Routing question...

[LadyL2013]

I posted this in SLF, but they suggested I ask you guys in here:

I've been looking at the LGW - CUN flights over the last couple of weeks.

I have noticed that often, you might expect for aircraft to follow a similar route as other aircraft doing that route, but they have been vastly different. For example the Thomson flight yesterday took a southerly route, the BA flight took a middle-ish route and then a dog leg south and the Thomas Cook flight did a very northerly route over Greenland. This changes all the time, for example the Thomson flight today is doing a northerly route.

My question is what determines these routes if not weather? Why would they go a southerly route one day and a northerly next if the weather has not changed particularly etc etc? And is there a way to know roughly in advance which route they might take for the purposes of selecting your seat to see the 'best' views of things? Not just this route, but other routes too?

[confused atco]

My question is what determines these routes if not weather

weather has not changed particularly
The weather system for example that was off Florida yesterday is now off New York.
Or the High Pressure system off the west coast of Ireland has drifted so yesterdays optimal routes are not today's.
But its still sunny in the UK on both days.

On the ocean weather is the main driver of aircraft routing.

On the North Atlantic what are called "organised tracks" are used. They change twice daily, eastbound at night and westbound during the day depending on the location of the jet stream. They are fixed 1 degree apart which equates with 60NM.

The optimal track would depend on a number of factors and may vary from company to company, from aircraft type to aircraft type.

The optimal route for airline A may be on an organised track while for airline B it may be a totally different random route even using the same generic aircraft.
Another factor is aircraft equipment. Where an aircraft is incapable of meeting the "minimum standard" to operate in a given airspace block it must then route "clear" which may be fly above/below or simply fly around the airspace concerned.

And is there a way to know roughly in advance which route they might take
Each operator planning to operate in the North Atlantic would get a copy of the proposed tracks each day.

They would examine the route options as to which best suits their operation that day.
So typically you are looking at 14 hours notice as tracks are published around 11 pm.

but other routes too?
Most routes over land follow pretty predictable paths.

[HEATHROW DIRECTOR]

Yes, over land aircraft tend to fly the airways system with major cities joined by airways, something like motorways.

[kcockayne]

It's all down to weather; & more precisely, winds ie avoiding headwinds &/or picking up tailwinds. Or a combination of both.
I remember sitting down with a slide rule & upper winds chart in the afternoon at Prestwick (OACC) back in the '70s, & working out the next day's Atlantic tracks. Quite efficient method of doing it. I suppose it's all computerised now !
Before that, I used to listen to the NAT Oceanic a/c on HF from the''60s onwards. It never ceased to amaze me that an a/c from, say LIRF to KJFK could follow a track North of Iceland one day - & another South of the Azores the next !
It was all part of what got me interested in becoming an ATCO.