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An aircraft is flying from waypoint A (32°35'S 168°12'E) to waypoint B (32°35'S 165°48'W). Determine the great circle track (°T) on arrival at waypoint B.

  • A
    083°
  • B
    097°
  • C
    263°
  • D
    277°

Refer to figure.
Convergency VS Conversion Angle

Convergency is the difference between two Great Circle Tracks at two separate positions, i.e. the difference in Great Circle Tracks between A and B.

  • Convergency = Change of Longitude x Sin of the Mean Latitude

The difference between the great circle and the rhumb line at any point is Conversion Angle. This angle between the great circle and rhumb line tracks at either end is half the convergency.

  • Conversion Angle = 1/2 Convergency

Regarding this question:

The Latitude of both points A and B is the same (32°35'S). Point B is located East of point A (crossing Greenwich Anti-Meridian) => The Rhumb line track is, therefore, 090°.

Both points are situated in the Southern Hemisphere, the Great Circle will be below the Rhumb Line Track.
Rule of Thumb (D.I.I.D.):
N. Hemisphere:
Eastbound => Heading continuously increase if maintaining a constant track.
Westbound => Heading continuously decrease if maintaining a constant track.

S. Hemisphere:
Eastbound => Heading continuously decrease if maintaining a constant track.
Westbound => Heading continuously increase if maintaining a constant track

Change of Longitude = 360° - (168°12'E + 165°48'W) = 26°
Convergency = Change of Longitude x sin (Lat)
Convergency = 26° x sin (32°35'S) = 14°
Conversion Angle = 14° / 2 = 7°

  • Initial Track at A = Rhumb Line Track + Conversion Angle
    Initial Track at A = 090° + 7° = 097°
  • Final Track at B = Initial Track at A - Convergency
    Final Track at B = 097° - 14° = 083°

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