Why do flight times differ for outbound and inbound flights?

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Those who often travel overseas may have pondered this question. Observant travelers may have already noticed this before when booking round trips, but others may be surprised to hear this.

When flying between two places, it’s easy to assume that the duration of the flight would be the same even if the departure point and the destination were switched. But the fact of the matter is, they are different! Why do the flight times differ?

Must-Know Tips at Incheon Airport #9! Why do flight times differ when going the opposite direction? Let’s find out!

Is it because of the Earth’s rotation?

Generally speaking, flight times are shorter when traveling from west to east, than when traveling from east to west. For example, a flight from Incheon to Rome is about 12 hours and 10 minutes long, while a flight from Rome to Incheon is 11 hours and 15 minutes long, nearly a whole hour shorter.

Those who loved science classes back in school may have thought that the ‘rotation of the Earth’ would have something to do with this. After all, it sounds plausible that a plane traveling in the opposite direction of the Earth’s rotation would arrive at its destination faster than a plane flying in the same direction as the rotation.

However, the Earth’s rotation is not the main culprit. 😥 While the rotation of the Earth does influence the flight times, it is not the direct cause.

The real reason behind flight time differences! What are ‘Jet Streams’?

To understand exactly why flight times differ depending on the flight direction, we must first find out more about “jet streams”.

Different regions on the Earth have different climates and temperatures. Low latitude regions receive more heat from the sun compared to high latitude regions, and therefore will always have warmer air rising and moving toward high latitudes. Since the globe is always rotating on its axis, circulating air is deflected toward the right in the Northern Hemisphere. This causes a stream to form near the 60 degree latitude zone moving from west to east, and this stream is known as the ‘jet stream.’

The same jet stream also causes the temperature fluctuations observed in Korean winters. The uneven jet stream passes over the peninsula, causing the temperatures to rise and fall regularly. In Korean summers, it affects the rainy season as well.

How does the ‘Jet Stream’ affect flight times?

The jet stream travels at a height of around 9,000~16,000m at an average speed of 50m/s, but its speed can also reach up to 150m/s. It just so happens commercial aircrafts typically fly at around 30,000~40,000ft (around 9,000~12,000m), which is why the jet stream affects flights and flight times as much as it does.

You may have felt like the wind was giving your plane a little push on a particularly windy day. In fact, aircrafts can fly faster and even save fuel costs when the winds are to their advantage. On the other hand, when flying in the opposite direction, aircrafts must avoid or fly around jet streams when they are moving against them, and it’s the detour that results in longer flights.

What did you think of Must-Know Tip #9? It’s the kind of information that you may not have known but always wanted to know, right? It would make a great conversation topic for your next flight, wouldn’t you say?

Stay tuned for more fun and useful information~

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