@Franzl
Autotrim is a separate system from the protections and the autoflight, as such under manual control and without protections it does exactly what the pilot commands. It does exactly what it says on the tin and trims automatically in the same way that manual trim is applied on older aircraft - there have never been any hard limits on manual trim wheels, why should there be one on their modern automatic descendents?
Autotrim is commanded by the FCPC´s, not by the pilot. The pilot is ordering a loadfctor and the FCPC commands the elevators (short term) and THS trim (long term) to achieve and to maintain this loadfactor.
That is quite a difference to your saying and to older conventional aircraft. The FCPC will trim the THS all the way nose up with the stick untouched, if in 1 g flight (like in a climb) the speed decays. We discussed that before more then once.
And it is an operating difference as well. Trimming by turning a wheel is a deliberate act to trim, whereas automatic trim by the FCPC is a programmed syytem behaviour. Wether that is a seperate system or an incorporated one is of no relevance at all. Therefore there can be measures incorporated to prevent the trim reaching values, which are insane in FL350. There are enough data available after a pitot failure (altitude, attitude, AOA, GPS data, you name some more) to compute a normal trim zone (with trimming by the FCPC) and one where the pilot should decide wether he really wants the trim that far up by turning the wheel.
@ infrequentflyer
In contrast, the cessation of autotrim when things start to go wrong is a least a contributory factor in some crashes, if not a killer.
I remeber only those, where the trim beforehand wound all the way NU and ceased in the full NU position. If you refer to those, then it would have been better beforehand that the trim stayed in normal trim region.
If ceasing of trimming action in ALT1 is not a bad thing, i cannot follow the argument, why it would be bad in ALT 2.
What trim values are reached in normal operation except takeoff and landing?
Is Full NU a player above FL100 in any kind of normal maneuvering? In which one?