Pressure altitude
Encyclopedia
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.
The relationship between static pressure and pressure altitude is defined in terms of the properties of the International Standard Atmosphere.
Aviation
Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...
, pressure altitude is the indicated altitude when an altimeter
Altimeter
An altimeter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth underwater.-Pressure 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
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
) in the International Standard Atmosphere (ISA
International Standard Atmosphere
The International Standard Atmosphere is an atmospheric model of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes. It has been established to provide a common reference for temperature and pressure and consists of tables of...
). 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.
The relationship between static pressure and pressure altitude is defined in terms of the properties of the International Standard Atmosphere.
See also
- QNHQNHQNH is one of the many Q codes. It is defined as, "barometric pressure adjusted to sea level." It is a pressure setting used by pilots, air traffic control , and low frequency weather beacons to refer to the barometric setting which, when set on an aircraft's altimeter, will cause the altimeter to...
- Flight LevelFlight levelA Flight Level is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of 1013.25 hPa , the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either...
- density altitudeDensity altitudeDensity 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, or, in other words, the height when measured in terms of the density of the air rather than the distance from the ground...
- Standard conditions for temperature and pressureStandard conditions for temperature and pressureStandard condition for temperature and pressure are standard sets of conditions for experimental measurements established to allow comparisons to be made between different sets of data...
- Barometric formulaBarometric formulaThe barometric formula, sometimes called the exponential atmosphere or isothermal atmosphere, is a formula used to model how the pressure of the air changes with altitude.-Pressure equations:...