Originally Posted by CONF iture
I would easily conceive a fuel flow restriction by mechanical means, like a partial spar valve closure, but I don't see how the fuel itself would produce its own restriction in a way that such a restriction stabilizes for the remaining of the flight and don't deteriorate any further ?
The slush (icy/waxy particle) theory can explain the fuel flow restriction with the following conditions met:
a) That there is a location for the "slush" particles to accumulate. (a screen, a partially open valve, a matrix of tubes (FOHE?))
b) That the particles are of sufficient size and properties to accumulate.
c) That the particles can move from their formative location, or that they form in a location with the right characteristics to restrict fuel flow.
d) That there is sufficient time for the particles to accumulate. (that there is enough time at the end of the flight and during the descent that the engines require no more than low/moderate fuel flow.)
The "slush" would allow fuel to flow through at a steady state as long as the fuel flow demand was low/moderate. At high fuel flow levels, the fuel would be restricted to near the low "steady state" value. (sucking fuel through ice using a straw so to speak)
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There are some hurdles to the theory:
a) That the AAIB report identifies that there were "no significant quantities of water." (Definition of significant?) This can be explained if the "slush" was mostly pulled through the system at the time of the crash. Even at ppm of water, 79,000 kg of fuel would result in a few kg of water/ice, which would be enough to cause mischief. Not to mention the legacy water in the system.
b) That the FOHE were clean of blockage and that the fuel feed lines did not reveal any defects or restrictions. This could be explained also with the "slush" being pulled through the system. There may also have been some loss of the fuel downstream of the HP fuel pump from the crash impact, therefore losing the evidence.
If the "slush" was more waxy components than ice, then they could have redisolved into solution, again leaving minimal evidence.