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The lifting capability of an aircraft depends upon the airfoil design of the wing,
the speed at which the wing moves through the air, and the density of the air.
It is the design of the aircraft wing that limits the amount of available lift, and
it is the available power from the engine(s) that likewise limit(s) the speed at
which the wing can be made to move through the air. The efficiency of the engine/wing
combination is reduced when air is less dense than the established standard day
(barometric sea level pressure of 29.92 inches of mercury at a temperature of 59 degrees F).
Therefore, every pilot should ensure during preflight preparation that the aircraft
gross weight is within safe limits for the intended flight, considering the aircraft
performance capabilities. The total weight of baggage, cargo, and fuel load should
be adjusted accordingly to provide an adequate margin of safety.
Pilots must understand that in many general aviation aircraft, it is not possible to
fill all seats, load the baggage compartment to capacity, carry full fuel, and
remain within approved weight and balance center of gravity (CG) limits. In many
four-place and six-place airplanes, the fuel tanks may not be filled to capacity
when a full complement of passengers and their baggage is carried. It will be
necessary to reduce the number of passengers or baggage weight if the proposed flight
distance requires a full fuel load.
The aircraft performance characteristics adversely affected by overweight are:
- Increased takeoff speed.
- Increased takeoff runway length.
- Rate of climb.
- Maximum altitude capability.
- Operational range.
- Maneuverability.
- Controllability.
- Stall Speed.
- Approach speed.
- Landing distance.
Every pilot must consider how these characteristics would affect the aircraft in an
emergency situation. Another consideration is high elevations, and/or hot and humid
weather (density altitude), which is the subject of another publication in the
Accident Prevention Program series.
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