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Required (factored TODA) is 92% of
the TODR.
Part of the Clearway may be able to
support an aircraft while stopping,
although not under take-off
conditions. This may be declared as
Stopway which may be added to the
TORA to form the Emergency Distance
Available (EDA). This is the ground
run distance available for an aircraft
to abort a take-off and come to rest
safely—the essential point to note is
that Stopway is ground-based. EDA
is sometimes also referred to as the
Emergency Distance or Accelerate-Stop
Distance. The greater the EDA, the
higher the speed you can accelerate
to before the point at which you
must decide to stop or go when an
engine fails.
Obviously, the TODR must not be
more than the TODA. If not already
done in the Flight Manual, the
TODR must be factored by 1.33,
after the corrections below have
been multiplied together and applied
(factoring means that the distances
are multiplied by those figures to
provide a safety margin).
The Landing Distance Available must
similarly not be less than the Landing
Distance Required. If there's a choice
of runways, the LDR is the greater
of that on the longest one in zero
wind or on the runway used due to
forecast winds. Don't forget the
LDR is from 50 feet. Unless the
Flight Manual states otherwise, the
LDR must be factored by 1.43
(giving 70% of distance available),
again, after applying the following
corrections.
Airfield altitude and ambient
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
1000-foot increase in aerodrome
altitude and 10% per 10o C increase
in temperature (factor by 1.1).
LDR will increase by 5% for each
1000-foot increase in pressure
altitude and 10o C increase in
temperature (factor by 1.05).
Aircraft weight
Greater mass means slower
acceleration/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). Very
few aircraft allow you to fill all the
seats with full fuel.
140 Operational Flying
Some manuals give take-off and
landing weights that should not be
exceeded at specific combinations of
altitude and temperature, thus
ensuring 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
rate of climb of 700 fpm if it has
retractable landing gear, and 500 fpm
otherwise. In a multi, if you can't
visually avoid obstacles during climb
or descent, you must be able to
climb at 150 fpm with one engine
out at the relevant altitudes and
temperatures (that's 500 feet in five
miles!). This means all obstacles—
you can't exclude frangible ones.
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 the handling
problem, crosswinds may also
increase the TODR if you need to
use the brakes to keep you straight.
Forecast winds must be factored by
50% for a headwind and 150% for a
tailwind—this may already 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).
Surface
Performance information is based
on a dry, hard surface. The runway
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