In 1945, a new type of airplane engine was invented. It was much lighter and more powerful than earlier engines, and enabled warplanes to fly faster and higher than ever. This type of engine was called the jet engine because it belows a large jet of hot air backwards at high speed. The first airplane to use the new jet engine was built in Britain and it began carrying passengers in 1952. It had two jet engines and flew much higher than petrol-engine airplanes. At this height the air is thinner and very cold, and so the airplane can cut through the air more easily. However, the cabin has to be air-conditioned and has to be at normal pressure so that the passengers may eat, read and sleep in comfort.
Today all long distance airplanes have jet engines. The modern jet airplanes are very big and can carry hundreds of passengers on two different floors, which makes air travel much cheaper.
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