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Diagram showing the face of the "three-pointer" sensitive aircraft altimeter displaying an altitude of 10,180 ft (3,100 m). Reference pressure of about 29.92 inHg (1013 hPa) is showing in the Kollsman window. An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. [1]
A barometric altimeter, used along with a topographic map, can help to verify one's location. It is more reliable, and often more accurate, than a GPS receiver for measuring altitude; the GPS signal may be unavailable, for example, when one is deep in a canyon, or it may give wildly inaccurate altitudes when all available satellites are near the horizon.
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 ...
The altimeter is adjustable for local barometric pressure which must be set correctly to obtain accurate altitude readings, usually in either feet or meters. As the aircraft ascends, the capsules expand and the static pressure drops, causing the altimeter to indicate a higher altitude. The opposite effect occurs when descending.
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]
When taken together, autonomous civilian GPS horizontal position fixes are typically accurate to about 15 meters (50 ft). These effects also reduce the more precise P(Y) code's accuracy. However, the advancement of technology means that in the present, civilian GPS fixes under a clear view of the sky are on average accurate to about 5 meters ...
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
A geoid is needed to convert the 3D position to sea-level elevation. Pressure altimeter measuring atmospheric pressure, which decreases as altitude increases. Since atmospheric pressure varies with the weather, too, a recent local measure of the pressure at a known altitude is needed to calibrate the altimeter. Stereoscopy in aerial photography.
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