Originally Posted by
meleagertoo
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....
The wording in the FCTM, P 8.17 is rather different to the technique discussed, the nicest thing that can be said is that it is understated and leaves a great deal to the imagination. It may just be that we are all separated by a common language, but being kind, perhaps the FCTM leaves a great deal to the creativity of the TCI/TRI etc. The technique is great sport, not so sure it adds confidence in the strength provided by certification standards. Conceptually, both pilots needed on the controls to deal with a fault that is not impossible to occur seems to be untidy at best. Expecting the crew to undertake aerobatics without having a tail wheel and another set of wings over the top painted in chequers seems to be out of place. There is a silver lining however, that is that the operators should be able to charge more for the disneyland ride that is considered to be appropriate.
If a runaway trim event was about as remote as me winning the lottery, there wouldn't be a problem, it would be hypothetical, and the matter would be just a curious gedankenexperiment, but the recent events suggest it is not, and the 50 years that this has been accepted as a solution may speak loudly to the state of the art. Had Orville suggested to Lt Selfridge that one of the plans of recovery was to follow the wright flyers FCTM in such a manner, the selfless Lt would have probably stayed landside, after all, that was before the time of airline coffee, pretzels and peanuts being served airborne.
FAA Part 142, manual trim use, Yes, manual trim use post stabiliser runaway, No. Yo-yo? Nope. Jack stall from military training only.