What bothers me is the video says that there was clear weather. I’m just a private pilot, but I’m used to going along at a steady altitude (unless there are severe updrafts and downdrafts) and only adjust the trim manually by small amounts when I expect to have to change altitude.
Then again, I’ve never focused on social media when I fly. That may have taken higher priority in this case than, “Aviate, navigate, communicate.”
Punkalouver said that the mis-trim must have been done manually, but I can’t imagine why you would intentionally would “mistrim” the plane to such a degree that you’d send it into a fatal nosedive.
Perhaps they were confused by the autopilot, and were adjusting the trim the wrong way to try to compensate for the increased variation in altitude and, consequently, airspeed.
I admit, I’ve never had to adjust the trim in an emergency, and never changed it by more than slight increments. I’ve never flown with an autopilot.
I did know a private pilot that had the cable to the trim tab break, causing them to go into a steep dive, but they managed to muscle the plane into a safe landing at the nearest airport after declaring an emergency.