Pressure altitude


Pressure altitude

In aviation, pressure altitude is the indicated altitude when an altimeter is set to an agreed baseline pressure setting. This setting - 101,325 Pa, equivalent to 1013.25 millibar (or hectopascals), or 29.92 inches Hg - 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. [cite web
last = Brandon
first = John
authorlink =
coauthors =
title = Altitude and altimeters
work =
publisher = Recreational Aviation Australia Inc
date = 2007-04-12
url = http://www.auf.asn.au/groundschool/umodule3.html#altitude
format =
doi =
accessdate = 2008-10-05
]

The relationship between static pressure and pressure altitude is defined in terms of the properties of the International Standard Atmosphere. Up to 36,090 ft this can be expressed as:

z =left (1-left(frac{P_o}{101.325} ight)^{0.190263} ight ) imes frac{288.15}{0.00198122}

Where:

*z = pressure altitude (feet)
*P_o = static pressure (kPa)

For example:

implification

One simplification of the Pressure Altitude that is a bit more practical to pilots than the above formula is the following:

A_{pressure}~=~A_{ASL}~+~(~29.92~inHg-P_{at~Altitude})*1000~ft/inHg.

Where
* A_{pressure} = Pressure Altitude (z of the previous equation) in feet,
* A_{ASL} = Physical Altitude above Sea Level in feet,
* P_{at~Altitude} = Measured or estimated Pressure at the Altitude of interest in inches of mercury (inHg).

ee also

*QNH
*flight level
*density altitude
*Standard conditions for temperature and pressure
*Barometric formula

References


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Look at other dictionaries:

  • pressure altitude — noun : the altitude corresponding to a given pressure in a standard atmosphere * * * Meteorol. the altitude for a given pressure in a standard atmosphere, such as that registered by a pressure altimeter. * * * pressure altitude noun (aeronautics) …   Useful english dictionary

  • pressure altitude — An atmospheric pressure expressed in terms of altitude which corresponds to that pressure in the standard atmosphere (ICAO). It is the height of an aircraft as measured from an assumed sea level atmospheric pressure level of 1013.2 hectopascals… …   Aviation dictionary

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  • pressure altitude — An atmospheric pressure expressed in terms of altitude which corresponds to that pressure in the standard atmosphere. See also altitude …   Military dictionary

  • pressure altitude — Meteorol. the altitude for a given pressure in a standard atmosphere, such as that registered by a pressure altimeter. * * * …   Universalium

  • Altitude — For other uses, see Altitude (disambiguation). Not to be confused with Attitude. Altitude or height is defined based on the context in which it is used (aviation, geometry, geographical survey, sport, and more). As a general definition, altitude… …   Wikipedia

  • altitude datum — The arbitrary level from which vertical displacement is measured. The datum for height measurement is the terrain directly below the aircraft or some specified datum; for pressure altitude, the level at which the atmospheric pressure is 29.92… …   Military dictionary

  • altitude — i. The vertical distance of a level, a point, or an object considered as a point, measured from mean sea level (ICAO). In the case of aircraft in flight, it is normally expressed in flight levels or hundreds of feet. For example, an aircraft… …   Aviation dictionary

  • altitude datum — The arbitrary level from which vertical displacement is measured. The datum for height measurement is the terrain directly below the aircraft or some specified datum; for pressure altitude, the level at which the atmospheric pressure is 1013.2… …   Aviation dictionary

  • altitude — The vertical distance of a level, a point or an object considered as a point, measured from mean sea level. See also density altitude; drop altitude; elevation; minimum safe altitude; pressure altitude; transition altitude; true altitude …   Military dictionary


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