# Why does my flight to Japan not follow a great-circle route? **URL:** \ **Category:** Factual Questions\ **Created:** [September 17, 2019, 11:01am UTC](https://boards.straightdope.com/t/why-does-my-flight-to-japan-not-follow-a-great-circle-route/840370 "2019-09-17T11:01:47Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [September 17, 2019, 11:01am UTC](https://boards.straightdope.com/t/why-does-my-flight-to-japan-not-follow-a-great-circle-route/840370/1 "2019-09-17T11:01:47Z")
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.](https://en.wikipedia.org/wiki/Korean_Air_Lines_Flight_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.](https://thepointsguy.com/2018/03/do-ultra-long-haul-flights-pose-higher-radiation-risks/) So what’s the deal? Why isn’t my flight taking the shortest distance possible? ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [September 17, 2019, 11:20am UTC](https://boards.straightdope.com/t/why-does-my-flight-to-japan-not-follow-a-great-circle-route/840370/2 "2019-09-17T11:20:37Z")
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,](http://www.gcmap.com/mapui?P=dtw-NGO&MS=wls&DU=mi&E=90&EV=200&EU=kts) 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. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [September 17, 2019, 11:35am UTC](https://boards.straightdope.com/t/why-does-my-flight-to-japan-not-follow-a-great-circle-route/840370/3 "2019-09-17T11:35:43Z")
I learned (via Youtube? 😕 ) 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.) ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [September 17, 2019, 11:43am UTC](https://boards.straightdope.com/t/why-does-my-flight-to-japan-not-follow-a-great-circle-route/840370/4 "2019-09-17T11:43:46Z")
I’m guessing the first one is the major factor. ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [September 17, 2019, 12:09pm UTC](https://boards.straightdope.com/t/why-does-my-flight-to-japan-not-follow-a-great-circle-route/840370/5 "2019-09-17T12:09:52Z")
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. ---
**Author:** ![Lord\_Feldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lord_feldon/32/341_2.png) [@Lord\_Feldon](https://boards.straightdope.com/u/Lord_Feldon)\ **Post date:** [September 17, 2019, 12:14pm UTC](https://boards.straightdope.com/t/why-does-my-flight-to-japan-not-follow-a-great-circle-route/840370/6 "2019-09-17T12:14:31Z")
> [@Balthisar](#): > > On one flight leaving DTW, we actually flew over Greenland. Not sure how that worked out. Detroit to Shanghai via Thule is [only 271 miles/3.8% longer](http://gc.kls2.com/cgi-bin/gc?PATH=DTW-PVG%0D%0ADTW-THU-PVG&RANGE=&PATH-COLOR=red&PATH-UNITS=mi&PATH-MINIMUM=&SPEED-GROUND=&SPEED-UNITS=kts&RANGE-STYLE=best&RANGE-COLOR=navy&MAP-STYLE=) than the great circle.