Why Do Planes Not Fly in a Straight Line?
They almost always do — on a globe · Updated May 2026
Planes usually do fly something very close to a straight line — they just do it on a sphere, not on a flat map. The shortest path between two points on a globe is a great circle, and on the common Mercator projection a great circle looks like a curve, often arcing well north or south of what looks like the "straight" path on the screen. A New York to Tokyo flight, for example, naturally curves up over Alaska and the Bering Sea on a flat map, even though that is the geometrically shortest path. On top of that geometry, flights also deviate for jet streams (winds aloft), airway and airspace structure (ATC routes are predefined corridors), weather (storms, turbulence, volcanic ash), and airspace constraints (closed FIRs, restricted areas).
The Earth is round; your screen is flat
The Mercator projection, which most maps and flight-tracker websites use, preserves angles (it's a "conformal" projection — handy for navigation) but distorts distances and areas, increasingly so toward the poles. Greenland looks bigger than Africa on Mercator; in reality, Africa is about 14× larger.
A consequence: a great-circle route — the actual shortest path between two points on a sphere — appears as a curve on the Mercator. The route between two cities at similar latitudes, like London and Vancouver, arcs strongly toward the north over Greenland on Mercator, even though it is the straight line on the globe.
A simple way to verify it for yourself: pick up a globe (a real one, or a 3D globe in Google Earth) and stretch a string between two cities. That string is what the aircraft is approximately following — and it almost never matches the visually straight line on your flat-map flight tracker.
Why the path still isn't a perfect great circle
Even after correcting for the Mercator illusion, real flight paths deviate from the pure great-circle line for several reasons:
Powerful, narrow ribbons of high-altitude wind blow eastward across mid-latitudes at 100–250 knots. Eastbound flights deliberately route into the jet stream to gain a tailwind — they may fly hundreds of miles north or south of the great circle to find favorable winds. Westbound flights do the opposite: they detour to avoid the strongest headwinds. Across the North Atlantic, the daily "North Atlantic Tracks" published by Nav Canada and the UK NATS are redrawn every day based on the current jet stream position. See transatlantic route page.
Most controlled airspace is divided into predefined airways connecting named waypoints — like highways in the sky. Even with modern "free-route" airspace areas, flights still file plans through specific points so air-traffic control can sequence and separate them. The flight plan is a series of straight segments connecting waypoints that approximate a great circle.
Thunderstorms, severe turbulence, icing, and volcanic ash all prompt route changes. Pilots use onboard radar and ATC info to deviate around storm cells, typically by 20+ nautical miles, then return to course.
Closed flight information regions (FIRs), restricted military areas, permit and overflight-fee regimes, and regulatory advisories all push routes off the geometric optimum. See: why airlines reroute.
Twin-engine aircraft on long over-water routes must stay within a certified flight time of a diversion airport (the ETOPS / EDTO rule — 120, 180, or 330 minutes depending on the aircraft and operator). That can push the route toward a more northerly arc to stay within reach of suitable airports in Iceland, Greenland, or the Aleutians. See ETOPS explainer.
Some departure and arrival paths follow specific tracks to avoid high terrain, populated areas with noise restrictions, or sensitive overflight zones. These add small dog-legs near the airport.
Worked example: London (LHR) → Tokyo (HND)
A great-circle line from London to Tokyo arcs strongly north — across Scandinavia, then the Russian Arctic, then down into Japan. On a Mercator map, that looks like a wild detour, but it's the shortest path on a sphere.
In practice (2026), many carriers cannot use Russian airspace, so the route flexes further: either via Central Asia (a south-of-great-circle arc through the Caucasus, Kazakhstan, China) or via the North Pacific Rim (a north-of-great-circle arc closer to the Bering Sea). Either alternative adds roughly 60–120 minutes versus the pure great circle. See polar Europe–Asia route page.
Why the curve sometimes looks bigger than it should
A few visual artefacts amplify the impression that a flight is "not flying straight":
- →Mercator distortion gets worse with latitude. A flight near 60° N looks like it's covering far more horizontal distance than it actually is.
- →Wind correction angle. If the aircraft is fighting a strong crosswind, the nose may be pointing 5–10° off-track to compensate. The ground track is straight, but the aircraft's nose isn't.
- →Step climbs. On long flights, the aircraft climbs in stages as it burns off fuel and gets lighter. The track on the horizontal map doesn't show the altitude profile, which can affect perception.
- →ATC vectors near busy airports. The final 50–100 nautical miles often involve heading changes for traffic separation; the en-route portion is much straighter than the terminal-area portion.
How to test it yourself
- →Open Google Earth (the actual 3D globe view, not Maps), drag a measurement line between two airports, and rotate to compare with what Flightradar24 shows.
- →Use a "great circle mapper" tool (such as gcmap.com) to plot routes on both Mercator and orthographic projections.
- →On long flights, the in-flight entertainment map often offers a "globe" view alongside the flat-map view — toggle it and the path looks dramatically straighter.
Sources
- • ICAO Annex 11 — Air Traffic Services, on ATS routes and waypoints.
- • FAA Aeronautical Information Manual — flight planning, airways, performance-based navigation.
- • IATA — Industry papers on flight planning efficiency and great-circle routing.
- • Nav Canada / NATS — North Atlantic Tracks daily publications.
- • GIS Geography — "Why Are Great Circles the Shortest Flight Path?" (cartographic background).