5 ms·

That’s absolutely applicable here. It means that an engine cutoff shouldn’t be allowed at all during certain parts of flight. It’s not crazy to think that a de

That’s absolutely applicable here. It means that an engine cutoff shouldn’t be allowed at all during certain parts of flight. It’s not crazy to think that a design fix would be to prevent those engagements during certain parts of takeoff (a certain window). It’s fly by wire anyway so it could presumably be done programmatically. MCAS was basically made to prevent user input that would send the plane into a dangerous angle. The computer overrode the inputs. So there’s precedent for something like it.

WalterBright 1y ago
> The computer overrode the inputs. This is incorrect. The manual stabilizer trim thumb switches override MCAS.
- interestica 1y ago
  Are we not in agreement? MCAS overrode the inputs and the thumb switches could override MCAS?
  - invalidator 1y ago
    MCAS autonomously adjusts trim downward. The trim switches override MCAS, but when released, MCAS can resume trimming down again. The trim adjustments don't "override" the pilot's elevator inputs (MCAS has no direct control over the elevators), but they can make the controls so heavy that it's impossible to pull up.
    - WalterBright 1y ago
      If MCAS is running the trim, the thumb switches override it. MCAS affects the stabilizer, the thumb switches affect the stabilizer, the cutoff switch affects the stabilizer. The elevators are controlled by the control column and the autopilot. > The trim switches override MCAS, but when released, MCAS can resume trimming down again. That is correct. That is why the procedure is to return the trim to normal with the thumb switches, then turn off the trim system. That's it. That's all there is to it. > but they can make the controls so heavy that it's impossible to pull up. Almost right - the trim has more authority than the elevators. The trim's ability to travel far is to provide great ability to get out of trouble. I don't really know what factors the aerodynamics guys used to calculate the max travel required. I do know there is a travel limiter on it (as I worked on that, too!) which reduces the max travel at higher speeds, because otherwise it can rip the tail section off, which is a big no-no. There are sooo many constraints on the design of an airplane I sometimes wonder how anyone manages to make one that works at all. The Wright Bros calculated that their machine would fly, and it did, barely. Their contemporaries did seat of the pants design, which is why they failed.
      - throwaway48476 1y ago
        It's good that you're still around to correct misinformation about MCAS. I've seen so much misinformation about it, including from paid "experts". The Wright brothers succeeded because they were pioneers in wind tunnels and aluminum engine blocks.
        WalterBright 1y ago
        Thank you. I've had commercial pilots email me telling me I was correct and to keep on the good fight :-) The Wrights did a lot more than that to be successful. Their innovations were: 1. using a wind tunnel to correctly get lift and drag coefficients for various wing sections (as you wrote) 2. first aviation engine (high power/weight ratio) (as you wrote) 3. first propeller theory, enabling 90% efficiency (other aviation propellers were 50% efficient) 4. first 3-axis control system 5. identified and solved adverse yaw problem 6. first research and development program, where problems were identified in advance, and a machine was developed to solve each problem, then the solutions were put together to make the 1903 Wright Flyer 7. kept meticulous notes on all their work and preserved the evidence of their success, such as photographs and notebooks. Exacting replicas have been built, and their flight characteristics match the Wright's results
      - invalidator 1y ago
        > Almost right - the trim has more authority than the elevators. Thank you, I'll update my brain and future explanations. :)
  - WalterBright 1y ago
    The pilot's inputs are the thumb switches, and they override MCAS. Additionally, the stab trim cutoff switch overrode both MCAS and the thumb switches. Using both easily and successfully averts MCAS crashes, as proven in the first incident (there were three, but only two are reported on).
    - throwaway48476 1y ago
      There were also a lot of MCAS near misses.
      - WalterBright 1y ago
        I only heard of one. I'm interested in others, if you have references.
        throwaway48476 1y ago
        https://www.dallasnews.com/business/airlines/2019/03/12/several-boeing-737-max-8-pilots-in-u-s-complained-about-suspected-safety-flaw/ https://www.dallasnews.com/business/airlines/2019/03/12/seve... I just remember that it happened commonly enough to US pilots. American pilots always recovered quickly enough that it didn't make the news before the fatal crashes.
        WalterBright 1y ago
        Thank you, but it's behind a paywall. I did find this: https://www.nytimes.com/2019/09/18/magazine/boeing-737-max-crashes.html https://www.nytimes.com/2019/09/18/magazine/boeing-737-max-c... which has detailed information, but I don't trust the NYT. The article also erroneously reports that the MCAS trim rate is twice the speed of manual trim. The trim rate for both is 0.27 degrees per second.
hinkley 1y ago
Do you mean the MCAS System that sent two planeloads of people to their deaths? That MCAS system?

WalterBright 1y ago

> The computer overrode the inputs. This is incorrect. The manual stabilizer trim thumb switches override MCAS.

interestica 1y ago
Are we not in agreement? MCAS overrode the inputs and the thumb switches could override MCAS?
- invalidator 1y ago
  MCAS autonomously adjusts trim downward. The trim switches override MCAS, but when released, MCAS can resume trimming down again. The trim adjustments don't "override" the pilot's elevator inputs (MCAS has no direct control over the elevators), but they can make the controls so heavy that it's impossible to pull up.
  - WalterBright 1y ago
    If MCAS is running the trim, the thumb switches override it. MCAS affects the stabilizer, the thumb switches affect the stabilizer, the cutoff switch affects the stabilizer. The elevators are controlled by the control column and the autopilot. > The trim switches override MCAS, but when released, MCAS can resume trimming down again. That is correct. That is why the procedure is to return the trim to normal with the thumb switches, then turn off the trim system. That's it. That's all there is to it. > but they can make the controls so heavy that it's impossible to pull up. Almost right - the trim has more authority than the elevators. The trim's ability to travel far is to provide great ability to get out of trouble. I don't really know what factors the aerodynamics guys used to calculate the max travel required. I do know there is a travel limiter on it (as I worked on that, too!) which reduces the max travel at higher speeds, because otherwise it can rip the tail section off, which is a big no-no. There are sooo many constraints on the design of an airplane I sometimes wonder how anyone manages to make one that works at all. The Wright Bros calculated that their machine would fly, and it did, barely. Their contemporaries did seat of the pants design, which is why they failed.
    - throwaway48476 1y ago
      It's good that you're still around to correct misinformation about MCAS. I've seen so much misinformation about it, including from paid "experts". The Wright brothers succeeded because they were pioneers in wind tunnels and aluminum engine blocks.
      - WalterBright 1y ago
        Thank you. I've had commercial pilots email me telling me I was correct and to keep on the good fight :-) The Wrights did a lot more than that to be successful. Their innovations were: 1. using a wind tunnel to correctly get lift and drag coefficients for various wing sections (as you wrote) 2. first aviation engine (high power/weight ratio) (as you wrote) 3. first propeller theory, enabling 90% efficiency (other aviation propellers were 50% efficient) 4. first 3-axis control system 5. identified and solved adverse yaw problem 6. first research and development program, where problems were identified in advance, and a machine was developed to solve each problem, then the solutions were put together to make the 1903 Wright Flyer 7. kept meticulous notes on all their work and preserved the evidence of their success, such as photographs and notebooks. Exacting replicas have been built, and their flight characteristics match the Wright's results
    - invalidator 1y ago
      > Almost right - the trim has more authority than the elevators. Thank you, I'll update my brain and future explanations. :)
- WalterBright 1y ago
  The pilot's inputs are the thumb switches, and they override MCAS. Additionally, the stab trim cutoff switch overrode both MCAS and the thumb switches. Using both easily and successfully averts MCAS crashes, as proven in the first incident (there were three, but only two are reported on).
  - throwaway48476 1y ago
    There were also a lot of MCAS near misses.
    - WalterBright 1y ago
      I only heard of one. I'm interested in others, if you have references.
      - throwaway48476 1y ago
        https://www.dallasnews.com/business/airlines/2019/03/12/several-boeing-737-max-8-pilots-in-u-s-complained-about-suspected-safety-flaw/ https://www.dallasnews.com/business/airlines/2019/03/12/seve... I just remember that it happened commonly enough to US pilots. American pilots always recovered quickly enough that it didn't make the news before the fatal crashes.
        WalterBright 1y ago
        Thank you, but it's behind a paywall. I did find this: https://www.nytimes.com/2019/09/18/magazine/boeing-737-max-crashes.html https://www.nytimes.com/2019/09/18/magazine/boeing-737-max-c... which has detailed information, but I don't trust the NYT. The article also erroneously reports that the MCAS trim rate is twice the speed of manual trim. The trim rate for both is 0.27 degrees per second.

hinkley 1y ago

Do you mean the MCAS System that sent two planeloads of people to their deaths? That MCAS system?