Great article! The only thing missing is a discussion of whether manual retrim after disabling the stabilizer trim motor was actually possible given the aerodynamic constraints. This theory's been discussed quite a bit here on HN and pilot forums.<p>The theory is that, on the Ethiopian flight, after disabling the stabilizer trim motor while there is mistrim, the aerodynamic load on the jackscrew was too great for it be movable by the copilot using their crank. The pilot was perhaps using their strength to pull the yoke back, which meant both that he was unavailable to help crank, and that the aerodynamic load was increased by the elevator directing airflow in opposition to the stabilizer.<p>There is an old “yo-yo maneuver” that stopped being mentioned in Boeing manuals decades ago that describes having to relieve load on the stabilizer before manually trimming, in this case by releasing the elevator and pushing the nose down even further, which I’m sure would have been very unattractive given their high airspeed and low altitude if the pilots even understood the procedure, which is no longer part of simulator training.<p>This may explain why the trim motor appears to have been re-enabled towards the end of the Ethiopian flight: because purely manual trim was impossible.