Explained: The Boeing 737 MAX Aircraft Family

DALLAS — The Boeing 737 MAX has been at the center of one of the biggest crises in aviation history, following two fatal crashes that resulted in the grounding of the entire fleet before the COVID 19 pandemic took hold of the world.

Despite this, the Boeing 737 MAX remains one of the most popular aircraft in the world, with a rich history and a vast network of operators and suppliers.

The Boeing 737 MAX series is the fourth generation of the manufacturer's narrowbody 737 airliner family. The MAX includes new engines and other improvements in comparison to the company’s Next-Generation (NG) 737 series. The single-aisle market benefits from the Boeing 737 MAX's increased efficiency, improved environmental performance, and increased passenger comfort.

The type delivers outstanding economics, decreasing fuel use and pollutants by 20% while producing a 50% smaller noise footprint than the aircraft it replaces. It also has cutting-edge winglets and effective engines. When compared to its rivals, the 737 MAX delivers up to 14% cheaper airframe maintenance costs.

Inauguration, Launch History

The Boeing 737 MAX series was introduced in December 2011 after receiving an order from Southwest Airlines. A Boeing 737-8 with the serial number 42554 and the registration N8701Q made the series' inaugural flight on January 29, 2016, from Renton Field in Washington state. The 737-8 was certified by the FAA on March 8, 2017, following a nearly 14-month flight-testing procedure.

Boeing announced the fifth variant of the MAX series, the 737-10, at the 2017 Paris Air Show, a variant that is designed to directly compete with Airbus’s A321neo (new engine option). When it was launched in June 2017, the 737-10 had orders for 240 airplanes from operators and leasing companies.

This included AerCap, Aviation Capital Group (ACG), Copa Airlines, Donghai Airlines, GE Capital Aviation Services, Lion Air, Malaysian Airlines, TUI Group, United Airlines, and Xiamen Airlines.

Boeing subsequently rolled out the first 737-10 airframe—Serial No. 66122, registered as N27751—at Renton in November 2019, with the first flight occurring on June 18, 2021. At the time of the variant’s first flight, Boeing stated that it expected this 737 MAX airframe to enter into service in 2023.  

The type certificate for all variants of the 737 series—from the -100 to the -9—is held by The Boeing Company of Renton, Washington.

The Boeing 737 MAX series includes several variants with distinct FAA certification dates. The 737-8 was certified on March 8, 2017, followed by the 737-9 on February 15, 2018. Later, the 737-8200, also known as the 737-8-200, received its certification on March 31, 2021. This series offers a range of configurations to meet various operational needs.

Cabin Configurations, Outfitting

The 737-7, which is intended to have a maximum seating capacity of 172, is at the low end of the MAX series capacity range. This capacity is feasible in a single-class cabin with seats that have a 28- or 29-inch pitch. The -7's dual-class seating capacity is decreased to 138–153 people, with the higher end of that range being feasible in a configuration that comprises eight business-class seats with a 36-in. pitch and 145 economy-class seats with a 29–30.

Boeing claims that the 737-8's 189-passenger maximum capacity is feasible in a single-class cabin with seats that have a 29- or 30-inch pitch. The -8 can accommodate 162-178 passengers in a two-class arrangement, and the -9 can accommodate 178–193 passengers.

12 of the 178 passengers may be accommodated in business class seats with a 36-inch pitch, while the remaining 166 seats would be located in the economy cabin, which would have seats with a pitch of either 29 or 30 inches.

This is one conceivable layout for a 178-passenger dual-class -8. The 737-8-200 is the higher-capacity version of the 737-8 and may be configured with 200 seats, each with a 28-inch pitch.

The seating comparison between the Boeing 737 MAX and the 737 Next Generation (NG) series highlights differences in passenger capacity across variants. The Boeing 737-7 has a maximum certified passenger capacity of 172, compared to the 737-700’s 149 in the NG series.

The 737-8 and the 737-800 share the same capacity of 189 passengers. The Boeing 737 8-200 accommodates up to 212 passengers, while the 737-900ER in the NG series holds up to 220.

The Boeing 737-9 also matches the 737-900ER with a capacity of 220 passengers. Finally, the Boeing 737-10 leads with a maximum certified capacity of 230 passengers.

The -9 and -10, which have maximum passenger capacities of 220 and 230, respectively, are the highest capacity variants of the 737 MAX series. Similar to the -7 and -8, the -9's single-class layout is capable of accommodating those maximum capacities, with seats in a such arrangement having a 28-inch pitch.

The -9's interior includes 177 economy-class seats with a 29- or 30-inch pitch and 16 business-class seats with a 36-inch pitch, and it can accommodate the high end of the dual-class seating range discussed earlier.

Cargo Capacity, Avionics

Two cargo compartments, labeled forward and aft, offer extra space in addition to the cabin's usable space. For the 737-7, those compartments' respective bulk volumes are 433 and 706, for a combined 1,139 ft3 of bulk cargo volume. The total space increases to 1,540 ft3, divided between 657 ft3 in the front cabin and 883 ft3 in the aft compartment on the 737-8 and -8-200.

The -9 sees an increase in those volumes, with a total volume of 1,811 ft.3 indicated in Boeing's airport planning document, with 815 ft.3 of that space located in the front compartment and 996 ft.3 in the aft compartment. 

The 737-10, as anticipated, will feature the largest combined bulk cargo volume of 1,961 ft.3, with 911 ft.3 of that space being held in the forward compartment and the remaining 1,050 ft.3 being located in the rear compartment.

The avionics system also improved, and flight crews now fly variations of the MAX series—from a flight deck equipped with Collins Aerospace displays. 

Mission, Performance

The 737 MAX series is marketed by Boeing as "building" on the dependability of the 737NG versions and offering notable enhancements in emissions, operating costs, and performance.

Despite parallels to the 737 airframes from earlier generations, the Airbus' A320neo family serves as the main rival for the 737 MAX series, with the specific comparisons given below.

The performance specifications of the Airbus A320neo family and the Boeing 737 MAX series reveal several key differences. In terms of maximum certified passenger capacity, the A319neo seats up to 160 passengers, the A320neo accommodates 195, and the A321XLR holds 244. Comparatively, the 737 MAX variants range from the 737-7 with 172 seats to the 737-8 and 737-8-200 with 189 and 212, respectively, the 737-9 with 220, and the 737-10 with 230 passengers.

Regarding range, the A319neo offers 3,700 nautical miles (nm), the A320neo 3,400 nm, and the A321XLR leads with 4,700 nm. In the 737 MAX family, the 737-7 achieves 3,850 nm, the 737-8 and 737-8-200 reach 3,550 nm, the 737-9 offers 3,300 nm, and the 737-10 delivers shorter distances.

Both families feature advanced engines: the A320neo series uses CFM International LEAP-1A or Pratt & Whitney PW1100G-JM engines, while the 737 MAX employs the CFM International LEAP-1B. The maximum takeoff weight (MTOW) for Airbus models spans from 166,449 lb. for the A319neo to 222,667 lb. for the A321XLR. The 737 MAX series ranges from 177,000 lb. for the 737-7 to 197,900 lb. for the 737-10.

The aircraft dimensions also vary. The A319neo has a wingspan of 117 ft. 5 in., increasing slightly to 117 ft. 10 in. for the A320neo and A321XLR. Boeing's 737 MAX family maintains consistent wingspans, but lengths vary: the shortest is the 737-7 at 116 ft. 8 in., and the longest is the 737-10 at 143 ft. 8 in. Heights also differ, with Airbus models reaching up to 40 ft. 4 in. and the 737 MAX series presenting similar profiles.

The 737NG series—the -600, -700, -700C, -800, -900, and -900ER—and the 737-8 and -9 share additional characteristics, such as a maximum operating limit speed (MMO) of 0.82 Mach and a maximum operating altitude of 41,000 ft.

The values for the -9 and -10 are based on the range estimates for the MAX mentioned above and below, which assume an airframe with a single auxiliary fuel tank. Moreover, even though the -8 and -9 are both touted as having the same 3,550-nm range, the earlier model can reach that range without an additional fuel tank. 

The 737-7 will have 1,000 nm more range than the 737-700 thanks to the "technological enhancements" built into that airframe, and it will also be able to transport more passengers. The bigger -8, according to Boeing, has a range that is 14% longer than "the latest 737-800" when using the same amount of fuel.

Changes that are shared by all four 737 MAX variants include an increased wingspan—to 117 ft. 10 in., and the "dual-surface, laminar-flow winglets provide 2% over the blended winglets fitted to" 737NG airframes, even if the LEAP-1B engines "mostly" enable the range boost.

737 MAX Variants

Boeing 737-7

The 737-7, the smallest model in the 737 MAX series, is the model that has the longest range and is produced by Boeing in Renton. The fuselage of the -7 was stretched by 76 inches to accommodate two additional rows of seats, resulting in the addition of 12 more seats compared to the 737-700 in response to comments from -7 customers Southwest Airlines and WestJet Airlines.

In addition to having a longer fuselage, the revised -7 design increases range, improves performance in hot and high-altitude circumstances and increases maximum takeoff weight (MTOW) by 6,000 pounds over the 737-700's increased-gross-weight (IGW) model.

Fuel expenses for the -7 are 18% lower per seat than for the -700 of the previous generation, which is another advancement. Moreover, Boeing claims that the -7 can travel "12 more passengers 400 nm further" than the A319neo while having operating expenses that are 7% lower per seat.

Boeing 737-8, -8-200

Similar to the -800 variant, the MTOW of the 737-8 is enhanced by 7,000 lb. while maintaining a fuselage length that is almost comparable. Boeing claims that the -8's fuselage is 6 ft. 5 in. longer than that of its main rival, the A320neo, giving operators greater room and flexibility in the cabin.

The inclusion of the mid-exit door of the -9, which "increases the exit limit," allows for the enhanced capacity of the 737-8-200 (737 MAX 200), an aircraft that is said to be built on the 737-8. In addition, it is claimed that the MAX 200 has 20% greater fuel efficiency per seat than "today's most efficient single-aisle airplanes"

Boeing 737-9, -10

The longer fuselage of the -9 allows for the installation of three more rows of seats compared to the 737-8. The main landing gear of the -10 is extended by 9.5 in. in order to provide "sufficient clearance of the longer body for rotation" during takeoff and landing, adding to the 8-in. extension of the MAX's nose gear that was necessary to allow proper ground clearance for the LEAP engines.

To "ensure the airplane remains stall—rather than pitch—limited" was also included. The main landing gear's increased height does indeed enable the fuselage to extend, and the design also enables the larger landing gear to fit "within the existing wheel well area." 

Further alterations to the -10 include a "lighter flat aft pressure bulkhead," a "variable exit-limit rating mid-exit door," and a wing that was altered for "low-speed drag reduction" in addition to the lengthened fuselage and changes to the main landing gear to accommodate it.

NG vs MAX: Other Comparisons

For maximum range, the NG series achieves 3,010 nautical miles (nm) with the 737-700, 2,935 nm with the 737-800, and 2,950 nm with the 737-900ER. The MAX series improves on this with ranges of 3,850 nm for the 737-7, 3,550 nm for the 737-8/-8-200, 3,300 nm for the 737-9, and a slightly shorter range for the 737-10.

The engines differ between generations, with the NG series using CFM International CFM56-7B engines, while the MAX series incorporates the more advanced CFM International LEAP-1B engines. The maximum takeoff weight (MTOW) varies, starting at 154,500 lb. for the 737-700 in the NG series and increasing to 187,700 lb. for the 737-900ER. In the MAX series, MTOW ranges from 177,000 lb. for the 737-7 to 197,900 lb. for the 737-10.

Maximum landing weight also shows variability. The NG models range from 129,200 lb. for the 737-700 to 157,300 lb. for the 737-900ER, while the MAX series spans from 145,600 lb. for the 737-7 to 167,400 lb. for the 737-10. Usable fuel capacity in the NG series is 6,820 gallons, supporting its performance.

Aircraft dimensions highlight further differences. The wingspan increases slightly from 117 ft. 5 in. in the NG series to 117 ft. 10 in. in the MAX series. Lengths vary, with the shortest being the 737-700 at 110 ft. 4 in. and the longest being the 737-10 at 143 ft. 8 in. The heights of the NG and MAX families are similar, with slight differences depending on the model.

LEAP-1B Engines

All airframes in the MAX series are powered by LEAP-1B engines made by CFM International, replacing the CFM56. The improvements provided by the LEAP engines include a reduction in fuel consumption—which, according to CFM, is 15% better when compared to “today’s best CFM56 engines”—and emissions, while retaining the “life-cycle maintenance costs” and reliability of the CFM56.

Specific emissions reductions made possible by the LEAP include a 50% reduction in nitrogen oxide (NOX) emissions in comparison to the Committee on Aviation Environmental Protection’s CAEP/6 standards. CFM states that reduction is made possible through the inclusion of a “second-generation” Twin-Annular, Pre-Mixing Swirler Combustor (TAPS II), a type of combustor that “pre-mixes” fuel and air prior to combustion.

The engine’s FAA TCDS notes that in addition to the TAPS II combustors, the variants of the LEAP-1B—which are high-bypass turbofan engines—have a multi-stage low-pressure turbine and compressor, as well as a two-stage high-pressure turbine. Driving the coaxial front fan/booster of the LEAP-1B is the multi-stage low-pressure turbine, while the engine itself incorporates a full authority digital engine control (FADEC) system.

Other technologies incorporated into the LEAP engine series include fan blades that are “manufactured from 3D-woven RTM (resin transfer molding) carbon-fiber composite,” a technology that decreases weight and increases durability. When compared to conventionally manufactured parts, the LEAP’s fuel nozzles are “five times more durable,” while also being “25% lighter than previous models.”

Despite incorporating those advanced materials, the increase in the size of the LEAP-1B in comparison to the CFM56—the LEAP-1B’s 18-blade carbon-fiber fan has a 69.4-in. diameter in comparison to the 61-in. diameter of the CFM56-7’s 24-blade titanium fan—means the total weight of the engine also increased to 6,128 lb.

The 737 MAX series features a range of engine variants tailored to different models. The 737-8 and 737-8-200 are powered by the CFM International LEAP-1B25G05 and LEAP-1B25G06 engines. The 737-9 offers multiple engine configurations, including the LEAP-1B27G05, LEAP-1B27G06, LEAP-1B28G05, and LEAP-1B28G06.

Additionally, the 737 MAX series includes advanced engine variants such as the LEAP-1B28B1G05 and LEAP-1B28B1G06, which provide optimized performance for specific operational needs. This diversity in engine options underscores the 737 MAX's adaptability to varying airline requirements and performance goals.

Environmental Performance

Alaska Airlines, a Boeing and MAX customer, stated on June 3, 2021, that an Alaska 737-9 would be used as part of the airframe manufacturer's ecoDemonstrator program to "flight test roughly 20 innovations" with the aim of enhancing both the sustainability and safety of operations.

The usage of recycled carbon composite material in the cabin sidewall panels—material that was sourced from the manufacturing of the 777X's wings—will be tested during those tests, which the firms stated would last five months.

The -9-based ecoDemonstrator will also test a fire-extinguishing agent that is meant to replace Halon 1301—the production of which “was banned in 1994”—with the goal of lowering the impact of the agent on the ozone layer substantially.

Program Status/Operators

All Boeing 737 MAX versions are made at Boeing's factories in Renton, Washington. The 737-8 program used four test airframes for flight testing, compared to two each for the -7 and -9 programs.

Following the 737-8 and -9's entrance into service, three MAX series variants—the -7, -8-200, and -10—remain to be certified, with the first flights of the first two taking place in 2018 and early 2019, respectively.

The first of those mishaps happened on October 29, 2018, when a Lion Air 737-8 with the registration PK-LQP was lost around 13 minutes after taking off from Jakarta, Indonesia.

Less than five months later, on March 10, 2019, an Ethiopian Airlines -8 with the registration number ET-AVJ was involved in a second accident 6min. post takeoff.

A Global Concern

Global aviation authorities gradually grounded the MAX fleet after the loss of the second MAX airframe and after initial intelligence showed similarities with the Lion Air catastrophe. A flight-control regulation known as Boeing as Maneuvering Characteristics Augmentation System was the subject of the accident investigations and the cause of the worldwide grounding of 737 MAX airframes (MCAS). In particular, at low speeds and steep angles of attack, the MCAS was "added in the 737 MAX to make it handle like a 737NG."

Following the disaster involving an Ethiopian Airlines 737-8 in March 2019, all MAX airframes were gradually stopped by aviation regulators. This process was started by the Civil Aviation Administration of China, which made the decision to halt MAX models on March 11. The following day, operations were prohibited by the Civil Aviation Safety Authority of Australia (CASA) and the Civil Aviation Authority of Singapore. On the same day, Indonesian authorities grounded aircraft used by Lion Air and Garuda Indonesia "for inspections" (March 12).

The European Union Aviation Safety Agency (EASA), which made the decision in reaction to the Ethiopian Airlines crash, also issued an airworthiness directive on March 12 that banned MAX operations throughout Europe. Finally, on March 13, Canada and the U.S. decided to halt MAX operations. As a result, airlines like WestJet, American Airlines, Air Canada, Southwest Airlines, and United Airlines were affected. Also, all MAX deliveries were stopped as a result of the grounding.

The flight-test program for the 737-7 resumed on May 15, 2019, following the use of the first -7 flight-test airframe—1E001—to carry out evaluations related to upgraded MCAS software, despite the uncertainty at the time regarding when Boeing would finish the changes and upgrades that would enable the 737 MAX series to return to service.

Uncertainties, Suspension

On Nov. 18, 2020, Boeing declared that the FAA had withdrawn its order halting "commercial operations" of the 737 MAX models that were certified at the time that order was issued, the -8 and -9, after additional testing that lasted more than 4,400 hours and 1,350 flights. In addition, it permitted Boeing to resume 737 variant deliveries, according to the company's press release announcing the event. "Airlines that are under the FAA's jurisdiction, including those in the U.S., can take the measures necessary to restore service," it stated.

However, a number of conditions must be satisfied before airlines governed by the FAA can resume scheduled service with 737 MAX variants. These conditions include "de-preservation activities" for stored airframes, adjustments to separate wiring, pilot training, and the installation of software updates for the flight computer. The airframe's MCAS is affected by the new software and the FAA-mandated training requirements, and the software updates include "changed logic."

The FAA lifted an order that prohibited the commercial operation of -8 airframes in that nation a week later, on Nov. 25, 2020, and the Brazilian National Civil Aviation Agency [Agencia Nacional de Aviacao Civil (ANAC)] followed suit. EASA announced on January 27, 2021, that it had approved the 737 MAX series' return to service, subject to many of the same requirements as the FAA—such as modifications to the wiring and maintenance of the airframe, as well as training and software upgrades—while Transport Canada's and Australia's CASA's suspension of operations were lifted on January 18, 2021, and February 26, 2021, respectively.

Back in the Air

As the orders that had obstructed operations were gradually lifted in late 2020 and early 2021, Brazilian low-cost carrier Gol Airlines became the first user to relaunch the 737 MAX. A 737-8 was deployed to complete the journey from So Paulo to Porto Alegre. On a flight between Miami and New York LaGuardia on December 29, 2020, American Airlines formally inaugurated its services.

When Czech charter airline Smartwings operated a -8 between Prague and Malaga, Spain, on February 25, 2021, it became the first European carrier to use a 737 MAX airframe—nearly a month after EASA stated that it had authorized the series' return to operation. Boeing estimates that the first -10 deliveries will take place in 2023, following the initial shipments of the MAX 200 and -7 in early 2021.

After the MAX was put back into service, a problem with production line adjustments made in "early 2019" led to "electrical bonding and grounding difficulties" that affected more than 100 already-delivered airframes to operators. 350 "undelivered aircraft [that Boeing had in its inventory" also needed alterations, in addition to the changes that had to be made to the already-delivered aircraft. The business also made adjustments to the 737 MAX production line.

Boeing 737 MAX Orders, Deliveries

As of late March 2023, there were 954 active Boeing 737 MAX aircraft in airline fleets. This is up from around 580 the previous year. The 737-8 is by far the most dominant (with 711 of the active aircraft), followed by the larger -9 and the higher capacity -8200.

Southwest Airlines has long been the largest operator of the MAX, with 156 737-8 aircraft in the fleet. Ryanair is the second-largest operator, with 94 aircraft (all -8200 aircraft) across the group.

The top 12 operators of the Boeing 737 MAX showcase a significant global presence, with varying fleet sizes across different variants. Southwest Airlines operates the largest fleet, consisting of 156 737-8 aircraft. Ryanair Group exclusively operates the 737-8-200, with a total of 94 in service. United Airlines has a mixed fleet, including 40 737-8s and 5 737-9s, for a total of 45 aircraft.

Aeromexico's fleet includes 31 737-8s and 14 737-9s, amounting to 45 aircraft. flydubai operates 41 737-8s and 3 737-9s, for a total of 44 aircraft. American Airlines and Alaska Airlines each operate exclusively 42 and 41 737-8 aircraft, respectively. Air Canada and GOL also rely solely on the 737-8, with 39 and 37 aircraft, respectively.

Turkish Airlines operates a diverse fleet with 27 737-8s and 5 737-9s, totaling 32 aircraft. TUI Group and WestJet have fleets of 31 and 29 aircraft, respectively, with WestJet utilizing 22 737-8s and 7 737-9s. These operators demonstrate the global appeal and versatility of the 737 MAX family in meeting various airline needs.

Aircraft deliveries were suspended during the grounding, but these have now been 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.

Boeing's 737 MAX orders and deliveries have shown signs of stabilization and growth in recent months:

Orders

• In July 2024, Boeing received 57 single-aisle orders, primarily for the 737 MAX, valued at US$5.2 billion.
• Notable orders included 35 737 MAX airplanes from Aviation Capital Group and 20 from Macquarie AirFinance.
• As of July 31, 2024, Boeing had 4,741 MAX aircraft in its backlog.

Deliveries

• In August 2024, Boeing delivered 32 737 MAX aircraft, unchanged from July.
• September 2024 saw a slight decrease with 27 737 MAX deliveries.
• Year-to-date through September 2024, Boeing had delivered 291 commercial aircraft in total.

Production and Challenges

• Boeing is currently producing 737 MAX aircraft at a rate below the official 38 per month due to increased quality checks.
• The company aims to return to the official production rate of 38 per month by the end of 2024.
• A major strike involving 33,000 unionized workers has affected recent deliveries.

Market Position

• As of September 2024, Boeing was 80 deliveries behind its 2023 year-to-date totals.
• Airbus continues to lead in deliveries, with 497 aircraft delivered year-to-date through September 2024.

Despite ongoing challenges, Boeing's 737 MAX program shows signs of recovery, with stable monthly deliveries and continued new orders.

References: Airways Archives, EASA TCDS (A320), FAA TCDS (737 and CFM LEAP-1B), Airbus, Boeing, and CFM International Commercial Materials, Seeking Alpha, Flightplan Forecaster International.