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flying conditions, but up there the
West wind is the culprit, as well as
large swings between low and high
pressure which will often bear no
relation to what the weather is doing
(so don’t rely on cloud shadows over
the ground as an indicator of surface
wind speed). Aside from barometric
changes, look out for wind shifts,
which will bring changes in wind
speed and amounts of blowing snow
and less visibility – even a difference
of 100 feet in elevation can mean the
difference between snow or not.
Temperature changes often mean
bad weather is approaching from the
North – if it drops, expect ice crystal
fog, which is the low level equivalent
of contrails made at high altitude,
and created by air disturbance, which
could actually be from the aircraft
itself. Rising temperatures will
produce melting and poor visibility.
The chill factor from rotors can
reduce the ambient temperature by
several degrees.
When it gets to below -20 or so,
contact gloves will prevent your skin
freezing when it comes in contact
with cold metal, which is a more
efficient conductor of heat than air
is. You may also need sunglasses.
Always dress properly—in a forced
landing it could be that the clothes
you wear will be the only protection
you have. Also, being cold when you
are actually flying is a Flight Safety
hazard – metal foot pedals will
conduct heat away from your boots
very quickly. Extra time for planning
should always be allowed and the
pre-flight inspection should include
you—being improperly dressed and
making a series of short exposures
will fatigue you more quickly,
especially when the clothes you are
wearing are bulky and awkward to
move in. Maintain blood sugar levels
as more calories are consumed in the
cold (you need 3000 calories a day in
Norway). If the air is very dry (like in
the Arctic), you will lose fluids more
quickly through the usual ways, but
especially breathing. Losing 10%
causes cause delirium, and a 20%
loss is fatal. You could try and eat
snow, but the conversion to water
takes more energy, so melt it first.
Preserve your machine’s heat as
much as possible on the ground, by
covering vital areas as soon as
possible after landing, not opening
and closing doors too much, etc. It’s
very important that it does not get so
cold that it won’t start again, so you
might consider starting up every
couple of hours or so, which will
both use fuel and battery capacity –
certainly, in the average car, it takes
about half an hour’s driving to
replace the energy taken by one start,
and I’m sure it’s worse with a
helicopter – a depleted battery will
sooner or later result in an expensive
hot start. At the very least, remove
the battery and keep it warm. If you
see fan heaters around the helipad,
they are for putting under the covers
to keep the engine and gearbox
warm (all night).
Special attention should also be paid
to the following:
78 The Helicopter Pilot’s Handbook
·  That correct oil and grease is
used and special equipment (like
winter cooling restrictors) is
fitted to keep engines warm.
For Bell 206s, at least, below –
40C, your oil must meet MIL
L7808 specifications, and you
will need fuel additives in all
fuels other than JP4 below –
18C. 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 also not be
detected by water finding paste,
which is not, in any case, meant
to detect water in suspension.
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.
·  Use deicing fluid if possible—
scrapers do not leave pretty
results. Fluid, if it's thick
enough, helps prevent further
ice forming (see the tables in
Chapter 6). Don't forget to fit
engine blanks, etc. before using
them. Bear in mind that deicing
fluids are also efficient
　
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本文鏈接地址：The Helicopter Pilot’s Handbook(52)