Boeing 737

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. Preliminary design work began on May 11, 1964, and Boeing's intense market research yielded plans for a 50- to 60-passenger airliner for routes 50 to 1,000 mi (80 to 1,609 km) long. Lufthansa became the launch customer on February 19, 1965, with an order for 21 aircraft, worth $67 million in 1965, after the airline received assurances from Boeing that the 737 project would not be canceled. Consultation with Lufthansa over the previous winter resulted in an increase in capacity to 100 seats.

On April 5, 1965, Boeing announced an order by United Airlines for 40 737s. United wanted a slightly larger airplane than the original 737. So Boeing stretched the fuselage 91 centimeters (36 in) ahead of, and 102 cm (40 in) behind the wing. The longer version was designated 737-200, with the original short-body aircraft becoming the 737-100.

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-111, Douglas DC-9, and Fokker F28 were already into flight certification. To expedite development, Boeing used 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 BAC-111 and DC-9's five-abreast layout. 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 inspection and servicing. Many thickness variations for the engine attachment 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, the 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 thicker. However, a substantial improvement in drag at high Mach numbers was achieved by altering these sections near the nacelle. The engine chosen was the Pratt & Whitney JT8D-1 low-bypass ratio turbofan engine, delivering 14,500 lbf (64 kN) thrust. 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.

Production and testing

The initial assembly of the 737 was adjacent to Boeing Field (now officially named King County International Airport) because the factory in Renton was filled to capacity with the building of the 707 and 727. After 271 aircraft were built, production moved to Renton in late 1970. A significant portion of fuselage assembly occurs in Wichita, Kansas, which was previously done by Boeing but now by Spirit AeroSystems, which purchased some of Boeing's assets in Wichita.

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.

The first of six -100 prototypes rolled out in December 1966, and made its maiden flight on April 9, 1967, piloted by Brien Wygle and Lew Wallick. On December 15, 1967, the Federal Aviation Administration certified the -100 for commercial flight, issuing Type Certificate A16WE. The 737 was the first aircraft to have, as part of its initial certification, approval for Category II approaches. 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. Lufthansa was the only significant customer to purchase the 737-100. Only 30 aircraft were produced.

The 737-200 had its maiden flight on August 8, 1967. It was certified by the FAA on December 21, 1967, and the inaugural flight for United was on April 28, 1968, from Chicago to Grand Rapids, Michigan. 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. However, 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. 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 short-field performance. 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. This became known as the 737-200 Advanced, which became the production standard in June 1971.

In 1970, Boeing received only 37 orders. Facing financial difficulties, Boeing considered closing the 737 production-line and selling the design to Japanese aviation companies. After the cancellation of the Boeing Supersonic Transport, and scaling back of 747 production, enough funds were freed up to continue the project. In a bid to increase sales by offering a variety of options, Boeing offered a 737C (Convertible) model in both -100 and -200 lengths. This model featured a 340 cm × 221 cm (134 in × 87 in) freight door just behind the cockpit, and a strengthened floor with rollers, which allowed for palletized cargo. A 737QC (Quick Change) version with palletized seating allowed for faster configuration changes between cargo and passenger flights. With the improved short-field capabilities of the 737, Boeing offered the option on the -200 of the gravel kit, which enables this aircraft to operate on remote, unpaved runways. Until retiring its -200 fleet in 2007, Alaska Airlines used this option for some of its rural operations in Alaska. Northern Canadian operators Air Inuit, Air North, Canadian North, First Air and Nolinor Aviation still operate the gravel kit aircraft in Northern Canada, where gravel runways are common.

In 1988, the initial production run of the -200 model ended after producing 1,114 aircraft. The last one was delivered to Xiamen Airlines on August 8, 1988.

Improved variants

Development began in 1979 for the 737's first major revision. 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.

Boeing engineer Mark Gregoire led a design team, which cooperated with CFM International to select, modify and deploy a new engine and nacelle that would make the 737-300 into a viable aircraft. They chose the CFM56-3B-1 high-bypass turbofan engine to power the aircraft, which yielded significant gains in fuel economy and a reduction in noise, but also posed an engineering challenge, given the low ground clearance of the 737 and the larger diameter of the engine over the original Pratt & Whitney engines. Gregoire's team and CFM solved the problem by reducing the size of the fan (which made the engine slightly less efficient than it had been forecast to be), placing the engine ahead of the wing, and by moving engine accessories to the sides of the engine pod, giving the engine a distinctive non-circular "hamster pouch" air intake. Earlier customers for the CFM56 included the U.S. Air Force with its program to re-engine KC-135 tankers.

The passenger capacity of the aircraft was increased to 149 by extending the fuselage around the wing by 2.87 meters (9 ft 5 in). The wing incorporated a number of changes for improved aerodynamics. The wingtip was extended 9 in (23 cm), and the wingspan by 1 ft 9 in (53 cm). The leading-edge slats and trailing-edge flaps were adjusted. The tailfin was redesigned, the flight deck was improved with the optional EFIS (Electronic Flight Instrumentation System), and the passenger cabin incorporated improvements similar to those developed on the Boeing 757. The prototype -300, the 1,001st 737 built, first flew on 24 February 1984 with pilot Jim McRoberts. It and two production aircraft flew a nine-month-long certification program.

In June 1986, Boeing announced the development of the 737-400, which stretched the fuselage a further 10 ft (3.0 m), increasing the passenger load to 188. The -400s first flight was on February 19, 1988, and, after a seven-month/500-hour flight-testing run, entered service with Piedmont Airlines that October.

The -500 series was offered, due to customer demand, as a modern and direct replacement of the 737-200. It incorporated the improvements of the 737 Classic series, allowing longer routes with fewer passengers to be more economical than with the 737-300. The fuselage length of the -500 is 1 ft 7 in (48 cm) longer than the 737-200, accommodating up to 140 passengers. Both glass and older-style mechanical cockpits arrangements were available. Using the CFM56-3 engine also gave a 25% increase in fuel efficiency over the older -200s P&W engines.

The 737-500 was launched in 1987 by Southwest Airlines, with an order for 20 aircraft, and flew for the first time on June 30, 1989. A single prototype flew 375 hours for the certification process, and on February 28, 1990, Southwest Airlines received the first delivery.

After the introduction of the -600/700/800/900 series, the -300/400/500 series was called the 737 Classic series.

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. Consequently, in that year carriers retired Classic 737 series aircraft to reduce fuel consumption; replacements consisted of more efficient Next Generation 737s or Airbus A320/A319/A318 series 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 Airbus A320 jets taken from its Ted subsidiary, which has been shut down.

Next-Generation models

Prompted by the modern Airbus A320, Boeing initiated development of an updated series of aircraft in 1991. After working with potential customers, the 737 Next Generation (NG) program was announced on November 17, 1993. The 737NG encompasses the -600, -700, -800, and -900, and is to date the most significant upgrade of the airframe. The performance of the 737NG is, in essence, that of a new aircraft, but important commonality is retained from previous 737 models.

The wing was redesigned with a new airfoil section, greater chord, increased wing span by 16 ft (4.9 m) and area by 25%, which increased total fuel capacity by 30%. New, quieter, more fuel-efficient CFM56-7B engines were used. The wing, engine, and fuel capacity improvements combined increase the 737's range by 900 nautical miles to over 3,000 nautical miles (5,600 km), now permitting transcontinental service. With the increased fuel capacity, higher maximum takeoff weight (MTOW) specifications are offered. The 737NG included redesigned vertical stabilizers, and winglets were available on most models. The flight deck was upgraded with modern avionics, and passenger cabin improvements similar to those on the Boeing 777, including more curved surfaces and larger overhead bins than previous-generation 737s. The Next Generation 737 interior was also adopted on the Boeing 757-300.

The first NG to roll out was a -700, on December 8, 1996. This aircraft, the 2,843rd 737 built, first flew on February 9, 1997. The prototype -800 rolled out on June 30, 1997, and first flew on July 31, 1997. The smallest of the new variants, the -600s, is the same size as the -500. It was the last in this series to launch, in December 1997. First flying January 22, 1998, it was given certification on August 18, 1998. A flight test program was operated by 10 aircraft; 3 -600s, 4 -700s, and 3 -800s.

In 2004, Boeing offered a Short Field Performance package in response to the needs of Gol Transportes Aéreos, which frequently operates from restricted airports. The enhancements improve takeoff and landing performance. The optional package is available for the 737NG models and standard equipment for the 737-900ER. The CFM56-7B Evolution nacelle began testing in August 2009 to be used on the new 737 PIP (Performance Improvement Package) due to enter service mid-2011. This new improvement is said to shave at least 1% off overall drag and have some weight benefits. Overall, it is claimed to have a 2% improvement on fuel burn on longer stages. In 2010, new interior options for the 737NG included the 787-style Boeing Sky Interior.

Boeing delivered the 5,000th 737 to Southwest Airlines on February 13, 2006. Boeing delivered the 6,000th 737 to Norwegian Air Shuttle in April 2009. Boeing delivered the 8,000th 737 to United Airlines on April 16, 2014. The Airbus A320 family has outsold the 737NG over the past decade, although its order totals include the A321 and A318, which have also rivaled Boeing's 757 and 717, respectively. The 737NG has also outsold the A320 on an annual basis in past years, with the next generation series extending the jetliner's run as the most widely sold and commonly flown airliner family since its introduction. The 10,000th aircraft was ordered in July 2012.

Boeing produces 42 of the type per month in 2015, and expects to increase to 52 per month in 2018. The slow selling 737-600 is no longer being marketed and was removed from the Boeing website as of 2016, its position as the smallest model being taken by the more popular 737-700.

The 737, particularly the 737 Next Generation, has been featured in many flight simulation games, including Infinite Flight and Microsoft Flight Simulator X.

Replacement or re-engining

Since 2006, Boeing has discussed replacing the 737 with a "clean sheet" design (internally named "Boeing Y1") that could follow the Boeing 787 Dreamliner. A decision on this replacement was postponed, and delayed into 2011. In November 2014, it was reported that Boeing plans to develop a new aircraft to replace the 737 in the 2030 time frame. The airplane is to have a similar fuselage, but probably made from composite materials similar to the Boeing 787 Dreamliner. Boeing also considers a parallel development along with the 757 replacement, similar to when the 757/767 were developed in the 1970s.

On July 20, 2011, Boeing announced plans for a new 737 version to be powered by the CFM International LEAP-X engine, with American Airlines intending to order 100 of these aircraft. On August 30, 2011, Boeing confirmed the launch of the 737 new engine variant, called the 737 MAX, with new CFM International LEAP-1B engines.

On September 23, 2015, Boeing announced a collaboration with Commercial Aircraft Corporation of China Ltd. to build a completion and delivery facility for the 737 in China, the first outside the U.S.

Design

The 737's main landing gear under the wings at mid-cabin rotates into wells in the aircraft's belly. The legs are covered by partial doors, and "brush-like" seals aerodynamically smooth (or "fair") the wheels in the wells. The sides of the tires are exposed to the air in flight. "Hub caps" complete the aerodynamic profile of the wheels. It is forbidden to operate without the caps, because they are linked to the ground speed sensor that interfaces with the anti-skid brake system. The dark circles of the tires are clearly visible when a 737 takes off, or is at low altitude.

737s are not equipped with fuel dump systems. The original aircraft were too small to require them, and adding a fuel dump system to the later, larger variants would have incurred a large weight penalty. Boeing instead demonstrated an "equivalent level of safety". Depending upon the nature of the emergency, 737s either circle to burn off fuel or land overweight. If the latter is the case, the aircraft is inspected by maintenance personnel for damage and then returned to service if none is found.

Engines

Engines on the 737 Classic series (300, 400, 500) and Next-Generation series (600, 700, 800, 900) do not have circular inlets like most aircraft. The 737 Classic series featured CFM56 turbofan engines, which yielded significant gains in fuel economy and a reduction in noise over the JT8D engines used on the -100 and -200, but also posed an engineering challenge given the low ground clearance of the 737. Boeing and engine supplier CFMI solved the problem by placing the engine ahead of (rather than below) the wing, and by moving engine accessories to the sides (rather than the bottom) of the engine pod, giving the 737 a distinctive non-circular air intake.

The wing also incorporated a number of changes for improved aerodynamics. The engines' accessory gearbox was moved from the 6 o'clock position under the engine to the 4 o'clock position (from a front/forward looking aft perspective). This side-mounted gearbox gives the engine a somewhat triangular rounded shape. Because the engine is close to the ground, 737-300s and later models are more prone to engine foreign object damage (FOD). The improved CFM56-7 turbofan engine on the 737 Next Generation is 7% more fuel-efficient than the previous CFM56-3 in the 737 classics. The newest 737 variants, the 737 MAX family, are to feature CFM International LEAP-1B engines with a 1.73 m fan diameter. These engines are expected to be 10-12% more efficient than the CFM56-7B engines on the 737 Next Generation family.

Flight systems

The primary flight controls are intrinsically safe. In the event of total hydraulic system failure or double engine failure, they will automatically and seamlessly revert to control via servo tab. In this mode, the servo tabs aerodynamically control the elevators and ailerons; these servo tabs are in turn controlled by cables running to the control yoke. The pilot's muscle forces alone control the tabs. For the 737 Next Generation, a six-screen LCD glass cockpit with modern avionics was implemented while retaining crew commonality with previous generation 737.

Most 737 cockpits are equipped with "eyebrow windows" positioned above the main glareshield. Eyebrow windows were a feature of the original 707 and 727. They allowed for greater visibility in turns, and offered better sky views if navigating by stars. With modern avionics, they became redundant, and many pilots actually placed newspapers or other objects in them to block out sun glare. They were eliminated from the 737 cockpit design in 2004, although they are still installed at customer request. These windows are sometimes removed and plugged, usually during maintenance overhauls, and can be distinguished by the metal plug which differs from the smooth metal in later aircraft that were not originally fitted with the windows.

Winglets

The 737 has four different winglet types: 737-200 Mini-winglet, 737 Classic/NG Blended Winglet, 737 Split Scimitar Winglet, and 737 Max Advanced Technology Winglet. The 737-200 Mini-winglets are part of the Quiet Wing Corp modification kit that received certification in 2005.

Blended winglets are in production on 737 NG aircraft and are available for retrofit on 737 Classic models. These winglets stand approximately 8 feet (2.4 m) tall and are installed at the wing tips. They help to reduce fuel burn (by reducing vortex drag), engine wear, and takeoff noise. Overall fuel efficiency improvement is up to five percent through the reduction of lift-induced drag.

Split Scimitar winglets became available in 2014 for the 737-800, 737-900ER, BBJ2 and BBJ3, and in 2015 for the 737-700, 737-900 and BBJ1. Split Scimitar winglets were developed by Aviation Partners Inc. (API), the same Seattle based corporation that developed the blended winglets; the Split Scimitar winglets produce up to a 5.5% fuel savings per aircraft compared to 3.3% savings for the blended winglets. Southwest Airlines flew their first flight of a 737-800 with Split Scimitar winglets on April 14, 2014. The next generation 737, 737 Max, will feature an Advanced Technology (AT) Winglet that is produced by Boeing. The Boeing AT Winglet resembles a cross between the Blended Winglet and the Split Scimitar Winglet.

Carbon brakes

As of July 2008 the 737 features carbon brakes manufactured by Messier-Bugatti. These new brakes, now certified by the Federal Aviation Administration, weigh 550–700 lb (250–320 kg) less than the steel brakes normally fitted to the Next-Gen 737s (weight savings depend on whether standard or high-capacity brakes are fitted). A weight reduction of 700 pounds on a Boeing 737-800 results in 0.5% reduction in fuel burn.

Short-field design package

A short-field design package is available for the 737-600, -700, and -800, allowing operators to fly increased payload to and from airports with runways under 5,000 feet (1,500 m). The package consists of sealed leading edge slats (improved lift), a two-position tail skid (enabling greater protection against tail strikes that may be caused by the lower landing speeds), and increased flight spoiler deflection on the ground. These improvements are standard on the 737-900ER.

Interior

The 737 interior arrangement has changed in successive generations. The original 737 interior was restyled for the 737 Classic models using 757 designs, while 777 architecture was used for the debut of the Next Generation 737. Designed using Boeing's new cabin concepts, the latest Sky Interior features sculpted sidewalls and redesigned window housings, along with increased headroom and LED mood lighting. Larger pivot-bins similar to those on the 777 and 787 have more luggage space than prior designs. The Sky Interior is also designed to improve cabin noise levels by 2–4 dB. The first 737 equipped with the Boeing Sky Interior was delivered to Flydubai in late 2010. Continental Airlines, Malaysia Airlines, and TUIFly have also received Sky Interior-equipped 737s.

Variants

The 737 models can be divided into three generations, including nine major variants. The "Original" models consist of the 737-100, 737-200/-200 Advanced. The "Classic" models consist of the 737-300, 737-400, and 737-500. The "Next Generation" variants consist of the 737-600, 737-700/-700ER, 737-800, and 737-900/-900ER. Of these nine variants, many feature additional versions such as the T-43, which was a modified Boeing 737-200 used by the United States Air Force (USAF).

The fourth generation derivative - the 737 MAX - is currently under development and will encompass the 737-MAX-7, 737-MAX-8, and 737-MAX-9 which will replace the -700, -800 and -900/900ER versions of the NG family, respectively.

737-100

The initial model was the 737-100. It was launched in February 1965. The -100 was rolled out on January 17, 1967, had its first flight on April 9, 1967 and entered service with Lufthansa in February 1968. The aircraft is the smallest variant of the 737. A total of 30 737-100s were ordered and delivered; the final commercial delivery took place on October 31, 1969 to Malaysia–Singapore Airlines. No 737-100s remain in commercial service. The original Boeing prototype, last operated by NASA and retired more than 30 years after its maiden flight, is on exhibit in the Museum of Flight in Seattle.

737-200

The 737-200 is a 737-100 with an extended fuselage, launched by an order from United Airlines in 1965. The -200 was rolled out on June 29, 1967, and entered service at United in April 1968. The 737-200 Advanced is an improved version of the -200, introduced into service by All Nippon Airways on May 20, 1971. The -200 Advanced has improved aerodynamics, automatic wheel brakes, more powerful engines, more fuel capacity, and longer range than the -100. Boeing also provided the 737-200C (Cargo), which allowed for conversion between passenger and cargo use and the 737-200QC (Quick Change), which facilitated a rapid conversion between roles. The 1,095th and last delivery of a -200 series aircraft was in August 1988 to Xiamen Airlines. Many 737-200s have been phased out or replaced by newer 737 versions. In July 2015, there were a combined 99 Boeing 737-200s in service, mostly with "second and third tier" airlines, and those of developing nations.

With a gravelkit modification the 737-200 can use unimproved or unpaved landing strips, such as gravel runways, that other similarly-sized jet aircraft cannot. Gravel-kitted 737-200 Combis are currently used by Canadian North, First Air, Air Inuit, Nolinor and Air North in northern Canada. For many years, Alaska Airlines made use of gravel-kitted 737-200s to serve Alaska's many unimproved runways across the state.

Nineteen 737-200s were used to train aircraft navigators for the U.S. Air Force, designated T-43. Some were modified into CT-43s, which are used to transport passengers, and one was modified as the NT-43A Radar Test Bed. The first was delivered on July 31, 1973 and the last on July 19, 1974. The Indonesian Air Force ordered three modified 737-200s, designated Boeing 737-2x9 Surveiller. They were used as Maritime reconnaissance (MPA)/transport aircraft, fitted with SLAMMAR (Side-looking Multi-mission Airborne Radar). The aircraft were delivered between May 1982 and October 1983.

After 40 years the final 737-200 aircraft in the U.S. flying scheduled passenger service were phased out in March 2008, with the last flights of Aloha Airlines. The variant still sees regular service through North American charter operators such as Sierra Pacific.

737 Classic series

The Boeing 737 Classic is the name given to the -300/-400/-500 series of the Boeing 737 after the introduction of the -600/700/800/900 series. The Classic series was originally introduced as the 'new generation' of the 737. Produced from 1984 to 2000, 1,988 aircraft were delivered.

737 Next Generation

By the early 1990s, it became clear that the new Airbus A320 was a serious threat to Boeing's market share, as Airbus won previously loyal 737 customers such as Lufthansa and United Airlines. In November 1993, Boeing's board of directors authorized the Next Generation program to replace the 737 Classic series. The -600, -700, -800, and -900 series were planned. After engineering trade studies and discussions with major 737 customers, Boeing proceeded to launch the 737 Next Generation series. Variants include the P-8 Poseidon.

737 MAX

In 2011, Boeing announced the 737 MAX program. Boeing will be offering three variants-the 737 MAX 7, 737 MAX 8 and the 737 MAX 9. These aircraft will replace the 737-700, 737-800 and 737-900ER, respectively. The main changes are the use of CFM International LEAP-1B engines, the addition of fly-by-wire control to the spoilers, and the lengthening of the nose landing gear. Deliveries are scheduled to begin in 2017. Southwest Airlines announced on December 13, 2011 that it would order the 737 MAX and became the launch customer. Ryanair, Norwegian Air Shuttle, and others have also placed firm orders for 737 MAX aircraft.

Boeing Business Jet (BBJ)

The Boeing Business Jet is a customized version of the 737. Plans for a business jet version of the 737 are not new. In the late 1980s, Boeing marketed the 77-33 jet, a business jet version of the 737-300. The name was short-lived. After the introduction of the next generation series, Boeing introduced the Boeing Business Jet (BBJ) series. The BBJ1 was similar in dimensions to the 737-700 but had additional features, including stronger wings and landing gear from the 737-800, and had increased range (through the use of extra fuel tanks) over the other 737 models. The first BBJ rolled out on August 11, 1998 and flew for the first time on September 4.

On October 11, 1999 Boeing launched the BBJ2. Based on the 737-800, it is 5.84 meters (19 ft 2 in) longer than the BBJ, with 25% more cabin space and twice the baggage space, but has slightly reduced range. It is also fitted with auxiliary belly fuel tanks and winglets. The first BBJ2 was delivered on 28 February 2001.

Boeing's BBJ3 is based on the 737-900ER. The BBJ3 has 1,120 square feet (104 m²) of floor space, 35% more interior space, and 89% more luggage space than the BBJ2. It has an auxiliary fuel system, giving it a range of up to 4,725 nautical miles (8,751 km), and a Head-up display. Boeing completed the first example in August 2008. This aircraft's cabin is pressurized to a simulated 6,500-foot (2,000 m) altitude.

Freighter

Boeing is studying plans to offer passenger to freighter conversion for the 737-800. Boeing has signed an agreement with Chinese YTO Airlines to provide the airline with 737-800 Boeing Converted Freighters (BCFs) pending a planned program launch.

Operators

The 737 is operated by more than 500 airlines, flying to 1,200 destinations in 190 countries. With over 10,000 aircraft ordered, over 7,000 delivered, and over 4,500 still in service, at any given time there are on average 1,250 airborne worldwide. On average, somewhere in the world, a 737 took off or landed every five seconds in 2006. Since entering service in 1968, the 737 has carried over 12 billion passengers over 74 billion miles (120 billion km; 65 billion nm), and has accumulated more than 296 million hours in the air. The 737 represents more than 25% of the worldwide fleet of large commercial jet airliners.

Civilian

As of August 2013, 140 Boeing 737-200 aircraft were in civilian service.

Military

Many countries operate the 737 passenger, BBJ, and cargo variants in government or military applications. Users with 737s include:

Competition

The Boeing 737 Classics and the Boeing 737 Next Generation have faced main challenges from the Airbus A320 family introduced in 1988, which was developed to compete also with the McDonnell Douglas MD-80/90 series and the Boeing 717 (formerly named McDonnell Douglas MD-95).

Boeing has shipped 9,295 aircraft of the 737 family since late 1967, with 7,859 of those deliveries since March 1, 1988, and has a further 4,430 on firm order as of January 2017. In comparison, Airbus has delivered 7,442 A320 series aircraft since their certification/first delivery in early 1988, with another 5,625 on firm order (as of January 2017).

Total production

In total, 9,365 units of the Boeing 737 have been built and delivered as of January 31, 2017.

Units by generation

As of 31 January 2017, 13,795 units of the Boeing 737 have been ordered, with 4,430 units still to be delivered. Units built by model type for 737 Original, Classic, Next Generation, and Boeing Business Jet families are as follows:

Data from Boeing.com through end of January 2017

Accidents and incidents

For incidents involving other 737 variants see Boeing 737 Classic incidents and Boeing 737 Next Generation incidents.

As of October 2015, a total of 368 aviation accidents and incidents involving all 737 aircraft have occurred, including 184 hull-loss accidents resulting in a total of 4,862 fatalities. The 737 has also been in 111 hijackings involving 325 fatalities.

An analysis by Boeing on commercial jet airplane accidents in the period 1959–2013 showed that the original series had a hull loss rate of 1.75 per million departures versus 0.54 for the classic series and 0.27 for the Next Generation series.

Aircraft on display