Originally Posted by TTex600
In the narrowbodies, I've attempted manual trim as per the FCOM' statement that manual trim is available and primary at all times. The manual lies. Auto trim fights the man trim wheel and removes any pilot applied man trim as soon as the pilot releases the wheel. When forced, the trim wheel will make jerk-y pitch movements.
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.