Definition
Pressure altitude corrected for non-standard temperature. It is the altitude at which the standard atmosphere would have the same air density as the air the aircraft is currently flying in. Density-altitude rises as temperature, humidity, or field elevation increases, and it directly affects engine power, propeller efficiency, and lift produced by the wing.
Plain English
It is the altitude the airplane and engine actually feel, based on how thin the air is right now. Hot, high, or humid conditions make the air thinner, so the airplane performs as if it were at a higher altitude than the runway sign says.
Context Anchor
Seen in aircraft performance planning, especially before takeoff from high-elevation airports or on hot days.
Derivation
‘Density’ comes from Latin densus, meaning thick or crowded — a measure of how much air is packed into a given space. Pairing it with ‘altitude’ gives a height value that reflects how thick or thin the air actually is, rather than just how high above the ground the aircraft sits.
Why Pilots Care
High density altitude reduces engine power, propeller thrust, and wing lift, lengthening takeoff and landing distances and lowering climb performance.
Analogy
Density-altitude is like the airplane’s “performance altitude.” The runway may be at 3,000 feet, but on a hot day the airplane may perform more like it is at 6,000 feet.
Grounding Statement
When the air is hot or thin, there is less air for the engine, propeller, and wings to work with.
Intuition Check
Density-altitude does not mean the aircraft’s actual height above the ground or sea level. It means the altitude the airplane feels, based on how dense the air is.
Example Sentence 1
On a 95°F afternoon at a 5,000-foot field, the pilot calculated a density-altitude of nearly 8,000 feet and revised the takeoff distance accordingly.
Example Sentence 2
The pilot used the density altitude chart to confirm the airplane could still clear obstacles on the departure path before accepting the short-field departure.