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6.10 Position Referencing
6.10.2 Define:
(a) Ground Position;
The point on the Earth’s surface directly beneath the aircraft at any given moment.
(b) Dead Reckoning (DR) Position;
A Dead Reckoning position is the aircraft’s estimated ground position determined by calculation, using the previously known position, heading, airspeed, time, and estimated wind.
Because the values used (such as wind, heading, and airspeed) are not perfectly accurate, the calculated DR position will always contain some error.
(c) Fix;
A fix is the accurately determined position of an aircraft, obtained from two or more independent observations or position lines.
These observations may be obtained using visual bearings, radio navigation aids, or electronic navigation systems.
(d) Position Line.
A Position Line is a line drawn on a chart that passes through the aircraft’s position at a particular time, based on an observation.
The aircraft is not flying along the position line.
The line simply shows that the aircraft is somewhere on that line at that moment, but the exact point is not known.
When two position lines intersect, their crossing point shows the aircraft’s position, called a Fix.