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Old 20th Apr 2019, 05:44
  #4154 (permalink)  
FrequentSLF
 
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Originally Posted by L39 Guy
The Runaway Stabilizer checklist states "Condition: Uncommanded stabilizer trim movement occurs continuously". I think we can agree that an MCAS event is "uncommanded".
What does continuous mean? 5 seconds, 10 seconds, 1 minute, one hour? And let's say that the uncommanded stabilizer trim movement is caused by an intermittent short circuit somewhere (trim switch, wiring harness, etc) that produces a 5 second, 10 second, 1 minute uncommanded stabilizer trim movement? How can you tell the difference? Do you really care what the source is? Doesa) the source affect the outcome? Do you really think that someone flying along, fat, dumb and happy and suddenly has the nose pitch down will have the presence of mind to count how long the trim is moving? I would suggest the shock value would preclude that.

As well, one does not want to get into the game of diagnosing the source of the failure (MCAS or otherwise) while the control of the aircraft is at stake. One checklist to cover all scenarios is more than adequate. Secure the malfunction, fly the airplane and land asap and save the diagnosis and troubleshooting once you're back on terra firma.
other than MCAS can be stopped by a simple use of the thumb switch on the yoke, MCAS will not be keep going runaway, will just pause for 5 seconds and than restart.
MCAS has also a much different logic, including new cutoff logic than previous versions, a runaway trim can be in both directions, while MCAS is only in nose down, and can be stopped without cutout...to me as non pilot does not look like a memory item
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