Definition
Pressure altitudes corrected for nonstandard temperature. Density altitude is the altitude in the standard atmosphere at which the air would have the same density as the air currently surrounding the aircraft. As temperature rises, humidity increases, or pressure drops, the air becomes less dense and the density altitude rises above the actual elevation.
Plain English
A way of describing how 'thin' the air feels to the airplane. On a hot, humid day at a high airport, the air acts like the airplane is much higher up than it really is, which hurts engine power, propeller bite, and wing lift.
Context Anchor
Seen in aircraft performance planning, especially when checking takeoff, climb, and landing performance for hot days, high-elevation airports, or heavy loading.
Derivation
From Latin densus (thick, crowded) and altitudo (height). The term literally points at the height that matches a given air thickness — useful because the airplane responds to air density, not to the number painted on the airport sign.
Why Pilots Care
Higher density altitude reduces engine power, propeller thrust, and wing lift, which lengthens takeoff rolls and lowers climb rates.
Grounding Statement
Same airport, same runway — but on a hot day the airplane behaves as if it were taking off from a much higher field.
Intuition Check
Do not read density altitude as the airplane’s actual height. It is a performance number based on air density; higher density altitude means the airplane performs like it is at a higher altitude.
Example Sentence 1
Before departing the mountain strip at midday, the pilot checked the temperature and pressure and found the density altitude was nearly 9,000 feet, well above the field elevation of 6,200 feet.
Example Sentence 2
We checked the density altitude before takeoff and decided to reduce our load to keep the climb performance safe.