The Boeing 737 has been one of the most successful aircraft of all time. As of mid-2020, it remains the most delivered aircraft to date but has been overtaken by the Airbus A320 for orders. First flying in 1967, it has been through several variants since then, each time improving and updating its offering.
This guide takes a look at the history of this long-serving aircraft, through each of the generations and variants produced. It will also look at the future, following the grounding of the latest 737 MAX aircraft, and discuss where Boeing may head next.
The 737 – a long term success story
The 737 has been a major success for Boeing. It was envisioned in the 1960s as a supplement, and eventual replacement, to the Boeing 727. It has remained in production ever since, moving through four different generations, each with several variants to serve different airline requirements.
To date, 10,580 737 aircraft have been delivered (according to data from Boeing as of July 2020), and 14,801 have been ordered. This makes it the most sold aircraft to date, but the Airbus A320 has now caught up in orders, with 15,572 orders (as of May 2020, according to Airbus).
Part of this success has been its well-engineered design and constant evolution to meet airline demands. The 737 was designed to beat the competition at the time (mainly the Douglas DC-9, but also the BAC One Eleven and the Caravelle from Sud Aviation).
As the 737 has moved through its variants, its offering has changed. This has included options such as combined cargo models, and adaptions for gravel landing, designed to gain market share. It has also, of course, evolved with the times, with subsequent generations adding new engines and offering more efficient operation to keep up with the competition.
By variant, 737 orders and deliveries break down as follows:
| Variant | Orders | Deliveries |
|---|---|---|
| 737-100 | 30 | 30 |
| 737-200 | 1114 | 1114 |
| 737-300 | 1113 | 1113 |
| 737-400 | 486 | 486 |
| 737-500 | 389 | 389 |
| 737-600 | 69 | 69 |
| 737-700 (including BBJ1) | 1167 | 1164 |
| 737-800 (including BBJ2) | 5189 | 5143 |
| 737-900 (including 737-900ER and BBJ3) | 564 | 564 |
| 737 MAX | 4559 | 387 |
Evolution of the 737 – switching to twin engines
It may not seem as obvious today, with the prevalence of twin-engine aircraft flying, but at the time of its design and launch, one of the key offerings of the 737 was two engines. The Boeing aircraft preceding it, the 707 and the 727, were four and three engine aircraft. Market attention was shifting to a more economical two engine possibility, and this is what the 737 set out to offer.
Other manufacturers were, of course, also developing twin-engine aircraft. Boeing opted for a different design, though, which ultimately proved very successful. It mounted the two engines under the wings, whereas many other manufacturers chose to mount the engines on the rear of the fuselage.
This move allowed Boeing to offer a wider fuselage, and the 737 featured six across seating (five across was typical with other manufacturers). It also meant that standard width freight containers could be loaded, allowing for dual-use that become popular with many airlines. Maintenance was easier, too, with engines closer to the ground.
The 737 Original: 737-100 and 737-200
New construction location
Construction of the first 737 aircraft took place at Boeing’s plant at Boeing Field in Seattle, in the same building (Plant 2) where aircraft such as the B-17 Flying Fortress, B-52 Stratofortress were built. According to Boeing, this building was not large enough to accommodate the 737’s tail, which was added outside the building before the aircraft was transferred to the new production line. Production soon moved to Renton, Washington, where it remains today.
The first 737 aircraft was unveiled on January 17th, 1967. Boeing recalls the event on its website:
“At a ceremony inside the Thompson Site on Jan. 17, 1967, the first 737 was introduced to the world. The festivities included a christening by flight attendants representing the 17 airlines that had ordered the new plane.”
The original generation and variants
The first aircraft launched was the 737-100. The launch customer was Germany’s Lufthansa – the first non-US based airlines to launch a Boeing aircraft. It first flew in February 1968.
The 737-100 featured the introduction of twin engines. Boeing chose Pratt & Whitney JT8D low-bypass engines. It was smaller than any model that followed it, offering a typical two-class capacity of just 85 (with a maximum exit limit of 124). Only 30 737-100 aircraft were ever delivered, however, and it was soon improved by the 737-200.
The 737-200 quickly followed the 737-100. It first flew in August 1967 and entered service with United Airlines in April 1968. The main difference was an extended fuselage, requested by United and preferred by most airlines. This offered a typical seating capacity of 102 (and a limit of 136). It also added improved engines (the same JT8D engines but with higher thrust).
Despite airline requested improvements, sales were still slow. Boeing even considered canceling the project in the early days of slow 737-200 sales, but it picked up with an order from the US Air Force for 19 T-43 military variants.
Adaptions to meet customer demand
There was also a 737-200 Advanced model, launched in 1971. This included improved aerodynamics, higher thrust engines, and increased fuel capacity and range. These improvements worked well, addressing airlines’ concerns with the first model, and the 737-200 went on to sell 1095 aircraft, with production lasting until 1988.
The focus on meeting customer requirements continued, with options including an ‘Unpaved Strip Kit‘ allowing landing on gravel runways, popular with some airlines in places such as Canada and Alaska.
Boeing also developed a convertible version for passenger and cargo use (the 737-200C). This variant had a larger cargo door and strengthened cabin floor. In total, 104 were delivered.
The 737-200 proved to be a popular and versatile plane. As of July 2020, there were still 36 737-200 aircraft operational. This was more than the number of active A380 aircraft at the time! These remain in passenger service with some Canadian airlines, and in operation with several government operators. Simple Flying took a look at these and highlighted the oldest 737s still operating – a couple of them are over 50 years old.
The 737 Classic: 737-300, 400 and 500
Introducing the first major improvements
Boeing went on to make several improvements for the next generation of 737s. The Classic series was launched with the 737-300 in 1984. There were many changes and improvements, but importantly the new models kept commonality (in both design and flight operation) with earlier models.
The main changes in the Classic series were improvements in capacity and fuel efficiency.
The 737-300 was powered by a new CFM56 turbofan engine, offering increased thrust (up to 23,500 lbf compared to 16,400 lbf for the Pratt & Whitney engines on the 737-200). However, with a larger engine diameter and low ground clearance of the 737, they had to be placed ahead of the wing.
Other structural improvements for the Classic series included:
- An increase in wingspan and extension of the wingtips, offering improved aerodynamics.
- A new design of the tailfin.
- Several cabin improvements (based on features developed for the Boeing 757).
This marked the real start of the success of the 737 family. The Original series picked up eventually after initial slow sales, but it was with the Classic series that orders really increased, The Classic series remained in production until 2000, and a total of 1,988 aircraft were delivered.
The Classic series and variants
The Classic series had three variants offering different capacities and range, with the same main airframe design. This choice of size and range became the standard with all future generations of the 737.
The 737-300 was the middle-sized option, with a typical two-class capacity of 126 (an increase of 24 over the previous generation 737-200).
The 737-400 continued this expansion. Stretching the 737-300 around three meters increased the capacity to 188. The range was slightly reduced to 3,820 kilometers (compared to 4,176 kilometers with the -300).
And the 737-500 was offered as a smaller model. This model reverted to the size and capacity of the 737-200, with a typical two-class capacity of 110. This also pushed the range up to 4,398 kilometers. It made a perfect replacement for the aging -200 aircraft at the time.
The 737 Next Generation: 737-600, 700, 800, and 900
Competing with the A320
The next major update to the 737 started in 1991 when Boeing began working on the 737 Next Generation series, or 737NG. Airbus’ development of the A320 prompted this.
During the 1980s, there was a gap in the market for a new European constructed single-aisle aircraft. Governments realized this and worked with several manufacturers to develop plans. Airbus eventually went on to design three aircraft of differing sizes, later to become the A320 family. The A320 entered service in April 1988 with Air France.
Boeing faced serious competition from the A320. It offered more efficient operation than the 737 Classic series, and full fly-by-wire design. Several Boeing customers, including Lufthansa and United Airlines, placed orders with Airbus early on.
Its solution was the Next Generation series program, launched in 1993. The first aircraft did not fly, however, until December 1997, with launch customer Southwest Airlines.
Next Generation improvements
Fuel efficiency was the main improvement with the series. This was to compete with the A320 as well as address the high oil prices at the time. It also offered improved range and higher capacity options than the Classic series.
The 737NG was a significant update to the 737, with new airframe and wing designs, and a glass cockpit. Importantly though, it maintained commonality with previous 737 variants, helping airlines with maintenance and crew operations.
The main aircraft updates include:
- Upgraded CFM56-7 engines, with improved fuel efficiency.
- A re-designed wing, with increased span and area (and allowing increased fuel capacity).
- New digital cockpit.
- Interior cabin improvements, including larger bin space (several updates based on 777 designs).
The Next Generation series and variants
There are four 737NG models of differing sizes. The 737-600 first flew with SAS in 1998. It is the smallest variant, with a typical two-class capacity of just 108, and an exit limit of 149. With its small size, it was designed as a replacement for the 737-500, and as a competitor for the A318, the smallest member of the A320 family.
The 737-700 is stretched by around 2.4 meters, taking its typical capacity up to 128 (but retained the same exit limit). This was the first variant launched, entering service with Southwest Airlines in December 1997. The 737-700 was also offered as a convertible cargo version, the 737-700C.
The 737-800 entered service in April 1988 with Hapag-Lloyd Flug (later to become TUIfly). It is stretched further than the 737-700, making it a suitable replacement for the 737-400. It takes passenger capacity up to 189.
The 737-800 has been the best selling of any 737 variant, totaling up 4,991 orders (according to Boeing data). Simple Flying looked previously at how compromise has made it such a success. The 737-800 offers an excellent combination of range and capacity, not the largest of either, but a very versatile option for many airlines.
The longest version, the 737-900, entered service last, in 2000. An extended range version, the 737-900ER increased range as well as passenger capacity (up to a maximum of 220 as it added a second set of exit doors).
Military variants of the 737NG
The 737 has been popular with many government and military operators, as well as airlines. The 737NG is notable for its conversion for two military uses:
- The 737 AEW&C (737-700W) is an airborne early warning and control aircraft, developed from the 737-700. It was launched first with the Australian government and has since also been delivered to the Turkish Air Force, the Republic of Korea Air Force and the UK Royal Air Force (17 aircraft in total).
- The P-8 Poseidon (737-800A) is a military maritime patrol aircraft, first developed for the US Navy, to replace a Lockheed version introduced in the 1960s. It is based on an extended range version of the 737-800. Boeing has sold 175 of these aircraft to seven countries.
Boeing Business Jet series
Boeing has been offering business jet versions of the 737 since the late 1980s, with the 737-300. The series was expanded and renamed as Boeing Business Jet (BBJ) with the 737NG series.
Three BBJ variants are offered:
- BBJ1 was the first to be launched, first flying in September 1998. It is based on the 737-700, but with some features (including a stronger landing gear and increased range) of other 737NG variants.
- BBJ2 was first delivered in February 2001. It is based on the larger 737-800 and offers increased range and cabin space.
- BBJ3 is a larger variant, based on the 737-900ER. Only three have been ordered (compared to 121 BBJ1 and 23 BBJ2 aircraft).
The BBJ series was launched with the 737NG, but it covers other aircraft as well. There are BBJ versions of the 737 MAX, as well as the 757. 767, 777, 787, and 747.
The 737 MAX series: 737 MAX 7, MAX 8, MAX 9 and MAX 10
Further efficiency improvements
Moving forward to 2011, Boeing again responded to developments from Airbus in its next generation of the 737. Airbus launched the A320neo (new engine option) family in 2010. This offers significantly improved efficiency with new engines and other improvements.
The 737 MAX series was announced in 2011 and was introduced in May 2017 with the Indonesian airline Malindo Air.
Efficiency is the main improvement. The 737 MAX uses new CFM International LEAP engines and has several aerodynamic modifications, including distinctive winglets.
According to the website The 737 Information Site, there is a 14% improvement between the Next Generation and 737 MAX series. To demonstrate how this has improved significantly since the introduction of the 737, take a look at previous improvements. The same website quotes fuel burn reduction of 20% moving from the Original to the Classic series and a further 7% improvement in the Next Generation series.
MAX series variants
Like the Next Generation series, the MAX series has four main variants of differing capacity and range. In general, these offer an improvement over the Next Generation models, but of course, at an increased cost. Simple Flying looking in more detail at these differences and prices in a previous article.
| Variant | Passengers (exit limit) | Range |
| 737 MAX 7 | 172 | 7,130 kilometers |
| 737 MAX 8 | 200 | 6,570 kilometers |
| 737 MAX 9 | 220 | 6,570 kilometers |
| 737 MAX 10 | 230 | 6,110 kilometers |
There is also a 737 MAX 200, a high capacity version of the MAX 8 that has been ordered by Ryanair. This has additional exits to allow more passenger capacity. Delivery was delayed with the grounding of the 737 MAX, but Ryanair hopes to take delivery by 2021.
Grounded in 2019
The 737 MAX may offer improvements in efficiency, capacity, and range, but it has also had problems. It was involved in two fatal crashes, Lion Air Flight 610 in October 2018 and Ethiopian Airlines Flight 302, in March 2019. Following these, the aircraft was grounded by the FAA on March 13th, 2019.
The problems were with the Manoeuvering Characteristics Augmentation System (MCAS). MCAS is designed to move the nose down if an increased angle of attack is detected, to help avoid a stall. In the case of the MAX, there were several problems, including erroneous readings from the sensors, and the removal of specific MCAS descriptions from aircraft manuals.
As of July 2020, changes have been made to the MAX flight control systems, and test flights have been completed. This is the first stage of recertification of the type, and Boeing is hopeful this will happen by the end of 2020.
The grounding has been costly for Boeing. As of July 2020, Boeing has accrued over $9 billion in liability. It has also, of course, suffered reputational damage and several canceled orders.
What’s next for the 737?
Airbus edging ahead in orders
For a long time, the 737 was the best selling narrowbody aircraft. Boeing got ahead of the competition with its innovations in the original 737 and has maintained its focus on improvements that match customers’ needs since.
Airbus changed this, however, with the A320. It has been quicker at launching new, more efficient versions and has gained market share. The grounding of the 737 MAX gave Airbus a further boost, and in late 2019 the A320 moved ahead of the 737 for aircraft sold.
As of July 2020, Boeing has 14,801 orders across the whole 737 family. But Airbus has moved ahead with 15,572 orders for the A320 family. Boeing is still ahead in deliveries, for the time being.
Reduced production in 2020
In July 2020, Boeing updated its plan for reduced construction of aircraft due to the slowdown in aviation. In a letter sent to staff, CEO Mr. Calhoun explained the reasoning:
“The reality is the pandemic’s impact on the aviation sector continues to be severe (…) This pressure on our commercial customers means they are delaying jet purchases, slowing deliveries, deferring elective maintenance, retiring older aircraft, and reducing spend — all of which affects our business and, ultimately, our bottom line,” Boeing said in its statement.
“To align to a smaller market, we lowered commercial production rates and took tough workforce actions throughout the quarter. Unfortunately, it’s become clear that we need to make further adjustments based on the prolonged impact of COVID-19.”
This will affect the 737, the 777 and 777X, and the 787. Production of the 737 will gradually increase to a rate of 31 per month by the beginning of 2022.
Before the slowdown, production had been stead at 42 aircraft per month, but with plans to increase the rate to 57 per month (according to FlightGlobal).
A fifth 737 generation?
As of July 2020, it is still not clear what the next version of the 737 will look like, but based on previous plans from Boeing, there could be a major re-design coming.
Boeing first proposed changes to the 737 as part of the Yellowstone project. This looked at updates to all aircraft series, using new technologies, electrical control systems, and composite structures. The 787 was delivered as part of this. But the project has stalled for the 737, with Boeing launching the 737 MAX in 2011 instead of pursuing it.
There have been more developed plans for a larger aircraft, though. In 2015, it was reported that Boeing was pursuing a design for a New Midsize Aircraft (NMA), possibly entering service in the mid-2020s, and perhaps becoming the Boeing 797. It would be a twin-aisle seven across aircraft, with both 225 and 275 seat variants. It would not really be a replacement for the 737, addressing a gap between the 737 and the larger widebody market instead.
This, too, was put on hold, with Boeing announcing in January 2020 that it would focus instead on returning the 737 MAX to service, and look again at new aircraft design.
Simple Flying looked at the NMA and whether similar plans could return. When markets recover, there is likely a need for a larger, efficient point-to-point plane that the NMA could address. Especially with aging 757 and 767 aircraft, and a completing A321XLR offering from Airbus.
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The slowdown may well have given Boeing some time to look again at the NMA design as well as options for the 737. But it remains likely that in the near future, we will see a returned 737 MAX being offered alongside a larger, newly designed, NMA of some form.
What are your thoughts about the Boeing 737? Let us know what you think in the comment section.