Gentlemen... has your discussion of cold-fuel flow-characteristics lost the plot?
Unctuous, you led-off with a thought-provoking and (for many forumites) plausible hypothesis (January26/16:34). This has provoked a long discussion, which I have been following with increasing bewilderment.
Your argument seems to hinge on one premise: that the Trent-engine equivalent of the GE90's Ps3 and P3B sensors (which you refer to as "FADEC's reference port lines") could have been blocked by the icy component in cold, waxy fuel (see your post, paragraphs f, g and h).
But these types of sensors and their lines to the FADEC/EEC do not contain or transmit any fuel. They are situated in the engine itself, to sense the air pressure at whatever stage of the engine that the FADEC needs to know about (in this case, one of the compressor stages). They are not connected in any way to the engine fuel system.
The quoted FAA AD (Airworthiness Directive) relating to the GE90 engine seems to have been addressing a problem in which water had entered the probes during flight or on the ground, and then frozen before it had a chance to drain out through the drain-holes provided.
I quote from the original (superseded) AD:
"The investigation revealed that water can accumulate in the Ps3 and P3B pressure sensing system, which can freeze in the full authority digital engine control (FADEC) sensing ports or pressure line. Frozen water can result in a restriction or a blocked signal to the FADEC. This blocked signal can cause a corruption of the FADEC signal and result in abnormal engine start characteristics on the ground or lack of engine response to commanded thrust levels in flight."
The "water" they are referring to comes from rain or spray, not water in fuel.
The FADEC/EEC needs to know these air pressures, in order to assess an engine's current thrust setting. It will then adjust the fuel flow accordingly (among other things).
Hope that helps...
Last edited by Chris Scott; 27th Jan 2008 at 15:11.