High above the Earth's surface between about 9000-15,000 metres, powerful winds known as the jet stream flow from west to east, providing a strong shove along when an aircraft is travelling in that direction. When they fly east, helped along by a powerful jet stream current, it's not uncommon for commercial jet aircraft to reach a ground speed in excess of 1000kph. When they head west, they're flying into a headwind, and their ground speed is slower and flight times longer. 123RF High above the Earth's surface between about 9000-15,000 metres, powerful winds known as the jet stream flow from west to east. Not only does it save time, but taking advantage of jet stream currents is also a huge fuel saving for airlines.

Source: Stuff March 07, 2019 22:18 UTC