The map on the seat-back screen shows your flight from London to Los Angeles arcing north over Greenland, hundreds of miles from anything resembling a straight line, and some part of your brain quietly files it as inefficiency. It is the opposite. That curve is the shortest path available, and the aircraft is flying it because flying straight on the screen would cost you an hour.
Almost every route that looks strange has a specific, unglamorous explanation. Five of them account for nearly all of it, and once you can name them you can look at any flight path and read the reasoning behind it.
The map is lying, not the aeroplane
The Earth is roughly spherical and the screen is flat, and there is no way to move one onto the other without distorting something. The projections used for most maps preserve angles at the cost of distance and area, which is why Greenland looks continental and why the genuinely shortest route between two distant points looks like a detour.
The shortest path across a sphere is a great circle: the arc you would get by slicing the planet through both airports and its centre. On a globe with a piece of string it is obviously straight. On a flat map it bends toward the nearer pole, and the further apart the two cities are, the more dramatic the bend becomes. A London to Los Angeles great circle really does pass near southern Greenland, and it really is shorter than the route that looks straight.
A curved line on a flat map is a straight line on a round planet. The distortion is in the paper, not the flight plan.
This is why every flight page on this site draws the route as an arc and reports a great-circle distance. It is also why two flights over the same city pair always quote the same distance, even when their actual tracks differ by a hundred miles on the day.
Wind: The reason the return leg takes longer
Great circles explain the shape. Wind explains why the aircraft often does not fly them.
At cruising altitude the atmosphere contains fast, narrow ribbons of west-to-east wind called jet streams, which can exceed 200 km/h and occasionally far more. An aircraft flying east can climb into that current and gain most of its speed for free. Flying west, the same current is a wall.
Dispatchers therefore do not plan the shortest route; they plan the shortest time, which means deliberately deviating from the great circle to sit in helpful wind or dodge unhelpful wind. A transatlantic crossing may swing a long way north or south of the geometric ideal because the fuel and time saved exceed the cost of the extra distance.
This is the whole reason a route has different scheduled durations in each direction. Our flight pages show the block time and the average speed it implies, and the eastbound leg of a long route is routinely an hour quicker than the westbound one over identical ground.
| Reason | Effect on the track | How to spot it |
|---|---|---|
| Great circle geometry | Route curves toward the pole on a flat map | Consistent, symmetrical arc on long routes |
| Jet stream | Deliberate deviation north or south | Eastbound and westbound tracks differ noticeably |
| ETOPS diversion planning | Track bends to stay near suitable airports | Twin-engine ocean crossings hugging island chains |
| Airspace closure or overflight restriction | Long, obvious dogleg around a region | Sharp corners rather than smooth curves |
| Weather avoidance | Short-notice deviations mid-flight | Kinks in an otherwise smooth track |
ETOPS: Never too far from somewhere to land
A twin-engine aircraft crossing an ocean operates under ETOPS rules, which cap how far it may be from a suitable diversion airport, expressed in flying time on one engine. An ETOPS-180 approval means the aircraft must stay within 180 minutes of somewhere it could land.
In practice this shapes routes across the North Atlantic and Pacific, pulling tracks toward Iceland, Greenland, the Azores or the Aleutians rather than the emptiest water. Modern approvals extend much further than early ones, which is precisely why twins now fly routes that used to require four engines, a shift covered in our guide to narrowbody and widebody aircraft.
The constraint is invisible until you know it exists, and then it explains a great many gentle bends over open ocean.
Did you know?
Because a great circle bends poleward, a flight between two cities at similar latitudes on opposite sides of the world can pass remarkably close to the North Pole. Several routes between East Asia and eastern North America spend time inside the Arctic Circle, which is why they carry cold-weather fuel planning and why crews watch space weather forecasts.
Airspace: The sharp corners
Geometry and wind produce smooth curves. Politics produces corners.
Airspace can be closed by conflict, sanctions, overflight disputes or restricted military activity, and an aircraft must route around the whole block. These deviations look completely different from wind routing: instead of a gentle arc you see a long straight leg, a distinct turn, and another long straight leg. Some of the most-flown corridors in the world have been reshaped this way, adding hours to routes that were previously direct.
Weather adds a smaller-scale version of the same thing. Convective storms are avoided tactically, in real time, by the crew asking for a deviation, which is why an otherwise smooth track sometimes shows a brief kink and then rejoins its planned path.
Reading a track for yourself
Put these together and most flight paths decode quickly. Smooth poleward arc on a long route: great circle. Eastbound and westbound differing by hundreds of miles: jet stream. Ocean crossing hugging islands: ETOPS. A hard dogleg with corners: closed airspace. Small kinks mid-ocean or over land: weather.
What almost never explains an odd route is inefficiency. Fuel is among an airline's largest costs, and every extra mile is money, so a route that looks wasteful is nearly always the cheapest one available once the constraints are honoured. Our guides to satellite flight tracking and where tracking data comes from explain how these tracks reach your screen in the first place, and reading a flight tracker map covers the symbols.
Key takeaways
- A curved line on a flat map is the shortest path on a sphere, not a detour.
- Jet streams make dispatchers plan the fastest route rather than the shortest one.
- Eastbound legs are routinely quicker than westbound legs over identical distance.
- ETOPS rules pull twin-engine ocean crossings toward island chains and diversion airports.
- Closed airspace produces sharp corners; wind and geometry produce smooth curves.
- Fuel is expensive, so a route that looks wasteful is nearly always the cheapest legal option.
The moving motorways of the North Atlantic
There is one more reason a route looks unusual, and it is the most elegant: over parts of the ocean, aircraft do not choose their own path at all. They join a published track system that is redrawn twice a day.
Across the North Atlantic, where radar coverage has historically been absent and traffic is dense and strongly directional, controllers publish a set of parallel tracks each day. Westbound tracks are defined for the daytime flow, eastbound tracks for the overnight flow, and their positions shift depending on where the jet stream sits that day. An aircraft is assigned a track, an entry point and a speed, and it flies that lane with defined separation from the aircraft ahead and alongside.
This is why transatlantic flights on the same evening appear to fly in neat parallel lines rather than fanning out individually. They are not converging by coincidence; they have been allocated adjacent lanes on a motorway that was drawn a few hours earlier around that day's winds.
Twice a day, someone redraws the busiest airspace over the Atlantic to match where the wind happens to be.
Improved surveillance has loosened the system considerably. Satellite-based tracking, described in our guide to satellite flight tracking, gives controllers position data over open ocean that simply did not exist before, which allows reduced separation and more flexible routing. Aircraft with the right equipment can increasingly fly user-preferred routes rather than fixed tracks.
The visible consequence on a tracker is a gradual loosening of those parallel lines over the last few years. Where you once saw rigid lanes you now see something closer to a broad braid, each aircraft optimising slightly differently around the same wind field.
Frequently asked questions
Why does my flight path look curved instead of straight?
Because the shortest route between two distant points on a sphere is a great circle, and flat map projections distort that arc into what looks like a detour. On a globe the same path is obviously straight, and it is genuinely shorter than the line that appears straight on screen.
Why does the return flight take longer?
Jet streams blow broadly west to east at cruising altitude. Flying east the aircraft rides that current and gains speed over the ground; flying west it fights the same current. On long routes the difference routinely exceeds an hour despite identical distance.
What is ETOPS and how does it change the route?
ETOPS limits how far a twin-engine aircraft may be from a suitable diversion airport, measured in single-engine flying time. It pulls ocean crossings toward island chains and coastal airports rather than the shortest line across empty water.
Why do some flights make a sharp turn in the middle of nowhere?
Sharp corners usually mean airspace, not weather. Closed or restricted airspace from conflict, sanctions or military activity forces aircraft to route around an entire block, producing straight legs joined by distinct turns rather than smooth curves.
Do airlines ever fly longer routes to save money?
Frequently, if longer means faster or cheaper in fuel. Dispatchers optimise for cost and time rather than distance, so a route that adds miles but sits in a favourable jet stream is the economical choice.
The next time a track looks wrong, treat it as a puzzle with five possible answers rather than evidence of a mistake. The aircraft is following geometry, wind, regulation and geopolitics in that order, and the shape it draws is a fairly precise record of all four. Watch it happen on the live map.
