- #141
PeterDonis
Mentor
- 47,062
- 23,454
cyboman said:From my understanding, adjusting the trim manually does disable MCAS. But it can reengage after 5 seconds or so if all the same logic like AoA and airspeed are true.
Yes, that's my understanding as well. And of course in the presence of faulty AoA sensor data which is not detected as faulty, this will cause MCAS to keep on adding nose down trim again and again, creating the "tug of war" situation.
cyboman said:To really disable it apparently, I've pointed out in a previous post, you actually need to correct the trim electrically first, then disconnect it using cutouts, then use manual trim for the rest of the flight. And then in a post I pointed out a pilot commenting that disabling those cutouts is what a pilot would do first in a nanosecond and that they don't disable MCAS.
I'm not sure this is true. The various comments online don't all appear consistent. But the preliminary report from Indonesia on the Lion Air incident includes a description of key events on the previous flight of that aircraft; on that flight, it appears that the pilots noticed that automatic nose down trim was being put in, used the cutout switch, and there were no further trim problems for the rest of the flight. That flight was the night before; in the morning, the flight that crashed, there was, as far as I can tell, a different flight crew, who apparently did not use the cutout switch at all, but kept trying to put in nose up trim manually to counter the repeated automatic nose down trim.