Maybe all the cockpit screens went blue with the dreaded message 'Windows fatal error'.
Seriously, at that stage of a long flight, which tanks would be in use? Wing tanks, fuselage tanks or both? Would both engines draw fuel from the same tank at that late stage of the flight? What would make two engines, designed to operate independently, cease functioning together so late in the flight? Cross-feeding contaminated fuel? Well, maybe but surely that would have manifested itself as a problem earlier. I would bet that they didn't
run out of fuel - there are reports in this forum of fuel leakage after the event and in an earlier post I mentioned the fire brigade hosing down under the aircraft long after the incident took place. I think the answer to this has to be (somehow) fuel management systems (computer) related so let's see.
Another (late) thought. Avgas floats on top of water (hence drain tests on my C152 for first flight of each day). What happens with Avtur? Is it lighter than water too?