The DM said that, during the accident airplane’s
departure, as the airplane rotated for takeoff, if water
was present in the bottom of the nacelle tank, it would
shift aft covering the fuel intake port to the engine.
This “slug” of water would then flow to the engine’s 14
fuel nozzles, where it could extinguish the engine’s
fire; the engine would stop producing power and its
propeller would move from coarse to fine pitch.
Subsequently, jet fuel would follow the water, and the
engine’s internal heat would likely be sufficient to
relight the atomized fuel. The engines were equipped
with auto ignition systems, and if they were in the on
position, they may also have been triggered to relight
the engine. The DM believes that the two pops he heard
were attempts by the engine to relight the reintroduced
fuel. He said that each pop would have been accompanied
by grayish white smoke.
The DM also said that water found in airplane fuel tanks
does not necessarily come from contaminated fuel trucks.
Airplane refueling trucks have stringent checks and
documentation requirements of their filters and are
subject to regular tank sump sampling. He believes that
the biggest source of introduced water into fuel tanks
is daily temperature variations and atmospheric
temperature variations. That is, if a fuel tank is not
completely full, there is a cavity of air above the
fuel, and due to the tank’s venting system, the air in
that cavity will move in and out as daily temperature
rise and fall, or as the airplane climbs to cruise
altitude and descends at its destination.
The United States Air Force has a fuels engineering
research laboratory located at Wright-Patterson Air
Force Base. One of their Senior Research Engineers
stated that “the cavity above fuel in a partially filled
fuel tank is vulnerable to aircraft fuel tank breathing
through its vent system.
This breathing of air, in-and-out, causes water to
condense within the fuel tanks.” He said that there
are many variables which affect this phenomenon,
including: diurnal temperature and pressure
variations, flight altitude pressure variations,
relative atmospheric humidity, fuel tank size and
volume above the fuel, and fuel storage time. The
senior engineer further stated that good
housekeeping practices of an airplane’s fuel source
and regular draining of the fuel tank sumps is the
simplest way to reduce the presence of water in
aircraft fuel tanks.