Originally Posted by flybymike
3. Most A/P's have a test or self test facilty which together with an operational check must be carried out prior to departure. First time engagement of the A/P in the air without a ground test first is not a good idea and can result in some A/P's inducing some very dramatic attitude excursions in the air!
As others have said it is not usually the A/p which is the problem, It's the pilot!
True indeed and most GA autopilots are relatively easy to overpower. This again is checked as per the operating manual eg when the autopilot is set to command a left roll, the pilot ensures that a right roll can be executed against the autopilot without a need for excessive force. Generaly autopilots that control the elevator electric trim system trim are set so that the trim circuit breaker will pop with a runaway trim. This should happen in the case of at least one system when the out of trim forces are about 15Lb. Not a great force to overcome but one which as said above could catch one unawares if the autopilot was disconnected while not holding on to the controls and not properly strapped in.
Reminds me of the story about the pimply computer whizz first officer and the crusty old Captain in the new Airbus some years back. First officer operates the sector totally by jabbing away at the flight management system until at top of descent the aircraft does not descend! Much trashing of keys and a shocked statement of "It's not descending Captain" resulted in the Captain leaning forward and pushing the yoke towards the pannel. "It's descending now son isn't it!"
Regards,
DFC