Originally Posted by
Tomaski
This aspect of the manual stab trim system has been there on the 707, 727, and the entire 737 line since inception, and it was apparently okay with the EASA and its predecessors. What changed?
The diameter of the trim wheel.
Only an inch I know, but this reduces the turning moment by over 10%. This seems to have reduced the gearing to an extent where something which was ‘difficult but not impossible’ has become ‘impossible’ in some cases.
Earlier in the thread, a poster described using the ‘rollercoaster method’ in a former life and said that he lost 5,500 feet of altitude from start to finish. As a method to reduce aerodynamic load on the HS this is therefore only satisfactory above altitudes of 6000 feet plus.
And it is not just EASA expressing concern, the FAA is also reassessing the amount of force needed to move the trim wheel in extreme circumstances.