FlightAware Discussions

Why the trans-Pacific flight path change?

All flights on all airlines from LAX to Taipei and Hong Kong were all following a mid-latitude flight path over the Pacific every day in October until a sudden change from around October 30 to the present time; all the same flights on the same airlines and same aircrafts have now, for the last 5 or 6 days, all flown a much more northerly path up over Alaska and the Bering Sea. Any ideas about why? Is it a seasonal thing? Or maybe due to fuel prices? Or maybe because of Typhoon Malou and its remnants?

https://www.skybrary.aero/index.php/Pacific_Organised_Track_System_(PACOTS)
https://www.skybrary.aero/index.php/North_Pacific_(NOPAC)_Route_System

The exact tracks chosen vary with weather / jetstream conditions. You’ll see the same sort of variation in the North Atlantic tracks.

There’s also limitations on how far from land the routes can go - not all routes are possible.

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Same sort of variations happen accross the Indian Ocean in and out of Australia.

S.

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Yes, I already knew all those factors, but what I am asking is why were the tracks all mid-latitude tracks for every day of October until October 30 (I had checked all the flight tracks on FlightAware) and then suddenly changed and remained in the exact same changed polar track for all the consecutive days since October 30? Do the prevailing wind patterns in the Pacific have a major change around the end of October every year? Or was it maybe because of recent Typhoon and Tropical Storm Malou? (Do such storms even impact winds at flight altitudes?) Or is it due to some other factor such as military activity (which is specifically mentioned in that PACOTS page) ? Can any pilots here give us some clues as to what is going on?

The PACOTs page says: “The planners may develop more or fewer tracks based on user needs, significant weather, military activity or other limitations.”

I just learned now that the Northern Hemisphere’s subtropical jet stream is re-established every year starting in October and then disappears in the summer. BUT, critically, “the subtropical jet stream is located in the upper troposphere above where the Hadley cell descends”, so can someone here help me understand that? Do commercial airline jets fly up there or are affected by that area called “the upper troposphere above where the Hadley cell descends” ??

The top of this cell is around 10-15km (~ 33000-50000ft) and yes commercial aircraft do fly up there, at least at the lower end of the range.

For comparison the polar jetstreams are lower, at ~ 9-12km.

Wikipedia has a decent overview of all this. This is a good illustration: Jet stream - Wikipedia

For a quick visual of the winds, try this site: Ventusky - Wind, Rain and Temperature Maps

So mid October, the winds at about 39,000 feet look like this. On the map, the least winds from LAX to Hong Kong would be sliding in between the dark areas, so more or less from a map view, a straight shot across the Pacific. As you saw.

This morning, 06-Nov-2021, the winds look like this. The path with the least winds at about 39,000 feet would take you up over Alaska and down. As you are seeing. The airlines will balance distance, wind speed, flight level, etc. to find the most fuel and time efficient route.

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markrrichardson:

Thanks so much! That site is awesome! Especially as it shows forecasts for the high-altitude winds for the upcoming days and weeks. Also, if I could trouble you, would you be able to take a look at the winds over the next couple weeks and share your best guess about a couple days within that time frame, if any, when the LAX - TPE flights might resume a more “straight shot” track?

obj:

Thanks very much for that helpful information. However, on one little detail, I see now that what they meant by “above where the Hadley cell descends” means simply that the subtropical jet stream’s geographical location is at a latitude (not altitude) above (more north than) the latitude at which the Hadley cell air descends.