B737-300 Seat Map

[Lupita Calvi]

TheBoeing 737 is an American narrow-body airliner produced by Boeing at its Renton factory in Washington.Developed to supplement the Boeing 727 on short and thin routes, the twinjet retained the 707 fuselage width and six abreast seating but with two underwing Pratt & Whitney JT8D low-bypass turbofan engines. Envisioned in 1964, the initial 737-100 made its first flight in April 1967 and entered service in February 1968 with Lufthansa.The lengthened 737-200 entered service in April 1968, and evolved through four generations, offering several variants for 85 to 215 passengers.

As of June 2024[update], 16,527 Boeing 737s have been ordered and 11,797 delivered.Initially, its main competitor was the McDonnell Douglas DC-9, followed by its MD-80/MD-90 derivatives. In 2013, the global 737 fleet had completed more than 184 million flights over 264 million block hours since its entry into service. It was the highest-selling commercial aircraft until being surpassed by the competing Airbus A320 family in October 2019, but maintains the record in total deliveries. The 737 MAX, designed to compete with the A320neo, was grounded worldwide between March 2019 and November 2020 following two fatal crashes.

Boeing had been studying short-haul jet aircraft designs, and saw a need for a new aircraft to supplement the 727 on short and thin routes.[2] Preliminary design work began on May 11, 1964,[3] based on research that indicated a market for a fifty to sixty passenger airliner flying routes of 50 to 1,000 miles (100 to 1,600 km).[2][4]

The initial concept featured podded engines on the aft fuselage, a T-tail as with the 727, and five-abreast seating. Engineer Joe Sutter relocated the engines to the wings which lightened the structure and simplified the accommodation of six-abreast seating in the fuselage.[5] The engine nacelles were mounted directly to the underside of the wings, without pylons, allowing the landing gear to be shortened, thus lowering the fuselage to improve baggage and passenger access.[6] Relocating the engines from the aft fuselage also allowed the horizontal stabilizer to be attached to the aft fuselage instead of as a T-tail.[7] Many designs for the engine attachment strut were tested in the wind tunnel and the optimal 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.

At the time, Boeing was far behind its competitors; the SE 210 Caravelle had been in service since 1955, and the BAC One-Eleven (BAC-111), Douglas DC-9, and Fokker F28 were already into flight certification.[8] To expedite development, Boeing used 60% of the structure and systems of the existing 727, particularly the fuselage, which differs in length only. This 148-inch (3.76 m) wide fuselage cross-section permitted six-abreast seating compared to the rivals' five-abreast. The 727's fuselage was derived from the 707.[9]

The proposed wing airfoil sections were based on those of the 707 and 727, but somewhat thicker; altering these sections near the nacelles achieved a substantial drag reduction at high Mach numbers.[10] The engine chosen was the Pratt & Whitney JT8D-1 low-bypass ratio turbofan engine, delivering 14,500 pounds-force (64 kN) of thrust.[11]

The concept design was presented in October 1964 at the Air Transport Association maintenance and engineering conference by chief project engineer Jack Steiner, where its elaborate high-lift devices raised concerns about maintenance costs and dispatch reliability.[5]

The original 737 continued to be developed into thirteen passenger, cargo, corporate and military variants. These were later divided into what has become known as the four generations of the Boeing 737 family:

On April 5, 1965, Boeing announced an order by United Airlines for 40 737s. United wanted a slightly larger capacity than the 737-100, so the fuselage was stretched 36 inches (91 cm) ahead of, and 40 inches (102 cm) behind the wing.[7] The longer version was designated the 737-200, with the original short-body aircraft becoming the 737-100.[14] Detailed design work continued on both variants simultaneously.

The first -100 was rolled out on January 17, 1967, and took its maiden flight on April 9, 1967, piloted by Brien Wygle and Lew Wallick.[15] After several test flights the Federal Aviation Administration (FAA) issued Type Certificate A16WE certifying the 737-100 for commercial flight on December 15, 1967.[16][17] It was the first aircraft to have, as part of its initial certification, approval for Category II approaches,[18] which refers to a precision instrument approach and landing with a decision height between 98 and 197 feet (30 and 60 m).[19] Lufthansa received its first aircraft on December 28, 1967, and on February 10, 1968, became the first non-American airline to launch a new Boeing aircraft.[16] Lufthansa was the only significant customer to purchase the 737-100 and only 30 aircraft were produced.[20]

The -200 was rolled out on June 29, 1967, and had its maiden flight on August 8, 1967. It was then certified by the FAA on December 21, 1967.[17][21] The inaugural flight for United Airlines took place on April 28, 1968, from Chicago to Grand Rapids, Michigan.[16] The lengthened -200 was widely preferred over the -100 by airlines.[22] The improved version, the 737-200 Advanced, was introduced into service by All Nippon Airways on May 20, 1971.[23]

The 737 original model with its variants, known later as the Boeing 737 Original, initially competed with SE 210 Caravelle and BAC-111 due to their earlier entry into service and later primarily with the McDonnell Douglas DC-9, then its MD-80 derivatives as the three European short-haul single aisles slowly withdrew from the competition. Sales were low in the early 1970s[24] and, after a peak of 114 deliveries in 1969, only 22 737s were shipped in 1972 with 19 in backlog. The US Air Force saved the program by ordering T-43s, which were modified Boeing 737-200s. African airline orders kept the production running until the 1978 US Airline Deregulation Act, which improved demand for six-abreast narrow-body aircraft. Demand further increased after being re-engined with the CFM56.[5] The 737 went on to become the highest-selling commercial aircraft until surpassed by the competing Airbus A320 family in October 2019, but maintains the record in total deliveries.[25]

The fuselage is manufactured in Wichita, Kansas, by Boeing spin-off company Spirit AeroSystems, before being moved by rail to Renton.[26] The Renton factory has three assembly lines for the 737 MAX; a fourth is planned to open at the Everett factory in 2024.[27]

The original engine nacelles incorporated thrust reversers taken from the 727 outboard nacelles. They proved to be relatively ineffective and 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.[31] 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. The improvement became standard on all aircraft after March 1969, and a retrofit was provided for active aircraft. Longer nacelle/wing fairings were introduced, and the airflow over the flaps and slats was improved. 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 short-field performance.[16]

After 40 years, in March 2008, the final 737-200 aircraft in the U.S. flying scheduled passenger service were phased out, with the last flights of Aloha Airlines.[37] As of 2018, the variant still saw regular service through North American charter operators such as Sierra Pacific Airlines.[38] With the improved short-field capabilities of the 737-200, Boeing offered the option of the gravel kit modification features preventing foreign object damage, which enables this aircraft to operate on remote, unimproved or unpaved runways, such as gravel runways, that other similarly sized jetliners cannot.[39] Until retiring its -200 fleet in 2007, Alaska Airlines used this option for some of its combi aircraft rural operations to serve many unimproved runways in Alaska.[40][41] Gravel-kitted 737-200 Combis are still used by Canadian North (which is due to retire their last one in early 2023),[42] Air Inuit, Nolinor Aviation and Chrono Aviation in Northern Canada where gravel runways are common.

As of September 2023[update], a relatively high number of 737-200s remain in service compared to other early jet airliners, with 50 examples actively flying for 30 carriers.[43] During the 737 MAX groundings, older 737s, including the 200 and Classic series, were in demand for leasing.[44]

Close to the next major upgrade of single aisle aircraft at Airbus and Boeing, the price of jet fuel reached a peak in 2008, when airlines devoted 40% of the retail price of an air ticket to pay for fuel, versus 15% in 2000.[47][48] Consequently, in that year carriers retired Boeing 737 Classic aircraft to reduce fuel consumption; replacements consisted of more efficient 737 Next Generation or A320 family aircraft. On June 4, 2008, United Airlines announced it would retire all 94 of its Classic 737 aircraft (64 737-300 and 30 737-500 aircraft), replacing them with A320 family jets taken from its Ted subsidiary, which has been shut down.[49][50][51] This intensified the competition between the two giant aircraft manufacturers, which has since become a duopoly competition.

Development began in 1979 for the 737's first major revision, which was originally introduced as the 'new generation' of the 737.[53] Boeing wanted to increase capacity and range, incorporating improvements to upgrade the aircraft to modern specifications, while also retaining commonality with previous 737 variants. In 1980, preliminary aircraft specifications of the variant, dubbed 737-300, were released at the Farnborough Airshow.[54] This first major upgrade series was later renamed 737 Classic. It competed primarily with the MD-80, its later derivative the MD-90, and the newcomer Airbus A320 family.

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