Shortest Path between the US and UK

Now wait. Are we here for a shortest path Dijikstra's algorithm, Geography, Flight dynamics/kinetics, Psychology, SQL 2008 Spatial Data Type or something? Well almost all but everything in part :)

Longtime back, I had a doubt running on the back of my mind which nobody seemed to completely answer. Why does a flight-path from UK to US or vice-versa go along an elliptical path in a planar map covering Ireland, Iceland, Greenland, Canada and then to USA and instead not go in a straight line moving Trans-Atlantic thereby saving a lot of time and fuel?

(The Red Line is what I expect, but the Black line is how it goes. You.. You.. Damn airline.. Its our money and our time !! )

I have got a variety of unsatisfactory answers but the closest till date which I thought right was - 'The aircraft wants to travel close to the shore as much as possible to force an emergency landing if at all necessary'. That was given by one of my Managers during a chit-chat, and seemed to satisfy me until today when I found what the original reason was!

I was randomly looking into Spatial Data Types in SQL Server 2008 for a reason i-don't-know-why and there I saw the answer right in front of my eyes. Mouth wateringly delicious ! Why didn't I even think about this in perspective!? Lifting it straight from there.

The shortest distance between two points is a straight line. But, a straight line on a flat-earth model is far different than a straight line on an ellipsoidal model. To demonstrate, consider the shortest path from Redmond, WA, USA to Cambridge, England, UK:

On this planar projection, it certainly looks like the shortest path. Even when examined on a 3D model, it looks correct:

But, if the camera is moved towards the North Pole, then the error becomes apparent:

In the ellipsoidal model, the shortest path between the points is not the red line, which roughly parallels the lines of Latitude, but rather the black arrow! Converted back to a planar projection, this actual shortest path appears curved:

(in this view, the black curve was [hastily] plotted by hand)

Original Source Credit: http://jasonfollas.com/blog/archive/2008/05/16/sql-server-2008-spatial-data-part-7.aspx