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In aviation, pressure altitude is the height above a standard datum plane (SDP), which is a theoretical level where the weight of the atmosphere is 29.921 inches of mercury (1,013.2 mbar; 14.696 psi) as measured by a barometer. [2]
TA [3] - Transition Altitude - altitude at which the pilot changes the aircraft's altimeter setting (usually from QNH) to standard pressure (1013.25 hPa) TL - Transition Level - the lowest flight level available for use above the transition altitude; TLY - Transition Layer - the airspace between the transition altitude and the transition level
The rule affected only those aircraft operating under IFR when in level flight above 3,000 ft above mean sea level, or above the appropriate transition altitude, whichever is the higher, and when below FL195 (19,500 ft above the 1013.2 hPa datum in the UK, or with the altimeter set according to the system published by the competent authority in ...
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth.The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, [1] 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. [2]
Very high altitude = 3,500–5,500 metres (11,500–18,000 ft) Extreme altitude = above 5,500 metres (18,000 ft) Travel to each of these altitude regions can lead to medical problems, from the mild symptoms of acute mountain sickness to the potentially fatal high-altitude pulmonary edema and high-altitude cerebral edema .
Aircraft operating at higher altitudes (at or above what is called the transition altitude, which varies by country) set their barometric altimeters to a standard pressure of 29.92 inHg (1 atm = 29.92 inHg) or 1013.25 hPa (1 hPa = 1 mbar) regardless of the actual sea level pressure.
Altitude awareness is crucial at all times during the jump, and determines the appropriate response to maintain safety. Since altitude awareness is so important in skydiving, there is a wide variety of altimeter designs made specifically for use in the sport, and a non-student skydiver will typically use two or more altimeters in a single jump: [6]
Once above the transition altitude, the altimeter is set to the international standard atmosphere (ISA) pressure at MSL which is 1013.25 hPa or 29.92 inHg. [33]