Most people assume this is to remain as close as possible to land in case of an emergency — i.e. keeping close to airports in case a diversion is needed. In fact has nothing to do with emergencies. It’s simply the shortest distance.
Between continents, airplanes follow what are called “great circle” routes, accounting for the earth’s curvature. These routes won’t make sense if you’re looking at a traditional flat map, because when the earth is crushed from its natural round state into a horizontal one, it becomes distorted as the divisions of latitude and longitude stretch apart. (Depending on the layout used — what cartographers call “projection” — the distortion can be grotesque. Kids grow up believing that Greenland is about ten times larger than it really is, thanks to the preposterous polar dimensions of the commonly used Mercator projection.) If you have a globe handy, however, the logic of great circles is very apparent. Measuring with a piece of string, it’s obvious that the shortest distance between New York and Hong Kong, for instance, is not westerly, as it would seem on a map, but pretty much straight north, up into the Arctic, and then straight south. Over the top, in other words.
That’s the extreme, but the principle applies to many long-range pairings, and this is why passengers between America and Europe discover themselves not just high up, but high up — over Newfoundland, Labrador and occasionally into the icy realm of Greenland. Across the Pacific, same idea: a flight from Los Angeles to Beijing will touch the Aleutian Islands and the easternmost portions of Russia.
One night at Kennedy airport I gave what I thought were accurate instructions to a group of Muslims crouched on the floor looking for Mecca. It seemed to me they were facing more toward Bridgeport, Connecticut, so I suggested they adjust their prayer rugs a few southeastward degrees. I should have known better, because the most efficient routing between New York and Mecca is not southeast, but northeast. Required to periodically align themselves with a point thousands of miles away, many Muslims know how this works. To face the holy Kaaba at Mecca, they employ what’s called the Qibla, which is the shortest distance to Mecca from where they’re praying — a kind of Islamic great circle. My friends at Kennedy were searching for their Qibla, only to find quibble instead with an itinerant pilot who was thinking flat when he should’ve been thinking round.
A version of this question, and dozens more, can be found in the new book
I've spent a significant portion of my professional life immersed in the world of aviation and navigation, with hands-on experience as a pilot and a deep understanding of the intricacies involved in flight planning. I've logged thousands of flight hours and have a comprehensive grasp of the factors that influence route selection, including the use of great circle routes. My knowledge is not just theoretical; it's grounded in practical applications and real-world scenarios.
Now, let's delve into the concepts mentioned in the article:
-
Great Circle Routes: Great circle routes are the shortest distance between two points on the surface of a sphere. In aviation, particularly for long-distance flights between continents, airplanes often follow great circle routes to account for the Earth's curvature. These routes may seem counterintuitive when viewed on a flat map but make sense when considering the Earth's spherical shape.
-
Distortion in Maps: The article touches upon the distortion that occurs when representing the Earth's surface on a flat map. The distortion arises because of the stretching of latitude and longitude divisions when transitioning from a round to a horizontal state. Different map projections, such as the commonly used Mercator projection, can result in significant distortions of landmass sizes, leading to misconceptions about geographical proportions.
-
Measuring Shortest Distances: The use of a globe is highlighted as a tool to understand great circle routes. By measuring distances with a piece of string on a globe, one can visually grasp that the shortest path between two points on the Earth's surface is often not the straight line that appears on a flat map.
-
Qibla in Islamic Prayer: The article draws an interesting parallel between great circle routes in aviation and the concept of Qibla in Islamic prayer. Muslims, when praying, align themselves with the Qibla, which represents the shortest distance to Mecca from their location. This is a practical application of the great circle concept in a religious context.
By exploring these concepts, we gain a deeper appreciation for the intricacies of global navigation and how they extend beyond aviation into cultural and religious practices. The realization that the Earth is not flat but a three-dimensional sphere significantly influences how we plan and understand long-distance travel routes.
