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https://aviation.stackexchange.com/questions/61203/what-is-the-technique-or-procedure-to-disable-disengage-the-mcas-on-boeing-737-m https://aviation.stackexchan

https://aviation.stackexchange.com/questions/61203/what-is-the-technique-or-procedure-to-disable-disengage-the-mcas-on-boeing-737-m https://aviation.stackexchange.com/questions/61203/what-is-t... That article I think summarizes the state of the pilot error arguments back when people were still discussing this online. Two methods of disabling an out of control MCAS were mentioned but only one would actually work with a faulty AoA sensor: lowering the flaps. I wonder why Boeing did not mention just lowering the flaps to disable MCAS in an emergency situation. Could that also have saved the flights? This is actually the first I've heard anyone mention the simple method of using the electric trim to fight MCAS until reaching a neutral trim and only then hitting CUTOFF, but would this still work if you were already at max trim and heading nose down toward the water? This method seems to depend on the electric trim being fast enough to fight MCAS to a neutral or near neutral trim even from a maxed trim stab position. Is it fast enough to do that? https://www.reuters.com/article/us-ethiopia-airplane-procedures-explaine/explainer-ethiopia-crash-raises-questions-over-handling-of-faults-on-boeing-737-max-idUSKCN1RG2PP https://www.reuters.com/article/us-ethiopia-airplane-procedu... >“It appears the flight crew reactivated electric trim,” former Boeing engineer Peter Lemme said. “But they only made a very small nose up adjustment - I would have expected them to immediately and without stopping move the stabilizer back into trim. The last MCAS command comes 5 seconds after their last manual trim command.” This does appear very strange to me. Why let go of the electric trim before getting to neutral or even a bit nose up? Did they think the trim could only be used in small increments or something? Were they so focused on the mystery of what was causing the trim adjustments that they didn't think to just jam down the electric trim switch until trim neutralized? https://projects.seattletimes.com/2019/boeing-737-max-12-problems/ https://projects.seattletimes.com/2019/boeing-737-max-12-pro... Here is another good article that summarizes what happened. Seems to me that there are essentially 3 ways the flights could have been saved although I'm less sure about your method of just electric trimming to neutral and then hitting CUTOFF because the electric trim adjustment would have to be fast enough to overcome the MCAS counter-adjustments. Surely electric trim would not have been designed for such a race. And also that seems like such an obvious thing to do even if you haven't read the airworthiness directive you cite. Something is messing with the trim. There is a button that adjusts trim ffs. Why not try to just hold it down? Even a child might think of that simple solution. But these pilots didn't? Some of them were even experienced. The other two methods are lowering the flaps which seems to have worked well for them even if it was by accident or slowing down the plane and then hitting the CUTOFF switches and hoping you can spin the trim wheels fast enough. Probably the Ethiopian pilots were unaware of the airworthiness directive and reverted back to the standard runaway trim procedure without realizing their high speed would make the wheels more or less impossible to turn. I am not a pilot so I am not clear on how easy it is to slow down a plane that is already in the nose down position. Gravity is a harsh mistress.

WalterBright 6y ago
> This is actually the first I've heard anyone mention the simple method of using the electric trim to fight MCAS until reaching a neutral trim and only then hitting CUTOFF, but would this still work if you were already at max trim and heading nose down toward the water? Yes, and it did indeed work. The pilots, though, did not cut off the stab trim. > This method seems to depend on the electric trim being fast enough to fight MCAS to a neutral or near neutral trim even from a maxed trim stab position. Is it fast enough to do that? Yes, and it doesn't "fight" MCAS. It overrides it electrically in hardware (not software). > I'm less sure about your method of just electric trimming to neutral and then hitting CUTOFF because the electric trim adjustment would have to be fast enough to overcome the MCAS counter-adjustments. Surely electric trim would not have been designed for such a race. I'm sure about it. The electric trim moves just as fast as the MCAS would, because the trim is electrically ON or OFF. There's no speed control on it. It's not a race, either. The electric trim switches are between the MCAS and the motors, they override it. Furthermore, in the LA flight before the LA crash flight, the same problem happened. The pilots restored trim and hit the cutoff switches, and landed safely. The mystery to me was why that airplane was allowed to take off again before being repaired. > And also that seems like such an obvious thing to do even if you haven't read the airworthiness directive you cite. Something is messing with the trim. There is a button that adjusts trim ffs. Why not try to just hold it down? Even a child might think of that simple solution. But these pilots didn't? Some of them were even experienced. Exactly, and that's what the pilots did in the first non-crashing incident. > Probably the Ethiopian pilots were unaware of the airworthiness directive Yup, and that was a contributing factor to the crash.

WalterBright 6y ago

> This is actually the first I've heard anyone mention the simple method of using the electric trim to fight MCAS until reaching a neutral trim and only then hitting CUTOFF, but would this still work if you were already at max trim and heading nose down toward the water? Yes, and it did indeed work. The pilots, though, did not cut off the stab trim. > This method seems to depend on the electric trim being fast enough to fight MCAS to a neutral or near neutral trim even from a maxed trim stab position. Is it fast enough to do that? Yes, and it doesn't "fight" MCAS. It overrides it electrically in hardware (not software). > I'm less sure about your method of just electric trimming to neutral and then hitting CUTOFF because the electric trim adjustment would have to be fast enough to overcome the MCAS counter-adjustments. Surely electric trim would not have been designed for such a race. I'm sure about it. The electric trim moves just as fast as the MCAS would, because the trim is electrically ON or OFF. There's no speed control on it. It's not a race, either. The electric trim switches are between the MCAS and the motors, they override it. Furthermore, in the LA flight before the LA crash flight, the same problem happened. The pilots restored trim and hit the cutoff switches, and landed safely. The mystery to me was why that airplane was allowed to take off again before being repaired. > And also that seems like such an obvious thing to do even if you haven't read the airworthiness directive you cite. Something is messing with the trim. There is a button that adjusts trim ffs. Why not try to just hold it down? Even a child might think of that simple solution. But these pilots didn't? Some of them were even experienced. Exactly, and that's what the pilots did in the first non-crashing incident. > Probably the Ethiopian pilots were unaware of the airworthiness directive Yup, and that was a contributing factor to the crash.