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much the same as for day, though
there are some aspects that demand
some thought. Plot your route on
the chart in the normal way, but
navigate with electronic aids or
features that are prominent at night,
such as town lighting, lighted masts
or chimneys, large stretches of water
(big black holes), aerodromes,
motorways, etc.
One of the optical illusions you
might come across is the apparent
motion of a stationary object which
isn't helped by rain on the
windscreen. Apart from reducing
visibility, it's a particular threat when
fixing your position by a single light
source. When little or no light is on
the surface and a prominent one
comes into view, it may seem that
the light is above the horizon, which
could lead you to pitch into a steep
attitude in keeping with the resulting
false horizon.
Sometimes the effect is not much
more than an uncomfortable
76 The Helicopter Pilot’s Handbook
climbing sensation even when you're
straight and level, but an obscured
windscreen could make objects
appear lower than they really are.
This will be more apparent with high
intensity runway lighting, which may
also give you the same effect that
actors have on stage, where they
can't see the audience through the
bright lighting. The lack of normal
contrast will also upset your altitude
perception, making you feel further
away and higher than you are. As a
result, on a final approach you could
find yourself too low and fast. The
solution is to use every piece of
sensory information you can,
including landing lights and
instruments. Problems will arise if
several of the above factors affect
you at once, especially if the landing
point is sloping—this is where more
frequent cross-referencing of
altimeters is important.
Helicopter landing sites must be
checked out in daylight on the same
day as they are to be used at night.
Preflight checks should allow for
night flying—carry a torch, and 2
landing lights are preferred.
Permission to enter the rotor disc is
given by flashing landing lights.
Hovertaxi higher and slower than by
day, making no sideways or
backwards movements. Great care
should be exercised in pointing the
Schermuly flares to a safe place at all
times (which is admittedly a bit
difficult when they're fitted and the
fuelling truck pulls up right alongside
them). The flares should not be
armed at this stage, but at the
holding point immediately before
take-off and disarmed at the same
place after final approach. They
should also be disarmed after
reaching cruising altitude.
The maximum useful height for
discharging a flare is around 1800
feet. Its burn time is 80 seconds,
during which time it will fall about
1500 feet. Therefore, having
established autorotation after an
engine failure at night, the first flare
should be discharged immediately, or
on passing through 1800 feet,
whichever is later. Don't bother
doing it before this, as they will be
useless. Due to the way the switches
work, and depending on the height
at which your engine stops, you may
not be able to set off more than one
flare before landing, but, if possible,
the second should be discharged
between 800-1000 feet agl.
In autorotations at night, use a
constant attitude, at whatever speed
is comfortable, to keep the beam
from the landing light in the same
position on the ground, because
otherwise it will shine up into the air
when you flare, from which position
it's no good to you at all.
Winter Operations
Although colder air means there's
less danger of exceeding temperature
limits, there are hazards, too,
including freezing precipitation, low
ceilings and cold temperatures.
Rapid changes in these are typical,
and it’s possible to get weathered in
for days at a time, so don’t forget
your chocolate bars (you need lots
more calories).
The Weather
In the Frozen North, the best
conditions are in late winter or early
spring, with one of the major
problems being darkness. Once the
Specialised Tasks 77
snow is down, the air is quite dry
and it can stay clear and cold for
long periods, so you can usually
ignore fog and the rest until it gets a
bit warmer.
Above the 60th parallel, don’t expect
the weather to behave rationally at
all. For example, further South, the
East wind is responsible for bad
　
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本文鏈接地址：The Helicopter Pilot’s Handbook(51)