Originally Posted by
Green-dot
the spar valves. They only have 2 positions: open or closed. These mechanical parts in the engine fuel feed lines are nothing but slaves to what the electrical parts, the control relays, of this "symbiosis" instruct them to do.
The electrical parts of this hybrid design are buried deep inside the aircraft's hull, nowhere near their mechanical "slaves." If for whatever reason these electrical parts were to be disrupted in their normal functioning and moved their mechanically slaved "other half" from open to closed position, starvation of fuel to both engines would be guaranteed.
Interesting theory...
Problem: I would expect spar valve position would be recorded (although I don't know details on 777 FDR or QAR), and that a difference between recorded and commanded position would raise a warning (which would also be recorded). AAIB reported no recorded anomalies.
Counter: I think you've previously theorised that spar valve could be detected / recorded as only open/shut and therefore "partly shut" could go unrecorded ?
Problem: Spar valves were found to be open.
Counter: [Again, I think you've theorised this] could be a transient effect that reset/cleared before impact.
Problem: The issue
didn't clear before impact, because we know the engines stayed at below commanded thrust until impact (AAIB).
Thoughts: impact cleared the problem - bounced the valves open again, or the electrical disruption ceased at impact. Hmm.
Or, there is a return flow of fuel around the HP pump, and that feedback makes me wonder if this system could possibly get kicked into an abnormal flow state which then self-sustains. ie. your transient spar valve incident causes reduced flow and cavitation at the HP pumps, affects the return flow, which then continues to cause reduced flow even after the spar valve is open again.
My gut feeling is it can't happen like that, on the other hand, it's a long time since I did any fluid dynamics, so maybe...