Flight Paths and Great Circles—Or Why You Flew Over Greenland
We’re often asked why an individual flight is flying a particular route, or put another way—“why did we fly over Greenland?” Long distance flight paths are designed to be the most efficient way to get from point A to point B on the other side of the world. The shortest distance between two points is a straight line, but when a line on a globe is shown on a two-dimensional map, it looks like an arc. In the example above, an Air Canada flight from Toronto to Hong Kong looks like it’s taking a very long route to Hong Kong, but it’s actually the shortest distance between the two cities.
If we show Air Canada 15’s route on a polar plot, it’s easy to see that the flight is traveling in a straight line over the northern polar region. Flights like this one follow what are know as Great Circle routes. These routes make use of great circles, the name for the shortest distance between two points on a sphere. To see the great circle route between any two airports around the world, gcmap.com is a useful tool.
But as simple as it would be for flights to just travel along a great circle path, they rarely fly in a perfectly straight line. In the early days of aerial navigation, pilots followed a system of giant arrows on the ground to reach their destination. Concrete arrows were soon supplanted by radio beacons and radar.
Currently, much of the air navigation system relies on VOR and NDB ground stations and, increasingly, GPS-based navigation. As aircraft fly, they pass over ground station waypoints, which helps air traffic control properly space aircraft. Those waypoints are visible in this track of Qantas flight 11. It’s possible to see the shortest distance path (the red arc) versus the actual route flown.
In this zoomed image, it’s possible to see QF11 passing over the navigational aides.
But what about flights over the ocean where there are no navigational aides? Aircraft follow tracks that are made up of predetermined sets of latitude and longitude coordinates across the ocean. For example, these are the North Atlantic Tracks (the same general principle applies to the Pacific Ocean as well).
Flights enter and exit the track via a pair of waypoints on either side of the ocean so that all flights are properly aligned and air traffic control can estimate their position over the ocean correctly. You can even view each day’s NAT tracks with a Gold or Business subscription to see which tracks are active and how busy they are.
So the next time the moving map on your flight shows you heading north when you want to be going east, remember that you’re actually taking the shortest path to your destination. And you might even get to see the north pole.