Longer Flight East to West

Why does it take longer to fly from east to west?

Reading time: 5 min

Have you ever wondered why most fly routes to the west are longer than their east-bound counterparts?

For instance, you see that an eastbound flight from New York to London with British Airways is scheduled to take seven hours, and the return from London to New York takes nearer to eight hours.

Likewise, a flight from London to Hong Kong is scheduled to take approximately 12 hours, while the return westbound is over an hour longer.

It’s caused by the rotation of Earth, but with a twist!

Earth rotates from west to east. And at quite fast actually – at the equator, rotational velocity is around 1,609 km/hr.; through simple logic, one might expect a westbound flight take less time, as the planet is moving towards the aircraft.

This, though, is not the case. In reality, the aircraft is also moving away from the destination as it continues to spin with the Earth because it’s not just the surface that rotates, but the atmosphere too, so What matters is the velocity of the aircraft in relation to Earth.

The winds come into the fray

It’s important to talk a little about Coriolis effect to understand why the air moves in tandem with the Earth rotation.

Coriolis effect is the apparent deflection or curvature of objects like air or water, caused by the planetary rotation. To better imagine this effect, imagine you’re standing on a spinning merry-go-round; if you throw a ball to someone directly in front of you, it would curve instead of going straight because both you and the ball are subject to the rotation of your surroundings.

The same principle applies to Earth too. The wind moves with the ground underneath it. Points closer to the equator, the Earth rotates faster than the areas closer to the poles, so when the wind moves northward (or southward), it is moving faster than the ground under it.

In addition to this, winds are affected by solar heating and will flow from areas of high pressure to low pressure. Combined, these effects result in winds which always move from the west to the east in the mid latitudes.

Therefore, it’s these jet streams that affect the flight duration; when moving eastbound, piggybacking on a strong wind can boost travel speed over long physical distances. Likewise, sometimes westbound flights need to be re-routed to avoid the effect of jet streams or avoid severe conditions.

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