Both high pressure fuel pumps had damage consistent with excessive aeration, or blockage. However, the manufacturer says that both were capable of providing full flow to the engines. There were two periods of flight where temps went below -34C and down to -76C over China/Russia.

i read `elsewhere` that the blend was Jet-A1 ; whats the differences between the blends?

The fuel wouldnt be exposed to the ambient temperature, right?

In order:

Other flights may HAVE had problems, just that they weren't as spectacular as this one was, so they either didn't get reported, or they didn't even get noticed. There may have only been one or two flights operating in that area, that high. It states in the report that I read that they made the initial descent because temps were too low.

The difference in the jet fuels is mostly the freezing point. Jet A has a freezing point of -40C, where Jet A-1 is -47C. That's the most important difference between them. They are the same basic density, same ignition point, same flash point, etc. Jet B has an even lower freeze point (-50C) but it has a lower density as well, so you get less range for the same weight of fuel. Jet A and Jet A-1 have a nominal density of 6.76 lbs/gallon at 15C. They have the same density range of 6.46-7.00 lsb/gallon.

Everything would without a heater. The fuel would be exposed to the extreme cold that's transmitted through the wing skin. Even with a heater temps of -76C would still cause you problems. There is a hydraulic sytem heat exchanger that tries to warm up the fuel before it enters the engines, but outboard wing tanks can gel before they transfer the fuel to the main tanks on their way to the engines. With -76C temps even a heat exchanger would have problems keeping all the fuel warm and keeping it from gelling.

I would LOVE to get my hands on the full dataset for this flight. I'm curious too as to what the engine temps were running at over the Urals. They said the crew was monitoring them the entire flight and didn't really notice any major issues until landing, but I'd love to see what they were running at.

The current theory for why BA38 crashed on approach to LHR is (well there is no Current theory) that holds water, as the fuel was to spec and did not have excessive water or other contamination.

I have read all of the airline pilots speculations at pprune prior to this last AAIB update they all focused on contamination and low temp of the fuel. The lastest report says at no time did the fuel go below -37C so no waxing of the fuel.

One Pilot (shutdown in main Topic relegated to their skunkworks, they call if WAGS aka Wives and Girlfriends) speculated that EMI could have cycled the main fuel valves outside of any control from EEC or FADEC he said he saw it happen personally when EMI was introduced into the plane he was on.

He went on to say that the time to cycle the valves from on to off to on was approx 16 seconds (from my memory) due to a glitch in the signaling.

In my opinion this cycling would have caused the fuel to temporarily be reduced long enough to cause cavitation of the High Pressure pumps on the engines. Another pilot (this time in the main stream topic) said that once the HP pumps start to cavitate the only way to recover is to reduce the demanded flow of fuel ie “Pull back on the Throttles” Which is just the Opposite of what they did. They push the throttles forward opening the
High pressure metering valves more causing more cavitation.

Not sure if there are any cavitatoin sensors on the engines recorded by the DFR maybe the QAR but the QAR lost the last 45 seconds of info. What kind of system is that?? At a minimum there should be multiple QAR’s with overlap. (My understanding iof the QAR is that it records specific engine performances not covered by the black boxes)

Summary,
1. One pilot said in his experience an outside RFI/EMI can cause the main fuel valves to cycle open to closed to open.

2. Another pilot said closing the fuel valves (and demanding more fuel at the fuel
metering valves on the engine side of the HP pumps will cause cavitation in the HP pump.
3. Once cavitation starts only way to recover is to reduce throttle until cavitation stops then increase throttle.

Seems to fit the observed conditions unless the FDR records all positions of the valves not just the commanded positions, after all the valves did not have to cycle all the way closed to start this series of events.


[edit on 19-2-2008 by Eagle1229

[edit on 19-2-2008 by Eagle1229]

I'm still waiting to see what they come up with. There are a few other things out there that could have caused the problem. Cavitation can be caused by several different things, not just the valve issue you mentioned. There is other evidence the accident board is looking at besides what's been posted here.

I've been reading the pages they've released so far. They don't have a theory yet, but they have several different causes to the cavitation, and a couple of different things that they're looking into still.

who makes the EMI on that specific aircraft?

Boeing engineers have found that both the Delta 777 that suffered a power loss on 26 November, and the British Airways 777 that crashed at Heathrow suffered from icing along the lines for the fuel oil heat exchanger. The problem appears to be limited to the Trent 895 engines.

By running hot oil along lines next to the fuel lines, that allows them to use a simple system to cool the oil with the fuel, and heat the fuel with the oil. Under certain conditions the heat from the oil is not enough to keep water in the fuel from freezing. This will block fuel from the exchanger, which causes a fuel starvation power loss.

GE and Pratt and Whitney engines don't have a similar problem because they have a feedback look that loops hot oil back around to the front of the exchanger, preheating the fuel going into it.