Originally Posted by freezingflyboy

We had something published (it was either an ops bulletin or it might even be in the FOM or CFM) stating that the break even point for sitting at the gate with an engine running waiting for ground power vs. starting the APU was 8 minutes. Meaning you would have to sit there with the brake set and an engine running for EIGHT minutes before it was more cost effective to start the APU. Now of course that number varies depending on fuel prices and the terms associated with the APU lease, company policy, etc. but personally, I was rather surprised to learn that.