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 North America and the UK altitude is usually measured in feet. Everywhere else in the world the altitude is measured in Metre s.
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
The
Altitude records
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