What is density altitude?

• A. The pressure altitude corrected for nonstandard temperature.
• B. The altitude indicated when the barometric scale is set to 29.92.
• C. The altitude above the ground plus terrain height.
• D. The altitude indicated when QNH is set.

Answer: (A)

Density altitude describes how the air behaves compared with the standard atmosphere. It’s the altitude in the standard atmosphere at which the air density matches what you actually have today. In practice, you find it by taking the pressure altitude and correcting for nonstandard temperature. If the air is warmer than standard for a given height, the density altitude is higher, meaning thinner air and reduced lift and performance. This concept is key for gliders because their performance depends on air density: higher density altitude makes it harder to generate lift at a given speed.

The other readings are different: the reading with the barometer set to 29.92 is pressure altitude, which doesn’t account for temperature. The reading with QNH set gives altitude above mean sea level, not density. And altitude above ground height is unrelated to density altitude.