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°F/C 60/15.6 70/21.1 80/26.7
1,000’ 1300 2000 2700
2000’ 2350 3100 3800
3000’ 3600 4300 5000
4000’ 4650 5600 6300
5000’ 6350 6900 7600
6000’ 7400 8100 8800
7000’ 8600 9300 1,0000
Flight Planning 163
°F/C 60/15.6 70/21.1 80/26.7
8000’ 9700 10400 11100
9000’ 11,000 11600 12400
1,0000’ 12250 13000 13600
11,000’ 13600 14300 15000
12000’ 14750 15400 16000
It shows that, at 6,000 feet and 21°C,
for example, you should enter
performance charts at 8100 feet.
If you want to work it out for
yourself, try this formula:
DA = 145,366[1 - (X0.235)]
where X is the station pressure in
inches divided by the temperature in
Rankin degrees, which are found by
adding 459.69 to Fahrenheit totals.
Altitude
Air density drops off by .002 lbs per
cubic foot (i.e. 2 ½ %) for every
1000 feet in the lower layers of the
atmosphere.
Humidity
Adding water vapour to air makes it
less dense because the molecular
weight is lower (dry air is 29 –water
vapour is 18). On cold days,
humidity is less of a problem simply
because cold air holds less vapour. A
relative humidity of 90% at 70°F
means twice as much than at 50°F.
Temperature
As heat expands air, it becomes
thinner. Thinner air is less dense
(Boyles Law). On the surface, an
increase in temperature will decrease
density and increase volume, with
pressure remaining constant. At
altitude, however, pressure reduces
more than temperature does, and
will produce an apparent
contradiction, where temperature
will decrease from the expansion.
Pressure
Air density reduces with atmospheric
pressure (Charles Law). When you
compress air, its density increases.
Runway length
Getting the wheels off the runway is
only part of the story. You must also
clear an imaginary screen (usually 35
feet) at the end of the TODA
(TORA + Clearway). The distance
to do this is the Take-off Distance
Required. Obviously, the TODR must
not be more than the TODA.
The Stopway may be added to the
TORA to form the Emergency Distance
Available (EDA), or the ground run
distance available to abort a take-off
and come to rest safely. 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.
The Landing Distance Available must
similarly not be less than the Landing
Distance Required.
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.
TODR will increase by 10% for each
1,000' increase in aerodrome altitude
and 10% per 10°C increase in
temperature (factor by 1.1). LDR
164 Canadian Private Pilot Studies
will increase by 5% for each 1,000'
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).
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
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