Is there a keyboard command to activate APU? If not, is there a way to set one? Thank you
No default airplanes have APU's. And there is no key command as I know of. Maybe if you have the PMDG 747 you can set one. Only some pay-ware planes have functional APU's.
I couldn't find it on the keyboard command sheets I have.
Why not download and print them out, they come in handy sometime.