Ever so "Slightly" off topic.
Pre Sept11, I was on a [Domestic] Fam Flt ex LHR. North Deps were [heavily] slotted. A/c arrives at the hold and
shut down 
Not enough gas from LHR to dest if held at the holding point for more than 10mins
No reroute just park with only the APU running.
we aim to please, it keeps the cleaners happy