Steve Fossett's plane seems to be low on fuel:

Moore said fuel sensors in the 13 tanks onboard the single-engine jet differ from readings of how quickly fuel is burning during the flight. Moore said the crew has been forced to assume that 2,600 pounds of the original 18,100 pounds of fuel aboard "disappeared" early in the flight.

Where does 2600 pounds of fuel "disappear" to? Overconsumption early due to a cold engine, or stuck valve?

They should be able to tell if it's a gauge problem or if the fuel is actually gone. A change in weight of 2600 pounds should have a performance impact, and Rutan should have performance curves for that airplane. Tell Fossett to climb at speed X, measure the rate of climb, and see how that matches with what his fuel gauges are telling him. I'll bet they are planning those tests right now.

On the other hand, with a fuel-critical airplane like this, I'll bet they are measuring fuel consumption with redundant methods. A fuel totalizer in the fuel line measuring absolute flow, and a gauge in the tank itself to measure fuel that's lost through spillage, leaks, evaporation, or whatever. If both readings agree that the fuel is missing, then it almost certainly is. If they're getting conflicting readings, then I'd bet on measurement error and do some in-flight tests.

Still, the question is whether you want to ultimately bet your life on that test.

On re-reading, I see that they apparently are getting conflicting readings from the tank sensors and the fuel flow totalizer. That would mean either gauge error or a leak before the totalizer.

The report on the VA-GF website mentioned that the mission saw improved performance and altitude early in the mission that could now be attributed to the early fuel loss.

Also according to the VA-GF website, they have decided to leave Japan and re-assess as they near Hawaii. It all depends on tail-winds at this point, but all of their calculations are taking the lost fuel into account. No "unsafe" assumptions are being made at this point.

As far as disappearing fuel, the VA-GF press release also mentioned that they anticipated leaks and loss due to evaporation, but they hadn't ever tested the fuel tanks at full capacity, so they could very well have leaked and/or had evap problems for the first part of the flight.

I wonder who's ultimately responsible if the tank tests all passed with "full minus 1500" pounds of fuel, but were never tested with more than that...

I have to say it would seem a case of leaks versus over usage. I'm not an aircraft mechanic, but I am a fair car mechanic. To use 2600 pounds too much fuel would have shown up in rough running or engine temps it seems to me.

Unless they didn't have good numbers for usage or engine temp, from their trial flights. Poor testing leads to poor operation.

I was a gas turbine tech in the Navy, we used to do fuel efficiency runs once a month to see if we had any engine/fuel system problems. It all depended on good info from the initial trials of the engines and systems concerned. If you didn't do your homework right to start with, you can't trust that next set of numbers.

If Fosset doesn't have enough fuel to make it, I sure he will try again. (Assuming no tragedy.) Either way, enough fuel or not, he earns my respect.

Several notes:
1)The system was never tested in flight with full fuel. The Full fuel takeoff was the highest risk part of the flight and rightfully should only be done once.

2)The tanks need fuel vents and in my reading between the lines I get the impression that the 2600 lbs was sucked out of the fuel vents.
If I had to speculate the fully loaded wing operating at a limit condition never before flown might have generated aerodynamic suction on one vent and pressure on another forcing fule out the low pressure vent.
This pressure differential might be small so it could only lift the fuel a few inches out of the tank. If the tank was never before filled to the last few inches then this problem never before had enough force to cause fuel venting.

I have about 500 hours in small planes.
Most planes have the fuel caps on top of the wing. If you do not get the fuel caps closed properly the low pressure area on top of the wing will suck the fuel out while in flight.

Tight properly closed and latched fuel caps are
a "check it twice" item on my preflight list.

Since most light plane fuel gagues are almost useless one counts alot on ones preflight planning
to gauge how much fuel is necessary for the flight plus adequate reserves. Thus fuel caps on and no fuel leaks is one of the few easily missed preflight actions that can kill you.

Most other normal ommisiona and errors will give you an indication something is wrong before they kill you. ;-)

In a former life I ferried a bunch of planes to Australia and other places, and you would be surprised how easy it is to not be able to account for fuel on board especialy if you have a complicated fuel system. It's probably still gurgling around inside somewhere, but you'll be damned if you can find it sometimes. The only likely explanation is venting of some kind but I find it hard to believe they wouldn't have noticed it in flight unless he has some restricted visibility problems.

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