Definition
A condition in which the density altitude is significantly higher than the actual field elevation, meaning the air is thinner than standard. It typically results from high temperature, high elevation, high humidity, or a combination of these. High density altitude reduces engine power, propeller efficiency, and wing lift, which lengthens takeoff and landing distances and decreases climb performance.
Plain English
The air is thinner than usual, so the airplane does not perform as well. It needs more runway to take off, climbs more slowly, and lands using more distance.
Context Anchor
Pilots encounter this during preflight planning and before takeoff, especially on hot days or at airports in higher terrain.
Derivation
Density altitude is pressure altitude corrected for non-standard temperature. 'High' here means the value is high relative to the actual elevation -- not that the airplane is high in the sky.
Why Pilots Care
High density altitude reduces engine power, propeller thrust, and wing lift, resulting in longer takeoff rolls, lower climb rates, and reduced performance margins that can make operations unsafe if ignored.
Analogy
It is like trying to exercise at a mountain town after living at sea level: the same action takes more effort because the air is thinner.
Grounding Statement
On a hot summer afternoon at a 6,000-foot airport, the airplane behaves as if it is taking off from 9,000 feet -- sluggish acceleration, weak climb, and a long ground roll.
Intuition Check
Do not read high density altitude as “high air density.” It means a high altitude value caused by thin air, and thin air reduces performance.
Example Sentence 1
Before departing the mountain strip on a hot afternoon, the pilot calculated a high density altitude and decided to wait until the cooler evening to take off.
Example Sentence 2
Waiting until evening reduced the temperature enough to lower the density altitude and improve climb performance.