I know that pressure altitude for a certain pressure is defined to be the altitude in the standard atmosphere which has that pressure.

But I can't find whatever standard, regulation, or glossary officially defines it to be so. I tried to look in the AIM, the P/CG, a search of the FARs for "pressure altitude" wading through a ton of results, and what searchable partial copies of the US Standard Atmosphere of 1976 I could find. I don't have access to a copy of the ISO standard that defines the International Standard Atmosphere.

Does anyone know of an FAA, ICAO, or ISO document providing this definition?

  • $\begingroup$ There's an FAA document that contains a definition at faa.gov/regulations_policies/handbooks_manuals/aviation/…. $\endgroup$
    – Terry
    Aug 16, 2014 at 2:20
  • $\begingroup$ An unanswered part of this question asks what document defines the International Standard Atmosphere. The answers below do define pressure altitude in terms of it, but the official definition of the international standard atmosphere is located in ICAO Doc 7488. $\endgroup$ Feb 24, 2016 at 18:10

2 Answers 2


Pressure Altitude

As defined by FAA in the Pilot's Handbook of Aeronautical Knowledge:

Pressure altitude is the height above a standard datum plane (SDP), which is a theoretical level where the weight of the atmosphere is 29.92 "Hg (1,013.2 mb) as measured by a barometer. An altimeter is essentially a sensitive barometer calibrated to indicate altitude in the standard atmosphere. If the altimeter is set for 29.92 "Hg SDP, the altitude indicated is the pressure altitude. As atmospheric pressure changes, the SDP may be below, at, or above sea level. Pressure altitude is important as a basis for determining airplane performance, as well as for assigning flight levels to airplanes operating at or above 18,000 feet.

The pressure altitude can be determined by either of two methods: 1. Setting the barometric scale of the altimeter to 29.92 and reading the indicated altitude. 2. Applying a correction factor to the indicated altitude according to the reported altimeter setting.

More info from the FAA here.

From Docket No. 18334, 54 FR 34304, Aug. 18, 1989, as amended by Amdt. 91-314, 75 FR 30193, May 28, 2010

§91.217 Data correspondence between automatically reported pressure altitude data and the pilot's altitude reference.

(a) No person may operate any automatic pressure altitude reporting equipment associated with a radar beacon transponder—

(1) When deactivation of that equipment is directed by ATC;

(2) Unless, as installed, that equipment was tested and calibrated to transmit altitude data corresponding within 125 feet (on a 95 percent probability basis) of the indicated or calibrated datum of the altimeter normally used to maintain flight altitude, with that altimeter referenced to 29.92 inches of mercury for altitudes from sea level to the maximum operating altitude of the aircraft; or

(3) Unless the altimeters and digitizers in that equipment meet the standards of TSO-C10b and TSO-C88, respectively.

(b) No person may operate any automatic pressure altitude reporting equipment associated with a radar beacon transponder or with ADS-B Out equipment unless the pressure altitude reported for ADS-B Out and Mode C/S is derived from the same source for aircraft equipped with both a transponder and ADS-B Out.

ICAO has described how they calculate Pressure Altitude

Pressure Altitude versus Pressure


In relation to QNE:

When the ISA mean sea level standard pressure of 1013.2 hPa is set on an aircraft altimeter subscale, the height so indicated upon landing at an airfield is known as the QNE reading. More widely, this is also the PRESSURE ALTITUDE, which is alternatively defined as the height of any level in the international standard atmosphere (ISA-see above), above the level corresponding to a pressure of 1013.2 hPa.

Here is a free tool to calculate standard atmospheric conditions (ISA) at a given geometric or pressure altitude and ambient temperature.

  • 2
    $\begingroup$ however comprehensive this answer is, I don't think any of the sources cited are authoritative. Even the PHAK is not regulatory. $\endgroup$
    – rbp
    Jan 13, 2015 at 0:34

Pressure-altitude is defined in ICAO Chicago Convention, annex 2 - Rules of the Air:

Pressure-altitude. An atmospheric pressure expressed in terms of altitude which corresponds to that pressure in the Standard Atmosphere.* * As defined in Annex 8

Annex 8 - Airworthiness of Aircraft:

enter image description here
......enter image description here


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.