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Found this odd to see the same airliner, same origin, same destination, and same time, yet different paths. More interesting is seeing that one aircraft is flying along the coast while the other is flying straight trough the pacific. Why is this, what would be the reasoning behind to take different paths?

ANA flight

AAL flight

Zoom In of AAL flight to show that there is actual geo data(purple) at this point(no dotted lines) enter image description here

Screenshot taken on 2024-04-08

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The routes for the flights shown in the question are correct (see the routes at the end of this answer). Airlines will typically try to choose the fastest route for their flights. Time is money. One of the most common reasons for picking a longer route is weather.

Winds aloft

You can see from the current winds aloft that the more northerly great circle route goes through an area of high headwinds of the west coast of the US (shown in the very light yellow color). At around the same time after departure, the route that heads straight west goes through an area of very low wind instead (the area that goes to green and then darker blue).

The AAL flight left 22 minutes later than the ANA flight, but is only currently forecast to get in 29 minutes later. This means the AAL flight will only be about 7 minutes longer, despite having a route that's over 200 miles longer.

These flights are almost 11 hours long, so the routes have to be chosen based on weather forecasts many hours in the future. Small deviations can be made enroute but a large choice such as between these two routes has to be made early. It's always a roll of the dice what the weather will actually do. Maybe the weather didn't turn out quite how AAL hoped, but 7 minutes is pretty small over a flight almost 11 hours long.

For reference, here are the two filed routes shown on FlightAware. You can see the latitude/longitude pairs on the ANA flight are going up above 50 degrees north, while the AAL flight's waypoints are down near 30 degrees north.

ANA105:
SUMMR2 MCKEY LIBBO BRINY BOARS AMAKR REDWD UNVER 4200N/13000W 4600N/14000W 5000N/15000W 5200N/16000W 5300N/17000W 5200N/18000E CHIPT CARTO CUTEE KALIG KALNA OTR5 ADNAP Y807 LALID Y804 INUBO Y108 MESSE

AAL169:
SUMMR2 DINTY DUETS BARAZ 3400N/14000W 3400N/15000W 3400N/16000W 3400N/17000W 3300N/18000E 3300N/17000E 3400N/16000E 3500N/15000E SEALS OTR13 LAPIL Y811 NOGIX Y807 LALID Y804 INUBO Y108 MESSE MESSEN

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    $\begingroup$ 20 ° difference in latitude!!!! had no idea $\endgroup$
    – Fattie
    Apr 8 at 15:07
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    $\begingroup$ @Fattie cos its such a long distance. One could imagine two flight paths exactly halfway around the globe, 90 or 180 degrees apart and they'd still have nominally the same distance travelled. $\endgroup$
    – Criggie
    Apr 10 at 1:39
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    $\begingroup$ @Criggie sure, I understand the math of great circle metrics - it['s just surprising eh!!! $\endgroup$
    – Fattie
    Apr 10 at 13:45
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    $\begingroup$ "Airlines will typically try to choose the fastest route for their flights." I think you'll find a more accurate answer will be that airlines pay for flight planning software to calculate the most efficient flight plan - which using forecast winds along with anticipated aircraft performance (booked passengers, aircraft technical information) - will run various models to find the most efficient routing and cruise alt. My company uses Lido, flight plans are typically only available ~5 hours before - so they are using the most up to date PAX, weather and aircraft data in the modelling. $\endgroup$ Apr 10 at 19:37
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To add on to @fooot's answer,

I put the 2 routings into SimBrief (https://dispatch.simbrief.com/options/new) and used the "Calculate & Compare" tool which gives me the ability to see the difference in flight times, fuel burnt, wind component etc. between 2 generated flight plans. Now the 2 aircraft types are not exactly the same, but for comparison purposes I used the B787-9 with GE engines and a cost index of 100, and kept the payload values the same for both flights. SimBrief calculated that the AAL flight would travel an extra 307 nautical miles, and burn about 400 or so kilos of extra fuel. This isn't a lot, especially for such a long flight, but the AAL flight would also have an extra 12 minutes of flight time.

There could also be different flight planning and dispatch philosophies between AAL and ANA, with the ANA guys staying a bit lower and cruising a bit faster to negate some of the effects of the strong headwinds along their path, in return burning more fuel.

Additionally, as the airspace over the Pacific is not under radar control, it could be possible that the AAL flight couldn't secure a slot on the tracks it wanted to take because the ANA flight departed first. Not sure of the separation standards over the Pacific, but the 2 flights pushed back 5 minutes apart and took off 13 minutes apart at LAX, if they were to fly the same route AAL's pushback would certainly be delayed by at least a few minutes (10 minutes separation minimum I believe is what they use, have a look at PBCS). Sometimes ATC will offer a different route so you won't have to take on a delay, or ask you to take on a different cruising level. All comes down to a decision by the flight crew and dispatch.

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    $\begingroup$ The two dispatch offices may be using different wind forecast products, or may have planned the routes at different times; forecasts can change in the hours before a flight, and a fairly small shift in forecast winds might make a route that used to look optimal no longer look as efficient under an updated forecast. Also, depending on flight-specific factors (aircraft type, engines, gross weights), they may be planning different cruise altitudes & step-climb profiles, which could also change which route has the more favorable winds. $\endgroup$
    – Ralph J
    Apr 8 at 15:39
  • $\begingroup$ Would there not be some benefit in having 2 flights nearby on the same track over uncontrolled space, because they would (assumedly) be able to communicate with each other easily by radio at all times? Or is this not a significant enough factor compared to the rest of it? $\endgroup$ Apr 11 at 15:45

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