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You seem quite knowledgeable. You disagree with the statement that roughly the urge to avoid recertifying pilots caused Boeing to not mention MCAS even in manu

by x0x0 7y ago

You seem quite knowledgeable. You disagree with the statement that roughly the urge to avoid recertifying pilots caused Boeing to not mention MCAS even in manuals, leading directly to these deaths? Because from my pov, Boeing introduced a new failure mode (MCAS failure leading to intermittent forcing of the nose down) without any warning to the pilots. Now maybe the pilots' standard training should have compensated, and there are obviously maintenance or training deficiencies, but Boeing also knew good and well they were selling planes to pilots with these existing training deficiencies. And should have designed a plane to be operated by real world pilots. Very curious for your thoughts; thank you!

mlyle 7y ago
I disagree that deciding to stretch the 737 is fundamentally bad engineering. Yes, it realistically requires some control augmentation (and maybe earlier 737's should really have had something like MCAS, too). Yes, bigger engines and heavier 737's have the problem worse, but it isn't unreasonable to fix this with systems. I think there were failures across the board. The fundamental analysis of MCAS was flawed: it was much less reliable than was thought, and failures of it provided a much more difficult situation for pilots than anticipated. I suspect the analysis boiled down to "MCAS provides a little defense against getting the nose excessively high on departure; it shouldn't be necessary so no big deal if it fails. And the worst failure we can think of is like stabilator trim runaway, which everyone knows how to deal with." This was compounded by the fact that many developing countries do not require pilots to demonstrate they can deal with runaway trim as part of a checkride and recurring training. Not disclosing information about the system made the problem even worse-- and this is harder to attribute purely to being part of bad initial analysis. I do not understand some of the aircrew actions, even in retrospect. If I am fighting pulling the yoke back-- I am going to have my finger on the trim switch to try and get rid of those control forces, even before I am thinking about the problem. This would have inhibited MCAS and retrimmed the plane. I think that Boeing assumed that this would happen. I am lazy and would rather not have to tug the yoke so I use trim a lot. :P
- x0x0 7y ago
  Just for clarity, I have no qualms about stretching the plane. It's building in a new control system and not telling the pilots about it that seems crazy to me. Thanks so much for your thoughts!
  - mlyle 7y ago
    Yup, I agree completely. There's some people who say that because the longer 737 is less stable in pitch it should have never been built, and I think that's over the top. Thank you for the discussion and questions!
    - Zak 7y ago
      > There's some people who say that because the longer 737 is less stable in pitch it should have never been built, and I think that's over the top. I know that aerodynamic instability requiring continuous correction by fly-by-wire systems has become common on fighter jets because it's necessary to achieve some of the maneuvering characteristics necessary to make them competitive. These are, of course very different priorities from commercial passenger aircraft. Has a jetliner been certified before the 737 MAX that is aerodynamically unstable in any of the tests that it's required to pass without control inputs made by the computer without direct input from the pilot, or in contravention of the pilot's input? I know Airbus is fond of its "do what I mean" system, but that in some circumstances, Airbus flight control systems revert to essentially emulating an analog airplane. Would their flight characteristics pass certification in that mode?
      - mlyle 7y ago
        Concorde's Safety Flight System is in some ways similar to MCAS, in that it'll nudge elevons itself. I don't know if Airbus would meet certification requirements in direct control law. I suspect not. Definitely not in mechanical control law. Just like more conventional jetliners wouldn't meet certification guidelines without all of their control rigging, counterweights, and trim systems. It's just now tempting to make adjustments to those systems with software instead of fiddling with everything else.

by x0x0 7y ago

mlyle 7y ago

I disagree that deciding to stretch the 737 is fundamentally bad engineering. Yes, it realistically requires some control augmentation (and maybe earlier 737's should really have had something like MCAS, too). Yes, bigger engines and heavier 737's have the problem worse, but it isn't unreasonable to fix this with systems. I think there were failures across the board. The fundamental analysis of MCAS was flawed: it was much less reliable than was thought, and failures of it provided a much more difficult situation for pilots than anticipated. I suspect the analysis boiled down to "MCAS provides a little defense against getting the nose excessively high on departure; it shouldn't be necessary so no big deal if it fails. And the worst failure we can think of is like stabilator trim runaway, which everyone knows how to deal with." This was compounded by the fact that many developing countries do not require pilots to demonstrate they can deal with runaway trim as part of a checkride and recurring training. Not disclosing information about the system made the problem even worse-- and this is harder to attribute purely to being part of bad initial analysis. I do not understand some of the aircrew actions, even in retrospect. If I am fighting pulling the yoke back-- I am going to have my finger on the trim switch to try and get rid of those control forces, even before I am thinking about the problem. This would have inhibited MCAS and retrimmed the plane. I think that Boeing assumed that this would happen. I am lazy and would rather not have to tug the yoke so I use trim a lot. :P

x0x0 7y ago
Just for clarity, I have no qualms about stretching the plane. It's building in a new control system and not telling the pilots about it that seems crazy to me. Thanks so much for your thoughts!
- mlyle 7y ago
  Yup, I agree completely. There's some people who say that because the longer 737 is less stable in pitch it should have never been built, and I think that's over the top. Thank you for the discussion and questions!
  - Zak 7y ago
    > There's some people who say that because the longer 737 is less stable in pitch it should have never been built, and I think that's over the top. I know that aerodynamic instability requiring continuous correction by fly-by-wire systems has become common on fighter jets because it's necessary to achieve some of the maneuvering characteristics necessary to make them competitive. These are, of course very different priorities from commercial passenger aircraft. Has a jetliner been certified before the 737 MAX that is aerodynamically unstable in any of the tests that it's required to pass without control inputs made by the computer without direct input from the pilot, or in contravention of the pilot's input? I know Airbus is fond of its "do what I mean" system, but that in some circumstances, Airbus flight control systems revert to essentially emulating an analog airplane. Would their flight characteristics pass certification in that mode?
    - mlyle 7y ago
      Concorde's Safety Flight System is in some ways similar to MCAS, in that it'll nudge elevons itself. I don't know if Airbus would meet certification requirements in direct control law. I suspect not. Definitely not in mechanical control law. Just like more conventional jetliners wouldn't meet certification guidelines without all of their control rigging, counterweights, and trim systems. It's just now tempting to make adjustments to those systems with software instead of fiddling with everything else.