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expand with Density Altitude. On
approach, you have your hands on
the controls and are using less than
cruise power, so the same figures
don't work.
The other shaded area is called the
high speed section, and the clear area
between them is the takeoff corridor.
Takeoffs and performance
calculations should definitely take
account of the curve, which is
constructed at maximum weight,
with no wind at a density altitude of
at least 7,000 feet. Those of lesser
quality must be verified (that is,
flown) by the relevant Authority.
A Question
1. If you plan to fly for an hour and
a half, and your machine uses 10
gals/hr, and you must land with 10
gals on board, what is your
minimum fuel before takeoff?
An Answer
2. 25 gals.
Flight Operations
Fuelling
Jet and piston fuels mix differently
with contaminants (particularly
water), which is due to variations in
their specific gravities and
temperature. The specific gravity of
water, for example, is so close to
Avtur that it can take up to 4 hours
for it to settle out, whereas the same
process may take as little as half an
hour with Avgas. As a result, there is
always water suspended in jet fuel,
which must be kept within strict
limits, hence two filtration stages, for
solids and water. The latter doesn’t
burn, of course, and can freeze, but
it’s the fungi that gather round the
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: It has been found that 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.
Aircraft parked overnight should
ideally have tanks completely filled
to stop condensation.
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
170 JAR Private Pilot Studies
you're in a remote place. All you
need is one drop – if there is no
water, 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.
Each day before flying, and when
the fuel is settled, carry out a water
check in aircraft and containers (but
see below, for drums). Collect
samples in a transparent container
and check for sediment, free water
or cloudiness—if there is only one
liquid, ensure it is not all water. The
instructions for using water
detectors are displayed on the
containers, but water-finding paste
will not detect suspended water, and
is as an additional test, not a
replacement for a proper inspection.
Naturally, only competent and
authorised personnel should operate
fuelling equipment, who must also
be fully briefed by their Company. In
practice, of course, refuellers know
very well what they're doing, but you
should still be in full communication
with them. In general, the following
precautions should be taken:
·  Documentation must reflect the
fuel’s origins and its correct
handling.
·  Vehicles used for transportation
must be roadworthy and
regularly inspected.
·  Fire extinguishing equipment
must be available and crews
familiar with its use.
·  Maintain a clear exit path for
removal of equipment in
emergency.
　
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