The Boeing 727 is an American narrow-body trijet that was developed and produced by Boeing Commercial Airplanes. After the heavier 707 quadjet was introduced in 1958, Boeing addressed the demand for shorter flight lengths from smaller airports. On December 5, 1960, the 727 was launched with 40 orders each from United Airlines and Eastern Air Lines. The first 727-100 rolled out on November 27, 1962, first flew on February 9, 1963, and entered service with Eastern on February 1, 1964.
The only trijet aircraft to be produced by Boeing, the 727 is powered by three Pratt & Whitney JT8D low-bypass turbofans below a T-tail, one on each side of the rear fuselage and a center one fed through an S-duct below the tail. It shares its six-abreast upper fuselage cross-section and cockpit with the 707 that was also later used on the 737. The 133-foot-long (41 m) 727-100 typically carries 106 passengers in two classes over 2,250 nautical miles [nmi] (4,170 km; 2,590 mi), or 129 in a single class. Launched in 1965, the stretched 727-200 flew in July 1967 and entered service with Northeast Airlines that December. The 20 ft (6.1 m) longer variant typically carries 134 passengers in two classes over 2,550 nmi (4,720 km; 2,930 mi), or 155 in a single class. A freighter and a "Quick Change" convertible version were also offered.
The 727 was used for domestic flights and on international flights within its range. Airport noise regulations have led to hush kit installations. Its last commercial passenger flight was in January 2019. It was succeeded by the 757 and larger variants of the 737. There have been 353 incidents involving the Boeing 727. Production ended in September 1984 with 1,832 having been built. The 727 was an industry workhorse for many years, often fondly referred to as "the DC-3 of the Jet Age".
The Boeing 727 design was a compromise among United Airlines, American Airlines, and Eastern Air Lines; each of the three had developed requirements for a jet airliner to serve smaller cities with shorter runways and fewer passengers. United Airlines requested a four-engine aircraft for its flights to high-altitude airports, especially its hub at Stapleton International Airport in Denver, Colorado. American Airlines, which was operating the four-engined Boeing 707 and Boeing 720, requested a twin-engined aircraft for efficiency. Eastern Airlines wanted a third engine for its overwater flights to the Caribbean, since at that time twin-engine commercial flights were limited by regulations to routes with 60-minute maximum flying time to an airport (see ETOPS). Eventually, the three airlines agreed on a trijet design for the new aircraft.
In 1959, Lord Douglas, chairman of British European Airways (BEA), suggested that Boeing and de Havilland Aircraft Company (later Hawker Siddeley) work together on their trijet designs, the 727 and D.H.121 Trident, respectively. The two designs had a similar layout, the 727 being slightly larger. At that time Boeing intended to use three Allison AR963 turbofan engines, license-built versions of the Rolls-Royce RB163 Spey used by the Trident. Boeing and de Havilland each sent engineers to the other company's locations to evaluate each other's designs, but Boeing eventually decided against the joint venture. De Havilland had wanted Boeing to license-build the D.H.121, while Boeing felt that the aircraft needed to be designed for the American market, with six-abreast seating and the ability to use runways as short as 4,500 feet (1,400 m).
In 1960, Pratt & Whitney was looking for a customer for its new JT8D turbofan design study, based on its J52 (JT8A) turbojet, while United and Eastern were interested in a Pratt & Whitney alternative to the RB163 Spey. Once Pratt & Whitney agreed to go ahead with development of the JT8D, Eddie Rickenbacker, chairman of the board of Eastern, told Boeing that the airline preferred the JT8D for its 727s. Boeing had not offered the JT8D, as it was about 1,000 lb (450 kg) heavier than the RB163, though slightly more powerful; the RB163 was also further along in development than the JT8D. Boeing reluctantly agreed to offer the JT8D as an option on the 727, and it later became the sole powerplant.
With high-lift devices on its wing, the 727 could use shorter runways than most earlier jets (e.g. the 4,800 ft (1,500 m) runway at Key West International Airport).
A later 727 model, the 727-200, was stretched by 20 feet (6.10 metres) to carry 58 more passengers and replaced earlier jet airliners on short- and medium-haul routes such as the Boeing 707 and Douglas DC-8, as well as aging propeller airliners such as the DC-4, DC-6, DC-7, and the Lockheed Constellations.
For over a decade, more 727s were built per year than any other jet airliner; in 1984, production ended with 1,832 built and 1,831 delivered, the highest total for any jet airliner until the 737 surpassed it in the early 1990s.
The airliner's middle engine (engine 2) at the very rear of the fuselage gets air from an inlet ahead of the vertical fin through an S-shaped duct. This S-duct proved to be troublesome in that flow distortion in the duct induced a surge in the centerline engine on the take-off of the first flight of the 727-100. This was fixed by the addition of several large vortex generators in the inside of the first bend of the duct.
The 727 was designed for smaller airports, so independence from ground facilities was an important requirement. This 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. Hijacker D. B. Cooper used this hatch when he parachuted from the back of a 727, as it was flying over the Pacific Northwest. Boeing subsequently modified the design with the Cooper vane so that the airstair could not be lowered in flight. The design included an auxiliary power unit (APU), which allowed electrical and air-conditioning systems to run independently of a ground-based power supply, and without having to start one of the main engines. An unusual design feature is that the APU is mounted in a hole in the keel beam web, in the main landing gear bay. The 727 is equipped with a retractable tailskid that is designed to protect the aircraft in the event of an over-rotation on takeoff. The 727's fuselage has an outer diameter of 148 inches (3.8 m). This allows six-abreast seating (three per side) and a single aisle when 18-inch (46 cm) wide coach-class seats are installed. An unusual feature of the fuselage is the 10-inch (25 cm) difference between the lower lobe forward and aft of the wing as the higher fuselage height of the center section was simply retained towards the rear.
Nosewheel brakes were available as an option to reduce braking distance on landing, which provided reduction in braking distances of up to 490 ft (150 m).
The 727 proved to be such a reliable and versatile airliner that it came to form the core of many startup airlines' fleets. The 727 was successful with airlines worldwide partly because it could use smaller runways while still flying medium-range routes. This allowed airlines to carry passengers from cities with large populations, but smaller airports to worldwide tourist destinations. One of the features that gave the 727 its ability to land on shorter runways was its clean wing design. With no wing-mounted engines, leading-edge devices (Krueger, or hinged, flaps on the inner wing and extendable leading edge slats out to the wingtip) and trailing-edge lift enhancement equipment (triple-slotted, Fowler flaps) could be used on the entire wing. Together, these high-lift devices produced a maximum wing lift coefficient of 3.0 (based on the flap-retracted wing area). The 727 was stable at very low speeds compared to other early jets, but some domestic carriers learned after review of various accidents that the 40° flap setting could result in a higher-than-desired sink rate or a stall on final approach. These carriers' Pilots' Operation Handbooks disallowed using more than 30° of flaps on the 727, even going so far as installing plates on the flap lever slot to prevent selection of more than 30° of flaps.