The Boeing 737 is one of the most successful aircraft in history - and the most delivered to date (although the battle with the A320 family is close). Its latest generation, the 737 MAX, carries on this long success and brings further updates. The 737 MAX has had its challenges, though. It was grounded in 2019 over safety concerns, with major consequences for Boeing and airline operators. It is now flying again but still faces delays and challenges.

The Boeing 737 has been flying since 1967

Boeing developed the 737 during the 1960s as a supplement and eventual replacement for the popular Boeing 727. It was also 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).

One of the main changes Boeing made with the 737 was the introduction of just two engines. Its preceding jets (the 707 and 727) were four and three-engine aircraft. Two was seen as the economic way forward, and Boeing responded to the market. Unlike its competition, it chose to mount the two engines in pods under the wings, instead of the rear of the fuselage.

Boeing 737-100
Photo: Boeing

This enabled Boeing to offer a wider cabin, with six across seating (five was typical with other aircraft), and to fit in standard-width freight containers. Having the engines lower to the ground also made maintenance easier. This led to issues later, however, when larger engines on the 737 Classic meant the engine bottoms had to be flattened, giving the distinctive 'hamster pouch' shape.

The first 737 was unveiled in 1967, and it entered service in February 1968 with Lufthansa. The 737-100 was much smaller than we are used to today, offering a typical two-class capacity of just 85 (with a maximum exit limit of 124). The 737-200 soon followed, with an increased capacity of 102 (with a limit of 136) and higher thrust engines.

Moving through the generations

Boeing has stuck with the 737 since 1967, making modifications and new variants to match changing needs of airlines. Adaptions began early, with an Unpaved Strip Kitallowing landing on gravel runways. This proved popular with airlines in places such as Canada and Alaska. It also developed a convertible passenger-to-cargo version (the 737-200C).

The Classic series

But it was the movement through several generations, or series, that brought the big changes. Boeing launched the Classic series with the 737-300 in 1984. Keeping commonality with earlier versions was the key here. This saved development and certification costs, as well as time, and allowed airlines to mix fleets easily. Engines were upgraded (to the CFM56) with fuel efficiency improvements. Size options were widened too, with three different capacity variants. The largest of these, the 737-400, took the typical capacity up to 188.

The Next Generation series

Improvements in efficiency took another leap forward with the 737 Next Generation (NG) series, launched in 1993 but not entering service until 1997. This was motivated by the development of the Airbus A320. It entered service in 1988 and offered more efficiency, as well as full fly-by-wire operation.

Again, the new series maintained commonality but introduced upgraded and more efficient CFM56-7 engines, a re-designed wing, and cabin and cockpit improvements. The number of variants increased to four, and the maximum capacity to 200 with the 737-900ER.

The second-largest variant, the 737-800, has gone on to become the best-selling so far, with its popular compromise of range and capacity.

Thai Lion Air 737-800 landing
Photo: Komenton / Shutterstock.

Launching the 737 MAX

The Boeing 737 MAX Series was announced in 2011 and was introduced in May 2017, with Indonesian airline Malindo Air as the launch customer. Like previous generations, the 737 MAX aimed to incorporate new technology and efficiency improvements whilst maintaining commonality. And like the NG, it also followed an upgrade from Airbus - this time, the improved Airbus 320neo family (which Airbus launched in 2010, entering service in 2016).

737 MAX
Photo: Boeing

There are four MAX variants:

Variant

Capacity

Range

737 MAX 7

138 - 153

7,130 kilometers

737 MAX 8

162 - 178

6,570 kilometers

737 MAX 9

178 - 193

6,570 kilometers

737 MAX 10

188 - 204

6,110 kilometers

There is also a 737 MAX 200. This is based on the 737 MAX 8 but with an increased passenger capacity of 200. It has so far entered service with Ryanair and is on order with other airlines, including VietJet Air and Akasa Air. Akasa Air has an impressive 52 aircraft on order.

A Ryanair Boeing 737 MAX 8-200 in Prague kamilpetran
Photo: kamilpetran | Shutterstock

Efficiency improvements

Again, engines took a step up in performance and improvement, with CFM International LEAP-1B engines for all variants. Boeing chose a larger fan diameter for these engines, which would further improve efficiency.

But the larger size once again caused issues with its low ground clearance, leading to the lengthening of the nose landing gear and further forward placement of the powerplants. The engine nacelles have chevrons added for noise reduction, much like the Boeing 787.

A Boeing 737 MAX with the Leap engine.
Photo: Wirestock Creators / Shutterstock

Other aerodynamic improvements take this efficiency improvement further, most notably its distinctive split winglets. Winglets work by reducing vortex drag, where different air pressures converge at the wingtips. Over the past years, there have been several different winglet designs, with the split winglets first introduced by Boeing as an improvement for the 737 NG. The MAX's winglets are a new in-house design that Boeing claims improves efficiency even further. According to Boeing, there is an overall 14% fuel efficiency reduction between the Next Generation series and the 737 MAX series.

Boeing 737 MAX
Photo: Andreas Zeitler | Shutterstock

The grounding of the 737 MAX

At the moment, at least, many people remember the 737 MAX not for its efficiency upgrades but for its long and damaging grounding. This followed two fatal crashes. The US FAA grounded the MAX on March 13th, 2019 - many other regulators had grounded it even earlier.

  • Lion Air Flight 610 in October 2018. It crashed in the Java Sea shortly after take-off from Soekarno–Hatta International Airport, Jakarta. All 189 people aboard were killed.
  • Ethiopian Airlines Flight 302, in March 2019. It crashed shortly after take-off from Addis Ababa, Ethiopia. All 157 people aboard were killed.

Problems with the MAX

The circumstances of both crashes were similar, and it was suspected that problems with the Manoeuvering Characteristics Augmentation System (MCAS) were at least partly to blame. Following the NTSB investigation, this was confirmed. The MCAS system is designed to move the nose down if an increased angle of attack is detected, to help avoid a stall. The problems that led to the two crashes included erroneous readings from sensors and a lack of training for pilots in how to respond.

MCAS was added to overcome the tendency for the MAX to pitch up, caused by the larger engines and their location further forward. It was not present or needed in earlier 737 generations. This was part of the problem, as Boeing obviously wanted to maintain commonality for the new aircraft.

Boeing 737 MAX 8
Photo: BlueBarronPhoto | Shutterstock

MCAS ommissions

The addition of this new system was ultimately wrongly handled. Errors included changes to the MCAS plan during implementation (including reducing sensor inputs from two to one) and pressure for Boeing to get the aircraft certified for pilots without simulator training.

This training issue - both the omissions of MCAS for conversion training and the plans needed for it going forward - has been a major issue in the investigation and re-certification plans.

In its conclusions, The NTSB report said:

"That Boeing used in its functional hazard assessment of uncommanded MCAS function for the 737 MAX did not adequately consider and account for the impact that multiple flight deck alerts and indications could have on pilots' responses to the hazard ... The specific failure modes that could lead to unintended MCAS activation (such as an erroneous high AOA input to the MCAS) were not simulated as part of these functional hazard assessment validation tests."

A costly problem

CNN refers to the MAX grounding as "the most expensive corporate blunder ever." While we are not going to compare it against others, it was certainly extremely damaging for airlines and Boeing.

Airlines sued Boeing for losses incurred. And there have been extensive costs for repairs to the aircraft. Boeing estimates it has incurred a direct cost of $20 billion due to the MAX grounding. This includes $8.6 billion paid to airlines in compensation. This does not include compensation and legal liability for the crash victim's families.

Lost orders

The grounding also took its toll on aircraft orders. Before this, the MAX was selling well. By January 2019, Boeing had recorded just over 5,000 orders for the MAX. Significant orders were lost through 2019 and 2020, though, despite Boeing's attempts to sell some of these to other airlines.

In 2019, it lost 93 orders. And in 2020, 641 were lost. This included cancelations from both airlines and leasing companies - Leasing company Avolon, for example, canceled 75 MAX orders. More orders have been lost when changes to accounting standards are taken into account.

Avolon 737 MAX
Photo: Boeing

Getting airborne again from 2020

The FAA issued guidance to repair the aircraft faults and improve pilot training in August 2020. It was cleared to resume service (subject to changes and training) in November 2020. The Canadian and European regulators cleared it in January 2021.

Flights resumed in December 2020, with American Airlines making a demonstration trip. The first commercial service flew on December 9th with Brazilian airline GOL (from Sao Paulo to Porto Alegre), and American Airlines flew the first US service on December 29th. United Airlines resumed services in February. Southwest Airlines, the type's largest customer, followed in March.

A GOL Boeing 737 MAX
Photo: Lukas Souza | Simple Flying

Current 737 MAX orders and status

As of late March 2023, there were 954 active 737 MAX aircraft in airline fleets (according to ch-aviation's data). This is up from around 580 a year previously. The MAX 8 is by far the most dominant (with 711 of the active aircraft), followed by the larger MAX 9 and the higher capacity MAX 8-200.

Southwest Airlines has long been the largest operator of the MAX, with 156 MAX 8 aircraft in the fleet. Ryanair is the second-largest operator, with 94 aircraft (all MAX 8 200 aircraft) across the group.

Southwest Boeing 737 MAX 8
Photo: Angel DiBilio | Shutterstock

The top 12 operators of the 737 MAX are as follows:

Airline

MAX 8

MAX 8 200

MAX 9

Total

Southwest

156

156

Ryanair Group

94

94

United Airlines

40

51

91

Aeromexico

31

14

45

flydubai

41

3

44

American Airlines

42

42

42

Alaska Airlines

41

41

Air Canada

39

39

GOL

37

37

Turkish Airlines

27

5

32

TUI Group

31

31

WestJet

22

7

29

Aircraft orders and backlog

Aircraft deliveries were suspended during the ground, but these have now well resumed. Orders are back too. As of early March 2023, there remain over 4,000 unfilled 737 MAX aircraft (according to data from Boeing)

This includes some very large orders that will significantly change some airline fleets - including 409 aircraft for United Airlines, 372 aircraft for Southwest Airlines, 229 for Lion Air, 200 for VietJet Air, 125 for Jet Airways, 129 for Spice Air, 102 for Alaska Airlines, and 100 for Delta Air Lines.

United Airlines Boeing 737 MAX 9 aircraft is airborne as it departs Los Angeles International Airport.
Photo: Phillip Pilosian | Shutterstock

This is a huge backlog to be delivered. With the fast resumption in service post-COVID, many airlines are keen to receive their new aircraft. United Airlines, for example, took delivery of its 100th MAX aircraft in April 2023 and was receiving two new aircraft a week at the time.

In 2022, Boeing was targeting the production of 31 737 aircraft per month. It missed this target but still delivered 357 aircraft by taking advantage of earlier produced aircraft. Airbus - for comparison - delivered 516 A320 family aircraft in 2022.

In January 2023, Boeing announced a new production line for the 737 MAX to help with these deliveries and future growth. This production line will open in its Everett facility, reportedly in the second half of 2024.

Boeing employees building a Boeing 787 jet at its Everett factory.
Photo: First Class Photography/Shutterstock

This is possible following the end of Boeing 747 production at Everett as well as the relocation of Boeing 787 production. The new line will likely focus on the latest variants of the 737 MAX, such as the Boeing 737 MAX 8-200 and the Boeing 737 MAX 10.

737 MAX 7 and MAX 10 certification

Despite a healthy order book and recovery from the earlier grounding, the problems are not over for Boeing and the 737 MAX. Most notably, two of the 737 variants - the 737 MAX 7 and MAX 10 - are still to receive certification. These were given a lifeline in late 2022 with a certification waiver from US Congress.

Without this, it was likely that late certification would lead to a different type certificate following the installation of new EICAS equipment. Having a separate type rating would harm the commonality across the 737 variants, which makes it popular with many airlines. Note too that Boeing is still required to eventually upgrade the 737 MAX 7 and MAX 10 aircraft and retrofit the existing fleet of 737 MAX 8 and MAX 9 aircraft.

Boeing 737 MAX 10
Photo: Boeing

However, there is still no sure indication of when the MAX 7 or MAX 10 will be certified. Certification of the MAX 7 is hoped for during the first half of 2023, potentially with entry to service also during the year. Southwest Airlines is the largest waiting customer for the MAX 7 (with up to 239 aircraft on order). The airline has already said it does not expect the MAX 7 to be in service until 2024, and has not planned for use before that.

Boeing 737 MAX 7
Photo: Boeing

There are more delays expected for the 737 MAX 10. Despite seeing this demonstrated during its testing program at Farnborough in 2022, certification is not expected until late 2023 or during 2024.

737 MAX 10
Photo: Justin Hayward / Simple Flying

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The future for the Boeing 737

The future for narrowbody aircraft looks strong. In its Commercial Market Outlook (CMO) for 2022-2041, Boeing expects the single-aisle market to experience the most significant expansion, with a projected 50% growth.

The 737 MAX may serve this demand well at the moment, but looking further ahead, what might be the next developments for the 737? One of the most discussed new aircraft is the Boeing NMA (New Midsize Aircraft), also dubbed the 797. This was originally seen as a replacement for the 757, sitting between Boeing's offerings of the 737 MAX and 787 Dreamliner. These plans were dropped in 2020, largely due to the issues and losses from the 737 MAX.

737 MAX family
Photo: Boeing

With Airbus launching the A321XLR, Boeing could look again at its plans. The A321XLR offers something different - an incredible range for a narrowbody aircraft. It is proving popular with many airlines, opening up new longer point to point possibilities on transatlantic routes and in other regions.

A new narrowbody design that builds on the 737 MAX would be one option for Boeing to compete with this. Additional fuel tanks could offer the extra range needed, but the MAX 10 is already sized to the limit. Without significant and expensive re-design, passenger capacity would suffer.

A321XLR Giant QR Code Livery
Photo: Airbus

Alternatively, Boeing could make updates to the 757 or 767. A 757 MAX could seat around 240 passengers and offer improved range and efficiency with new engines. A 767 MAX could re-engine the original widebody with the General Electric GEnx engines.

The Boeing 737 has had a long history and is going nowhere soon. Commonality has been the key to this success, and this continues with the 737 MAX - at least for now. This article has given an overview of the 737 MAX and where it has come from, but there is a lot more to the 737 MAX's story. Feel free to discuss further in the comments section.

Sources: CNN, ch-aviation.com

  • 787-8 Dreamliner
    Boeing
    Stock Code:
    BA
    Date Founded:
    1916-07-15
    CEO:
    Dave Calhoun
    Headquarters Location:
    Chicago, USA
    Key Product Lines:
    Boeing 737, Boeing 747, Boeing 757, Boeing 767, Boeing 777, Boeing 787
    Business Type:
    Planemaker