Why does my flight to Japan not follow a great-circle route?

Factual Questions
1

I have flown several times between Detroit and Nagoya (Japan). A great-circle route would have us flying across north-central Alaska, but it never does. It invariably flies a more southerly route, generally over the Aleutian islands. This adds ~150 miles to a 6500-mile flight.

I can think of three possible reasons for this:

  • it stays away from the Kamchatka peninsula, avoiding anything like what happened to Korean Air 007.

  • it avoids disadvantageous jet streams, reducing headwinds and/or increasing tailwinds. When flying to Japan, they tend to fly a more northerly route, e.g. passing over Anchorage (southern coast of the AK mainland), and when returning to Detroit, they tend to fly a more southerly route, e.g. passing over Unalaska (down in the Aleutian chain). (Or maybe it’s the other way around, I can’t remember.) The weird thing is that both of these routes deviate to the same side of the great-circle route. If a northerly route is better in one direction, and a southerly route is better in the other direction, wouldn’t the outbound and return flight paths be on opposite sides of the GC route?

-it avoids/reduces the radiation exposure associated with transpolar flight.

So what’s the deal? Why isn’t my flight taking the shortest distance possible?

2

One possibility (though I don’t know if it’s the primary one) is that the airline needs/wants to stay within a certain distance of an emergency diversion airport at all times. Here’s a map showing the great circle route, with areas that are 90 minutes from a suitable diversion airport highlighted. You can see that there are several suitable candidates in the Aleutians, but not nearly so many in the high arctic.

3

I learned (via Youtube? :confused: ) that the Russian Federation charges a rather high fee for overflying its airspace. (It’s not trying to discourage over-flights; it just wants the money!)

(One of the passengers on KAL007 was my occasional drinking buddy. He might have offered me a job; I might have been on that flight.)

4

I’m guessing the first one is the major factor.

5

I used to fly rather frequently between Detroit and Shanghai, and most often the route took us over Russia. Sometimes we got close to North Korea and the route map showed a severe change in route. On one flight leaving DTW, we actually flew over Greenland. Not sure how that worked out.

6

Detroit to Shanghai via Thule is only 271 miles/3.8% longer than the great circle.