3 ms·
If the trim runs away far enough (which it clearly can, more easily because MCAS was also activating the stick shaker which is INCREDIBLY DISTRACTING) it can be
by SAI_Peregrinus 5y ago
If the trim runs away far enough (which it clearly can, more easily because MCAS was also activating the stick shaker which is INCREDIBLY DISTRACTING) it can become impossible for a pilot to physically turn the manual trim wheels to get back into trim.
So the procedure for runaway trim (turn off electric trim, use hand wheels) doesn't work. You have to instead use electric trim first to get back into normal trim, then turn off the electric trim, and never turn it back on for that flight.
- jcalvinowens 5y ago> ... it can become impossible for a pilot to physically turn the manual trim wheels to get back into trim I feel like this isn't talked about enough. I had no idea how bad it can actually get: https://youtu.be/aoNOVlxJmow?t=806 https://youtu.be/aoNOVlxJmow?t=806
- dhx 5y agoThe difficulty of using the manual trim wheels is also demonstrated in this simulator run showing the MCAS problem: https://www.youtube.com/watch?v=xixM_cwSLcQ&t=1011s https://www.youtube.com/watch?v=xixM_cwSLcQ&t=1011s There is some discussion amongst pilots at https://www.pprune.org/tech-log/619326-boeing-advice-aerodynamically-relieving-airloads-using-manual-stabilizer-trim.html https://www.pprune.org/tech-log/619326-boeing-advice-aerodyn... which further explains how difficult it can be to manually reduce load on the stabilizer and manually trim the nose up.
- salawat 5y agoI did some napkin math to try to calculate the force that'd have to be applied to the jackscrew to actuate under load, and it was not a small number. Basically, an electric motor with the torque of a sporty automobile. With the gear ratios we're talking with by hand actuation, I would not want to have to be one of those pilots.