Phil Gollin
My 2 cents, as a non engineer type, still relates to fuel and extended periods of very cold and very stable cruise. Both incidents occurred after very long periods of cold soaked and static cruising. All fuel has water in it, the spec allows small amounts. If the a/c tanks fuel prior to launch, it may already contain minute crystalline frozen water, albeit in trace amounts. Dispersed throughout the a/c tanks in some homogeneous mixture, it can certainly collect in small or "restrictive passages" (FOHE).
Built up as a "powdery" rather than a "solid" mass, it may collect in such a manner over time, that it allows cruise thrust, the flow of fuel acting to prevent continued necking down of the constricted passages so affected.
Without being specific due to my limited expertise, I can envision this "snowy" mass preventing higher thrust levels, or, due to additional accretion, maintaining current thrust, causing unresponsive power.
In the case of BA038, sudden full demand may have redistributed this occlusive mass downstream, packed it up and caused cavitation.
For Delta, the plug may simply have shifted on its own.
Anticipating the hue and cry from true believers in ETOPS, it isn't hard to imagine roughly simultaneous faults, given that at periods of long cruise, the systems acclimate and perform as one, essentially, given that there is no discrepancy in design, one from the other. Modern machining, chemistry and refining contributes to non anomalous behaviour of systems.
Then again, the Trent FOHE may melt and allow the ice to refreeze downstream. Over time, (long cruise) this could compromise fuel flow in the traditional way.
Last edited by airfoilmod; 26th Feb 2009 at 17:24.