What does density altitude measure?

Density altitude is a critical concept in aviation that measures the pressure altitude adjusted for temperature variations. It indicates the altitude at which the air density is equal to the standard atmospheric conditions at sea level.

When the temperature deviates from the standard atmospheric temperature, the air density changes. If the temperature is higher than standard, the density altitude increases, which means the aircraft will perform as though it is at a higher altitude than it actually is, negatively affecting engine performance, lift, and propeller efficiency. Conversely, if the temperature is lower than standard, the density altitude decreases, enhancing performance.

This measurement is essential for pilots when calculating takeoff, landing distances, and aircraft performance, as it provides a better understanding of how the aircraft will perform under varying atmospheric conditions, regardless of the aircraft's actual geographic altitude.

The other options do not accurately describe what density altitude measures. For instance, pressure altitude and wind speed are not directly related to the definition of density altitude. The altitude the airplane is flying at or air traffic control instructions are separate considerations that may affect flight but do not define density altitude.