Jet engines operate on the application of Newton's third law of motion: for every action there is an equal and opposite reaction. The most common type of jet engine is the turbojet engine. Air from the atmosphere enters the fan section at the front of the engine where it is compressed in the compressor section. Then it is forced into combustion chambers where fuel is sprayed into it and ignited. Gases that form expand rapidly and are exhausted out the rear of the combustion chambers. The energy from these gases spins the fan-like set of blades called a turbine, which rotates the turbine shaft. This shaft, in turn, rotates the compressor, thereby bringing in a fresh supply of air through the intake at the front of the engine. The rest of the energy is expelled out the tail pipe, providing forward thrust.
The jet engine entered the propulsion scene at a time when conventional reciprocating engines and propellers were reaching their physical limits. Propellers were already encountering supersonic tip-speeds that limited their efficiency, and engines had grown so complex that additional horsepower in the 3,000–4,000 range depended on a large number of cylinders and complex supercharging that generated problems in operation and maintenance.
Jetliners were able to fly much higher, faster, and farther than older piston‑powered propliners, making transcontinental and intercontinental travel considerably faster and easier: for example, aircraft leaving North America and crossing the Atlantic Ocean (and later, the Pacific Ocean) could now fly to their destinations non-stop, making much of the world accessible within a single day's travel for the first time. Since large jetliners could also carry more passengers than piston-powered airliners, air fares also declined (relative to inflation), so people from a greater range of socioeconomic classes could afford to travel outside their own countries.
The first airliners with turbojet propulsion were experimental conversions of the Avro Lancastrian piston-engined airliner, which were flown with several types of early jet engine, including the de Havilland Ghost and the Rolls-Royce Nene. They retained the two inboard piston engines, the jets being housed in the outboard nacelles. The first airliner with jet power only was the Nene-powered Vickers VC.1 Viking G-AJPH, which first flew on 6 April 1948.