Quote:
Originally Posted by Resolute 14
Is there a chance that they were trying what you suggest, but that the software kept overriding back into a 'crash me' state, for which they did not know how to disable?
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I'm going to link an article that explains MCAS in detail (it's been posted in this thread a couple times), and the spoiler boxes below have the two images from that article that will help illustrate my explanation.
Generally, the purpose of stabilizer trim is to help the pilot so he doesn't have to exert constant heavy pressure on the yoke. Both pilots have thumb switches on the yoke (see first spoiler box) that controls the stabilizer trim.
When the pilot presses that switch, the black electric trim wheel spins, making loud noises, and the stabilizer tilts in the direction the pilot wants it to, until he/she lets go of the switch. This is the switch the Captain of the Lion Air flight was pressing; pilots will adjust stabilizer trim quite often in normal flight.
MCAS trims the stabilizer automatically, and the electric trim wheel spins in the same way as if the pilot was commanding trim up/down motion.
When MCAS is trimming the stabilizer, it will temporarily disengage when the pilot presses the thumb switch on the yoke, and once the pilot lets go, it will re-engage after a few seconds. (see article + second spoiler box)
When you flick the trim cutoff switches (see first spoiler box), that disables the electric motion of the stabilizer trim, and hence, disables both MCAS and the pilot's thumb switch. When you disable automated trim, you have to crank the wheel by hand to adjust the trim, regardless of whether you're flying a 737-800, or a 737 MAX.
So on the Lion Air flight, the Captain knew there was something wrong with the stabilizer trim, because he kept counteracting the trim motion commanded by MCAS. When he handed over control of the plane to the First Officer so he could look through the emergency checklists, the F/O did not make the same trim commands. Whether the Captain told him to or not, we don't know.
But the Captain was obviously on the right track...it baffles me as to why he didn't think to disable the automated trim. If he kept trimming the nose up, he must have known something was constantly trimming it downwards. Whether you know about MCAS or not (or even the fact you're flying a MAX) is irrelevant, like FLAME ENVY said. Any trained/experienced pilot "should" (or so we think) catch onto the fact that "hey, I have a trim problem".
But it's easy for me to say that sitting in my office chair; in an emergency situation where you have NO idea what the plane is doing, your mind is moving a million miles an hour, and it can be easy to miss certain things that one would think should be basic.
None of us (licensed pilots and armchair experts alike) were up there in that situation, so it's impossible to know what was going on in the minds of the crew. And like Ryan Coke said, if two air crews were not able to diagnose this as a trim problem, it begs the question whether the MCAS problem is as obvious as we think.
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https://theaircurrent.com/aviation-s...em-mcas-jt610/