3 ms·

I'm starting to think that disabling MCAS isn't even a sane option because then the pilots are exposed to unexpected aerodynamic characteristics due to the plan

• linuxftw 8y ago
  Many people have this opinion. You can't both require MCAS and be okay with disabling it at the most critical portion of a flight where the system is needed most.
  • pdonis 8y ago
    > You can't both require MCAS and be okay with disabling it at the most critical portion of a flight where the system is needed most. If MCAS activates when it isn't supposed to, which is what happened here, disabling it is what you want to do--to stop it from doing an incorrect thing. The plane was not in a situation where MCAS was needed; it was perfectly flyable without MCAS in the flight regime it was in. The problem is that, if you disable MCAS (which requires disabling the entire electric stability trim system) without first using the electric trim system to get back to something close to neutral trim, you will be stuck with a lot of nose down trim that you can't remove fast enough with the manual trim wheel. It looks like that's the situation this flight got into. But if you first use the electrim trim system to get back to something close to neutral trim, and then, before MCAS has a change to mess it up again, disable the entire electric stability trim system, you're ok. How do we know? Because that's what the first Lion Air flight (the one the day before the one the crashed) did, because an off duty pilot that was riding in the jump seat figured out what was happening and how to deal with it and told the pilots what to do.
    • linuxftw 8y ago
      > The plane was not in a situation where MCAS was needed; As far as I can tell, there is no takeoff (pitch up) situation where MCAS is not needed on the MAX 800. It's required for safe operation of the plane, otherwise the nose might pitch up unexpectedly into a stall. As I said, the system can't both "be required for safe operation of the plane" and "it's safe to disable MCAS while it's malfunctioning during takeoff." You have to pick one.
      • pdonis 8y ago
        > As far as I can tell, there is no takeoff (pitch up) situation where MCAS is not needed on the MAX 800. Reference, please? I have not seen anything that says MCAS is required for safe operation at a normal angle of attack for takeoff and climb to altitude. Note that the key parameter is angle of attack, not pitch angle; if the plane is climbing the angle of attack is lower than the pitch angle, because the plane is climbing so the relative wind is coming from somewhat above the horizontal direction.
    • PunchTornado 8y ago
      God, the people on that flight should thank that off duty pilot. So close to death.