Originally Posted by
vilas
And why would you do that?
If someone is actually putting the master switch on without the APU running, then I'm guessing they want to get a leg up on a possible APU start after takeoff (engine failure, generator drops off line, etc) since they won't have to wait for the ram air door to cycle open. My thought would be if they are really that concerned, then just start the APU. That said, I understand some airlines track APU usage by flight crews and discourage unnecessary use. This may be one person's technique of threading the needle between having the APU readily available during takeoff and not getting a call from their Flight Department about excessive APU use.