Density altitude
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Density altitude is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation. "Density Altitude" is the pressure altitude adjusted for non-standard temperature.
Both increase in temperature and increase in humidity cause a reduction in air density. Thus in hot and humid conditions the density altitude at a particular location may be significantly higher than the geometric altitude.
Air density is perhaps the single most important factor affecting airplane performance. It has a direct bearing on the power output of the engine, efficiency of the propeller, and the lift generated by the wings.
[edit] Calculation
Density altitude can be calculated from atmospheric pressure and temperature (assuming dry air).
![\mathrm{DA} = 145426 \left[1-\left(\frac{P_0/P_{SL}}{\mathrm{T}/T_{SL}}\right)^b\right]](../../../math/c/e/c/cec8bc7c476f6cbf9fdfd196491e214a.png)
where
DA = density altitude in feet
P0 = atmospheric (static) pressure
PSL = standard sea level atmospheric pressure (101.325 kPa)
T = true (static) air temperature in Kelvin (K) [add 273.15 to the Celsius (C)] figure
TSL = standard sea level air temperature (288.15 K)
b = 0.235
[edit] References
- (1 December 1989) Air Navigation. Departments of the Air Force and Navy. AFM 51-40 / NAVAIR 00-80V-49.
- Air Density and Density Altitude. Retrieved on January 9, 2007.
- Advisory Circular AC 61-23C, Pilot's Handbook of Aeronautical Knowledge, U.S. Federal Aviation Administration, Revised 1997
