Great Circle, Small Circle, Rhumb Line, Convergency & Conversion Angle |The Earth | GenNav EASA ATPL

This video explains the concept of Great Circle, Small Circle, Rhumb Line, Convergency & Conversion Angle, which is a part of EASA ATPL ground training syllabus. Great Circle is any line on the surface of the earth where its plane cut the earth centre.

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The shortest distance between two positions on the surface of the earth is connected via a Great Circle. When flying along great circle track will continually changing.
A small circle is any line on the surface of the earth where it plane does not cut the earth centre. All parallel of latitude is a small circle except equator.
Rhumb line is a line on the earth's surface, cutting all meridians at the same angle. When you fly a Rhumb line track, you are not flying a Great Circle Track, except when Flying along Equator and Meridian (Longitude).

Covergency is the angle that one meridian on the earth’s surface makes with another. It equals the angular difference between the measurements of the great circle at each meridian. Convergence and Convergency gave similar meaning and can be used interchangeably.
Convergence formula:
• Earth
Conv = CHLong × Sin Mean Lat
• Chart
• Polar Stereographic
Conv = CHLong

• Lambert Conformal
Conv = CHLong × Sin Parallel of Origin

• Mercator
Conv = CHLong × Sin Parallel of Origin

Conversion angle is the angle between the Great Circle Track and Rhumb Line Track.

Reference
Convergency Definition: http://aviation_dictionary.enacademic.com/1700/convergency

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