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not, taxi higher and slightly faster
then normal to keep out of the
resulting snow cloud. If you have
wheels, act as if you have no brakes.
Marshallers should be well clear and
move slowly themselves. If the
heater is required to be off in the
hover, ensure the blower is on, to
help clear the windscreen.
80 The Helicopter Pilot’s Handbook
Whiteout
Defined by the American
Meteorological Society as “An
atmospheric optical phenomenon of
the polar regions in which the
observer appears to be engulfed in a
uniformly white glow”. That is, you
can only see dark nearby objects –
no shadows, horizon or clouds, and
you lose your depth perception. It
occurs over unbroken snow cover
beneath a uniformly overcast sky,
when the light from both is about
the same. Blowing snow doesn’t
help. Once you suspect whiteout,
you should immediately climb or
level off towards an area where you
can see things properly.
Taking off
In snow, the accepted takeoff
method is the towering type, because
a normal one may produce a large
snow cloud to blind air and ground
crews, and a failed engine (you may
be able to blow a lot of loose snow
away with a little application of
collective before the take-off
proper). If a white-out does happen,
apply maximum collective for an
immediate climb and forward cyclic
(i.e. no hover), keeping the ball
centred and using the A/H if
necessary, but the real key is keeping
a visual reference. If you have it,
exercise the gear once or twice to
dislodge slush, etc. that may have
stuck to the legs, to stop it freezing.
With any piston engine, use carb
heat regularly and check frequently
for carb icing. Have carb heat fully
on or off, but not on for prolonged
periods—it increases fuel
consumption markedly (see also
Engine Handling, in Techie Stuff).
The Cruise
Mountain wave clouds can be loaded
with heavy ice at remarkably low
temperatures (remember that low
pressures and low temperatures will
cause your altimeter to read high).
When using anti-icing, take into
account the inaccuracy of the
temperature gauges, so if you must
turn it on at 4°, and the temperature
gauge is only accurate to within 2,
start thinking about it at 6°.
Wet and sticky snow has more
chance of icing, and is associated
with low visibility, which would
indicate that you shouldn’t be flying
anyway. Luckily, light powdery snow
tends not to accumulate, but will still
give you the leans. Whatever you fly
in, make sure the baffles are fitted.
Visibility, by the way, includes the
inside! When it’s very cold, water
vapour (from clothes, breath, etc.)
will freeze on the windscreen, so
warming up the machine before
passengers get in will help a lot.
Navigation
Sun Tables are used for resetting
your DI in the Arctic, with true sun
bearings taken every 20 minutes or
so (assuming you can see it), based
on the fact that we know where the
Sun will be with reference to True
North for a given time, date, latitude
and longitude. Having obtained the
local time, look in the tables for the
Sun’s bearing, point the nose
towards it and set the DI to True
North. The two types of navigation
used are True North and Grid North
(to find Grid North, add your
longitude to True North, and vice
versa). In True North navigation,
headings have to be measured from
your point of departure, using its
Specialised Tasks 81
longitude as a base line. Every time
you cross a longitude, you add a
degree going East, and subtract
going West, so if you cross 10
longitudes enroute on a heading of
090T, your return heading will be
280T, not 270.
Many pilots drop dye balloons en
route so they can find their way
back. Others fly low enough to
create a disturbance in the snow
surface with their downwash, with
the obvious dangers.
Landing
Landing Sites should be selected
with a view to pulling out of a
resulting snow cloud if necessary.
That is, you need escapes.
As with landing on mountains, there
are various schools of thought about
landing on snow. One is the
zero/zero method (zero speed, zero
height), for which you carry out a
normal approach, using a constant
attitude with minimum changes,
losing translational lift at the last
minute. Aim to keep going forward
and downward until a few inches
　
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本文鏈接地址：The Helicopter Pilot’s Handbook(54)