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climb or level off towards an area
where you can see things properly.
Clear Air Turbulence
This can sometimes be avoided by
simply changing the cruising level.
Listen out for other aircraft reports.
Rain, Snow and Other Precipitation
On the ground, you may need slower
taxying speeds and higher power
settings to allow for reduction in
braking performance and the
increase in drag from snow, slush or
standing water, so watch your jet
blast or propeller slipstream doesn't
blow anything into nearby aircraft.
When taxying
Try not to collect snow and
slush on the airframe, don't taxi
directly behind other aircraft,
and take account of banks of
cleared snow and their proximity
to wing- and propeller-tips or
engine pods. Delay flap selection
to minimise the danger of
damage, or getting slush on their
retraction mechanisms.
On the runway
A contaminated runway has
significant amounts of standing
water, ice, slush, snow or even
heavy frost along its surface.
The most important factors are
loss of friction when
decelerating, and displacement
of (and impingement drag when
accelerating through) whatever
is on it, so it may be difficult to
steer, and take-off and
accelerate-stop distances may be
increased due to slower
acceleration, as will landing
distance because of poor
braking action and aquaplaning,
which is a condition where the
built-up pressure of liquid under
the tyres at a certain speed will
equal the weight of the aircraft.
Higher speeds will lift the tyres
completely, leaving them in
contact with fluid alone, with
the consequent loss of traction,
so there may be a period during
which, if one of your engines
stops on take-off, you will be
unable to either continue or stop
within the remaining runway
length, and go water-skiing
Operational Procedures 113
merrily off the end (actually,
you're more likely to go off the
side, so choosing a longer
runway won't necessarily help).
The duration of this risk period
is variable, but will vary
according to your weight.
Reverted Rubber Hydroplaning
happens when a locked tyre
generates enough heat from
friction to cause the resulting
steam to lift the tyre off the
runway. The heat causes the
rubber to revert to its basic
chemical properties.
A rough speed at which
aquaplaning can occur is about 9
times the square root of your
tyre pressures, 100 pounds per
square inch therefore giving you
about 90 kts—if this is higher
than your expected take-off
speed you're naturally safer than
otherwise. The point to note is
that if you start aquaplaning
above the critical speed (for
example, when landing), you can
expect the process to continue
below it, that is, you will slide
around to well below the speed
you would have expected it to
start if you were taking off.
Most factors that will assist you
under these circumstances are
directly under your control, and
it's even more important to
arrive for a "positive" landing at
the required 50 feet above the
threshold at the recommended
speed on the recommended
glideslope than for normal
situations. Under-inflating tyres
doesn't help—each 2 or 3 lbs
below proper pressure will lower
the aquaplaning speed by 1 knot,
so be careful if you've descended
rapidly from a colder altitude.
Aquaplaning aside, it's obviously
a good idea to avoid using a
contaminated runway, but if this
isn't possible, there are
techniques that may assist you to
reach a speed at which you can
continue if an of engine fails, or
stop in the shortest practicable
distance, which will include not
taking off with a tailwind
component or carrying
unnecessary fuel. The
recommended maximum depth
of slush or water for take-off
should not exceed 15mm, and of
dry snow 60mm. Wet snow
should be treated as slush.
The airfield must have either a
paved runway having an
Emergency Distance Available
of not less than 1½ x TODR
(say a PA23) or 2 x TODR (an
AA5) or 1500 feet, whichever is
the greater; or a grass runway
having an Emergency Distance
Available of not less than 2 x
TODR (PA23) or 2.66 x TODR
(AA5) or 2000 feet, whichever is
the greater. The minimum
cleared width should be 70 feet
(see Performance for definitions).
There should be provision for
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