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Are jet streams a net benefit in time and fuel savings? provides (basic) explanations about jet streams in the Pacific. However I'm looking for an answer focused on North Atlantic area, explaining the track system and the tracks location. In addition BA 185 route seems to be composed of two arcs, did they change their mind in flight because of the wind? or is this related to ETOPS or alternate airport at Santa Maria?

Looking at flights between NY and London (click to see route):

The FlightAware anticipated routes are quite similar in both directions, but the actual routes for past flights are really remote from each other:

enter image description here

The two westbound routes are either 800 km north or 1,000 km south of the eastbound route (the dotted line shows the shortest path).

  • Why are the two westbound routes different and so remote from each other? Why this difference of about 1,800 km?

  • Why BA 185 route seems to be composed of two arcs?
    Did the pilots changed their mind in flight because of the jet streams? Is it related to ETOPS constraints, or alternate airport at Santa Maria? or something else?

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    $\begingroup$ Possible duplicate of Are jet streams a net benefit in time and fuel savings?; The accepted answer explains it quite well. $\endgroup$
    – Lnafziger
    Commented Jul 1, 2016 at 14:56
  • $\begingroup$ Basically the same reason sailing ships follow the trade winds across the Atlantic. Of course, different winds at sea level than at cruise altitude. $\endgroup$
    – TomMcW
    Commented Jul 1, 2016 at 18:17
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    $\begingroup$ Could it also have at least something to do with possible emergency landing sites? I'd think the key sites in NE Canada could possibly guide the route coming westbound, and the sites in Ireland and coastal UK locations could direct the eastbound route??? And since the distance isn't as different as the map shows, it'd be worthwhile? $\endgroup$
    – JeopardyTempest
    Commented Jul 2, 2016 at 14:55
  • $\begingroup$ Cool :-) What day(s) were the trips from, so I can pull up an upper air map? $\endgroup$
    – JeopardyTempest
    Commented Jul 2, 2016 at 22:04

2 Answers 2

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The reason this is done is due to the winds aloft. The Jet Stream is a powerful current of air that blows in a west to east direction. Airplanes crossing the Atlantic from west to east take advantage of the jet stream to get there faster and save fuel, so a course is chosen to stay in the stream as much as possible. Airplanes going from east to west will be slowed by the jet stream, using more fuel and taking longer to get across, so a course is chosen to avoid the strongest winds.

The difference can be very significant, I've been on flights from NYC to London which take 6h 30m, and ones from London to NYC that take almost 9 hours.

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    $\begingroup$ I imagine both routes are approximately great circle arcs, meaning that the actual distance wouldn't be much different, even though they are so far apart. Worth mentioning if it's true. $\endgroup$
    – DCShannon
    Commented Jul 1, 2016 at 22:15
  • $\begingroup$ @mins Actually I guess you can't unless the two positions are on opposite sides of the sphere. Not sure what I was thinking there. $\endgroup$
    – DCShannon
    Commented Jul 2, 2016 at 0:39
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    $\begingroup$ @DCShannon still, the northerly route isn't as long as the map makes it look. $\endgroup$
    – hobbs
    Commented Jul 2, 2016 at 4:54
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    $\begingroup$ @DCShannon, there is only one great circle that connects any two given points on the globe. If the route from here to there is different from the route from there to here, then at most, one of the two can be a great circle. $\endgroup$
    – Solomon Slow
    Commented Jul 2, 2016 at 9:19
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    $\begingroup$ @jameslarge That is not true as DCShannon points out in the comment just below his original one. Assuming you're modelling the globe as a sphere any two points which are polar opposites get an infinite number of great circles. If you are not modelling the earth as a sphere you don't really get a great circle per se but you still get at least two distinct shortest paths for some points. $\endgroup$
    – DRF
    Commented Jul 2, 2016 at 14:09
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Wikipedia article about North Atlantic Tracks says it is to avoid jet stream winds (when flying west) or use it (when flying east):

They are aligned in such a way as to minimize any head winds and maximize tail winds impact on the aircraft. This results in much more efficiency by reducing fuel burn and flight time. To make such efficiencies possible, the routes are created twice daily to take account of the shifting of the winds aloft and the principal traffic flow

Article links to daily map of tracks, complete with the position of the jet stream.

Jet stream winds have average speed 100 mph (160 km/h) so they are significant.

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