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I notice that this flight from DFW to PVG has a path that’s not a single arc of a great circle. Rather, it looks like it flies to some city in California and then takes a direct route for the remainder.

Why might it do that, instead of following a more direct route, such as a great circle route? It didn’t stop along the way, so why would it need to overfly an intermediate location that’s not on the direct route?

enter image description here(flightaware.com) American Airlines 127 Thursday 04-May-2017

Compared to great circle route:

enter image description here
(gcmap.com)

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    $\begingroup$ Very rarely does a flight follow the great circle route all the way. Every day the route is changed due to winds - you want to find the tailwinds and avoid the headwinds. Other considerations include airspace restrictions (China is notoriously bad for that), ETOPS, or weather. $\endgroup$
    – Ben
    May 5, 2017 at 6:46
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    $\begingroup$ Possible duplicate of Why do pilots use airways instead of just "flying direct" every time? $\endgroup$
    – 60levelchange
    May 5, 2017 at 12:41
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    $\begingroup$ It looks to me like your Great Circle route would take them over North Korea. I don't see any problem with that, do you? $\endgroup$
    – abelenky
    May 5, 2017 at 13:33
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    $\begingroup$ That dogleg over Japan looks like what KAL 007 was supposed to have done. But I assume that Russia is less sensitive about overflights than the Soviet Union was. (At least for now.) $\endgroup$
    – Michael Seifert
    May 5, 2017 at 14:26
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    $\begingroup$ @mins I'm guessing the chance of American Airlines flying something that isn't ETOPS certified on a 14+ hour flight across the Pacific is roughly nil. Also, the great circle path itself is actually pretty well covered for ETOPS purposes in this case, thanks to how close Alaska and Russia come to each other. $\endgroup$
    – reirab
    May 5, 2017 at 19:36

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Looks like they were avoiding a storm system from Oregon north into Canada.

enter image description here

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    $\begingroup$ Makes sense - Blame Canada! was my first thought, too. $\endgroup$
    – Peter Kämpf
    May 5, 2017 at 12:30
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    $\begingroup$ I think the deviation near Japan may have been to avoid storms over the Sea of Okhotsk. Take a look at the images here from 5/4/17; the times listed are BST, so the plane would have been in the area around 06:00 that day (give or take an hour.) $\endgroup$
    – Michael Seifert
    May 5, 2017 at 14:41
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    $\begingroup$ @MichaelSeifert Probably a combination. I don't think American would overfly North Korea regardless of the weather unless the options were basically down to overfly DPRK or crash. It you look back through the history on that flight, you'll see that it always either makes that dogleg over Japan or else flies over Mongolia, remaining well clear of DPRK on the other side. $\endgroup$
    – reirab
    May 5, 2017 at 19:39
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    $\begingroup$ @MichaelSeifert Plus, the US Navy is currently running exercises in the Sea of Japan - basically poking the badger. Not a good time to overfly the area $\endgroup$
    – TomMcW
    May 5, 2017 at 19:42

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