China orders its airlines to suspend use of Boeing 737 Max aircraft

Re:China orders its airlines to suspend use of Boeing 737 Ma... by qaq on Monday March 11, 2019 @11:29AM (#19359670)

Well we might be jumping to conclusions here a quote on the issue from pilots forum: "Runaway stabilizer procedures in the 737 have remained pretty much unchanged since its first flight. The same can be said for pretty much any Boeing airliner. 1 - Turn off the autopilot to see if it's causing the problem. 2 - Oppose the trim manually with the yoke. If that stops it, you're done. 3 - If that doesn't work, then you turn off the stab trim cutout switches.

If MCAS is getting some kind of erroneous AOA signal and inputting an unwanted nose down pitch, guess what? Those procedures will stop it. If pilots at airline X get to step 2 and think they're good and MCAS starts another input after it's initial 10 second trim, then they go to step 3.

If you want to speculate about something, why not start with what position investigators in both of these crashes are going to find the stab cutout switches. If they're not "off", why? MCAS or poor procedures? " https://www.airlinepilotforums.com/2779459-post40.html

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Re:China orders its airlines to suspend use of Boeing 737 Ma... by iforgotpassword on Monday March 11, 2019 @04:30PM (#19362519)

OK just random stuff I come up with as someone with no expertise in this field:

> 3 - If that doesn't work, then you turn off the stab trim cutout switches.

And.. If this doesn't work either? What if it seems to make things worse? Is that switch implemented in hardware or software? I don't mean the switch itself: does it just pull a pin high/low for some controller or does it fully disconnect/shut down the offending part?

Especially for the case of "it actually makes things worse" finding that the switch was ultimately left in the "on" position doesn't really help; quite the opposite I'd say (but I'd assume any change to the switch would be logged by the black box to be able to identify this case).

Actually when I saw the altitude log of the first crash I wondered why there was such a steep descend the first time, while the following cycles were much less extreme. So that's my buildup for tomorrow's conspiracy theory, someone else do the flesh out. ;-)

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Re:China orders its airlines to suspend use of Boeing 737 Ma... by inferiorhuman on Monday March 11, 2019 @07:34PM (#19363956)

If you dig through the pprune thread on the Lion Air crash you'll find some schematics. The stabilizer trim switches cut power, but the circuits and switches are different between the NG and MAX generations. Assuming there was no damage from the near constant adjustment, disconnecting electrical power from the stabilizer trim motors almost certainly would've resulted in an improvement.

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