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I'll argue that making the MAX behave the same as a non MAX 737 is a reachable and reasonable engineering goal, the process failed because it didnt do it safely

by Aloha 7y ago

I'll argue that making the MAX behave the same as a non MAX 737 is a reachable and reasonable engineering goal, the process failed because it didnt do it safely. Airbus absolutely uses its fly-by-wire system to change the handling characteristics of its airplanes, to make them fly the same - I see no reason why Boeing couldn't do the same thing.

acqq 7y ago
> I'll argue that making the MAX behave the same as a non MAX 737 is a reachable and reasonable engineering goal And I argue the opposite: it can‘t be made to behave exactly the same as soon as the failure scenarios are considered. In computer speak, you just look from the point of view of a “most common” run, not all the special cases, exceptions etc. There are other impossibilities too, directly related to the certification requirements, already documented in the news articles before.
- YawningAngel 7y ago
  The normal failure scenario for safety critical electronics on an aircraft is that you have an entirely redundant system that takes over. I don't see why that approach wouldn't have been sufficient here.
  - acqq 7y ago
    It is documented in the articles: failure modes have to be trained if they aren’t the same, and with MCAS as it should be (not as if was and failed catastrophically twice) they can’t be the same. New devices have to be recertified. Two sensors can’t be redundant, three would be again not the same plane. Newer computers won’t be the same plane etc. Wait to see what the final opinion of European agencies are once the latest changes are evaluated and you’ll see that it’s not the same plane, even if Boeing all the time bent over backwards over the dead bodies of others.
gsnedders 7y ago
> Airbus absolutely uses its fly-by-wire system to change the handling characteristics of its airplanes, to make them fly the same - I see no reason why Boeing couldn't do the same thing. AFAIK, being on the same type rating means the A320neo has the same behaviour as the A320ceo _even when in direct law_, where there's a 1:1 mapping between input and behaviour. (Yet alone the very limited mechanical fallback!)
dTal 7y ago
>making the MAX behave the same as a non MAX 737 The purpose of the MCAS is to make the aircraft certifiable - full stop. The MAX is dynamically unstable, in the sense that at high angles of attack it will tend to continue increasing AOA into a stall - a terrible airframe sin which they tried to fix in software. This is the real story, not this type rating stuff. HN discussion: https://news.ycombinator.com/item?id=19695757 https://news.ycombinator.com/item?id=19695757
cmurf 7y ago
Of course the difference is, pilots have mandatory knowledge and training for all of an Airbus's "laws" including the direct mode that has no abstraction, i.e. joystick inputs directly translate to control surface deflections. Whereas with MCAS, pilots were not told about it, the operating manual has no mention of it, there was no training in sim based on it being upset due to a faulty angle of attack senstor, and most remarkably? No training with it disable via stabilizer trim set to cutoff. Appalling. As a pilot and former CFI, without any question whatsoever, a pilot must know how the airplane behaves near stall. Student pilots have demonstrated certified pilot level competency of their particular make/model aircraft stall behavior, before any CFI feels comfortable doing a student pilot sign off for solo flight. It's that goddamn basic. And 737 MAX airplanes have two such stall behaviors, with MCAS and without (via stabilizer trim cutoff). I'd like to see every Boeing pilot involved in these decisions put on a hot seat and asked if they really think it's appropriate to sign off a pilot, as competent to fly, when they aren't completely aware of two different stall behaviors for this aircraft. In my opinion it's unconscionable to have deprived pilots of this knowledge. I am aware of the make/model type certificate arguments. As yet no authority has said for sure whether MCAS knowledge requirements would have then required a new type certificate, or if in fact MCAS is improperly papering over an airworthiness deficiency. What we do know is, it's damn suspicious that this make/model has been grounded this long, with multiple supposedly official statements that software fixes are done and tested and should be ready for FAA approval and deployment any day now, and yet that's been postponed at least 3 times that I'm aware of. If this is strictly a software fix, and a mere tweak back to the original basis of certification, why all the delays?

by Aloha 7y ago

acqq 7y ago

> I'll argue that making the MAX behave the same as a non MAX 737 is a reachable and reasonable engineering goal And I argue the opposite: it can‘t be made to behave exactly the same as soon as the failure scenarios are considered. In computer speak, you just look from the point of view of a “most common” run, not all the special cases, exceptions etc. There are other impossibilities too, directly related to the certification requirements, already documented in the news articles before.

YawningAngel 7y ago
The normal failure scenario for safety critical electronics on an aircraft is that you have an entirely redundant system that takes over. I don't see why that approach wouldn't have been sufficient here.
- acqq 7y ago
  It is documented in the articles: failure modes have to be trained if they aren’t the same, and with MCAS as it should be (not as if was and failed catastrophically twice) they can’t be the same. New devices have to be recertified. Two sensors can’t be redundant, three would be again not the same plane. Newer computers won’t be the same plane etc. Wait to see what the final opinion of European agencies are once the latest changes are evaluated and you’ll see that it’s not the same plane, even if Boeing all the time bent over backwards over the dead bodies of others.

gsnedders 7y ago

> Airbus absolutely uses its fly-by-wire system to change the handling characteristics of its airplanes, to make them fly the same - I see no reason why Boeing couldn't do the same thing. AFAIK, being on the same type rating means the A320neo has the same behaviour as the A320ceo _even when in direct law_, where there's a 1:1 mapping between input and behaviour. (Yet alone the very limited mechanical fallback!)

dTal 7y ago

>making the MAX behave the same as a non MAX 737 The purpose of the MCAS is to make the aircraft certifiable - full stop. The MAX is dynamically unstable, in the sense that at high angles of attack it will tend to continue increasing AOA into a stall - a terrible airframe sin which they tried to fix in software. This is the real story, not this type rating stuff. HN discussion: https://news.ycombinator.com/item?id=19695757 https://news.ycombinator.com/item?id=19695757

cmurf 7y ago

Of course the difference is, pilots have mandatory knowledge and training for all of an Airbus's "laws" including the direct mode that has no abstraction, i.e. joystick inputs directly translate to control surface deflections. Whereas with MCAS, pilots were not told about it, the operating manual has no mention of it, there was no training in sim based on it being upset due to a faulty angle of attack senstor, and most remarkably? No training with it disable via stabilizer trim set to cutoff. Appalling. As a pilot and former CFI, without any question whatsoever, a pilot must know how the airplane behaves near stall. Student pilots have demonstrated certified pilot level competency of their particular make/model aircraft stall behavior, before any CFI feels comfortable doing a student pilot sign off for solo flight. It's that goddamn basic. And 737 MAX airplanes have two such stall behaviors, with MCAS and without (via stabilizer trim cutoff). I'd like to see every Boeing pilot involved in these decisions put on a hot seat and asked if they really think it's appropriate to sign off a pilot, as competent to fly, when they aren't completely aware of two different stall behaviors for this aircraft. In my opinion it's unconscionable to have deprived pilots of this knowledge. I am aware of the make/model type certificate arguments. As yet no authority has said for sure whether MCAS knowledge requirements would have then required a new type certificate, or if in fact MCAS is improperly papering over an airworthiness deficiency. What we do know is, it's damn suspicious that this make/model has been grounded this long, with multiple supposedly official statements that software fixes are done and tested and should be ready for FAA approval and deployment any day now, and yet that's been postponed at least 3 times that I'm aware of. If this is strictly a software fix, and a mere tweak back to the original basis of certification, why all the delays?