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This article makes a really good case overall, but it must be deliberate that it chooses not to mention the stabiliser trim cut-out switch. In the part about th
by ppod 6y ago
This article makes a really good case overall, but it must be deliberate that it chooses not to mention the stabiliser trim cut-out switch. In the part about the Cessna he says:
>There are instructions on how to detect when the system malfunctions and how to disable the system, immediately. Disabling the system means pulling the autopilot circuit breaker; instructions on how to do that are strewn throughout the documentation, repeatedly. Every pilot who flies my plane becomes intimately aware that it is not the same as any other 172. This is a big difference between what pilots who want to fly my plane are told and what pilots stepping into a 737 Max are (or were) told.
Which really implies that no such procedure existed for the Max, and that's just not true. There may have been problems with the procedure, as far as I know it's not fully known yet why that procedure didn't prevent the accidents, possibly inadequate pilot training.
https://www.flightglobal.com/safety/trim-cut-out-puzzle-emerges-from-ethiopian-crash-probe/132175.article https://www.flightglobal.com/safety/trim-cut-out-puzzle-emer...
- roelschroeven 6y ago> it's not fully known yet why that procedure didn't prevent the accidents The only way in the 737 Max to disable MCAS, is to disable electric trim altogether. That means only manual trim is available. When MCAS has trimmed all the way to one of the extremes (as happened in the Ethiopean flight), it requires many revolutions of the trim wheel and superhuman strength to return it to a more appropriate setting (see e.g. https://youtu.be/aoNOVlxJmow?t=750 https://youtu.be/aoNOVlxJmow?t=750). Previous generations of the 737 had two buttons related to the electric trim: one disabled the automatic trim system, the other one disabled electric trim altogether. The 737 Max still has two buttons, but they both have the same effect: disable the electric trim altogether. The old system could easily have prevented the crash by disabling MCAS but leaving the electrically assisted trim enabled. Boeing's procedure to make manual trim adjustments possible is to put the airplane in a dive, because that lowers the aerodynamic forces on the trim surface. When you're only a few hundred feet above the ground, that's not really an option. The pilots re-enabled the electric trim in the hope they could use it in their fight against MCAS. It's the only thing they could think of in the stress of the moment, faced with near-certain death and an airplane actively trying to crash. In hindsight, after reading accident reports and thinking about it in the comfort of chair that's not crashing, there were things they could have done. Lowering the throttle would have lessened the forces on the trim surface, activating the flaps once the speed was low enough would have disabled MCAS. I can't blame the pilots for not coming up with that in the heat of the moment.
- ppod 6y agoAll I said was that as far as I know it isn't fully known. The final report isn't out yet. I'm just an aviation enthusiast, but it's notable that in many discussions anything that could possibly be perceived as even possibly implying any pilot fault is kind of taboo. I'm not saying the pilots did anything wrong, I'm just saying that leaving the stab cut-out switch out of the story seems strange to me.
- roelschroeven 6y agoI don't really understand what you mean by "leaving the stab cut-out switch out of the story". Can you point me to a report that ignores the stab cut-out switch?
- ppod 6y agoI meant the OP IEEE article that these comments are on.