If GPU power was lost without the flightcrew being aware, then the 737NG will revert to DC power/standby and will deplete the battery dry within 30 minutes.
If the crew were aware of GPU loss, then there is a chance that the standby switch wasn't selected to battery or the flightcrew allowed the battery to deplete without powering the APU.
When AC power is lost the battery on standby converts DC to AC via static inverter to power the fuel cut off switch and fuel gauges. Basically GPU power loss will have no affect on re-fuelling as long as the standby switch was set to 'battery'.
Without any DC or AC power the fuel valves will close automatically, and will remain closed untill the red overide button is pressed continuously while refueling. A tool can be used to hold the spring in the valve to the 'open' position.
Basically the hose connected to the receptable will be pumping fuel into a closed fuel valve, this would normally be opened when AC power is available.
Also without DC or AC power there is no automatic fuel shut off, so there is no override to a over fuel situation in either tank.
Spillage could occur from both situations.
Last edited by photons; 27th August 2010 at 01:32.