MODERN JETLINERS HAVE ENABLED ordinary people to travel to places where once only the wealthy could afford to go. Compared with the first jetliners (which were introduced in the 1940s), modern ones are much quieter, burn fuel more efficiently, and produce less air pollution. These advances are largely due to the replacement of turbojet engines with turbofan engines . The greater power of turbofan engines at low speeds enables modern jetliners to carry more fuel and passengers than turbojet aircraft; a modern Boeing 747-400 (popularly known as a “jumbo jet”) can fly 400 people for 8,500 miles (13,700 km) without needing to refuel. Jetliners fly at high altitudes, typically cruising at 26,000-36,000 ft (8000-11,000 m), where they can use fuel efficiently and usually avoid bad weather. The pilot always controls the aircraft during takeoff and landing, but at other
times the aircraft is usually controlled by an autopilot. Autopilots are complex on-board mechanisms that detect deviations from an aircraft’s route and make appropriate adjustments to the flight controls.
Flight decks are also equipped with radars that warn pilots of approaching hazards, such as mountain ranges, bad weather, and other aircraft.
