I've had this argument many times at uni.
If the PPL had instruction from somewhere (lets say the flight crew were paralysed from the neck down), wouldn't it be possible for them to drive the autopilot and carry out an auto land (provided it is fitted of course)?
Having never flown anything bigger than bug smashers, I admittedly have no idea of what is involved with entering data into the autopilot of something big. I understand programming the FMS can be tricky and /or time consuming, but how difficult is it to enter HDG/NAV/ALT/APP hold data into the autopilot?