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While flying in the northern hemisphere, an aircraft has a VOR RMI reading of 285° M to ‘BUB’ VOR. Given the following information, what bearing should be plotted from the VOR to the aircraft on a Mercator chart?

Variation at the aircraft: 4°E
Variation at the station: 8°E
Earth convergence between the aircraft and the VOR: 6°

  • A
    112° T
  • B
    116° T
  • C
    108° T
  • D
    113° T

The bearing to be plotted on a Mercator Chart from VOR to the aircraft equals the Rhumb Line True Track from VOR to the aircraft at the VOR.

Magnetic Bearing from the aircraft to the VOR (QDM) = RMI Reading = 285º

Variation at VOR = 8ºE (Magnetic North is 8º East of the True North)

True Bearing from the aircraft to the VOR (QUJ) = QDM + 8ºE = 285º + 8º = 293º

True Bearing from the aircraft to the VOR (QUJ) equals the Great Circle True Track from the aircraft to the VOR at the VOR.

Great Circle True Track from the aircraft to the VOR at the VOR = 293º

Great Circle True Track from the VOR to the aircraft at the VOR = Great Circle True Track from the aircraft to the VOR at the VOR - 180º = 113º

The difference between great circle direction and rhumb line direction joining two points is called conversion angle and it is equal to half of the convergency (earth convergence) for the same two points.

Rhumb Line True Track from the VOR to the aircraft at the VOR = Great Circle True Track from the VOR to the aircraft at the VOR + Conversion Angle

Conversion angle = ½ Convergency = ½ x 6º = 3º

  • Rhumb Line True Track from the VOR to the aircraft at the VOR = 113º + 003º = 116º

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