Ref the open spar valves, (LP cocks) I am surprised that the anomaly had not been picked up on the simulator.
What kind of simulator are we talking about here... a flight simulator or a Boeing design program? The flight simulator would have to model damage to specific wiring (I know Level D sims are accurate, but this is ridiculous).
I talked to a QF engineer today who was totally convinced it was ice blocking the fuel-oil heat exchangers.
I'm not familiar with the layout of the Trent plumbing, but surely the fuel-oil heat exchangers are not the coldest part of the fuel feed system? The fuel line goes through the engine strut (which it probably shares with a hot bleed air duct), then through a LP engine pump which would also raise the temperature of the fuel. If it was an internal blockage in the heat exchanger, then wouldn't it have activated the differential pressure switch on the exchanger???
Now I'm sorry to show my ignorance here, but where is air drawn into the tanks when the fuel is pumped out.
From the atmosphere (the tanks have a slightly positive air pressure on them courtesy of NACA scoops)
3) It is important that LP tank pumps are immersed in fuel so that they don't introduce air into the system, also the fuel provides a cooling function for the pumps.
The pumps themselves don't necessarily have to be immersed in fuel. The pumps are actually well above the floors of the tanks. However, the pickups for these pumps are closer to the tank bottoms. The fuel running though the pumps, provides cooling/lubrication.
5) So, you're probably ahead of me, what if the sensors in the 777 center tank failed or were fooled and the pumps operated whilst the tank was dry? Would EICAS alert on something or could they keep going long enough to put enough air into the system to balls things up?
Pressure-wise, CWT Fuel pumps pumping air will be no match for fuel pumps pumping fuel. The wing tanks will simply pump fuel into the manifold causing a backpressure easily strong enough to close the check (one way) valves on the CWT pump outlets. Therefore no air. If BOTH check valves failed on the CWT pumps and they were running.... anybody's guess.
Is the low fuel warning EICAS message generated by the fuel in the tanks...or....only by the FMC?
The EICAS message is generated by fuel in the tanks (The low fuel warning is given by the tank totaliser system). However, the FMC also produces a message if the predicted fuel burn is below the pilot-entered minimum fuel value. There is also a message if the totaliser value varies by a certain amount from the FMC calculated level (but this is after engine start).
If the FMC had been selected as the primary source of fuel quantity on board
during FMC flight planning programming in China and not altered to silence a flashing fuel discrepency message during refuelling...and the
incorrect fuel loaded and signed for...this could be a masked low fuel condition with no warning generated...a rubbish in...rubbish out computer situation....
If the FMC was telling the pilots that the fuel at destination was below minimums, then he would surely double check the flight plan and his FMC programming and resolve the discrepancy. He certainly would NOT fool the FMC into not generating a message even if he could.
On the subject of lack of fuel in tanks.... Didn't the intial report say that one of the fuel tanks was intact? Surely a physical measurement of the remaining fuel would have been made.
Danny! Where are you????
