4 ms·

Another issue is that the engines on the Max version are larger than the NG version and didn’t fit under the wing. So they had to raise the mounting point forwa

Another issue is that the engines on the Max version are larger than the NG version and didn’t fit under the wing. So they had to raise the mounting point forward and up as well as extend the nose gear 18 inches. These changes caused the plane to have a different flight profile to the NG version. However it would have been disasterous if pilots already certified for the 737 couldn’t fly the 737 max. So boeing implemented the MCAS so make the max handle like the NG. That move is drawing a lot of skepticism because if the computer screws up then the pilots were never really trained to fly the Max https://theaircurrent.com/aviation-safety/what-is-the-boeing-737-max-maneuvering-characteristics-augmentation-system-mcas-jt610/ https://theaircurrent.com/aviation-safety/what-is-the-boeing...

JKCalhoun 8y ago
I'm ignorant of aviation, oversimplifying, but my summary: they fixed issues with the hardware in software. A little scary?
- oliveshell 8y ago
  > A little scary? Perhaps, but it’s not unprecedented. The B2 stealth bomber, for example, famously lacks a vertical stabilizer (tail fin) and so is inherently unstable and relies on computerized control surfaces to maintain stable flight [1]. This seems to have worked fine, although the things definitely log way fewer flight hours than an airliner. I believe several other aircraft do this as well (fighter jets and such). Still, the idea of it would give me the willies if I were in charge of flying one. [1]: https://en.m.wikipedia.org/wiki/Northrop_Grumman_B-2_Spirit#Flight_controls https://en.m.wikipedia.org/wiki/Northrop_Grumman_B-2_Spirit#...
  - azernik 8y ago
    Fighters, in particular, are designed to be unstable to increase their control authority. That is, as an intended design feature they are easy to turn intentionally, which means they are also prone to turn unintentionally.
  - woodrowbarlow 8y ago
    i don't know anything about aircraft, but i would be inclined to think that the lack of tail fin on a B2 isn't just a design flaw or technical debt from the previous model and that there were other reasons for it.
    - oliveshell 8y ago
      You’re right— the B2 was designed like it was in order to minimize radar cross-section at all costs. One could see, though, how a Boeing engineer could point to the B2 and fighters that rely on software for safe flight and say “See? They do it and it’s fine!” as a justification. Not that I’m saying that makes it right.
  - mirimir 8y ago
    I've also been reminded of that. But performance / safety tradeoffs are totally different for military vs civilian aircraft. Military pilots have agreed to far greater risks than civilian pilots. And far^N greater risks than civilian passengers.
- js2 8y ago
  The alternative would have been redesigning the 737 such that it would be a different plane. There are advantages to keeping it as similar as possible to the previous generation. Boeing was in a bit of a bind. They had a plane (the 737) originally designed for different requirements (the plane is low to the ground) in wide spread use that the airlines wanted them to make more fuel efficient to stay competitive with Airbus’s latest models. If they introduced a new plane that would require the airlines to retrain all their 737 pilots among other things. So Boeing found a way to put new engines on while keeping the plane similar enough as not to make it a new type. From what I understand, MCAS is a reasonable solution. Where it gets questionable is in not informing the pilots of this new system (but again, there were reasons for that, maybe as it turns out not good reasons), allowing the new system to override the yoke input (Boeing reasoned there was already a procedure for runaway trim pilots would follow), and keying the new system off a single AoA sensor and only having two AoA sensors total so it’s not clear what to do when they disagree.
  - michaelt 8y ago
    I'm not clear on why having different engines, different handling and MCAS makes it not-a-new-plane, but having the landing gear extend further down would make it a new plane?
    - deleted 8y ago
      [deleted]
    - mannykannot 8y ago
      I don't think it is a binary 'either its a new plane or its not' situation. I think every change has to be scrutinized for its safety implications, and for MCAS the analysis seems to have been, in part, that a failure could cause a trim runaway, but trim runaway is a circumstance for which there already exists a response, and that would not need changing (what this overlooked was that the pilots would experience it differently, as pulling back will not stop it, and if they stopped it with the trim button but didn't disable it, it would start up again ten seconds later.) Putting a longer undercarriage on an airplane is not a trivial matter. You have to design it, test it, get it certified (a new undercarriage raises obvious safety issues) and put it into production. It's not just the undercarriage - it won't fit into the existing wheel wells, and furthermore, the legs might have to be moved further out on the wing, and then you have to rework that, as well.
- mimixco 8y ago
  From a software development standpoint, it sounds like it. And that is scary (and unfeasible).
- leeoniya 8y ago
  i've read that B2's simply cannot be flown manually. https://www.quora.com/How-are-inherently-unstable-aircraft-such-as-the-B-2-made-stable-1 https://www.quora.com/How-are-inherently-unstable-aircraft-s... edit: oops someone already said this 30min ago

JKCalhoun 8y ago

I'm ignorant of aviation, oversimplifying, but my summary: they fixed issues with the hardware in software. A little scary?

oliveshell 8y ago
> A little scary? Perhaps, but it’s not unprecedented. The B2 stealth bomber, for example, famously lacks a vertical stabilizer (tail fin) and so is inherently unstable and relies on computerized control surfaces to maintain stable flight [1]. This seems to have worked fine, although the things definitely log way fewer flight hours than an airliner. I believe several other aircraft do this as well (fighter jets and such). Still, the idea of it would give me the willies if I were in charge of flying one. [1]: https://en.m.wikipedia.org/wiki/Northrop_Grumman_B-2_Spirit#Flight_controls https://en.m.wikipedia.org/wiki/Northrop_Grumman_B-2_Spirit#...
- azernik 8y ago
  Fighters, in particular, are designed to be unstable to increase their control authority. That is, as an intended design feature they are easy to turn intentionally, which means they are also prone to turn unintentionally.
- woodrowbarlow 8y ago
  i don't know anything about aircraft, but i would be inclined to think that the lack of tail fin on a B2 isn't just a design flaw or technical debt from the previous model and that there were other reasons for it.
  - oliveshell 8y ago
    You’re right— the B2 was designed like it was in order to minimize radar cross-section at all costs. One could see, though, how a Boeing engineer could point to the B2 and fighters that rely on software for safe flight and say “See? They do it and it’s fine!” as a justification. Not that I’m saying that makes it right.
- mirimir 8y ago
  I've also been reminded of that. But performance / safety tradeoffs are totally different for military vs civilian aircraft. Military pilots have agreed to far greater risks than civilian pilots. And far^N greater risks than civilian passengers.
js2 8y ago
The alternative would have been redesigning the 737 such that it would be a different plane. There are advantages to keeping it as similar as possible to the previous generation. Boeing was in a bit of a bind. They had a plane (the 737) originally designed for different requirements (the plane is low to the ground) in wide spread use that the airlines wanted them to make more fuel efficient to stay competitive with Airbus’s latest models. If they introduced a new plane that would require the airlines to retrain all their 737 pilots among other things. So Boeing found a way to put new engines on while keeping the plane similar enough as not to make it a new type. From what I understand, MCAS is a reasonable solution. Where it gets questionable is in not informing the pilots of this new system (but again, there were reasons for that, maybe as it turns out not good reasons), allowing the new system to override the yoke input (Boeing reasoned there was already a procedure for runaway trim pilots would follow), and keying the new system off a single AoA sensor and only having two AoA sensors total so it’s not clear what to do when they disagree.
- michaelt 8y ago
  I'm not clear on why having different engines, different handling and MCAS makes it not-a-new-plane, but having the landing gear extend further down would make it a new plane?
  - deleted 8y ago
    [deleted]
  - mannykannot 8y ago
    I don't think it is a binary 'either its a new plane or its not' situation. I think every change has to be scrutinized for its safety implications, and for MCAS the analysis seems to have been, in part, that a failure could cause a trim runaway, but trim runaway is a circumstance for which there already exists a response, and that would not need changing (what this overlooked was that the pilots would experience it differently, as pulling back will not stop it, and if they stopped it with the trim button but didn't disable it, it would start up again ten seconds later.) Putting a longer undercarriage on an airplane is not a trivial matter. You have to design it, test it, get it certified (a new undercarriage raises obvious safety issues) and put it into production. It's not just the undercarriage - it won't fit into the existing wheel wells, and furthermore, the legs might have to be moved further out on the wing, and then you have to rework that, as well.
mimixco 8y ago
From a software development standpoint, it sounds like it. And that is scary (and unfeasible).
leeoniya 8y ago
i've read that B2's simply cannot be flown manually. https://www.quora.com/How-are-inherently-unstable-aircraft-such-as-the-B-2-made-stable-1 https://www.quora.com/How-are-inherently-unstable-aircraft-s... edit: oops someone already said this 30min ago