoA sensor, but that's literally putting cost over safety. [0] See "Inaccurate limit": https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/ https://www.seattletimes.com/business/boeing-aerospace/faile...

CaptainZapp 8y ago
but that's literally putting cost over safety. Which seems to be fully in line with Boeing's business model and their behavior after the Lion Air crash. Even after the Ethiopian crash they did just about everything to deflect, blame and obfuscate until this behavior was just no more maintainable based on the known facts. Switching then to a "We apologise if your dead" marketing shtick. I find it hard to believe, based on all the evidence, that this company put lifes before profit.
carlmr 8y ago
>The fact that Boeing is able to skate by with two and a software off-switch if they disagree, while Airbus continues to be required to have triple redundancy says a lot about their respective regulators (EASA Vs FAA). I'm sure "cost" was discussed given the 350+ aircraft already produced and how impractical it is to add a third AoA sensor, but that's literally putting cost over safety. Looking at this image here: https://qz.com/1461400/pilots-werent-informed-of-risks-of-boeing-737-maxs-new-feature/ https://qz.com/1461400/pilots-werent-informed-of-risks-of-bo... My biggest doubt is regarding the symmetrical left-right placement of the AoA vanes. Isn't it realistic that they may freeze in the same position, thus not disagreeing, but still wrong? I'm not in aviation, so I'm not sure about this, but without deeper knowledge this seems like a realistic reason to ask for a 3rd sensor with a different placement at least.

deleted 8y ago

[deleted]

penagwin 8y ago

In these crashes though removing the sensor would have prevented them. The entire issue is that the plane could override pilot controls without pilots knowing and/or not knowing or being able to turn it off.

mikeash 8y ago

This sensor isn’t that important. You can fly the plane fine without it. The problem is when the sensor gives a bad reading and the system trusts it. Two sensors are enough to overcome that. If they disagree, ignore them both. The problem wasn’t that they only had two sensors, it was that they didn’t use them both simultaneously and ignore them when they disagreed.

kalleboo 8y ago
The question is if MCAS is safety critical or not. To me it looks like there are two options: 1. Keep claiming the MAX has the same flight characteristics as previous 737 models, keep the type certification (=minimal pilot retraining) and classify MCAS as safety-critical and require a third AoA vane 2. Classify MCAS as not safety-critical, disengage it on a disagree between left and right, and require pilots take simulator training on MCAS failure modes and how to fly the plane without MCAS (in situations where it differs from previous 737 models) My guess is they'll take the 2 tack. At this point 1 might not even be an option - regulators would probably require MCAS training no matter what.
- salawat 8y ago
  There's still a potential failure mode where both vanes get stuck at the same anomalous reading, so therefore still feed bad data to MCAS. There's more likely a threshold of equality rather than exact equality in measurement going on I'd imagine, but I'd have to see their code to know for sure what their definition of "equal" is.