The Eletrical power for the cargo doors comes from the Ground Handling Bus, which in turn is controlled by an Air / Ground switch on the Undercarriage. As soon as the Aircraft takes off, all Electrical power to the cargo doors is disabled, (regardless of Handle/Latch position)
So much for the APU feeding some juice to unlatch the door during flight...
For what reason would you want to operate the APU in cruise, just to burn off more fuel?
Extra thrust ?!
