"The fuel vents, instead, were put on
the central fuselage, on the engine cowling. The trouble was, when
the airplane was full of fuel, there's solid fuel in between the
booms and the main fuselage. So as the air expanded in the boom
tanks, as I climbed in altitude, it had the effect of forcing fuel
out the vents instead of air."
Source: GlobalFlyer Pilot Steve Fossett,
explaining the circumstances that led to the globe-girdling
project's concern for his fuel cpacity as the flight neared a
(thankfully) successful conclusion earlier this month.