Originally Posted by MachinBird
Not really a surprising result. In Normal and Alternate 1&2 Laws, holding the trim wheel can result in inadequate control effectiveness for proper operation of the flight control system.
Of course, if the flight control system is off in La La land, you still can seize control, but it will be at the expense of someones free hand and (apparently) smooth control. If you do this, you are fully responsible for observing all aircraft limits, so I can understand a bit of caution in applying this technique, but ultimately you do have the "hammer" should you want to use it. The crew of AF447 could have stopped the trim from its run to the nose up trim limits if they had been aware of the motion.
Just as there isn't any good reason to point the nose high in the air at cruise altitude, there is also no good reason to have full nose up trim dialed in at cruise altitudes.
Maybe you meant to say "touching the trim wheel" vs "holding the trim wheel". If you go back and read what I wrote, I spoke of attempting to trim the Bus with the manual trim wheel. I only "held" the trim wheel in an attempt to manipulate it for its primary purpose of trim control.
Can you confirm that the AF447 crew could have held the trim wheel and stopped the trim from its run to nose up limits? In my experience in a 320, I was able to eventually force a small pitch "bobble" when moving the trim wheel to the limit of the available "one hand grip" travel. The wheel feels like it's attached to a bungie cord and with a hundred fifty souls behind me, I had no intention of going anywhere further with trim than that initial "one handful movement".
Can anyone confirm what would happen if a pilot, on a test flight of course, just held the trim wheel?
Why weren't they aware of the continuous trim motion?
Why no "trim in motion" claxon, or other indication?
The system can warn of a jammed stab, but not a run away stab.
Oh I know, it wasn't run away, it was just doing as it was told. And a find job it did.