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The most direct route between London and Los Angeles takes an aircraft over northern Ireland, southern Greenland, Hudson Bay in Canada, and the Rocky Mountains before finally arriving in LA. You might think that it would just be a straight line, but this isn’t the case because the Earth is curved.
The Mercator projection that you often see depicts great circle routes as curved, but on a globe, these same routes reveal themselves as true straight lines. However, flight planning is more complicated than just drawing a straight line. Flight dispatchers create routes for each specific flight, and you often find deviations every day.
This is because factors like weather and winds can significantly change what is economical for the carrier to operate. Airlines aim to reduce operating costs where possible, which means cutting down on fuel burn and flying the most efficient route, which isn’t always a straight line. Even factors like overflight fees can play a major role, and dispatchers also need to take into account operational constraints.
Winds Over The Atlantic Ocean
A weather phenomenon that occurs over the North Atlantic is the polar jet stream. These fast-moving winds are located in the upper atmosphere where airliners fly, and traveling in them can significantly cut flight times due to their intensity. However, these winds flow eastwards over the North Atlantic, which means that flights from the US to Europe usually fly with a tailwind.
Aircraft traveling from Europe to the US, meanwhile, face a headwind, which means that they need to be routed around the jet stream. Typically, the airliners headed west will take a route closer to the great circle route over the ocean compared to eastbound flights, as they’re actively avoiding the jet stream instead of trying to catch the wind.
However, this isn’t always the case because the location, direction, and intensity of the jet stream change. In addition, flights need to route around severe weather as well. As such, exact routes vary depending on the day for transatlantic flights, although they usually correspond similarly to a true straight line. The northern polar jet stream flows across the North Atlantic, Europe, Asia, the North Pacific, and North America.
In addition, the polar jet stream exists in the Southern Hemisphere, mainly wrapping around Antarctica, while there are also two weaker subtropical jet streams located closer to the Equator. While jet streams exist throughout the world, the North Atlantic polar jet stream is arguably the most impactful due to the high volume of flights traveling through this corridor and the strength of the winds here.
The North Atlantic Tracks
The polar jet stream over the North Atlantic is strongest in a relatively small corridor, which concentrates flights together. What’s more, there is no radar over the ocean, resulting in an area dense with flights that can’t be monitored by radar. To maintain safety, separation requirements are increased over the ocean, and for further organization, flights operate within multiple designated flight routes, dubbed the ‘North Atlantic Tracks’.
This further keeps flights away from their great circle route. The tracks are used for aircraft traveling between flight levels 290 and 410 inclusive, and each set of tracks is published every day by Gander Centre and Shanwick Centre. Flight dispatchers plan routes in advance of the tracks being published and send route preferences to Gander/Shanwick, which are usually granted.
Because of how the tracks are developed, planes don’t always fly in straight lines from one end of the ocean to the other, and they often deviate away from a great circle route. The tracks are primarily used for flights between Europe and the US East Coast, meaning that many flights to the US West Coast often fly north of the tracks.
Catch what other flight trackers miss
Emergency squawks, holds, NOTAMs — live signals, no signup.
Open tracker
Catch what other flight trackers miss
Emergency squawks, holds, NOTAMs — live signals, no signup.
Open tracker
If winds favor a more southerly route, however, the flight may be routed via the tracks, which takes it off its great circle route but saves time overall because the aircraft travels at a higher ground speed. However, this mainly applies to eastbound flights, and less so to westbound flights that usually aim to fly north of the jet stream.
Taking Overflight Fees Into Consideration
It’s hardly something that comes to mind for those onboard the aircraft, but an operator (the airline flying the aircraft) is required to pay fees to certain foreign countries that its planes overfly during a given flight. These fees are set by the country, and they can even vary by which part of the country the aircraft operates over.
For flights between Europe and North America, most aircraft have to overfly Canada, and the country is notorious for charging extremely high overflight fees. For the most part, airlines simply have to pay the amount because there isn’t any way to fly around Canada on these routes.
However, when wind conditions permit, airlines may schedule routes to fly over US airspace or enter oceanic airspace earlier to pay less in Canadian overflight fees. This often adds time to the flight and can even increase the fuel cost for the flight, but the equation works out if the added flight time isn’t dramatic and the reduction in overflight fee costs offsets the added fuel burn. Canada isn’t the only country that charges high overflight fees due to its location.
However, it is the most relevant nation when discussing transatlantic routes. It’s another example of the complexities of planning flights, especially long-haul services. Airlines are hyperfocused on keeping costs low, but there are also a huge number of factors that can influence a given flight’s route. Accounting for these factors is why planes fly different routes essentially every day, and why it’s uncommon for a flight to simply go in a straight line.
An Airline’s Goal When Planning Flights
It doesn’t make much of a difference to the airline how long a flight takes. Airlines simply always fly their aircraft at their most fuel-efficient speed, and while dispatchers do aim to route flights through favorable tailwinds while avoiding headwinds, this is to cut down on fuel cost first.
If it’s more favorable to take the long way around Canada and pay less in overflight fees, then the airline will do that even if the flight gets extended, depending on wind conditions and just how significant the detour is. While it’s easy to compare the ground distance traveled with great circle distance, these numbers are somewhat meaningless to the airline.
Track Name | Meaning |
|---|---|
Minimum Distance Track | Calculates the shortest distance between two points |
Minimum Time Track | Calculates the route with the lowest flight time |
Minimum Fuel Track | Calculates the route with the lowest fuel burn |
Minimum Cost Track | Calculates the route with the lowest overall cost, taking into account all factors |
Airline dispatchers usually can calculate a minimum distance route, but this doesn’t account for factors like weather, making it an irrelevant figure in most cases. Dispatchers can also calculate routes with the least amount of time and the least amount of fuel burn, which are usually fairly similar. However, it’s the lowest-cost option that’s most relevant and usually ends up being selected. The fuel burn track can be informative to dispatchers, as can the lowest time and lowest distance figures.
However, the cost figure takes into account fuel burn, as well as overflight charges, possible missed curfew costs, crew costs, and more. Given the importance of keeping operating costs low and just how many variables are in play when planning long-haul services, this is by far the most common track that dispatchers plan for flight routes. If the flight happens to be shorter, then that’s an extra benefit.
The Most Extreme Examples
North America and the North Atlantic are fairly open regions, but across the ocean, there are significant airspace closures in the Middle East and Russia. Russian airspace in particular had become crucial for flights between Europe and Asia, but the shutdown of the airspace meant that many airlines now needed to route around the massive country.
Most flights now travel south of Russia, but some head north near the Arctic and follow the Russian coastline. Meanwhile, certain flights between Japan and the UK cross the Pacific, traverse North America, and fly over the Atlantic instead. Elsewhere, Singapore Airlines operates the world’s two longest nonstop flights, from Singapore to New York JFK and Newark Airport.
A great circle route would see the flight fly near the North Pole, but because of the jet stream, the departing flight travels over the Pacific and Canada instead. Meanwhile, the returning flight occasionally mirrors this route, but more often will fly over the Atlantic, Europe, and South Asia, catching tailwinds from the jet stream. Both of these routes traverse much longer distances, but take less time than a straight-line route because of winds.
Qantas is planning to begin flying from Sydney to JFK and London in 2027 as part of Project Sunrise. A great circle route for the Sydney services would see the aircraft fly westbound through the Middle East, but the airline has softly revealed that some flights between Sydney and London specifically (not the return) will fly over the North Pacific and the Atlantic, once again because of tailwinds.
