Book a return trip between London and New York and look closely at the times. The flight to New York is scheduled for longer than the flight home, even though the aircraft, the airports and the distance are the same. On busy North Atlantic routes the gap is often half an hour or more, and on a windy winter night it can be far bigger.
The reason is not the rotation of the Earth, as many people assume. It is wind, and one band of wind in particular.
The short answer: the jet stream
High above the weather you see from the ground, at roughly the altitude where airliners cruise, there are narrow bands of fast-moving air called jet streams. In the northern mid-latitudes the main one, the polar jet, flows broadly from west to east.
According to the Wikipedia summary of the meteorology, the polar jet sits at about 9 km (30,000 ft), near the 250 hPa pressure level, with typical speeds around 180 km/h and measured peaks of about 400 km/h. Airliners cruise at roughly 10 to 12 km, so they fly right through it.
An aircraft's speed through the air is set by its engines and its design. Its speed over the ground is that airspeed plus or minus the wind. Fly east with a 150 km/h tailwind and you cover the ground 150 km/h faster. Fly west into the same wind and you lose 150 km/h. Over a seven hour crossing, that difference adds up to a lot of time.
Why it is not the Earth's rotation
The Earth spins from west to east, so it is tempting to think a westbound plane should arrive sooner because its destination is "coming towards it". It does not work that way. The aircraft, the airport and the atmosphere all move with the planet. A plane sitting on the runway is already travelling with the Earth's surface, and once airborne it moves relative to the air around it, which also turns with the planet. As The Naked Scientists explain, what matters is the wind relative to the plane, not the spin underneath it.
If the atmosphere were perfectly still relative to the ground, eastbound and westbound flights between the same two airports would take the same time. The difference comes from the winds.
A transatlantic example: London and New York
Take British Airways' daytime and overnight flights on this route as an example. BA117 from Heathrow to New York JFK is scheduled at 7 hours 50 minutes (08:20 from London, 11:10 in New York), while BA112 from JFK back to Heathrow is scheduled at 7 hours 10 minutes (18:30 from New York, 06:40 the next morning in London). The aircraft fly the same 5,540 km great-circle distance (our calculation; the actual track is longer), yet the westbound schedule is around 40 minutes longer. Exact times vary by season and by schedule change, so treat these as typical, not fixed.
On our airport pages you will see a single estimated time for this pair: 7 hours 1 minute in both directions from JFK and from Heathrow. That figure is a simple estimate based on distance (great-circle distance divided by 850 km/h, plus 30 minutes). It cannot know about winds, which is exactly why real schedules are lopsided and our estimate is not.
| Direction | Typical scheduled time | Main wind effect |
|---|---|---|
| New York JFK to London Heathrow (eastbound) | about 7h 10m | Tailwind from the jet stream |
| London Heathrow to New York JFK (westbound) | about 7h 50m | Headwind, or a longer route to avoid it |
| Our distance-only estimate (either way) | 7h 01m | None, wind is ignored |
The extreme case
On the night of 8 to 9 February 2020, Storm Ciara pushed the jet stream over the North Atlantic to unusual strength. A British Airways Boeing 747 flew from New York to London in 4 hours 56 minutes, a record for a subsonic airliner on that route, with a top ground speed reported at about 800 mph (about 1,290 km/h). The flight was BA112, the same overnight service in the table above, which is normally scheduled at more than two hours longer. The aircraft was not flying faster through the air than usual. The air itself was moving east at extraordinary speed, and the plane rode it.
Nobody on a westbound flight that night enjoyed the same luck.
How airlines plan around the wind
Westbound flights dodge the jet, eastbound flights chase it
Flight planners do not simply accept the headwind. A westbound flight will often choose a path to the north or south of the jet's core, even if that path is longer over the ground, because a few hundred extra kilometres in light winds can be quicker than the shortest path into a gale. Eastbound flights do the opposite and position themselves in the fastest part of the stream.
This is why the curved line on our map, the great-circle route, is only the starting point for a real flight plan.
The North Atlantic Tracks
The North Atlantic is one of the busiest stretches of oceanic airspace in the world, and for decades it has been managed with the North Atlantic Organised Track System. Controllers in Gander (Canada) and Shanwick (UK and Ireland) publish a new set of tracks each day, based on the forecast winds. One set serves the westbound flow during the day and another serves the eastbound overnight flow, which is when most flights from North America to Europe cross. The eastbound tracks are placed to make the most of the jet stream; the westbound tracks avoid the strongest headwinds. Use of the tracks is not mandatory, and many flights now plan their own optimised routes.
Schedules are built on averages, plus a buffer
An airline publishes one timetable for a season, not a new one each day. The scheduled "block time" (gate to gate) is based on how long the flight typically takes at that time of year, plus taxiing and a buffer for delays. Research on US airline schedules, such as a 2011 MIT thesis on schedule padding that studied 2,359 domestic routes, found that distance and time of day are the biggest factors in how much buffer airlines add: the buffer in minutes grows with distance, even though it shrinks as a share of the total block time. This is why eastbound transatlantic flights often arrive early: the schedule has to cover days with weak tailwinds, so on a strong day the aircraft beats it comfortably.
Seasonal variation
The jet stream is generally stronger in winter: SKYbrary puts typical core speeds at about 100 knots, reaching 200 knots over North America and Europe in winter. Its strength comes from the temperature contrast between cold polar air and warmer air further south, and that contrast is biggest in the northern winter. The practical effect for travellers:
- Winter (roughly November to March): the biggest gap between eastbound and westbound times. Eastbound flights can arrive very early; westbound flights are most likely to run long.
- Summer: the jet is weaker and sits further north, so the difference narrows.
- Day to day: the jet meanders. Some days it sits right on your route and some days it is far away, so the same scheduled flight can vary by more than half an hour.
Climate change may make the gap bigger. A 2016 study by Paul Williams at the University of Reading, published in Environmental Research Letters, modelled London to New York flights under doubled atmospheric carbon dioxide. It found stronger jet stream winds and, in winter, eastbound crossings about 4 minutes shorter on average and westbound crossings about 5 minutes 18 seconds longer, so round trips grew by about 1 minute 18 seconds because the westbound penalty outweighs the eastbound gain. The share of westbound winter crossings taking more than 7 hours nearly doubled, from 8.6% to 15.3%.
It happens everywhere in the mid-latitudes
The North Atlantic is the best-known example, but the same physics applies on other routes that cross the westerlies:
- Across North America: flying east across the continent can be about 30 minutes shorter with the jet stream than the reverse.
- Across the Pacific: flights from Asia to North America ride the jet stream eastbound, and westbound flights across the Pacific are typically longer. Wikipedia notes that Tokyo to Los Angeles flights use the jet eastbound and follow a great-circle route westbound.
- Ultra-long haul: on the longest flights in the world, the difference between directions can exceed an hour: Air New Zealand's New York JFK to Auckland flight is scheduled at 17h 50m, and the return is about 1h 40m shorter. A strong seasonal headwind can be what forces a fuel stop on one direction of a route.
Routes that run mostly north to south, such as Europe to southern Africa, are much less affected because they cross the jet stream rather than flying along it.
What this means for your trip
- Expect the westbound leg to be longer, especially in winter, and plan connections with that in mind.
- Do not assume an early eastbound arrival. Schedules include a buffer, but you cannot count on a strong tailwind on a particular night.
- Overnight eastbound flights are short. London-bound flights from the US east coast often give you only five or six hours in the air, which is very little sleep. Our jet lag guide has practical advice for these.
- If a delay is long enough, you may be owed compensation. That depends on the cause and the route; see our EU261 guide for how the rules work.
Frequently asked questions
Why is my flight to New York longer than my flight back to London?
Because of the jet stream. It flows from west to east at cruising altitude, giving eastbound flights a tailwind and westbound flights a headwind. Airlines build that into their schedules, so the westbound flight is planned to take longer.
Does the Earth's rotation make flights faster in one direction?
No. The aircraft and the atmosphere move with the Earth, so the spin itself has no effect on flight time. The differences come from winds, mainly the jet stream.
How much faster can an eastbound flight be?
On a typical transatlantic day the scheduled difference is around half an hour. On exceptional days it can be much more: in February 2020 a British Airways 747 crossed from New York to London in 4 hours 56 minutes with the help of an unusually strong jet stream.
Are flights slower in winter?
Westbound flights in the northern hemisphere tend to take longest in winter, when the jet stream is strongest. Eastbound flights tend to be fastest in winter for the same reason.
Why does your site show the same time in both directions?
Our times are estimates based only on distance (great-circle kilometres divided by 850 km/h, plus 30 minutes). They are useful for comparing routes, but they ignore wind, so always check the airline's actual schedule.