Given the mundane nature of the flight and reliability of 777s, the set of circumstances leading to BA038 accident must be very rare.
My favourite, most unlikely alignment (of the Swiss cheeses) would be:
1. Outbound, centre tank fuel used first and remaining centre tank fuel later scavenged to main tanks.
2. Condensation froze on large inner surfaces of centre tank outbound.
3. Freezing surface temperature in Beijing so ice remained as ice on centre tank surfaces.
4. Refuelling melted some ice triggering water alert (138+ gallons) when taxiing but fuel cold and centre tank only 25% full so most ice remained frozen on centre tank surfaces.
5. Inbound, centre tank fuel used first and remaining centre tank fuel later scavenged to main tanks.
6. More condensation froze on large inner surfaces of centre tank inbound.
7. Ice on inner surfaces of centre tank only started to melt late on descent inbound.
8. Newly melted, very cold water scavenged (perhaps after change of attitude from flaps moved water between baffles closer to scavenge suction point) from centre tank to each of main tanks.
9. Main tank fuel well above Jet A1 freezing temp, but well below OAT and water freezing temp.
10. On entry to cold Jet A1, concentration of scavenged water froze forming ice particles suspended in or falling to bottom of each of main tanks.
11. Increased demand on finals sucked (and/or change of attitude from flaps moved) ice particles to inlets causing partial blockage to fuel line inlets from main tanks, exacerbated on right hand main tank by foreign object (scraper).
12. Fuel lines, heat exchangers, bypass, pumps, metering unit and engines continued to work but with a lot less fuel flow than desired.
13. Ice remained trapped in main tanks due to size of particles.
14. No water found in main tank sumps as did not settle there.
15. Only minute % of water found in each main tank as over 5+ tons of fuel in each.
First post – guess I will be on probation for a long time now.