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interface between it and the fuel that
is the real problem – it turns into a
dark-coloured slime which clings to
tank walls and supporting structures,
which not only alters the fuel
chemically, but will block filters as
well. Not much water is required for
this – trace elements are enough,
although, in reduced temperatures,
dissolved water will escape as free
water, and look like fog. Aviation
fuel is “clean” if a one-quart sample
is clear of sediment when viewed
through a clean, dry, clear glass
container, and looks clear and bright.
Note: When visible water is present
in jet fuel containing anti-icing
additive, the additive will separate
from the fuel and be attracted to
the water. After a certain amount,
thought to be about 15%, the
density of the new liquid changes
so much that it is not identified as
water, and will therefore pass
through water filters, and will not
be detected by water finding paste.
Where the ratio becomes 50%, as
much as 10% of whatever is going
through the filter could actually be
water, which is very likely to get to
the engine, since the filters on the
airframe itself are not as restrictive.
Turbine aircraft at high altitudes use
fuel heaters (actually heat exchangers
based on bleed air or engine oil) to
melt the ice crystals that form in the
fuel up there.
Aircraft parked overnight should
ideally have tanks completely filled
to stop condensation, but this is
impractical if you expect a full load
the next morning and don't have
room for full fuel as well, in which
case be prepared to do extensive
sampling from the tanks. Half filled
drums left overnight should not be
used for the same reasons, but, in
remote places (like the Arctic), fuel is
a precious commodity and you think
more than twice before discarding
any (as it happens, drums are scarce
too, and they may get used for all
sorts of things, particularly diesel for
drills, so beware – always smell the
contents first). Full drums are usually
delivered to a remote cache by Twin
Otter or something, and they should
be sealed straight from the
refuellers—as you tend to use any
remainder in a very short time, this
can be minimised somewhat. Look
for a fill date, as fuel over two years
old should be looked at sceptically.
Also look for a large X, which is the
accepted symbol for contamination,
although not everyone has a black
marker with them.
An unofficial, but excellent (if not
better) substitute for water paste or
detectors when using jet fuel is food
colouring, which you can at least get
in the local grocery store, even if
you're in Baffin Island. All you need
is one drop – if there is no water
present, it will disperse evenly over
the surface. If there is water, the
food colouring will go directly to the
water droplets, which will be more
visible anyway from the colour.
Drums should not be stored
vertically for long periods, because
the bungs are not airtight, even
though they might stop fuel from
leaking out (although it is good idea
to stand them vertically for about
half an hour before you use the fuel).
When the contents contract as the
air cools overnight, water inside the
rim and collecting around the bung
can be sucked in as well, so either
Operational Procedures 93
store the drums on their sides, with
openings at 3 or 9 o’clock, or stick
something underneath at 12 o’clock
that causes the drum to slant enough
to stop rainwater collecting and
covering the bungs. Other openings
or connections should be protected
with blanks or covers, or at least
have their openings left facing
downwards. Drain plugs, valves,
filter bowls, sumps and filter meshes
should be checked daily for
sediment, slime or corrosion. Always
have spare filters.
The reason why long-term storage is
not good for fuel (up to two years
for drums is the accepted maximum)
is partly because of daily temperature
changes. When it is warm, the fuel
expands and some of the vapour-air
mixture is driven out. When it gets
colder, the fuel contracts and fresh
air is sucked in, to mix with more
vapour. As the cycle repeats itself,
the fuel inside gradually loses its
effectiveness. Humidity will mean
that water vapour will get in, too,
and condense into liquid. The
presence of oxygen will also cause a
gum to form, which is more
　
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