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The Boeing 737 is one of the most successful aircraft of all time. It is certainly one of the longest in development – with the first aircraft entering service in 1968 and the latest MAX 10 still to do so. It has sold the most of any modern commercial aircraft (with over 11,000 aircraft delivered to date) – although the Airbus A320 has recently taken over for orders.

The 737 has evolved through several series and variants, with continual improvements. It has retained the same type rating throughout, however, which has been a great advantage for Boeing and for operating airlines.

Developing the 737 – revolutionary at the time

The twin engine appearance of the Boeing 737 seems normal today, but it marked a new design route at the time of its launch. The four engine Boeing 707 and the three engine Boeing 727 had been successful for Boeing, but airlines became increasingly interested during the 1960s in a more economical two engine offering.

Boeing was not the only manufacturer offering a twin engine narrowbody at the time. However, it took a different approach. It mounted the engines low under the wings, instead of high on the fuselage. This allowed for a wider fuselage and cabin (with six abreast seating instead of the five typical with the competition) and the stowage of standard sized freight containers. It also allowed easier access to the engines for inspection and maintenance. Ultimately, this design took off and has become the standard today.

The 737 Original Series – launched in 1967

Boeing launched the first variant, the 737-100, in January 1967. It first flew with Lufthansa in February 1968. Interestingly, this was the first time a non-US airline was a launch customer for a Boeing aircraft. Only 30 737-100 aircraft were ever delivered, as it was quickly updated with the larger Boeing 737-200 (entering service in April 1968). This increased typical capacity from 85 to 102 and proved much more popular.

The 737-200 was altered with several modifications to meet customer demands – something that has continued and helped make the 737 so successful. This included a version modified for landing on unpaved runways, and a convertible passenger and cargo version. All included, Boeing delivered 1095 Boeing 737-200 aircraft up to 1988, and some still remain in service in 2022.

The 737 Classic Series – launched in 1984

Boeing made several improvements to the 737, mostly focussed on capacity and fuel efficiency, leading to a new series launch in 1984. The 737-300 was the first variant launched, entering service with Southwest Airlines in December 1984. It introduced new higher thrust and more efficient CFM56 turbofan engines.

The 737-300 was followed by two more series variants, the larger 737-400 and the smaller 737-500. The 737-500 offered a typical capacity of 110, the mid-sized 737-300 a capacity of 126, and the larger 737-400 a capacity of 146 (with a maximum limit up to 188). The trade off, of course, was on range, and this introduced the size and range options for each series that Boeing still retains.

The 737 Next Generation Series – launched in 1997

The next updates to the 737 family were motivated by the development of the Airbus A320. Airbus saw a gap in the market for a European-manufactured narrowbody and introduced the A320 in 1988 (entering service with Air France). As a much newer aircraft, this was more efficient than the older 737 Classics.

Boeing responded with the updated 737 Next Generation Series. It did not enter service, however, until December 1997 (again with Southwest Airlines). Like the Classic Series before it, the main focus was on further efficiency improvements, with upgraded engines and a re-designed wing. It also offered higher capacity than previous variants.

The Next Generation Series has four different sized variants:

  • The Boeing 737-600 is the smallest variant, with a typical capacity of 108 (designed as a perfect replacement for the 737-500). It was the first variant introduced, entering service with SAS in 1998.
  • The 737-700 is a stretched variant, offering a typical capacity of 128.
  • The 737-800 is further stretched, with a capacity of 189. This variant has gone on to be the best selling of all 737 variants, accounting for almost 5,000 of all 737 orders.
  • The 737-900ER took capacity up to 220 by adding a second set of emergency exit doors.

The 737 MAX Series – launched in 2017

Airbus launched the improved A320neo family in 2010. Once again, Boeing responded with its own efficiency improvements, launching the 737 MAX Series in 2011. This introduced new CFM International LEAP 1B engines, and aerodynamic improvements including a new winglet design.

The first MAX aircraft entered service in May 2017 with the Indonesian airline Malindo Air. Again, the series has four different sized variants:

  • The 737 MAX 7 with a typical capacity of 153. With attention shifted to other MAX issues and delays, the MAX 7 has still not entered service.
  • The 737 MAX 8 with a typical capacity of 178.
  • The 737 MAX 9 with a typical capacity of 193.
  • The 737 MAX 10 with typical capacity of 204 (and a maximum of 230). This is currently (as of late 2022) undergoing testing.

Of course, the MAX Series has received plenty of media attention. The crashes of a Lion Air MAX aircraft in October 2018 and an Ethiopian Airlines MAX aircraft in March 2019 led to the grounding of the MAX Series. There were issues discovered with the manoeuvring Characteristics Augmentation System (MCAS), where following erroneous readings from sensors the autopilot was incorrectly changing pitch. This has now been resolved, but has been financially and reputationally very damaging for Boeing.

Boeing currently faces further potential issues with the MAX Series. Changes required to the cockpit from 2023 are likely enough to warrant a new type rating. If the latest MAX 10 is not certified by then, it will lose commonality with the rest of airline’s 737 fleets.

What’s next for the Boeing 737?

The 737s continued approval under the same type rating has been a big advantage of the series to date. It will be a significant change if this does not continue with the 737 MAX 10.

In terms of what follows the 737 MAX Series, nothing has been confirmed by Boeing. There were previously plans for a new Boeing NMA (New Mid-Sized Aircraft), but these were dropped recently. Issues with the MAX were partly to blame for this, as was the popularity of the upcoming Airbus A321XLR and its range.

There are various possibilities. Boeing could continue with the 737 Series by further updating the MAX, re-engine the popular Boeing 757 (or even 767), or develop a new clean sheet design. With the current economic climate, a new design seems unlikely but we will have to wait and see.

Final Thoughts

The Boeing 737 has been a great success, and now that the MAX issues are hopefully resolved, it continues to be. It forms a major part of many airlines’ fleets (and for some airlines, the entire fleet). We have seen it flying now for over 50 years, and whatever happens next with 737 development, we are likely to see it in airline fleets for decades to come.

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