737 Stuck Manual Trim Technique
Inability to operate the manual trim on a 737 is a hot topic just now.
During my 737 type conversion (3-400 series, UK, 1998) we were shown a techniqe for trimming manually even when aerodynamic loads were too large to allow normal movement of the wheel.
A large out-of trim input was provided and an attempt to turn the wheel manually proved it to be immovable. Recovery was for both pilots to pull the column back to give an appreciable pitch up, if only a few degrees, and then relax the pull. The resulting controlled pitch down released enough load on the stab to allow a bit of trim - perhaps less than half a turn initially, to be achieved. The procedure was repeated and with each repetition more and more manual trim was achieveable until a point was reached where normal though very stiff operation became possible.
I seem to recall this was a demonstration that manual trim remained available even in out of trim conditions way beyond those anticipated even in the worst concieveable runaway.
Is this a standard part of 737 conversions or was it an add-on by our very punctilious trainer? I'd be most interested to know how widely this technique is known because once seen, it would never be forgotten. I suspect the Ethiopian pilots hadn't seen this or there would be signs of pulls and bunts on the data, and possibly no acident to discuss either.
737 pilots - over to you....
Last edited by meleagertoo; 5th Apr 2019 at 11:22.