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Altitude

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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 as altitude increases. This principle is the basis of operation of the pressure altimeter, which is an aneroid barometer calibrated to indicate altitude instead of pressure. It is the fall in pressure that leads to a shortage of oxygen (hypoxia) in humans on ascent to high altitude. (Altitude pressure calculator)

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; this is referred to over the radio as altitude. (see QNH) (CAP413)
  • 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; this is referred to over the radio as height, where the specified datum is the airfield elevation (see QFE) (CAP413)
  • Indicated altitude is the reading on the altimeter.
  • Pressure altitude is the elevation above a standard datum plane (typically, 1013.2 millibars). Pressure altitude divided by 100 feet is referred to as the flight level; so when the altimeter reads 18,000 ft on the standard pressure setting the aircraft is said to be at "Flight level 180". Below FL180, altitudes are read in thousands, pronounced "one three thousand" for 13,000, "seven thousand" for 7,000 etc.
  • Density altitude is the altitude corrected for non-ISA International Standard Atmosphere (ISA) conditions at which the air density is unequal to ISA 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.
  • Absolute altitude is the height of the aircraft above the terrain over which it is flying.

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 (HACE). These conditions are caused by the profound hypoxia associated with travel to high altitudes.


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

Altitude records

  • August 1783 — 24 m Jean Francois Pilatre in a hot-air balloon.
  • 15 October, 1783 — 26 m Pilâtre de Rozier in a Montgolfier tethered balloon.
  • 1 December, 1783 — 610 m Professor Charles and assistant Robert in Charliere, his hydrogen-filled balloon.
  • 1 December, 1783 — 2.7 km Professor Charles in Charliere, his hydrogen-filled balloon.
  • 1784 — 4 km Pilâtre de Rozier and the chemist Proust in a Montgolfier.
  • 18 July, 1803 — 7.28 km Etienne Gaspar Robertson and Lhoest in a balloon.
  • 1839 — 7.9 km Charles Green and Spencer Rush in a free balloon.
  • 5 September, 1862 — 11.887 km Coxwell and English physicist Glaisher in a balloon.
  • November 1927 — 13.222 km Captain Hawthorne C. Gray of the US Army Air Corps. in a balloon.
  • 27 May 1931 — 15.787 km Auguste Piccard & Paul Kipfer in a hydrogen balloon.
  • 1932 — 16.2 km Auguste Piccard & Max Cosyns in a hydrogen balloon.
  • 30 September 1933 — 18.501 km USSR balloon.
  • 20 November 1933 — 18.592 km Auguste & Jean Piccard in Century of Progress balloon.
  • 30 January 1934 — 21.946 km USSR balloon.
  • 10 November 1935 — 22.066 km Anderson & Stevens in Explorer II.
  • 4 May 1961 — 34.668 km Victor Prather & Malcolm Ross of the US Navy in Strato-Lab V, a zero-pressure balloon.
  • 17 July 1962 — 95.94 km Robert White in an X-15 aircraft.
  • 19 July 1963 — 106.01 km Joseph Walker in an X-15 aircraft.
  • 22 August 1963 — 107.96 km Joseph Walker in an X-15 aircraft.
  • 04 October 2004 — 111.99 km (367,442 feet). Brian Binnie in Scaled Composites SpaceShipOne

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)
  • "Altitude pressure calculator". Apex (altitude physiology expeditions). Retrieved 8th August. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)

See also

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