Hi all, I regulary fly Heathrow to LA...However a question burning in my mind for some time now that I never got around to asking is:-Why, when flying do you fly over up over Scotland, over Iceland, down over Greenland and Canada..Why not just fly west coast of Ireland and straight over Atlantic into eastern US?

Because the earth is a globe and not flat.

Hello Ian,>>Hi all, I regulary fly Heathrow to LA...However a question burning in my mind for some time now that I never got around to asking is:-"Why, when flying do you fly over up over Scotland, over Iceland, down over Greenland and Canada..Why not just fly west coast of Ireland and straight over Atlantic into eastern US?"The shortest distance between any two points is of course a straight line. Get a piece of paper and make a point with your pencil and mark it as "A". Make another point some distance away from the first and mark it point "B". Join the two points up with a ruler and what do you get? a straight line. Great!Now, go and get a pack of balloons from your local store and blow one up as large as you safely can. Tie it off. Now get someone else to hold the inflated balloon upright and to keep it that way. Next, go and get a black or blue marker or felt tip pen and this time, make a mark on the upper right hand quadrant of the balloon (somewhere in the "northern hemisphere" part of it). Again, take your pen and now make another mark on the lower left side of the balloon (somewhere in the "southern hemisphere" part of it).Try to use a ruler to join them up? You can't because the balloon (substitute EARTH!) is curved!Now go and get a piece of string and with one hand holding the loose end, place that over the first point "A". With the other hand, take the string reel part and open the string up and hold it over the second point "B". Notice how the string "curves" across the face of the balloon (or the EARTH) to join up with the second point. The route is, in effect, a straight line - but the path from A to B follows the curvature of the earth and is both a straight line (point to point direct) but also a curve over the Earth's surface.If you were to plot this "curve" route onto a map that is "flat" - the route itself will curve or appear to distort. have a look at your route when you plot it next time you use FSNAV in map mode!I hope this is helpful to you.Cheers,Lee

Thanks :)Also found this page http://freeearth.poly9.com/ which helped explain it!

You can also just go to a flat world map, draw a straight line from London to LA and see what countries/continents it will take you over.In FS, a GPS direct flightplan will give you the same results.

Just get a globe and a piece of thread and try it yourself to see which route would be longer.RH

>You can also just go to a flat world map, draw a straight>line from London to LA and see what countries/continents it>will take you over.>>In FS, a GPS direct flightplan will give you the same>results.Huh? A flat world map? A great circle route which represents a straight line between two points on a globe (which is like a big round ball) is distinctly different than the line you will get on a flat world map. A great circle route placed on a flat world map will look like it curves between the two points. The flight planner in FS and any line between two points on either a real world or FS GPS shows the great circle route. The flight planner map in FS will show the curve since it is a flat map showing a great circle route. The cockpit display of a great circle route will be a straight line since it represents a great circle route on a great round sphere.

Kevin- I've got a North Pacific Route Chart published by NOAA for the FAA- and great circle routes here ARE pretty much straight lines- such as for example Hawaii- Australia.The secret of course, is the map projection. This chart uses the Lambert Conformal Conic Projection and shows all the pacific air routes/waypoints etc. Very handy.Alex Reid

"The secret of course, is the map projection. This chart uses the Lambert Conformal Conic Projection..."Exactly this is what makes a straight line work as a great circle route on these type of maps. For a more detailed look at map projections check out this website:http://erg.usgs.gov/isb/pubs/MapProjections/projections.html

>Kevin- I've got a North Pacific Route Chart published by NOAA>for the FAA- and great circle routes here ARE pretty much>straight lines- such as for example Hawaii- Australia.>The secret of course, is the map projection. This chart uses>the Lambert Conformal Conic Projection and shows all the>pacific air routes/waypoints etc. Very handy.>Alex ReidOf course, but the North Pacific Route Chart is a pretty specific projection covering a specifc area, and not a "flat world map" like what most people would think of.