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    Re: Pilots and Mariners
    From: John LeRoy
    Date: 2002 Feb 7, 22:35 +0000

    on 2/7/02 9:42 PM, Chuck Griffiths at griffiths_chuck@SI.COM wrote:
    > pilots flying around the states plotting their "courses" on aeronautical
    > charts are plotting rhumb lines on Mercator projections
    Actually aeronautical charts are hardly ever mercator projections, that is
    the projection of the earth's surface on a cylinder tangent to the earth at
    the equator with obvious distortions.
    Aeronautical charts are lambert confromal conic projections, that is the
    projection of the earth's surface on a cone whose axis is coincident with
    the axis of the earth, and which intersects the earth's surface at two
    parallels of latitude. These parallels are chosen to minimize any distortion
    for the area covered by the chart.
    > Pilots, for the most part
    > aren't taught to distinguish between rhumb line courses and great circle
    > courses.
    I can assure you that great circle navigation is very much in the mind of
    long range pilots these days. The route I flew from Chicago to Hong Kong
    proceeded over Milwaukee, Wisconsin, across a lot of Canada, then on many
    occasions, depending on wind, crossed the Bering Straits giving us somewhere
    around 100 miles over water on the whole trip! On one occasion we proceed
    well above the Arctic Circle, and make landfall on the North coast of
    Siberia proceeded over Beijing and into Hong Kong almost from the North.
    >The funny thing is, they generally follow radio navigation devices
    > that
    > guide airplanes over great circle courses. Good marine navigators, of course,
    > know that a radio bearing to a distant non-directional radio beacon is the
    > initial bearing of the great circle track to that aid, and plot it
    > accordingly.
    > These day few pilots worry about errors of that magnitude and draw radio
    > bearings as straight lines on Mercator charts. Once upon a time however,
    > flight
    > navigators were men with navigational skill to be reckoned with. Those of you
    > that are pilots might be interested to review the requirements for the flight
    > navigator certificate.(Appendix A of Part 63). Here's a
    > link:http://www.access.gpo.gov/nara/cfr/cfrhtml_00/Title_14/14cfr63_00.html
    > Chuck
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