# Why are many flight plans not straight lines? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [December 22, 2013, 5:56am UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938 "2013-12-22T05:56:31Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [December 22, 2013, 4:09pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/21 "2013-12-22T16:09:54Z")
all flights are not straight lines, you would fly into buildings and hills. it’s all spherical. ---
**Author:** ![JerrySTL](https://avatars.discourse-cdn.com/v4/letter/j/e274bd/32.png) [@JerrySTL](https://boards.straightdope.com/u/JerrySTL)\ **Post date:** [December 22, 2013, 4:27pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/22 "2013-12-22T16:27:14Z")
Another reason is that some aircraft are limited for over water travel. They need to be within X number of miles from land. Places like Newfoundland, Greenland, and Iceland have airports which is nice to know if your 2 engine jet aircraft loses an engine. ---
**Author:** ![Frazzled](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/frazzled/32/3368_2.png) [@Frazzled](https://boards.straightdope.com/u/Frazzled)\ **Post date:** [December 22, 2013, 4:43pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/23 "2013-12-22T16:43:01Z")
Take a look at number 38 on this link. It’s a map showing the longest straight line over water in the world. On the 2d map it’s curved, but when you watch the animation on the globe you can see it’s straight. [http://beforeitsnews.com/watercooler-topics/2013/08/40-amazing-maps-you-have-never-seen-2433780.html](http://beforeitsnews.com/watercooler-topics/2013/08/40-amazing-maps-you-have-never-seen-2433780.html) ---
**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:** [December 22, 2013, 7:14pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/24 "2013-12-22T19:14:04Z")
> [@Alessan](#): > > It’s not longer, it’s shorter. > > I suggest you get a globe and a piece of string and check for yourself. You’d be very surprised who deceptive flat maps can be. The modern equivalent is to use [Google Earth](http://www.google.com/earth/) and use the line tool to draw a straight line between two points. ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [December 22, 2013, 7:44pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/25 "2013-12-22T19:44:14Z")
> [@Giles](#): > > The most commonly used map projection is Mercator’s, which correctly maps directions like north-east, but distorts everything else, including areas (which is why Greenland looks larger that India). When you plot these shortest lines on map using Mercator’s projection, they don’t lok the shortest because of the way that the projection distorts things. This looks like as good an excuse as any to link [this clip](http://www.youtube.com/watch?v=n8zBC2dvERM). ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [December 22, 2013, 7:54pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/26 "2013-12-22T19:54:43Z")
> [@robert\_columbia](#): > > Interesting. How do US airlines handle flying to Jamaica? If wanted to fly from NYC to Kingston, Jamaica, the flight path goes right over Cuba. Will US airlines fly over Cuba? Yes, they can and do fly over Cuba or sometimes just off to the side of it. The U.S. has a military base on Cuba after all. There are North-South air corridors over Cuba that can be used just by requesting routine prior authorization even for U.S. airlines. I have flown over Cuba or just off the coast of it a bunch of times going from the Northeast U.S. to the US Virgin Islands. ---
**Author:** ![FXMastermind](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fxmastermind/32/7289_2.png) [@FXMastermind](https://boards.straightdope.com/u/FXMastermind)\ **Post date:** [December 22, 2013, 8:43pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/27 "2013-12-22T20:43:29Z")
> [@Kobal2](#): > > This looks like as good an excuse as any to link [this clip](http://www.youtube.com/watch?v=n8zBC2dvERM). “You can’t do that!” “Why not?” “Because it’s freaking me out!” ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [December 22, 2013, 8:55pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/28 "2013-12-22T20:55:03Z")
> [@Spectre\_of\_Pithecanthropus](#): > > Stretching a string across the surface of a globe can be surprising at times, like the fact that if you wanted to fly from L.A. to Johannisberg you start out flying slightly north of due East. Assuming you mean Johannesburg‎, South Africa, from Los Angeles, USA, show me how that works on a globe map. ---
**Author:** ![JRDelirious](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jrdelirious/32/9531_2.png) [@JRDelirious](https://boards.straightdope.com/u/JRDelirious)\ **Post date:** [December 22, 2013, 9:24pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/29 "2013-12-22T21:24:12Z")
Looks more like East itself at departure from LAX, bearing 93.8 ([bearings map](http://www.gcmap.com/mapui?P=lax-joh&MS=wls&MC=0n60w&DU=mi)); ([ortographic map](http://www.gcmap.com/mapui?P=lax-joh&MS=wls&MP=o&MC=10N50W&DU=mi)) ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [December 22, 2013, 9:34pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/30 "2013-12-22T21:34:10Z")
> [@Spectre\_of\_Pithecanthropus](#): > > Stretching a string across the surface of a globe can be surprising at times, like the fact that if you wanted to fly from L.A. to Johannisberg you start out flying slightly north of due East. > [@JRDelirious](#): > > Looks more like East itself at departure from LAX, bearing 93.8 ([bearings map](http://www.gcmap.com/mapui?P=lax-joh&MS=wls&MC=0n60w&DU=mi)); ([ortographic map](http://www.gcmap.com/mapui?P=lax-joh&MS=wls&MP=o&MC=10N50W&DU=mi)) Due East won’t get you below the Equator, ever. Slightly “north of due East” may get you to South Africa, but that’s the long way. East, then south, or slightly south of East (93.8 degrees), may work. **SoP** , it may be the orthographic map that made you think that you had to “start out flying slightly north of due East,” but it doesn’t work that way. ---
**Author:** ![Ximenean](https://avatars.discourse-cdn.com/v4/letter/x/aca169/32.png) [@Ximenean](https://boards.straightdope.com/u/Ximenean)\ **Post date:** [December 22, 2013, 9:58pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/31 "2013-12-22T21:58:27Z")
Surely all great circles, except ones directly over the poles, must go due east/west at some points? Anyway, maybe \*\*SoP \*\*meant to say slightly north of west? ---
**Author:** ![Ximenean](https://avatars.discourse-cdn.com/v4/letter/x/aca169/32.png) [@Ximenean](https://boards.straightdope.com/u/Ximenean)\ **Post date:** [December 22, 2013, 10:05pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/32 "2013-12-22T22:05:07Z")
…except of course that way round the great circle would be further :smack: ---
**Author:** ![Enola\_Gay](https://avatars.discourse-cdn.com/v4/letter/e/3ab097/32.png) [@Enola\_Gay](https://boards.straightdope.com/u/Enola_Gay)\ **Post date:** [December 22, 2013, 10:26pm UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/33 "2013-12-22T22:26:08Z")
Wow, learn/realize something new every day. I always assumed it was a longer route, but they chose it for strategic reasons. Forgot we live on a sphere… ---
**Author:** ![straight\_man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/straight_man/32/3027_2.png) [@straight\_man](https://boards.straightdope.com/u/straight_man)\ **Post date:** [December 23, 2013, 12:03am UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/34 "2013-12-23T00:03:55Z")
> [@Musicat](#): > > Due East won’t get you below the Equator, ever. Slightly “north of due East” may get you to South Africa, but that’s the long way. East, then south, or slightly south of East (93.8 degrees), may work. Note that your directional heading doesn’t stay the same for an entire journey on a globe —it changes slowly. Yes, you will eventually cross the equator if you go in a straight line that starts out heading due east. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [December 23, 2013, 1:13am UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/35 "2013-12-23T01:13:01Z")
> [@straight\_man](#): > > Note that your directional heading doesn’t stay the same for an entire journey on a globe —it changes slowly. Yes, you will eventually cross the equator if you go in a straight line that starts out heading due east. Not if you head east (90º) and continue heading east (90º), then continue heading east, etc. You are assuming a “straight” line that begins with an eastern heading, then bends with the earth. If you bend with the earth, you are no longer heading east, and your compass heading will change. You will never cross the Equator. ---
**Author:** ![Siam\_Sam](https://avatars.discourse-cdn.com/v4/letter/s/d78d45/32.png) [@Siam\_Sam](https://boards.straightdope.com/u/Siam_Sam)\ **Post date:** [December 23, 2013, 1:18am UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/36 "2013-12-23T01:18:30Z")
Flying across the Pacific, we always seem to be doing an arc. I’ve often wondered if this was due to the curvature of the globe really making it the shortest distance or if it’s to stay closer to land in the event an emergency landing is called for. ---
**Author:** ![PaulParkhead](https://avatars.discourse-cdn.com/v4/letter/p/7ea924/32.png) [@PaulParkhead](https://boards.straightdope.com/u/PaulParkhead)\ **Post date:** [December 23, 2013, 1:29am UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/37 "2013-12-23T01:29:14Z")
> [@Siam\_Sam](#): > > Flying across the Pacific, we always seem to be doing an arc. I’ve often wondered if this was due to the curvature of the globe really making it the shortest distance or if it’s to stay closer to land in the event an emergency landing is called for. Well, [here’s the great circle route](http://www.gcmap.com/mapui?P=BKK-LAX&MS=wls&DU=mi) (that is, the shortest one) from Bangkok to LAX. On a flat map it does look like an arc, but it’s undoubtedly the shortest straight line path. You can plug in different airports at that site, as others have done upthread. Edit: [This projection](http://www.gcmap.com/mapui?P=BKK-LAX&MS=wls&MP=p&DU=mi) makes it a bit clearer. ---
**Author:** ![Ximenean](https://avatars.discourse-cdn.com/v4/letter/x/aca169/32.png) [@Ximenean](https://boards.straightdope.com/u/Ximenean)\ **Post date:** [December 23, 2013, 1:32am UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/38 "2013-12-23T01:32:09Z")
> [@Siam\_Sam](#): > > Flying across the Pacific, we always seem to be doing an arc. I’ve often wondered if this was due to the curvature of the globe really making it the shortest distance or if it’s to stay closer to land in the event an emergency landing is called for. I think they’ll fly the most efficient route they’re allowed to. But even at ETOPS-180, parts of the eastern Pacific are off-limits. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [December 23, 2013, 2:45am UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/39 "2013-12-23T02:45:24Z")
> [@Musicat](#): > > Not if you head east (90º) and continue heading east (90º), then continue heading east, etc. You are assuming a “straight” line that begins with an eastern heading, then bends with the earth. If you bend with the earth, you are no longer heading east, and your compass heading will change. You will never cross the Equator. I would like to correct myself. The last line should read: Since your compass heading _will_ change, you WILL cross the Equator. If you keep a constant 90º heading, you will not. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [December 23, 2013, 6:24am UTC](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938/40 "2013-12-23T06:24:07Z")
Magnetic or true 90º? They are two different directions. Most non pilots or non long distance sailors do not make or understand the distinction in my experience. [Previous page](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938.md?page=1) [Next page](https://boards.straightdope.com/t/why-are-many-flight-plans-not-straight-lines/676938.md?page=3)