aerospace100
Topic Author
Posts: 2
Joined: Mon Jun 26, 2017 6:33 pm

Flight path changes

Thu Jan 16, 2020 1:26 pm

Hi Guys,

I routinely fly from LAX to LHR and have done for over 10 years now. Almost every time the flight takes us over the Hudson Bay area of Canada, which I understand is the shortest and most efficient route.

I just noticed on Flightradar that the same LAX-LHR flight had taken a route which seems to be around 1000 miles south of its usual course, it did not even enter Canadian airspace. Just wondering why this would be the case.

I understand that flight paths deviate but not by such a huge margin.


Thanks
 
zuckie13
Posts: 222
Joined: Fri Mar 02, 2018 8:23 pm

Re: Flight path changes

Thu Jan 16, 2020 3:49 pm

Most likely due to weather/winds. Temperatures and/or winds most likely I'd assume.
 
32andBelow
Posts: 4111
Joined: Mon Sep 03, 2012 2:54 am

Re: Flight path changes

Thu Jan 16, 2020 3:54 pm

The tracks are set by atc. If the winds are south the tracks will be south
 
sw733
Posts: 5874
Joined: Wed Feb 25, 2004 6:19 am

Re: Flight path changes

Thu Jan 16, 2020 4:02 pm

aerospace100 wrote:
which I understand is the shortest and most efficient route.


I think you misunderstood. Shortest by distance, sure. Shortest by time is a factor of other things, most notably wind. Sometimes you want the fastest route, sometimes you don't. Most efficient also isn't always the same thing as shortest distance - with winds, it can be more efficient and faster to take a longer route, distance wise.

One reason you may not care about the fastest route is if you risk having to go in to an extensive hold at your destination before landing, such as for curfew reasons. For example, BA's flight(s) that are scheduled to arrive around 4:45am often don't want to get there as quickly as possible because they may just end up in a long hold. I've seen various BA pilots on social media say they purposely fly at a slightly slower speed to get there right when they want to, versus the fastest time possible.
 
Northpole
Posts: 54
Joined: Wed Oct 10, 2018 7:55 pm

Re: Flight path changes

Thu Jan 16, 2020 7:28 pm

Jetstreams ?
 
spacecadet
Posts: 3512
Joined: Thu Sep 20, 2001 3:36 am

Re: Flight path changes

Thu Jan 16, 2020 10:07 pm

32andBelow wrote:
The tracks are set by atc. If the winds are south the tracks will be south


The tracks are actually set by dispatch and then approved by ATC, with or without changes. ATC doesn't know or care about an airline's fuel efficiency. It's up to the airline to set the routes up for best efficiency, and they have teams of dispatchers and either expensive off the shelf or fully custom software that does it.

Almost every long-ish flight is going to have a slightly different route almost every day due to winds, and that's all calculated and then filed to ATC by the dispatchers.
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GalaxyFlyer
Posts: 4404
Joined: Fri Jan 01, 2016 4:44 am

Re: Flight path changes

Thu Jan 16, 2020 10:20 pm

The North Atlantic tracks, from coast out to coast in, are established daily by Gander and Shanwick OACs, not dispatch. Airlines route according to their flight planning engines best guess on winds from origin to destination.
 
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gunsontheroof
Posts: 3571
Joined: Wed Jan 04, 2006 8:30 am

Re: Flight path changes

Thu Jan 16, 2020 11:24 pm

Flew a similar routing on AF (LAX-CDG) years ago, but that was during the summer. I believe we did pass over Canada, but it wasn't until somewhere around Lake Erie. As others have said, prevailing winds can change routings quite dramatically.
Picked a hell of a week to quit sniffing glue.
 
CosmicCruiser
Posts: 2381
Joined: Tue Feb 22, 2005 3:01 am

Re: Flight path changes

Fri Jan 17, 2020 12:41 am

We were usually flying against the tracks and were given random routes. Dispatch would file flight plans for the low altitude and then tell us to ask for higher. Usually it happened but if it didn't there was no fuel penalty to contend with.
 
spacecadet
Posts: 3512
Joined: Thu Sep 20, 2001 3:36 am

Re: Flight path changes

Fri Jan 17, 2020 3:01 am

GalaxyFlyer wrote:
The North Atlantic tracks, from coast out to coast in, are established daily by Gander and Shanwick OACs, not dispatch. Airlines route according to their flight planning engines best guess on winds from origin to destination.


My mistake, I misread LAX-LHR as something domestic (and I don't even remember what now).
I'm tired of being a wanna-be league bowler. I wanna be a league bowler!
 
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zeke
Posts: 14381
Joined: Thu Dec 14, 2006 1:42 pm

Re: Flight path changes

Fri Jan 17, 2020 3:45 am

GalaxyFlyer wrote:
The North Atlantic tracks, from coast out to coast in, are established daily by Gander and Shanwick OACs, not dispatch. Airlines route according to their flight planning engines best guess on winds from origin to destination.


The NOPAC tracks take into account winds before they are published to get the most traffic across as efficiently as possible.

Not every track is optimum, however on a “global” basis looking at the combined tracks it is the best compromise to facilitate both efficiency and safety (ie ATC separation ).
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N47
Posts: 61
Joined: Tue Sep 26, 2017 7:38 pm

Re: Flight path changes

Fri Jan 17, 2020 4:25 am

zeke wrote:
The NOPAC tracks take into account winds before they are published to get the most traffic across as efficiently as possible.

Not every track is optimum, however on a “global” basis looking at the combined tracks it is the best compromise to facilitate both efficiency and safety (ie ATC separation ).


Is that true for NAT tracks as well?
 
CosmicCruiser
Posts: 2381
Joined: Tue Feb 22, 2005 3:01 am

Re: Flight path changes

Fri Jan 17, 2020 12:52 pm

The last time I flew across the north Pacific there were 5 airways that didn't change. We tried to never fly the most northern one.
 
BravoOne
Posts: 3769
Joined: Fri Apr 12, 2013 2:27 pm

Re: Flight path changes

Fri Jan 17, 2020 3:26 pm

CosmicCruiser wrote:
The last time I flew across the north Pacific there were 5 airways that didn't change. We tried to never fly the most northern one.


Not sure why you you would avoid the most northern airway (R220)?. Close to Russian airspace for sure, but we have been flying further north in Russian airspace for years now.
 
GalaxyFlyer
Posts: 4404
Joined: Fri Jan 01, 2016 4:44 am

Re: Flight path changes

Fri Jan 17, 2020 3:47 pm

N47 wrote:
zeke wrote:
The NOPAC tracks take into account winds before they are published to get the most traffic across as efficiently as possible.

Not every track is optimum, however on a “global” basis looking at the combined tracks it is the best compromise to facilitate both efficiency and safety (ie ATC separation ).


Is that true for NAT tracks as well?


Yes, the central track is the minimum time track between the coast out and coast in points, based on winds. How, the tracks fit your routing from origin to destination is another story. Commonly flying random routes above the tracks, we’d often fly across multiple tracks, say a route MKE to RMI.
 
RetiredWeasel
Posts: 741
Joined: Sat Jul 05, 2014 8:16 pm

Re: Flight path changes

Fri Jan 17, 2020 9:53 pm

Unless things have changed since 2008, the NOPAC waypoints for R220, R580, A590, R591 and G344 didn't change for wind or anything else. PACOTs and NATs are a different story. That's my memory, but I welcome a correction.
 
BravoOne
Posts: 3769
Joined: Fri Apr 12, 2013 2:27 pm

Re: Flight path changes

Fri Jan 17, 2020 9:57 pm

RetiredWeasel wrote:
Unless things have changed since 2008, the NOPAC waypoints for R220, R580, A590, R591 and G344 didn't change for wind or anything else. PACTOPs and NATs are a different story. That's my memory, but I welcome a correction.



You are correct and this are Airways as opposed to Tracks as in the North Atlantic.
 
CosmicCruiser
Posts: 2381
Joined: Tue Feb 22, 2005 3:01 am

Re: Flight path changes

Fri Jan 17, 2020 10:39 pm

BravoOne wrote:
CosmicCruiser wrote:
The last time I flew across the north Pacific there were 5 airways that didn't change. We tried to never fly the most northern one.


Not sure why you you would avoid the most northern airway (R220)?. Close to Russian airspace for sure, but we have been flying further north in Russian airspace for years now.


Thinking back that might have been more of a DC-10 thing since it was longer ago and only INS. The later years in the -11, yes we did fly across Russian airspace often.
 
BravoOne
Posts: 3769
Joined: Fri Apr 12, 2013 2:27 pm

Re: Flight path changes

Sat Jan 18, 2020 12:00 am

CosmicCruiser wrote:
BravoOne wrote:
CosmicCruiser wrote:
The last time I flew across the north Pacific there were 5 airways that didn't change. We tried to never fly the most northern one.


Not sure why you you would avoid the most northern airway (R220)?. Close to Russian airspace for sure, but we have been flying further north in Russian airspace for years now.


Thinking back that might have been more of a DC-10 thing since it was longer ago and only INS. The later years in the -11, yes we did fly across Russian airspace often.



Perhaps you are correct. You may recall there were a couple of forced diversions into Petro in those days.

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