[WalterBright]

> Are you an experienced pilot, intimately familiar with the 737 MAX, or otherwise an aviation expert qualified to be a judge of this?

I am not a pilot, but I worked on the stab trim design for the 757. There are cutoff switches for the stab trim on the console, and their purpose is to stop uncommanded trim movement. They were successfully used on another Lion Air flight to recover from MCAS malfunction.

The electric thumb switches will also override MCAS and can be used to trim the stabilizer back to normal, and then cut off further trim with the cutoff switches. In both incidents the pilots were able to bring the trim back with the thumb switches, multiple times, but it apparently did not occur to them to shut off the trim after doing so.

I'm very interested to see the NTSB report on this.

[HarryHirsch]

The Seattle Times says that that isn't true: https://www.seattletimes.com/business/boeing-aerospace/boein...

In the 737-NG you could turn off autotrim and still have electric trimming. This was changed in the 737-MAX, if you turned on electric trimming you'd also turn on MCAS. That change was poorly documented, and at sufficient airspeed you had to rely on electric trimming because the aerodynamic forces on the horizontal stabilizer would be too high to turn the trim wheel manually.

[WalterBright]

> This was changed in the 737-MAX, if you turned on electric trimming you'd also turn on MCAS.

The electric trim switches override MCAS. This is according to Aviation Week, Aug 19, and is consistent with Boeing's bulletins on the matter and with the pitch profile from the flight data recorder - both sets of pilots had overridden MCAS with the electric trim switches in multiple cycles before their crashes.

[therealcamino]

That's not consistent with other reporting. From the FT:

https://www.ft.com/content/ee4246ea-5729-11e9-91f9-b6515a54c...

Four seconds later — and only 35 seconds after the nose down problem first occurred — the co-pilot suggested they initiate the emergency procedure recommended by Boeing, and disable the MCAS system by flipping switches in the cockpit.

“The pilots diagnosed and executed the procedure within 35 seconds — that’s lightning fast,” said Jason Goldberg, a spokesman for the pilots’ union of American Airlines, one of the biggest US operators of the 737 Max aircraft.

[WalterBright]

I'd be careful about using Financial Times as a source. I've seen so many articles about this not written by aerospace people and full of errors.

The flight data recorder showed that the pilots had successfully countered the MCAS input more than once with the electric trim switches. In the Lion Air crash, the pilots successfully countered it 25 times. At any one of those times, the pilots could then have turned it off with the cutoff switches. My source is Aviation Week, Aug 19, 2019.

It says: "Electric trim input will stop the automatic nose-down stabilizer movement" on a bulletin Boeing issued on Nov 6, and goes on to say "The only way to stop the cycle is to follow the runaway stabilizer checklist and toggle the console-mounted cutout switches."

This was apparently done by the previous Lion Air flight which encountered the same issue and landed safely.

The Ethiopian Air pilots also successfully used the electric trim switches to override MCAS. After two cycles of that, the pilots did think to throw the cutout switches, but with the nose down. They should have trimmed the plane to normal with the electric switches, then throw the cutout switches.

All according to AW, which I am much more inclined to believe than other reports, until we see the NTSB report.