John Kunkel wrote:


The air packs only consume fuel when the APU is used as an air source, in
flight the engine bleed air is the air source and uses very little if any
extra fuel.


Not true about the lack of fuel use. In the B-727, the center engine
does not typically provide bleed air for the packs in flight, and burns
200-300 less pounds-per-hour in cruise than the pod engines.

Happy Flying!
Scott Skylane