Useable Fuel?
I'm not aware of the fuel setup on the 777, but assuming it's like others I do know, is this possible, either on its own or in combination with other circumstances?
In aircraft I do know about, this is a possible scenario that came too close, far too close, to happening.
A) Aircraft takes of with fuel in both wing tanks and centre tank with all boost pumps on.
B) Due centre pumps having higher pressure they override the wing tank pumps and both engines feed from the centre tank.
C) Once all the fuel is used from the centre tank the wing tank pumps automatically take over as they have higher pressure then the now empty centre tank pumps.
D) Aircraft I am familiar with can suction feed from the wing tanks but not the centre tank.
Is it possible that the aircraft took off with the centre tank pumps not turned on?
Result, Everything is normal until the wing tanks run out of fuel at which time the engines EGT rapidly drops and due no engine-generator, electrics to power the centre tank pumps they don't work and as the aircraft cannot suction feed from the centre tank altitude is rapidly lost until such time as the aircraft makes contact with the ground after running out of fuel with the centre tank still full?