Density altitude

After the standard atmosphere can each density value of the air a certain altitude to be assigned. However, this density altitude is not a fixed altitude, as the air density, pressure, temperature and humidity dependent.

Since the performance of an aircraft depend on the air density, especially larger temperature variations in flight operations must be observed. On a hot day, the air is thinner and lighter. The start on an airfield with a field elevation of 1500 ft, for example, would have to be scheduled due to the lower air density as if he were on a higher Airfield (air pressure decrease with height).

The time required for the start of the aircraft runway length becomes longer; that is, one speaks on a hot day by a large density altitude. On a cold day, however, the air is heavier. Thus, the take-off distance is shorter for the same airfield and there is still a margin of safety for the required runway length.

The density altitude is therefore no altitude, but a technical value, a performance level.

Calculate the density altitude

First, from the height and the pressure QNH pressure altitude (pressure altitude, about 27 ft per hPa pressure difference to 1013.25 hPa ) is calculated, then corrected by about 120 ft per Kelvin temperature difference from the standard atmosphere.

• Aviation Meteorology