Originally Posted by
Ian W
That is the issue that I do not understand.
PF is flying manually in vmc with all non-pressure instruments serviceable and has things set up and while going through memory items for UAS the aircraft trims nose down. This is unwanted as it creates quite a pull force so the pilot retrims with the standard electric trim back to trimmed flight which unbeknown to the pilot inhibits MCAS for the next 10 seconds. So after 10 seconds of trimmed flight MCAS starts again it creates quite a pull force so the pilot retrims back to trimmed flight with the standard electric trim .......- surely at the third automatic stab trim down the pilot would cut off the stab trim - which just so happens to be what the memory items suggest anyway? It's not like the aircraft was IMC or at night, and all non-pressure instruments were functional. Not only that but the MCAS is not ratcheting down continually as the PF has trimmed back to level flight each time. This sequence of events would describe the porpoising that was observed from the FR24 near the beginning of the thread. This is what would be expected before the stab trim cut off.
It does not explain the apparent bunt into a power dive - something else happened at that point..
The point you make is precisely the one I've been attempting to make. The PF seems to have been counteracting uncommanded nose down trim for six minutes prior to the dive. Isn't that the definition of a stabiliser runaway? Why didn't he switch to CUTOUT.