"Further, I note now, having missed the text before, that the AAIB Special Bulletin 1/2008 concludes with:
"In addition, comprehensive examination and analysis is to be conducted on the entire aircraft and engine fuel system; including the modelling of fuel flows taking account of the environmental and aerodynamic effects.""
It seems to me this is the most likely way the AAIB will uncover the cause.
I dont know how much data they have recovered from the flight recorders, but must be enough for some detailed modeling. If the fuel flow is the common mode failure, it was asynchronous by 7 seconds between the engines. Is it not possible the initial response to a demand for thrust was using the fuel in the pipework and any other volumes after the restriction blockage.
So if we know the diameter of the pipework, the speed of the engines, caculated quantity of fuel used in the 3 seconds one engine and 7 seconds the other, cant one calculate the distance back along the fuel lines when the fuel stopped coming? Is there an offcentre pump, tank, point or junction that fits the data?
Just an idea
Martin2116, that is exactly what I was thinking. Furthermore the obstruction was not complete because the engines still had enough fuel to idle after the incident which means the obstruction could have occurred / formed at different times but being the engines were only requiring minimal fuel prior to throttle up it was not noticed. Once more power was requested, the result of the obstruction became noticeable after the excess fuel in the lines downstream of the obstruction was used up.
If both fuel paths are not symmetrical but one has the ability to store more fuel in the lines then it could explain the 4 second difference. If the obstructions happened at different points that would also explain the 4 second difference though not as plausible. A third explanation for the 4 second difference would be that one side's lines downstream of the obstruction weren't as full of fuel as the other, ie. half as full, that would also explain the difference. A final explanation would be that both engines weren't burning the same quantity of fuel per second on throttle up, but I doubt that would be the case.
If 7 seconds calculates to be the point of the fuel intakes at the fuel tanks, then being there are two intakes on each tank is it possible that one of the intakes was completely blocked, meaning the lines associated with that particular intake were dry of fuel, while the other three intakes were only partially blocked, thus allowing about double the fuel in the lines on one side as opposed to the other.
Hopefully the investigation team already has or soon will be doing all the calculations necessary to find these points in the fuel supply as they will be key points to examine for possible causes.