- Pressure altitude
In

aviation ,**pressure altitude**is the indicated altitude when analtimeter 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 thetransition 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 = 2008-10-05The 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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