My UK airline will allow taxi-IN on 1 after a set cooling time on the 767/767 but not taxy-OUT. All to do with fire watch on start-up. We also try fuel saving by not running the APU on the ground if we can get GPU power. My own question is....if you switch off the APU air bleed, the EGT goes up and therefore(?) the constant-speed-engine (aka the APU) must be burning more fuel. Someone suggested that the bleed air dump "port" thingy is quite small and therefore the APU needs more fuel with the bleed off than on.
Surely not?