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Pan Am Flight 103 was a flight from Frankfurt to Detroit with stops in London and New York.

Why after taking off in London did it fly all the way to Lockerbie instead of going directly to New York? Take a look at these pictures.

enter image description here

enter image description here

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    $\begingroup$ On your map projection, is Greenland really, really big? $\endgroup$ – Harper - Reinstate Monica Jun 27 at 23:36
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    $\begingroup$ I remember watching an episode on this aired on Air Crash Investigation/Mayday on NatGeo and recall this 747's glorious title: the Clipper Maid of the Seas. $\endgroup$ – William R. Ebenezer Jun 28 at 18:06
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The direct route you show is actually only a straight line on your map projection. The surface of the Earth is curved and the straight line between London Heathrow and New York JFK looks like this (courtesy of greatcirclemapper.net): Great Circle Route

That still does not quite get you over Scotland, but the actual flight path over the Atlantic typically uses a North Atlantic Track. These are routes, which are redefined twice a day to make optimal use of the prevailing enroute winds. Here is one example for such tracks: NAT Example (image source)

The entry points to these routes can be quite high north, therefore resulting in an optimum route over Scotland.

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    $\begingroup$ This whole topic is widely discussed. The path was, I believe, called the "Daventry Departure" from Heathrow, and was commonly used. $\endgroup$ – Michael Harvey Jun 27 at 14:34
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    $\begingroup$ Yes, the Daventry Departure goes north from Heathrow, but only about half the way to Lockerbie, so the SID is not the only explanation here. $\endgroup$ – Bianfable Jun 27 at 14:39
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    $\begingroup$ "That still does not quite get you over Scotland" It's quite a long way off! Lockerbie is about where the bottom of the "n" is in "United" and it's only about 10km inside Scotland. The great circle is about 200km from Lockerbie. $\endgroup$ – David Richerby Jun 28 at 18:44
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  1. Because the closest distance between two point on the Earth’s surface is a curve (we are NOT having a flat earth debate here and further posts, comments or answers on that subject will be promptly deleted).

  2. Said curve will run out over England, Greenland, then Canada and the United States.

  3. Airliners, because of the nature of jet routes, departure, and arrival procedures often do not fly purely direct routes to their destinations.

  4. Route selection can also be done as a compromise between to shortest route and headwinds aloft. A more circuitous route to a destination may be a little longer in mileage than a more direct route, but might save gas if headwinds are lighter on the former course.

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    $\begingroup$ That's need not be the primary reason why to fly this North. $\endgroup$ – yo' Jun 28 at 8:12
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    $\begingroup$ Yes. But you don't mention any of these. You mention only curvature and closest distance, but that does not explain why to fly that much North of it. $\endgroup$ – yo' Jun 28 at 10:59
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    $\begingroup$ If the earth were a perfect sphere (i.e. a ball, constant distance to the centre everywhere on the surface), the (closest) distance between any two points would be a straight line, it's just not very good for planes (they do well up in the air, not through the earth's interior). $\endgroup$ – JJJ Jun 28 at 17:30
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    $\begingroup$ @JJJ OK, so your comment is just being obtuse. I don't think it's at all helpful: it confused me and I know what the shortest path is, and I can only assume it's more confusing to anyone who doesn't. $\endgroup$ – David Richerby Jun 28 at 18:54
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    $\begingroup$ @DavidRicherby The term straight line is sometimes used for great circle lines because these Geodesics are straight on the curved surface (2D). The straight line you describe (tunnel) is the 3D straight line (in flat, i.e. not curved, space). $\endgroup$ – Bianfable Jun 28 at 19:19

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