Jump to content

Altitude

From Wikipedia, the free encyclopedia
This is an old revision of this page, as edited by J.k.baillie (talk | contribs) at 21:19, 20 July 2006. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
For other uses see Altitude (disambiguation)

Altitude is the elevation of an object from a known level or datum. Common datums are mean sea level and the surface of the WGS-84 geoid, used by GPS. In the United States, the UK and aviation altitude is usually measured in feet. Everywhere else in the world the altitude is measured in metres.

Atmospheric pressure decreases with altitude. This principle is the basis of operation of the pressure altimeter, which is an aneroid barometer calibrated to indicate altitude instead of pressure.

Altitude in aviation

In aviation, the term altitude can have several meanings. It is a fundamental tenet of flight safety that both parties exchanging information concerning this topic are absolutely clear which definition is being used. (AFM 51-40)

  • True altitude is the elevation above mean sea level. In UK aviation radiotelephony usage, the vertical distance of a level, a point or an object considered as a point, measured from mean sea level; below the Transition Level this is referred to over the radio as altitude. (CAP413)
  • Absolute altitude or height is the elevation above a ground reference point, commonly the terrain elevation. In UK aviation radiotelephony usage, the vertical distance of a level, a point or an object considered as a point, measured from a specified datum; below the Transition Level this is referred to over the radio as height, where the specified datum is the airfield elevation. (CAP413)
  • Indicated altitude is the reading on the altimeter when it is calibrated to the local barometric pressure, referred to as the "altimeter setting". (See also QNH and QFE).
  • Pressure altitude is the elevation above a standard datum plane (typically, 1013.2 millibars). Above a transition altitude, which varies by nation, pressure altitude is used to set the altimeter. Pressure altitude divided by 100 is referred to as the flight level.
  • Density altitude is the altitude in the International Standard Atmosphere (ISA) at which the air density is equal to local conditions. Aircraft performance depends on density altitude, which is affected by barometric pressure and temperature. On a very hot day, density altitude at an airport may be so high as to preclude takeoff, particularly for helicopters or a heavily loaded aircraft.

Altitude regions

Mountain medicine recognizes three altitude regions: (Non-Physician Altitude Tutorial)

  • High altitude = 1500 m – 3500 m
  • Very High altitude = 3500 m – 5500 m
  • Extreme altitude = 5500 m – above

Travel to high altitudes leads to a range of medical problems, from the relatively mild symptoms of acute mountain sickness to the potentially fatal high altitude pulmonary oedema (HAPE) and high altitude cerebral oedema (HAPE).


The Earth's atmosphere is divided into several altitude regions: (Layers of the Atmosphere)

Altitude records

References

  • Air Navigation. Department of the Air Force. 1 December 1989. AFM 51-40.{{cite book}}: CS1 maint: year (link)
  • Radiotelephony Manual. UK Civil Aviation Authority. 1 January 1995. ISBN 0860396010. CAP413.{{cite book}}: CS1 maint: year (link)
  • "Non-Physician Altitude Tutorial". International Society for Mountain Medicine. Retrieved 22 December. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  • "Layers of the Atmosphere". JetStream, the National Weather Service Online Weather School. National Weather Service. Retrieved 22 December. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)

See also

Retrieved from "https://en.wikipedia.org/w/index.php?title=Altitude&oldid=64922403"