page_title: Boeing 727
section_title: Design
hierarchical_section_title: Boeing 727 / Design
context_page_description: The Boeing 727 is a narrow-body airliner produced by Boeing Commercial Airplanes.
  After the heavy 707 quad-jet 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 November 27, 1962, first flew on February 9, 1963, and entered service with Eastern on February 1, 1964.
  Boeing's only trijet is powered by 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.
  It shares its six-abreast upper fuselage cross-section and cockpit with the 707.
  The 133 ft long 727-100 typically carries 106 passengers in two classes over 2,250 nmi, 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 longer variant typically carries 134 passengers in two classes over 2,550 nmi, or 155 in a single class.
  Besides the airliner accommodation, a freighter and a Quick Change convertible version were offered.
context_section_description: 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. Another innovation was the 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 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-degree 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.
caption: The 727 tail and rear airstairs
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