Density Altitude

Density altitude has a significant influence on aircraft and engine performance, so every pilot needs to thoroughly understand its effects. Hot, high, and humid weather conditions can cause a routine takeoff or landing to become an accident.

Density Altitude is formally defined as pressure altitude corrected for nonstandard temperature

Pilots sometimes confuse the term “density altitude” with other definitions of altitude. To review, here are some types of altitude:

  • Indicated Altitude is the altitude shown on the altimeter
  • True Altitude is the height above mean sea level (MSL)
  • Absolute Altitude is the height above ground level (AGL)
  • Pressure Altitude is the indicated altitude when an altimeter is set to 29.92 in Hg (1013 hPa in other parts of the world). It is primarily used in aircraft performance calculations and in high-altitude flight

The important thing to understand is that density altitude is an indicator of aircraft performance. The term comes from the fact that the density of the air decreases with altitude. A “high” density altitude means that air density is reduced, which has an adverse impact on aircraft performance.

A high density altitude means that air density is reduced, which has an adverse impact on aircraft performance.

Both an increase in the temperature and a decrease in the atmospheric pressure, and, to a much lesser degree, an increase in the 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.

In aviation, the density altitude is used to assess an aircraft’s aerodynamic performance. The lift generated by the aircraft’s airfoils, and the relation between its indicated airspeed (IAS) and its true airspeed (TAS), are also subject to air density changes. Furthermore, the power delivered by the aircraft’s engine is affected by the density and composition of the atmosphere.

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