QAVION,
'Tis true the a/p will trip in flight if the stab does not respond to FCC/SAM demands. It is also true that the system appears to work on the ground. I can only think that it is when the elevator i/p is sustained that it trips. Will try it again on 75 and 76 when I am next at work to see if I keep the i/p for a while that it trips.
Cheers.