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your sleeve. Once airborne, you can
use 100% of anything available.
Altitude and Temperature
The higher you are, the less dense
the air and the less the ability of the
wings (rotating or otherwise) and
engines to "bite" into it, thus
requiring more power and longer
take-off runs to get airborne.
Humidity has a similar effect, but is
usually allowed for in the graphs.
TODR will increase by 10% for each
1,000-foot increase in aerodrome
altitude and 10% per 10°C increase
in temperature (factor by 1.1). LDR
increases by 5% for each 1,000-foot
increase in PA and 10°C increase in
temperature (factor by 1.05).
Aircraft weight
Greater mass means slower
acceleration or deceleration and
longer distances. TODR will
increase by 20% for each 10%
increase in weight and LDR 10% per
10% increase in weight (factor by 1.2
and 1.1).
Some manuals give take-off and
landing weights that should not be
exceeded at specific combinations of
altitude and temperature, so that
climb performance is not
compromised. These are known as
WAT limits (Weight, Altitude and
Temperature), and are mandatory for
Commercial Air Transport flights.
Sometimes rates of climb are given
instead, so you need to be aware that
a Commercial Air Transport
aeroplane must be able to maintain a
certain rate of climb depending on
whether it has retractable landing
gear or otherwise. In a multi, if you
can't visually avoid obstacles during
climb or descent, you must be able
to climb at whatever rate with one
engine out at the relevant altitudes
and temperatures. This means all
obstacles—you can't exclude
frangible ones, so you may have to
restrict take-off weight.
Runway slope
Going uphill when taking off will
delay acceleration and increase the
distance required. The converse is
true of downhill slopes and a rule of
thumb is that TODR will increase
10% for each 2% of uphill slope,
and vice versa (factor both by 1.1).
When landing, an uphill slope aids
stopping, thereby reducing LDR.
Any gains from landing upslope or
taking off downslope should not be
made use of but accepted as a bonus
(that is, don't use them as part of
your planning).
Surface winds
Headwinds will reduce the distances
required and improve the flight path
after take-off. Tailwinds have reverse
effects and crosswinds may even
exceed the ability of the tyres to grip
the runway. Aside from handling,
crosswinds may also increase the
TODR if you need to use the brakes
to keep you straight. Forecast winds
should be factored by 50% for a
headwind and 150% for a tailwind,
346 Canadian Professional Pilot Studies
although this may be allowed for in
the charts. TODR and LDR will
increase by 20% for each tailwind
component of 10% of the lift-off
and landing speed (factor by 1.2).
The flight manual will state
maximum crosswinds for your
machine (try Limitations). A useful
guide (for American machines,
anyway) is that the maximum
crosswind will be about 20% of Vso.
When finding the angle between the
wind and the runway, remember that
runway headings are magnetic and
winds in forecasts are true.
You can also use the crosswind chart
to find a limiting wind, or the
maximum you can accept from any
given angle. Just draw a line upwards
from the maximum speed you can
accept, and stop when you reach the
line representing the wind direction.
The curved line at that point (or its
interpolation) is the maximum
windspeed you can take.
Surface
Performance information is based
on a dry, hard surface. A
"contaminated" runway has standing
water or slush more than 3mm thick,
or snow and ice anywhere along the
takeoff run or accelerate-stop
surface. However, your flight manual
may have different ideas.
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
increase due to slower acceleration,
as will landing distance because of
poor braking action and aquaplaning
(see Hydroplaning, below), 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.
CRFI
The Canadian Runway Friction Index is
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