Originally Posted by
misd-agin
MechEngr - the stabilizer cutoff switches are within a foot of the Captain's right hip/thigh. Possible as close as 6 inches. (12-25 cm).
I have about 4,500 hrs of listening to the trim wheel on Boeing aircraft. I have another 14,500+ hrs on Boeing jets without a trim wheel but the red guarded cutoff switches are still right next to the Captain's hip on those aircraft. In all of them utilizing the stab trim cutout switches is a known procedure for uncommanded or runaway stabilizer trim movement.
It's stunning to think a pilot wouldn't flip the red guarded cutoff switches next to their hip if the trim ran uncommanded for 9.2 secs. A fraction of pilots might let that happen. But then it starts a second time and runs ND for another 9.2 seconds and you feel the plane getting farther and farther out of trim? That's scary to even contemplate. If that happened to any of us it would be one of our top career aviation stories if it happened once. We know it's dangerous on any large jet. If we were telling the story and continued with "and then the trim started to run ND again!!!" would have every pilot listening on the edge of their seats.
Interestingly the 777 and 787 QRH say to not exceed, or perhaps maintain, the current speed. The 737/757/767 make no mention of maintaining your current speed or not exceeding a certain speed.
The 10 second run was not MCAS, all 3 cases had more than 2 MCAS activation's and the only survivors, are said to have reported STS running wrong direction (or similar wording). Numerous simulator with 20/20 hindsight benefit reenactments, tend to suggest that fraction is larger than expected.
From JT610 final report.
At 23:22:33 UTC, the flaps reached the fully retracted position and the automatic AND trim was active for about 10 seconds, during which the horizontal stabilizer pitch trim decreased from 6.1 to 3.8 units. At 23:22:41 UTC, the Captain instructed the FO to select flaps 1 and the DFDR recorded the flaps started to move. Three seconds later, the DFDR recorded the main electric trim moved the stabilizer in the aircraft nose up (ANU) direction for 5 seconds and the pitch trim gradually increased to 4.7 units.
At 23:25:27 UTC, the automatic AND trim activated by the Maneuver Characteristic Augmentation System (MCAS) for 2 seconds and was interrupted by the Captain who commanded ANU trim for 6 seconds. The pitch trim recorded 6.19 units.
At 23:25:40 UTC, MCAS activated for 6 seconds. The pitch trim recorded 4.67 units. This MCAS activation was interrupted when the Captain commanded ANU trim at 23:25:46 UTC for 7 seconds and again at 23:25:54 UTC for 1 second. The pitch trim recorded 6.27 units. At 23:26:00 UTC, MCAS activated for 7 seconds and was interrupted at 23:26:06 UTC when the Captain commanded ANU trim for 6 seconds. The pitch trim recorded 5.59 units. At 23:26:17 UTC, MCAS activated for 4 seconds until it was interrupted at 23:26:20 UTC when the Captain commanded ANU trim for 4 seconds. The pitch trim recorded 5.6 units At 23:26:29 UTC, MCAS activated for 3 seconds until it was interrupted at 23:26:32 UTC when the Captain commanded ANU trim for 3 seconds. The pitch trim recorded 5.0 units