In the pilot incapacitation scenario, the senior cabin attendant is trained to be competant in reading A/C checklists in order to assist the pilot flying. Also she or he, is much more akin to the surroundings of an airliner flight deck than your average PPL. They may even hold a licence of their own, who knows?! With regards to just finding the autopilot, disconnecting and then simply flying the machine raw data. Well consider the more than significant difference to your average spam can. Speed control, flying the correct attitude and configuration, trimming, setting thrust, the list goes on
. Whether it be a 'classic' or 400, I suspect most would be simply overwhelmed in no time.