The Boeing 737 is a short- to medium-range, twin-engine narrow-body jet airliner. Originally developed as a shorter, lower-cost twin-engine airliner derived from Boeing's 707 and 727, the 737 has developed into a family of nine passenger models with a capacity of 85 to 215 passengers. The 737 is Boeing's only narrow-body airliner in production, with the -600, -700, -800, and -900ER variants currently being built.
Originally envisioned in 1964, the initial 737-100 first flew in 1967, and entered airline service in February 1968.[4][5] It was followed by the lengthened 737-200, which entered service in April 1968. In the 1980s, Boeing launched the -300, -400, and -500 models, subsequently referred to as the Boeing 737 Classic series. The 737 Classics added capacity and incorporated CFM56turbofan engines along with wing improvements. In the 1990s, Boeing introduced the 737 Next Generation with multiple changes including a redesigned wing, upgraded cockpit, and new interior. The 737 Next Generation comprises the four -600, -700, -800, and -900ER models, ranging from 102 ft (31.09 m) to 138 ft (42.06 m) in length. Boeing Business Jet versions of the 737 Next Generation are also produced.
The 737 series is the best-selling jet airliner in the history of aviation.[4] The 737 has been continuously manufactured by Boeingsince 1967 with 6,919 aircraft delivered and 2,215 orders yet to be fulfilled as of September 2011.[1] 737 assembly is centered at the Boeing Renton Factory in Renton, Washington. Many 737s serve markets previously filled by 707, 727, 757, DC-9, and MD-80/90 airliners, and the aircraft currently competes primarily with the Airbus A320 family.[6] There are, on average, 1,250 Boeing 737s airborne at any given time, with two departing or landing somewhere every five seconds.[7]
| Produced | 1968–present |
|---|---|
| Number built | 6,919 as of September 2011[1] |
| Unit cost | 737-100: US$32 million[2] 737-600: US$56.9 million[3] 737-700: US$67.9 million 737-800: US$80.8 million 737-900ER: US$85.8 million |
Background
Boeing had been studying short-haul jet aircraft designs and wanted to produce another aircraft to supplement the 727 on short and thin routes.[8] Preliminary design work began on 11 May 1964,[9] and Boeing's intense market research yielded plans for a 50- to 60-passenger airliner for routes 50 to 1,000 mi (80 to 1,600 km) long.[8][10] Lufthansa became the launch customer on 19 February 1965,[11] with an order for 22 aircraft, worth $67 million[12] (1965, $190.28 million in 2008), after the airline, it was reported, received assurances from Boeing that the 737 project would not be cancelled.[13] Consultation with Lufthansa over the previous winter resulted in an increase in capacity to 100 seats.[11]
On April 5, 1965, Boeing announced an order by United Airlines for 40 737s. United wanted a slightly larger airplane than the original design; therefore, Boeing stretched the fuselage an extra 91 centimetres (36 in) ahead of, and 102 centimetres (40 in) behind the wing.[14] The longer version was designated 737-200, with the original short-body aircraft becoming the 737-100.[15]
Detailed design work continued on both variants at the same time. Boeing was far behind its competitors when the 737 was launched, as rival aircraft BAC 1-11, Douglas DC-9, and Fokker F28 were already into flight certification.[12] To expedite development, Boeing utilized 60% of the structure and systems of the existing 727, the most notable being the fuselage cross-section. This fuselage permitted six-abreast seating compared to the rival 1-11 and DC-9's five-abreast layout,[11]. Design engineers decided to mount the nacelles directly to the underside of the wings to reduce the landing gear length and kept the engines low to the ground for easy ramp operations.[16]. Many thickness variations for the strut were tested in the wind tunnel and the most desirable shape for high speed was found to be one which was relatively thick, filling the narrow channels formed between the wing and the top of the nacelle, particularly on the outboard side. Originally, span arrangement of the airfoil sections of the 737 wing was planned to be very similar to that of the 707 and 727, although somewhat more thick. However, a substantial improvement in drag at high Mach numbers was achieved by altering these sections near the nacelle.[17] The engine chosen was the Pratt & Whitney JT8D-1 low-bypass ratio turbofan engine.[18] With the wing-mounted engines, Boeing decided to mount the horizontal stabilizer on the fuselage rather than the T-tail style of the Boeing 727.[14]
Production and testing
The initial assembly of the 737 was adjacent to Boeing Field (now officially called King County International Airport) because the factory inRenton was at capacity building the 707 and 727. After 271 aircraft, production was moved to Renton in late 1970.[13][19] A significant portion of the fuselage assembly is in Wichita, Kansas previously by Boeing but now by Spirit AeroSystems, which purchased some of Boeing's assets in Wichita.[20] The fuselage is joined with the wings and landing gear, then moves down the assembly line for the engines, avionics, and interiors. After rolling out the aircraft, Boeing tests the systems and engines before its maiden flight to Boeing Field, where it is painted and fine-tuned before delivery to the customer.[21]
The first of six -100 prototypes rolled out in December 1966, and made its maiden flight on 9 April 1967 piloted by Brien Wygle and Lew Wallick.[22] On December 15, 1967 the Federal Aviation Administration certified the -100 for commercial flight,[23] issuing Type Certificate A16WE.[24] The 737 was the first aircraft to have, as part of its initial certification, approval for Category II approaches.[25] Lufthansa received their first aircraft on December 28, 1967 and on February 10, 1968 became the first non-American airline to launch a new Boeing aircraft.[23]Lufthansa was the only significant customer to purchase the 737-100. Only 30 aircraft were ever produced.[26]
The 737-200 had its maiden flight on August 8, 1967. It was certified by the FAA on December 21, 1967,[24][27] and the inaugural flight for United was on April 28, 1968 from Chicago toGrand Rapids, Michigan.[23] The lengthened -200 was widely preferred over the -100 by airlines.
Initial derivatives
The original engine nacelles incorporated thrust reversers taken from the 727 outboard nacelles. Unfortunately they proved to be relatively ineffective and apparently tended to lift the aircraft up off the runway when deployed. This reduced the downforce on the main wheels thereby reducing the effectiveness of the wheel brakes. In 1968, an improvement to the thrust reversal system was introduced. A 48-inch tailpipe extension was added and new, target-style, thrust reversers were incorporated. The thrust reverser doors were set 35 degrees away from the vertical to allow the exhaust to be deflected inboard and over the wings and outboard and under the wings.[28] The improvement became standard on all aircraft after March 1969, and a retrofit was provided for active aircraft. Boeing fixed the drag issue by introducing new longer nacelle/wing fairings, and improved the airflow over the flaps and slats. The production line also introduced an improvement to the flap system, allowing increased use during takeoff and landing. All these changes gave the aircraft a boost to payload and range, and improved the short-field performance.[23] In May 1971, after aircraft #135, all improvements, including more powerful engines and a greater fuel capacity, were incorporated into the 737-200, giving it a 15% increase in payload and range over the original -200s.[25] This became known as the 737-200 Advanced, which became the production standard in June 1971.
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