Stare at the moving map on a long-haul flight and two questions tend to surface. Why is the plane tracing a great arc across the screen instead of a straight line? And why does the flight take as long as it does — never quite matching the number you got from a quick online estimate? After two decades around aviation, these are the two things I am asked about most, and the answers are more elegant than people expect.
Both come down to a mix of geometry and weather. The curve is an illusion created by flattening a round planet onto a rectangular map; the plane is actually flying the shortest path there is. The timing comes down to that distance, the aircraft's cruising speed, and — by far the biggest variable — the wind. This guide explains all three, so the next time you look at that map it makes complete sense. When you want the actual numbers for a route, our flight time calculator does the maths.
The Short Answer
The curve is not a detour. On a globe, the shortest distance between two cities is an arc called a great circle, and when that arc is drawn on a flat map it bows toward the nearer pole. The plane is taking the most direct route possible; it is the map that is bent, not the flight path.
The flight time, meanwhile, is set by three things: the great-circle distance, a typical jet cruise speed of around 875 km/h (545 mph), and the wind. Tailwinds from the jet stream make eastbound flights faster; headwinds make westbound flights slower. Add airport time and a little schedule padding, and you have the duration printed on your ticket.
Great-Circle Routes: Why the Shortest Path Looks Curved
Earth is a sphere, and on a sphere the shortest distance between two points is an arc of a "great circle" — a circle whose centre is the centre of the planet. The equator is one; so is every line of longitude. That arc, not a straight line, is the genuinely shortest route between two airports.
The trouble starts when we draw it on a flat map. Most world maps use a projection — commonly the Mercator — that stretches the globe to fit a rectangle, and it does so more and more aggressively toward the poles. That is why Greenland can look as large as Africa when it is in fact about a fourteenth of the size. A projection like this simply cannot show a great circle as a straight line, except along the equator or directly north-south.
So the shortest three-dimensional path becomes a curve on the two-dimensional map, arching toward the nearer pole. A flight from New York to Tokyo sweeps up over Alaska and the edge of the Arctic; London to Los Angeles arcs over Greenland and northern Canada. Neither is wandering off course — both are flying as straight as the planet allows. The classic proof is a globe and a piece of string: pull the string taut between two cities and it lifts away from the equator toward the pole, exactly as the route on the map does.
The Jet Stream: Why Eastbound Flights Are Faster
If geometry explains the shape of a route, weather explains its timing — and the headline act is the jet stream. Jet streams are narrow ribbons of fast-moving air high in the atmosphere, right around the 9–12 km altitudes where airliners cruise. They generally flow from west to east, driven by the temperature difference between the warm tropics and the cold poles and bent into their meandering path by the Earth's rotation, an effect called the Coriolis force. Winds within them often run 100–250 km/h and occasionally far more.
Fly east and you ride those winds as a tailwind, arriving sooner. Fly west and you fight them as a headwind, taking longer. This is why a New York to London crossing is routinely an hour or more shorter than London to New York on the very same aircraft. It is not the distance changing — it is the air the plane is moving through.
Because the winds shift daily, airline dispatchers do not fly a fixed line. They plan each flight to ride the strongest favourable winds and avoid the worst headwinds, which is why the busy North Atlantic tracks are redrawn twice a day. Now and then the fastest route is not the shortest one at all: a slightly longer path through a powerful tailwind can beat a shorter path straight into a headwind.
Why Your Flight Takes Longer Than the Estimate
A flight-time estimate — including the one our calculator gives you — is deliberately simple: it takes the great-circle distance, divides by a typical cruise speed of about 875 km/h, and adds roughly half an hour for taxi, climb, descent and approach, all in still air. Think of that as the theoretical nonstop floor for a route.
What the airline prints is "block time" — measured from the moment the brakes come off at the departure gate to the moment they go on at the arrival gate — and a great deal happens in that window that a simple estimate cannot see:
| What happens | Typical effect on time |
|---|---|
| Taxi out and the takeoff queue | A few minutes, to 30+ at a congested hub |
| Routing along airways and ATC instructions | Slightly longer than a perfect great circle |
| Winds (the jet stream) | The biggest variable — can swing an hour or more |
| Descent, approach and any holding | Several minutes, more when an airport is busy |
| Taxi in to the gate | A few minutes, to 15+ at large airports |
| Schedule padding for reliability | Airlines pad block time so they can land on time |
Reading the Table
Winds aside, the most misunderstood line there is the last one. Airlines deliberately pad their schedules — a habit often called schedule creep — so that a flight which actually takes, say, six hours of flying is sold as a six-and-a-half-hour block. It lets them hit punctuality targets, and it is why the booked duration almost always exceeds pure flying time. So when your flight lands "early", it frequently has not: it has simply beaten a cushion that was built into the schedule.
Cruise Speed and Altitude: Why Planes Do Not Just Fly Faster
Airliners cruise at around Mach 0.78 to 0.85 — roughly 830 to 900 km/h through the air — at altitudes near 10 to 12 km. They climb that high for a reason: the air up there is thin, which cuts drag and fuel burn dramatically. The speed shown on your seat-back map is ground speed, which is airspeed plus or minus the wind, and that is why the figure jumps around so much during the flight.
You might wonder why they do not simply fly faster and shorten the trip. The answer is economics, not capability. Push much past about Mach 0.85 and the airflow over the wing starts to approach the speed of sound; drag and fuel consumption then climb very steeply for very little time saved. Airlines trade a small amount of speed for a large amount of efficiency — which is also why supersonic airliners are not, for now, a mainstream proposition.
Why Some Routes Bow Even More
Geometry and wind explain most of what you see, but two more forces shape the line. The first is ETOPS: twin-engine jets crossing oceans must stay within a certified flying time of a suitable diversion airport, which can nudge a route away from the pure great circle. The second is airspace — closed or restricted zones, whether for politics, conflict or military activity, force routes around them and can add real distance. The track you finally see is a balance of the shortest geometry, the best winds, the diversion rules, and the airspace that is actually open on the day.
How to Read the Numbers Like a Pro
- Treat a still-air estimate as the floor, then add airport time and a wind allowance for a realistic figure.
- Expect the booked block time to run a little longer than pure flying time — that is the schedule padding, not a slow aircraft.
- Eastbound legs are usually shorter than the same route westbound; bear that in mind when planning tight connections.
- The curve on the map is the shortest path, not a detour — and the flatter the map, the more dramatic it looks.
- For any specific route, run it through the [flight time calculator](/flights) and the [distance calculator](/distance) for the great-circle numbers.
Frequently Asked Questions
Because the shortest route over a round Earth — a great-circle path — cannot be drawn as a straight line on a flat map. Flat maps such as the Mercator projection distort the globe, especially near the poles, so the genuinely shortest path appears as a curve arcing toward the nearer pole. The plane is flying straight; it is the map that is bent.