Density altitude is a measure of air density and it is used in aviation to assess an aircrafts aerodynamic performance under certain weather conditions. It is the altitude relative to standard atmospheric conditions at which the air density would be equal to the indicated air density at the place of observation. In other words, it is the air density given as a height above mean sea level. The density altitude can also be considered to be the pressure altitude adjusted for a non-standard temperature. As temperature and altitude increase, air density decreases, and both an increase in temperature and a decrease in atmospheric pressure, and to a much lesser degree, an increase in humidity, will cause an increase in the density altitude. In hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.
The key points about density altitude are:
- It is the altitude relative to standard atmospheric conditions at which the air density would be equal to the indicated air density at the place of observation.
- It is the air density given as a height above mean sea level.
- It is the pressure altitude adjusted for a non-standard temperature.
- As temperature and altitude increase, air density decreases, and both an increase in temperature and a decrease in atmospheric pressure, and to a much lesser degree, an increase in humidity, will cause an increase in the density altitude.
- In hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.
Pilots need to know density altitude because it reflects air density, and the less the air density at high altitudes in hot weather, the less lift is generated over the wings. Having this information can help the pilot prepare for an aircraft's performance limitations.
