Boeing 737

In the early 1960s Boeing led the long- and medium-haul jet market with the 707 and 727, but had nothing for short sectors. Its market research pointed to demand for a fifty-to-sixty-seat aircraft flying stages of 50 to 1,000 miles (100 to 1,600 km), and preliminary design began on May 11, 1964. Boeing was late: the SE 210 Caravelle had been flying airline services since 1955, while the BAC One-Eleven, the Douglas DC-9 and the Fokker F28 were already moving through certification.

The first concept looked much like its rivals, with engines podded on the rear fuselage, a 727-style T-tail and five-abreast seating. Engineer Joe Sutter moved the engines under the wings, which lightened the structure and made six-abreast seating easier to arrange. The nacelles were attached directly to the underside of the wing without pylons, so the landing gear could be shorter and the fuselage lower, easing access for passengers and baggage; with the engines gone from the tail, the horizontal stabilizer could sit on the fuselage itself rather than on top of the fin. Many shapes for the wing-to-engine junction were tried in the wind tunnel, and the best at high speed proved to be a fairly thick fairing that filled the narrow channels between wing and nacelle.

To save time Boeing reused 60% of the 727's structure and systems, above all the fuselage, which differed only in length. That 148-inch (3.76 m) cross-section, itself derived from the 707, was the new aircraft's main selling point. The wing sections were based on those of the 707 and 727 but somewhat thicker, and reshaping them near the nacelles cut drag substantially at high Mach numbers. The chosen engine was the low-bypass Pratt & Whitney JT8D-1 turbofan rated at 14,500 pounds of thrust (64 kN). Chief project engineer Jack Steiner unveiled the concept in October 1964 at the Air Transport Association maintenance and engineering conference, where its elaborate high-lift devices raised concerns about maintenance costs and dispatch reliability.

Boeing's board approved a $150 million development programme on February 1, 1965, pitched on a simple promise: big-jet comfort on short-haul routes. On February 19 Lufthansa became launch customer with an order for 21 aircraft worth $67 million, after Boeing assured it the project would not be cancelled; consultations with the German airline over the preceding winter had raised the planned capacity to 100 seats.

On April 5, 1965, Boeing announced an order from United Airlines for 40 aircraft. United wanted a little more capacity, so the fuselage was stretched by 36 inches ahead of the wing and 40 inches behind it. The longer version became the 737-200 and the original short body the 737-100, with detailed design of both proceeding in parallel.

The first 737-100 was rolled out on January 17, 1967, and made its maiden flight on April 9, 1967, flown by Brien Wygle and Lew Wallick. After flight testing, the US Federal Aviation Administration (FAA) issued Type Certificate A16WE on December 15, 1967. It was the first aircraft approved for Category II approaches — precision approaches with a decision height between 30 and 60 m — as part of its initial certification. Lufthansa took its first aircraft on December 28, 1967, and on February 10, 1968, became the first non-American airline to launch a new Boeing type.

The 737-200 was rolled out on June 29, 1967, flew on August 8 and was certified on December 21, 1967. United Airlines flew its first service on April 28, 1968, from Chicago to Grand Rapids, Michigan. Airlines clearly preferred the longer aircraft, and the improved 737-200 Advanced entered service with All Nippon Airways on May 20, 1971.

Early sales were slow. The 737 first competed with the Caravelle and the One-Eleven, which had reached the market earlier, and later mainly with the McDonnell Douglas DC-9 and its MD-80 derivatives as the European twinjets faded away. After a peak of 114 deliveries in 1969, only 22 aircraft were shipped in 1972, with a backlog of just 19. The programme was kept alive by the US Air Force, which ordered T-43 trainers based on the 737-200, and by orders from African airlines, which kept the line running until the 1978 US Airline Deregulation Act boosted demand for six-abreast single-aisle aircraft. Re-engining with the CFM56 would increase that demand further.

The first generation, later called the 737 Original and sometimes nicknamed the '737 Jurassic', comprises the -100 and -200. Only 30 -100s were built: 22 for Lufthansa, five for Malaysia–Singapore Airlines and two for Avianca, the last delivered on October 31, 1969. The original thrust reversers, borrowed from the 727's outboard nacelles, proved ineffective and tended to lift the aircraft off the runway when deployed, unloading the main wheels and weakening the brakes. A 1968 fix added a 48-inch tailpipe extension and new target-type reversers; it became standard on all aircraft from March 1969 and was offered as a retrofit, and together with longer fairings and improved flaps and slats it raised payload, range and short-field performance.

The prototype, N73700, went to NASA on July 26, 1973, and flew as N515NA for 30 years until September 27, 2003; it is now on display at the Museum of Flight in Seattle as the last surviving -100. The -200 became the standard model: the 200 Advanced, with better aerodynamics, automatic brakes, more powerful engines and more fuel, offered 15% more payload and range and became the production standard in June 1971. Convertible 200C (Combi) and 200QC (Quick Change) versions were also offered. The 1,114th and final -200 went to Xiamen Airlines in August 1988. Its short-field ability led Boeing to offer an unpaved strip kit, with a gravel deflector on the nose gear and a vortex dissipator ahead of each engine, which operators in Alaska and northern Canada used for decades.

Work on the first major revision began in 1979, and preliminary specifications of the 737-300 were shown at Farnborough in 1980. The -300/-400/-500 series, later renamed 737 Classic, would compete with the MD-80, the derived MD-90 and the newly arrived Airbus A320 family. Engineer Mark Gregoire's team worked with CFM International to adapt the high-bypass CFM56-3B-1 turbofan, far more economical and quieter than the JT8D but larger in diameter — a serious problem on such a low aircraft. The answer was a smaller fan, an engine placed ahead of the wing and accessories moved to the sides of the nacelle, giving the intake its distinctive non-circular 'hamster pouch' shape.

The -300's fuselage was stretched by 2.87 m around the wing to seat 149 passengers; the wing gained extended tips and revised slats and flaps, the fin was redesigned, the flight deck offered optional electronic instruments (EFIS) and the cabin took improvements from the 757. The prototype, the 1,001st 737 built, flew on February 24, 1984, with Jim McRoberts at the controls. The 737-400, announced in June 1986, added another 3.0 m to reach 188 seats, with a tail bumper against tailstrikes and a strengthened wing spar; it flew on February 19, 1988, and entered service with Piedmont Airlines that October. The 737-500, launched in 1987 by Southwest Airlines as a direct replacement for the -200, flew on June 30, 1989, and was first delivered on February 28, 1990; its CFM56-3 engines made it 25 percent more fuel-efficient than the old -200. Boeing delivered 1,988 Classics between 1984 and 2000, the last two -400s going to CSA Czech Airlines on February 28, 2000. The fuel price spike of 2008 accelerated their retirement.

By the early 1990s the A320 family had become a serious threat, winning traditional 737 customers such as Lufthansa and United. In November 1993 Boeing's board authorised the Next Generation (NG) programme: a redesigned wing with greater span and area, more fuel, longer range, higher maximum weights, higher-pressure-ratio CFM56-7 engines, a glass cockpit and new interiors. Its four models, -600 to -900, seat 108 to 215 passengers, and the CFM56-7 was 7% more fuel-efficient than the Classic's CFM56-3.

The -700, the first NG, was launched in November 1993, and Southwest Airlines received the first in December 1997. The stretched -800 was launched on September 5, 1994, flew on July 31, 1997, and reached Hapag-Lloyd Flug in April 1998; it became the most widely used narrow-body airliner and the A320's direct rival. The smallest -600 reached only 69 units; the -900 flew on August 3, 2000, and its -900ER variant, with an extra pair of exits and a flat rear pressure bulkhead, seated up to 220 and entered service with Lion Air in April 2007. After Boeing's 1997 merger with McDonnell Douglas the NG was left as the A320's only rival; by May 2019 the series had 7,097 orders and 7,031 deliveries.

The A320neo family, launched in December 2010, reached 1,029 orders by June 2011 and broke Boeing's monopoly at American Airlines. Boeing's answer came on August 30, 2011: the 737 MAX, a re-engined NG with very-high-bypass CFM LEAP-1B turbofans with a 69-inch (1.76 m) fan, aerodynamic refinements such as split-tip winglets, and airframe changes. The MAX first flew on January 29, 2016, was certified by the FAA on March 8, 2017, and the first MAX 8 was delivered on May 6, 2017, to Lion Air subsidiary Malindo Air, which flew its first service on May 22. By January 2019 the series had 5,011 firm orders.

The family comprises the MAX 7, the MAX 8 — including the high-density MAX 200, launched in September 2014 and ordered by Ryanair — the MAX 9 and the MAX 10, stretched to take on the A321neo, which first flew on June 18, 2021, and is still awaiting certification. The FAA certified the MAX 7 on August 3, 2026. The flight deck adopted four 15.1-inch landscape displays derived from the 787 while keeping as much commonality as possible with earlier generations.

Lion Air Flight 610 crashed on October 29, 2018, and Ethiopian Airlines Flight 302 on March 10, 2019: two MAX 8s lost in similar circumstances, with 346 deaths in all. In both cases the Maneuvering Characteristics Augmentation System (MCAS) had activated — a system whose mention the FAA had allowed Boeing to remove from the flight manual in 2016. The FAA at first affirmed the aircraft's airworthiness, but on March 13, 2019, after 51 other regulators had acted, it grounded the type; by March 18 all 387 delivered aircraft were on the ground. Boeing suspended production in January 2020 and resumed it on May 27 that year.

The MAX's certification was investigated by Congress and several federal agencies, and engineering reviews uncovered further problems unrelated to MCAS in the flight computers and cockpit displays. On November 18, 2020, the FAA lifted the grounding after twenty months, the longest ever for a US airliner. Gol was the first airline in the world to resume passenger flights with the MAX, on December 9, 2020, and American Airlines the first in the United States, on December 29; Europe and Canada recertified it by January 2021. The cost to Boeing was estimated at $20 billion in fines, compensation and legal fees, plus more than $60 billion in indirect losses and some 1,200 cancelled orders.

On January 5, 2024, Alaska Airlines Flight 1282 lost a plug covering an unused emergency exit in mid-flight, causing a rapid decompression. The FAA grounded some 171 MAX 9s with a similar configuration and said it would not approve any production increase until it was satisfied with stricter quality control; Boeing published its Safety & Quality Plan on May 30, 2024.

Across four generations the 737 has kept the same basic design. Its nose and fuselage section come from the 707 and 727, as did the 'eyebrow' windows above the glareshield, which were never meant for celestial navigation — only the military T-43A had a sextant port — and were dropped from the design in 2004. The aircraft was deliberately built low for the small airports of the late 1960s, which often lacked jet bridges and powered belt loaders, so passengers could board by airstairs and bags could be lifted into the holds by hand; that same low stance became an obstacle every time larger engines had to be fitted. The main gear retracts into the belly with the tyre sides exposed, and the 737 has no fuel dump system, Boeing having demonstrated an equivalent level of safety instead.

Flight controls are hydro-mechanical: steel cables carry the pilot's inputs to hydraulic boosters, unlike the fly-by-wire systems of the A320 or 777. After a total hydraulic failure the primary controls revert to manual mode through servo tabs moved by the pilot's own strength. The NG introduced a six-screen glass cockpit, and the MAX added fly-by-wire control only for the spoilers. Passenger cabins drew successively on the 757 and the 777, and the Boeing Sky Interior, with LED lighting and larger bins, debuted with Flydubai in late 2010.

The flattened intakes of the Classic and NG are a direct result of fitting ever larger engines to such a low aircraft. The Classic's CFM56s were 25% more efficient than the JT8Ds and much quieter, and the MAX's LEAP-1Bs were expected to be 10 to 12% more efficient than the NG's CFM56-7Bs. The 737 has used four kinds of wingtip device: the -200 mini-winglets (certified in 2005), the blended winglets of the Classic and NG (standard on the NG since 2000, saving up to 5% of fuel), Aviation Partners' Split Scimitar winglets (available from 2014) and the MAX's Advanced Technology winglets.

The US Air Force received nineteen T-43s in 1973 and 1974, flying classrooms for navigator training derived from the 737-200 that served for 37 years until 2010. Indonesia ordered three 737-2X9 Surveiller maritime patrol aircraft, delivered between May 1982 and October 1983, and Brazil flew two 737-2N3s as VC-96s. The NG gave rise to the C-40 Clipper transport for the US Navy and Air Force, the E-7 Wedgetail airborne early warning aircraft — with its dorsal MESA radar, ordered by Australia, Turkey and South Korea — and the P-8 Poseidon anti-submarine aircraft, based on the 737-800ERX. On the civil side, the first Boeing Business Jet was rolled out on August 11, 1998; it was followed by the BBJ2, launched on October 11, 1999, and first delivered on February 28, 2001, and by the BBJ3, based on the -900ER, with a range of up to 8,751 km. Since 2016 the 737-800BCF programme has converted passenger jets into freighters.

From the Classic onwards the 737's great rival has been the A320 family, which entered service in 1988. Between March 1988 and December 2018 Boeing delivered 8,918 737s and Airbus 8,605 A320-family aircraft. The European family overtook the 737 in orders in October 2019 — the year 737 orders fell by 90% because of the MAX grounding — and in total deliveries in 2025: by September 2026 Airbus had delivered 12,900 A320s against 12,739 737s. The A220 at the small end and China's Comac C919 complete the competitive field.

In 2006 more than 4,500 737s were flown by over 500 airlines to 1,200 destinations in 190 countries. By 2013 the fleet had carried more than 16.8 billion passengers on over 184 million flights, and in 2018 more than 7,500 were in service, with around 2,800 airborne at any moment and some three million passengers a day. In June 2021 there were 9,315 737s in service against 9,353 A320-family aircraft. As of June 2024 the largest operators were Southwest Airlines, Ryanair, United Airlines, American Airlines and Delta Air Lines. Fuselages are built in Wichita, Kansas, by Spirit AeroSystems and travel by rail to Washington, where Renton has three MAX assembly lines and Everett a fourth that started production in July 2026.

By November 2023 the 737 family had been involved in 529 accidents and incidents, with 234 hull losses and 5,779 fatalities — figures that must be read against the size of the fleet. Boeing's analyses show the hull-loss rate per million departures falling generation by generation from the Original to the NG before rising again with the MAX accidents. In the 1990s a series of uncommanded rudder deflections on -200 and -300 aircraft caused two fatal accidents, United Airlines Flight 585 and USAir Flight 427, killing 157 people; the National Transportation Safety Board traced them to a design flaw, and the FAA ordered the rudder servo valves replaced on every 737 and introduced new pilot training protocols.