In aviation, pressure altitude is the indicated altitude when an altimeter is set to an agreed baseline pressure setting. The baseline pressure is 1013.25 hPa, equivalent to 1013.25 millibar, or 29.92 inches of mercury. This setting is equivalent to the air pressure at mean sea level (MSL) in the International Standard Atmosphere (ISA). Pressure altitude is primarily used in aircraft performance calculations and in high-altitude flight (above the transition altitude). In radio communication, the baseline pressure setting is referred to by the Q code QNE.
Aircraft transponders report the pressure altitude; corrections for atmospheric pressure variations are applied on the ground.
The relationship between static pressure and pressure altitude is defined in terms of the properties of the International Standard Atmosphere.
Famous quotes containing the words pressure and/or altitude:
“Amid the pressure of great events, a general principle gives no help.”
—Georg Wilhelm Friedrich Hegel (1770–1831)
“On a level plain, simple mounds look like hills; and the insipid flatness of our present bourgeoisie is to be measured by the altitude of its “great intellects.””
—Karl Marx (1818–1883)