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Technique - Calculating density altitude

Know exactly how your airplane will perform

Airplanes move through a fluid. The density of that fluid—air—changes as the weather and altitude change. The density of the air that flows over the wings, past the propeller, and into the engine for combustion affects how the airplane performs. As altitude and temperature increase, the air’s density decreases (more humid air is also less dense, but performance charts rarely take this into account). Because the airplane senses only ambient air, and not a true altitude or temperature, it’s density altitude we rely on to tell us how the airplane will perform.

Density altitude can’t be read on an altimeter or other quick-reference indicator in the cockpit. It must be calculated. The result is used to determine takeoff performance and nearly everything else you’ll find in the performance section of the handbook. Calculating density altitude is done one of two ways—with a chart or an E6B.