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6.12 Altimetry
6.12.2 Define:
(a) height;
The vertical distance of a level, point or object considered as a point, measured from a specified datum.
It is also used to describe the vertical dimension of an object, such as a tower or obstacle.
(b) altitude;
The distance in feet above mean sea level (AMSL)
Indicated by a pressure altimeter whose sub-scale is set to the current QNH for the location of the aircraft.
(c) mean sea level (MSL);
The average height of the sea surface, normally taken from long-term records of tide heights at any given place.
(d) AMSL;
Above Mean Sea Level
Using Mean Sea Level (MSL) as the datum, any height above mean sea level is referred to as Altitude, measured in feet.
(e) ground level;
Ground Level is any ground or water surface.
(f) AGL;
Above Ground Level
The height of an aircraft above ground level.
May be determined by radio altimeter (RadAlt), or by substracting the elevation of the ground from the flight altitude.