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on 2/7/02 9:42 PM, Chuck Griffiths at griffiths_chuck@SI.COM wrote:

 >Most
> 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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