In selecting a plane to fly each leg of an expedition, there are three variables that must be considered: length of the runway; distance, fuel required, fuel capacity, and weight; and flying conditions, including the climate and flying altitude.

Every plane should have a pilot operating handbook which indicates: how fast the plane can go; how far the plane can go; how much weight it can carry; how much fuel it can hold; and how much fuel it burns per hour.

Airplanes perform differently at different altitudes and temperatures because as you go up in altitude, the air gets thinner. There are less air molecules per cubic foot of air. The same thing occurs if the air is warmer than normal.

Warmer air is thinner air and makes the plane fly as if it were at a higher altitude. We call this "density altitude." For example, if you were at an airport at 5,000 feet and the temperature was 5o Celsius, the plane would fly as if it were at 5,000 feet. However, if the temperature was 30o Celsius at 5,000 feet, the plane would fly as if it were at 8,000 feet. We would then say the density altitude was 8,000 feet and would have to base our performance calculations on 8,000 instead of 5,000 feet.

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Please send any comments to:
Curator: Tom.Benson@grc.nasa.gov
Responsible Official: Kathy.Zona@grc.nasa.gov