For example, if I were in Tangier, Morocco, and wanted to fly to Whangarei, New Zealand (the antipode on the globe) – wouldn’t it be about the same time to go up instead of across?
ETA: Thanks so much for the detailed explanations!
For those who are wondering why I picked Tangier/Whangarei, it was just a hypothetical! The-Minmus-Derp explained it perfectly: *Whangarei and Tangier airports are antipodes to the point that the runways OVERLAP in that way – if you stand on the right part if the Tangier runway, you are exactly opposite a part of the Whangarei runway, making it the farthest possible flight.*
In: 2270
Every time I flew to Hong Kong for work we went over the Arctic. Usually Chicago to Hong Kong. One time when I was flying there, one of the inflight movies was The Grey with Liam Neeson. That’s not a great movie to watch while flying over the Artic for Liam Neeson reasons.
Great circle routes are the shortest distances between two points on a sphere. In an ideal world, this is the route planes would fly for max efficiency. Use the [GCMapper website](http://www.gcmap.com) to plot a GC route between points on Earth!!!
We do sometimes fly across the Northern polar regions to shorten trips. If you look at [live flights](https://flightaware.com/live/) at any given time, you’ll always see up to a couple dozen flying up to or down from the northern Arctic circle.
Flights stay over **established flight paths** for many reasons, including emergency response. If your plane goes down over Antarctica, there’s no chance you will be saved.
Those flight paths themselves take into account tons of factors (rotation of the Earth, predominant wind, where direct flights are in higher demand, population and infrastructure and more).
As other people have answered, we do, regularly.
Why were you under the impression that we didn’t?
When traveling long distances across the planet, what is the best?
If you were to slice the Earth into 2D circles, you can either do them through the center of the Earth (like longitude) or mostly missing the center of the Earth (like latitude.) We call the circles whose center is the same as the center of the Earth “great circles.” As it turns out, the absolute *shortest* distance between two points on a sphere is along a great circle. So to find the shortest route between two cities, you would draw a line from each to the center of the Earth, and then draw an arc between the two.
Of course, shortest is not always the fastest. Air movement also plays a role, and high-altitude air currents like jet streams can make air travel faster or slower. So even though you have found your great circle “shortest” route, you can make that route faster by using jet streams as an express lane, even if it means deviating outside your great circle a bit.
So now you’ve found the *fastest* route. But fast is no good if your plane crashes. You need to be fairly near to airports in case of emergencies, and try not to fly over any areas that are particularly dangerous. For this reason, you might modify your “fast” route to make the flight safer with just a little lost efficiency.
Next, you need to consider whether your flight is *legal.* Countries often designate “no fly zones” where civilian traffic is not allowed, and you probably want to stay away from military bases and countries unfriendly to yours who might not guarantee your plane’s safety (or even threaten to shoot it down.) So again, you need to modify your route to ensure it is legal.
Lastly, you need to consider traffic. Even though the skies are big, there are other planes there, and many are using the same routes. You need to make sure the route you are flying is clear so there’s little risk of running into another aircraft while taking your flight.
And this is what leads to the *best* routes: mostly based on great circles, but adjusted to account for things like air currents, safety, legality, and coordination with other flights.
You are correct that *in theory*, if you had exactly antipodal points, and you could fly in any direction from one to the other, then because of Earth being an oblate spheroid (longer circumference along the equator than across the poles) it would be shorter to fly straight north or south.
In practice, there are regulations for where aircraft can fly, for safety reasons. In addition to the political reality that if a flight overflies X country, the airline must pay that country an overflight fee (covers the use of air traffic control, plus the possibility that the country may be used for an emergency landing). Some countries charge excessive overflight fees in an attempt to discourage overflight.
The main regulations are known as “ETOPS”, which technically apply only to 2-engine aircraft, but the principles apply to aircraft in general. During flight you never want to be so far from available airports, so that in case of emergency you can go to those airports and land. And in polar areas, there usually aren’t many available airports for emergency landings.
But probably the biggest reason is the jet stream. The jet stream, which essentially is wind at an altitude that aircraft fly at, make it practically shorter to fly if you can follow it (since it gives the aircraft a tail wind). Jet streams go from west to east. (This is why you see eastbound flights try to follow the jet stream, while westbound flights try to avoid it.)
My dad was a test pilot for NASA. He did lots of long-distance flights. I asked him how they choose their routes, and he grabbed a rubber band and took me to our globe. We put the ends of the rubber band on each end of the route, and that’s the path they take, more or less. The shortest distance possible (with considerations for emergencies etc as others have noted.)
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