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Grid Navigation

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  • Grid Navigation

    Hi there, I am stuck with grid navigation, the way I understood the method was as follows: the convergence is the difference between the aircrafts longitude and the datum, depending on if this is east or west you then add or subtract that number from the track to get grid heading? Although I am a bit lost and this may be totally wrong!

    It does not seem to help me answer this type of question, could some one talk me through how to answer the following?

    A straight line is drawn on a polar stereographic chart between A (70N 110E) and B (70N 012W) A grid is overlaid with the Greenwich Meridian. The Track Direction from A to B in grid is?

    The possible answers are:

    A- 209
    B 029
    C 041
    D 221

    My line of thought would be to take the position 70N 110E think that is east in the northern hemisphere so it is convergence west true track best.

    I think they are heading west - 270 true because it's going from east to west.

    so 270 - 110 = 160 grid.

    but that is not even one of the available answers! so I am clearly way off!!

  • #2
    The reference to a straight line tells you that we are looking for a Great Circle Track

    270 would be the Rhumb Line track if you followed the 70N parallel of latitude- but it is not the GCT.

    Your GC True Track measured at the start point (A) is 331 and as you correctly say the grid convergence is 110 W
    So we would have 331-110 = 221

    Your GC True Track measured at the end point (B) is 209 and in this case the grid convergence would be 12E
    So we would have 209 + 12 = 221

    The grid track is the same all the way along the route.

    Hope this helps