Three hour delay ex Gatwick due to flat batteries and fuel filter changes, and also a fuel discrepancy of 3500kgs. The reason? Prior to this sector the a/c had been allocated as the standby a/c following its last sector and not used. However the APU had been left running during this period and finally shut down after the 3500kgs in the left tank had been burnt. The batteries then obviously took the dc load and ended up flat.
A fuel filter change was required as the left engine also uses the APU fuel line. At least the hydraulics were not pressurised during towing as they use the left tank fuel to cool the fluid and operation for any period without fuel is a big no-no.
The powers that be tried to cover-up the episode, and it was only the honest refueller who suggested that from the fuel he put in the tank it must have been empty.
Many years earlier on an early morning Trident departure from C28 (those of you who remember the stands at LHR) we passed eight aircraft on the way to ours, all with the APU's running (throughout the night) and totally deserted, having not yet been allocated to a service.
Comments to our then fleet management that perhaps an engineering apprentice could be given the job of checking that all aircraft are fully shut down after their last flight of the day. As usual with most suggestions from the shop floor it was dismissed as too difficult.
Perhaps if there had been a management bonus associated with reducing overnight fuel burns something might just have been done.
Full Circle, or perhaps Fuel Circle???