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Glossary - Navigation

Above Ground Level AGL Vertical distance above the ground
Above Mean Sea Level AMSL The average level of the sea water. The ellipsoid known as World Geodetic System 84 is used to define mean sea level for aviation. AMSL is used as a reference in defining Altitude.
Actual Time of Arrival ATA The time (to the nearest minute) at which the navigator of an aircraft logs the aircraft's position as overhead a nominated position.
Actual Time of Departure ATD The time (to the nearest minute) at which the navigator of an aircraft deems the aircraft to have set course on departure from immediately overhead the point of departure or airfield of departure.
Aerodrome of Departure ADEP The aerodrome where the flight commences from.
Aerodrome of Destination ADES The intended aerodrome where the flight concludes.
Agonic Line The line on the earth's surface along which the value of magnetic variation is zero degrees.
Airfield Elevation The designated height of an airfield in feet above mean sea level. This is the height of the highest point on the landing area of the airfield.
Altitude ALT The distance in feet above mean sea level (AMSL), indicated by a pressure altimeter whose subscale is set to the current QNH for the location of the aircraft.
Area Navigation RNAV (pronounced "AR-NAV")
A method of navigation which permits aircraft operation on any desired flight path within the coverage of ground- or space-based navigation aids or within the limits of the capability of self-contained aids, or a combination of these.
Note: Area navigation includes performance-based navigation as well as other operations that do not meet the definition of performance-based navigation.
Automatic Direction Finder ADF The airborne component of the radio navigation system which has been developed to provide the navigator with relative bearing information to a medium frequency transmitter located on the ground
Bearing The angular direction of a distant point expressed in degrees from a selected datum such as the nose of the aircraft (gives relative bearing).
Compass Swing (nautical) The process of swinging and compensating a ship or aircraft compass by determining and reducing the deviation coefficients and recording the residual deviations; now done by computer.
Flight Level The height of an aircraft as read from a pressure altimeter whose sub-scale is set to 1013.25 hPa and normally expressed to the nearest 500 ft.
Global navigation satellite system GNSS A means of navigation accurately by a global network of satellites. Most common system is GPS
Great Circle A circle on the earth where the centre of the circle cuts through the centre of the earth.
International Date Line A line of the earth's surface, across which the date changes by 1 day. The line approximately follows the 180 degree meridian but its position is adjusted to maintain the integrity of island groups and countries.
Knot kt A speed of 1nm/hr
Latitude LAT The angular distance from the equator to a point in the Northern or Southern Hemisphere measured along a meridian of longitude and expressed in degrees and relevant subdivisions if appropriate.
Local Mean Time LMT The time at a given meridian of longitude as determined by the position of the sun in terms of longitude in relation to that meridian.
Lubber Line The fixed datum point inscribed on the face of an aircraft instrument, marking the point from which data are read. It is usually applied to a compass or bearing indicator as the point from which bearings are read in degrees.
Magnetic Bearing MB The angular difference between the direction of an object and the direction of the magnetic North Pole at a place, expressed in degrees counted clockwise from the direction of magnetic north.
Magnetic Direction The direction in degrees as indicated by a magnetic compass in relation to the direction of the magnetic North Pole, corrected for any errors existing in the compass installation.
Magnetic North At any given place, it is the actual direction of the horizontal component of the Earth's local magnetic field.
Meridian of Longitude  
North Georgaphic Pole The point on the earth's surface which marks the northern end of the axis about which the earth rotates.
North Magnetic Pole The geographic location of one end of the geomagnet which allows a magnetic compass to sense direction. This point is currently located to the north of the Queen Elisabeth Islands, themselves north of Canada.
Reduced vertical separation minimum RVSM  
Required navigation performance RNP  
Small Circle  
Standard instrument arrival STAR  
Standard instrument departure SID  
Waypoint Waypoints are enroute positions, indicating a change in track direction, or a point along the route.

Usually associated with GPS or GNSS Navigation.