I have a (purely speculative) theory (for "brainstorming" purposes only.
The 787 is a totally "electric jet". The APU on the 787 only powers a big generator, no hydraulic pumps and no air. On the 787, Electricity powers everything, including all of the electric motors that drive the hydraulic pumps, and the electric motors that drive the cabin pressurization compressors.
FUELING PROCEDURES.
It is SOP that the wing tanks are always filled first.
The center tank is only filled as much as is necessary to make up the actual fuel load required for the particular flight. Rarely (if ever) is it fully filled.
The big red flag here is that SOP is that each engine should always be fueled from it's own wing tank, until well into the cruise.
Then the cener section tank is cross fed into the wing tanks, down to what is normally about ten percent of full, and the flight continues on wing tanks only.
I am of the opinion, that since the last flight was a short one from Delhi, that it is possible, that for some unknown reason, the center section cross feed pumps were still pumping their fuel into the engine cross feed manifold, instead of into the respective wing tanks, when the aircraft landed.
That crew possibly left the aircraft with the fuel system still in that configuration, instead of resetting it to "normal".
Thus, when the new crew got in the aircraft for London, the wing tanks would have been filled as per normal, and more fuel would have been put in the center tank, as per normal. So far so good.
What I am speculating may have happened, is this.
Just like in the Helios 737 disaster, the new crew did not check "EVERYTHING".
The Helios disaster was caused by the new crew not checking that the pressurization system controller was set to "normal" (because ground engineers had done some work on it overnight and had left the controller in "manual", since they needed it in manual to do their trouble shooting).
The "trap" here, is that when a particular system is "ALWAYS" in normal on the ground, it is at high risk of getting "skipped" during pre-takeoff checks.
I am speculating, that similarly, the fuel system is "ALWAYS" in normal on the ground.
I am speculating that the new crew did not check the fuel system configuration setup of the fuel pumps and the cross-feed valves, because they mentally expected them to be "NORMAL" on the ground.
As for the situation from pushback and engine start.
Startup and taxi out would have been perfectly normal with no alerts.
The takeoff roll commenced with "throttle up", and the fuel in the partially filled center tank sloshes aft under acceleration, but not enough to uncover the fuel pump pickups, but it may have been sloshing enough for the pumps to occasionally suck air, which might explain why the takeoff roll appears to have been longer than expected (unconfirmed at this time).
In any case, when the aircraft rotates and pitches up for lift off, the partial fuel load in the center section tank flows even further aft.
This almost certainly uncovers the fuel pump pickups, so the fuel pumps are now sucking air.
At that point, the fuel in the manifold lines from the center section tank to both pylons, and then to both engines, is only enough for 10 to 12 seconds of powered flight.
During this time the aircraft climbs only about 400 feet above runway ground level.
Then the engines are starved of fuel, they begin to roll back, and subsequently flameout seconds later.
Game over.
Thus, I am speculating, that the crew did not ever realize that the engines were not being fed from their wing tanks as they should be but were in fact being fed from the center tank, and it is the last thing they would have thought of in those final few seconds.
In short, simultaneous double engine failure, due to fuel starvation, due to incorrect fuel system configuration for takeoff.
Proximate cause: Human Error.
Ironically, if the center tank had been full, this would not have happened.
This aircraft (and many others) already has "takeoff configuration warning systems" that account for flap and slat configuration errors.
Draft Recommendation:
"Takeoff configuration warning systems" should be amended to add "checks and warnings for fuel system configuration errors".
Succinct and logical.
The 'post' above by Ventus _ HERE _(above) is informative and a logical theory, worthy of careful consideration and discussion – stand alone. Like most who have actually operated aircraft there is a natural, healthy need to discuss and theorise about 'WTF' happened. Last BRB for example there were some hypothetical notions and 'robust discussions; much like the MH 370 mystery. (Don't mention the 'war').
In among some of the rubbish and amateur wittering posted and videoed spread about, there is some sane speculation. I can't find it now but one post (somewhere) had me reaching for the manuals, like 'V's' post it was worthy of the research effort. FWIW the post mentioned the ground/air systems switch and the way it operates. As I read the 'books' it seems to be a likely candidate. That is 'unqualified' as there is still a heap of manual to sort through; so opinion reserved until I understand it all. But did anyone notice if 'engineering' had been called during the turn around; and, if so, what needed fixing? Insufficient data, but food for thought.
As always, sane, rational discussion is always welcomed by Aunt Pru; but. The play the ball rule is, as always, strictly enforced. Ventus now a Choc Frog recipient.
Toot – toot.
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