Originally Posted by
MurphyWasRight
Not exactly the same signs as stab trim runaway which would be trained/expected to be continuous whereas MCAS (unpatched) worked in up to 10 second bursts then stops until the next pilot trim input.
A MCAS checklist could stress both the need for and safety of -fully- trimming before using the cutout switches to avoid possibility of manual trim not working due to aero loads.
Had this been included in the AD in response to Lion Air it may have helped.
In roughly the time it takes to read this post MCAS provided 2 nose down inputs to ET.
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? Does 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.