Probably Materially Less.....
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2019-03-26 13:41 by Karl Denninger
in Editorial , 290 references Ignore this thread
Probably Materially Less.....
[Comments enabled]

Now comes this....

In flight simulations designed to recreate the problems from a doomed Boeing 737 Max airliner, pilots found that they had less than 40 seconds to override a controversial automated system and prevent a crash, according to The New York Times.

My understanding from talking to pilots of various aircraft (including some military ones) is that even in the event of a jammed trim you can fly, but you'll be doing "arm curls" (if locked in the "down" position) with the yoke to do it.

But I've also been told that the trim authority on the 737 is large enough that it's physically impossible, even if you put your feet on the panel, to pull the yoke back if the trim is jammed against you.

It's also true that the cutoff switches are right on the center pedestal and easily accessible.  But shutting them off shuts off all power trim operation; what you're left with is the handwheels near your knee and it takes a lot of rotations of that wheel to come back from the jackscrew racked one way to neutral.

So this report sounds entirely plausible -- if you don't immediately recognize what's going on you're in big trouble, especially if you're down low and unlike some aircraft which have "hybrid" trim systems (e.g. electric and hydraulic), where you can dump one of them and the other still works on the 737 it's electric-only and the only backup is physical/manual.

The electric motor can run the trim quite rapidly -- materially more-so than you can with hand power, which, if you yank the switches, is all you have left.

And furthermore since the system allegedly involved was not clearly-documented in terms of even being present, say much less what its total authority was (effectively unlimited) one has to wonder whether the intentional lack of disclosure and additional training requirement (which, I remind you, the carriers insisted on to avoid type-rating, training and certification costs)  was enough to lead to a situation where the odds of correctly resolving the problem if it occurred, were poor.

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