The Boeing 727 is an American narrow-body airliner developed and produced by Boeing Commercial Airplanes. After the heavier 707 quad-jet was introduced in 1958, Boeing addressed a growing demand for an aircraft to be used on shorter routes from smaller airports. The only trijet to be produced by Boeing, the 727 was designed for operations from smaller airports, so independence from ground facilities was essential. It led to one of the 727's most distinctive features: the built-in airstair that opens from the rear underbelly of the fuselage, which initially could be opened in flight. This allowed passengers to be embarked and disembarked without needing jetways or stairs. The 727 proved to be such a reliable and versatile airliner that it came to form the core of many airlines' fleets. One of the features that gave the 727 its ability to land on shorter runways was its clean wing design - the trijet configuration involving one engine mounted on each side of the rear fuselage, with the third in the tail. It was also helped by the use of advanced high-lift devices, including leading-edge slats and triple-slotted flaps. For over a decade, more 727s were built per year than any other jet airliner. Such was the design's ruggedness, dependability, and performance, that even as late as July 2013, a total of 109 Boeing 727s were still in commercial service with thirty-four airlines worldwide. An industry workhorse for many years, the 727 is often fondly referred to as 'the DC-3 of the Jet Age'. A pioneering and highly influential aircraft, the type's last scheduled commercial passenger flight took place in January 2019. The 727's popularity undoubtedly helped accelerate the jet age, by bringing jet service to many cities previously limited to propeller aircraft, and brought jet travel to the masses.