Blog 43: 7/15/23: The Disturbing Tale of the Boeing 737-MAX

First Boeing 737-MAX, a MAX-8 Prototype, in Flight

Welcome back to Brooke In The Air! This week we delve into the newest generation of the most popular airliner and arguably best-selling narrow-body jetliner of the 21st century. And by all rights, the most controversial aircraft of the 21st century: the Boeing 737-MAX.

The MAX succeeds the Boeing 737 Next Generation (NG) which includes the 737-700, -800, and -900 variants of the 737. The MAX competes directly with the Airbus A320neo family.

The new MAX series was announced on August 30, 2011. It took its maiden flight on January 29, 2016 and was certified by the United States Federal Aviation Administration (FAA) in March 2017.

The first delivery was the smallest of the three variants, a MAX 8, delivered to Malindo Air, and it then commenced service with the same on May 22nd, 2017.

The 737-MAX is based on earlier 737 designs, with more efficient CFM International LEAP-1B engines, aerodynamic changes, including distinctive split-tip (Scimitar) winglets, and airframe modifications. The 737-MAX series has been offered in four variants, offering 138 to 204 seats in typical two-class configuration, and a range of 3,300 to 3,850 nautical miles (nmi). The 737-MAX 7 -the smallest version, -MAX 8 (including the 200–seat, single-class limited edition -MAX 200, used almost exclusively by Ryanair), and -MAX 9 are intended to replace the 737-700, -800, and -900 of the NG or Next Generation series, respectively, and a further-stretched 737-MAX 10 is available. As of May 2023, the 737-MAX has 4,194 unfilled orders and 1,196 deliveries per Boeing’s official website.

THE SEVERE MCAS FAILURE

The 737-MAX suffered a recurring failure in the Maneuvering Characteristics Augmentation System or MCAS, causing two known fatal crashes, that of Lion Air Flight 610 and Ethiopian Airlines Flight 302, in which 346 people died, all total. It was subsequently grounded worldwide from March 2019 to November 2020. The FAA garnered criticism for defending the aircraft and was the last major authority to ground it. Independent investigations faulted an intentional Boeing cover-up of a defect and lapses in the FAA's certification of the aircraft for flight.

Ultimately, the accidents and grounding cost Boeing an estimated $20 billion USD in fines, compensation and legal fees as of 2020, with indirect losses of more than $60 billion from 1,200 cancelled orders as of 2022.

Initial Engine Fitting at the CFM plant

Further, in 2021, Boeing also paid $2.5 billion USD in penalties and compensation to settle the DOJ's fraud conspiracy case against the company out of court. Further investigations also revealed that the FAA and Boeing had colluded on recertification test flights, attempted to cover up important information and that the FAA had retaliated against whistleblowers.

The FAA cleared the type to return to service on November 18, 2020, subject to mandated design and training changes. Canadian and European authorities only followed in late January 2021, and Chinese authorities in December 2021, as over 180 countries out of 195 had lifted the grounding. Over 450 MAX aircraft were awaiting delivery in November 2020; 335 remained by January 2022. Boeing estimated that the backlog would be largely cleared by the end of 2023, after its order book was reduced by almost 1,000 aircraft due to cancellations from massive public loss of trust in the aircraft.

CONSEQUENCES

In the twenty months during the subsequent 737-MAX grounding, Boeing redesigned the computer architecture that supported the Maneuvering Characteristics Augmentation System (MCAS) while investigations faulted aircraft design and certification lapses. Flawed information from a single external sensor fed into the system caused it to repeatedly push the planes' noses down as pilots struggled to keep them in the air before both crashes. Boeing faces legal and financial consequences, as no deliveries of the MAX could be made while the aircraft was grounded, and airlines canceled more orders than Boeing produced during this period. Boeing found foreign object debris in the fuel tanks of 35 of 50 grounded 737-MAX aircraft that were inspected, and had to check the remainder of the 400 undelivered planes. Boeing had similar problems with 787 Dreamliners produced in non-unionized South Carolina as opposed to those produced in unionized Renton, Washington.

The FAA curtailed Boeing's delegated authority and invited global aviation stakeholders to comment on pending changes to the aircraft and to pilot training. The FAA lifted its grounding order in 2020; all aircraft must be repaired to comply with various airworthiness directives.

After being charged with fraud in connection of both crashes of the 737-MAX, Boeing settled by paying over $2.5 billion: a criminal monetary penalty of $243.6 million (10%), $1.77 billion in damages to airline customers (70%), and $500 million to a crash-victim beneficiaries fund (20%). In April 2022, families of U.S. crash victims began petitioning a U.S. federal judge in Texas to scrap the settlement and reopen the criminal case, arguing that the United States Department of Justice (USDOJ) violated the Crime Victims' Rights Act in settling without consulting with the families, and that the USDOJ should not have agreed to shield senior Boeing executives from prosecution.

USDOJ prosecutors assert that the settlement is lawful because it cannot be proven that a crime was committed against the crash victims. On January 20, 2023, a U.S. district court judge ordered Boeing representatives to appear at a January 26, 2023 - this year - arraignment to discuss whether the company should face a felony charge of criminal conspiracy in the case. Results are pending as of this writing in 2023.

In early January 2020, an issue was discovered in the MAX software update, which impacted its recertification effort. As of mid-January, Boeing expected the MAX to return to service by mid-2020. In late April, following the COVID-19 pandemic, Boeing then hoped to win regulatory approval by August 2020. Between June 29 and July 1, the FAA and Boeing conducted a series of recertification test flights. Transport Canada and EASA each concluded their own independent recertification flights in late August and early September.

On November 18 of that year, the FAA announced that the MAX had been cleared to return to service. Before individual aircraft could resume service, repairs were required as set out in an airworthiness directive from the FAA. The various airline training programs also required approval.

On December 3, American Airlines made a highly visible demonstration flight for various journalists to explain the FAA-required modifications, in order to regain public trust. The first airline to resume regular passenger service was Brazilian low-cost carrier Gol Airlines on December 9. The first in the United States was American Airlines on December 29.

Transport Canada and EASA both cleared the MAX in late January 2021, subject to additional requirements. Other regulators worldwide progressively ungrounded the aircraft, including those in the UAE, Australia, Kenya, and Brazil. The Indian Directorate General of Civil Aviation (DGCA) rescinded its ban on MAX airplanes in late August on the condition that they meet the requirements set by the FAA and EASA. China's civil aviation regulator (CAAC) cleared the 94 jets stored by 11 major carriers in China to fly again in December 2021. Deliveries of approximately 120 planes stored by Boeing resumed in early 2022, with over 180 countries out of 195 having lifted the grounding by 2022.

MCAS SYSTEM EXPLAINED

A cutaway illustration of how MCAS is supposed to work on then 737.

The Maneuvering Characteristics Augmentation System (MCAS) is a flight stabilizing feature developed by Boeing that became notorious for its role in two fatal accidents of the 737-MAX, which killed all 346 passengers and crew among both medium haul flights.

Systems similar to the Boeing 737 MCAS were previously included on the Boeing 707 and Boeing KC-46 Pegasus, a military tanker variant of the venerable 767 wide-body jetliner designed to supplement and eventually replace the aging quad-engined Boeing KC-135 Stratotanker for the USAF.

On the 737-MAX, MCAS was intended to mimic the flight behavior of the previous generation of the series, the Boeing 737 NG. During the MAX flight tests, Boeing discovered that the position and larger size of the engines tended to push the nose up during certain maneuvers. Engineers decided to use MCAS to counter that tendency, since major structural redesign would have been prohibitively expensive and time-consuming. Boeing's goal was to have the MAX certified as another 737 version, which would appeal to airlines with the reduced cost of pilot training.

SERIOUS NOTE HERE: The Federal Aviation Administration (FAA) approved Boeing's request to remove a description of MCAS from the aircraft manual, leaving pilots completely unaware of the system when the airplane entered full-service in 2017.

After the utterly fatal Lion Air crash in 2018, Boeing and the FAA, still not revealing MCAS, referred pilots to a revised checklist procedure that must be performed in case of a malfunction. Boeing then received many requests for more information from numerous airlines and finally revealed the existence of MCAS in another message, and, most crucially, that it could intervene without pilot input. According to Boeing, MCAS was supposed to compensate for an excessive nose up angle by adjusting the horizontal stabilizer before the aircraft would potentially stall, essentially averting s problem before it became one. Boeing denied that MCAS was an anti-stall system, and stressed that it was simply intended to improve the handling of the aircraft.

After the subsequent Ethiopian Airlines crash five months later in 2019, Ethiopian authorities stated that the procedure did not enable the crew to prevent the accident, which occurred while a fix to MCAS was under development at Boeing in Washington state in the US.

Boeing admitted MCAS played a role in both accidents, when it acted on false data from a single angle of attack (AoA) sensor. In 2020, the FAA, Transport Canada, and European Union Aviation Safety Agency (EASA) evaluated flight test results with MCAS disabled, and suggested that the MAX might not have needed MCAS to conform to certification standards.

Grounded Boeing 737-MAX aircraft outside Boeing’s factory in Renton, Washington during the mass grounding of 2017-2019

Later that same year, an official FAA Airworthiness Directive approved design changes for each MAX aircraft, which would prevent MCAS activation unless both AoA sensors register similar readings, eliminate MCAS's ability to repeatedly activate, and allow pilots to override the system only if necessary. The US FAA began requiring all MAX pilots to undergo MCAS-related crash and flight training in flight simulators by early in 2021.

MCAS was deemed necessary by Boeing to meet its internal objective of minimizing training requirements for pilots already qualified on the 737NG. MCAS was to automatically mitigate the pitch-up tendency of the new flight geometry due to the engines being located further forward and higher than on previous 737 models. During a reassessment of the aircraft in February 2020, both FAA and EASA determined that the stability and stall characteristics of the plane would have been acceptable with or without MCAS.

THE PIVOTAL ACCIDENTS

LION AIR FLIGHT 610

The accident aircraft, PK-LGP, of Lion Air

Snapshot of the Crash-site of Lion Air - LN610

Lion Air Flight 610 (LNI610) was a scheduled domestic passenger flight from Soekarno–Hatta International Airport, Jakarta, to Depati Amir Airport, Pangkal Pinang, in Indonesia. On 29 October 2018, the Boeing 737 MAX operating the route crashed into the Java Sea 13 minutes after takeoff, killing all 189 passengers and crew. It was the first major accident involving the new Boeing 737-MAX series of aircraft, introduced in 2017, and the highest death toll of any accident or incident involving a 737- family of aircraft, surpassing Air India Express Flight 812 in 2010. It was the deadliest accident in Lion Air's history, surpassing the 2004 Lion Air Flight 538 that killed 25, and the second-deadliest aircraft accident in Indonesia behind Garuda Indonesia Flight 152.

Preliminary investigations revealed serious flight-control problems that traumatized passengers and crew on the aircraft's previous flight, as well as signs of failures of an angle-of-attack (AoA) sensor and other instruments on that and previous flights, tied to a design flaw involving the maneuvering characteristics augmentation system (MCAS) of the MAX series. As a result, the United States Federal Aviation Administration and Boeing issued warnings and training advisories to all operators of the MAX series to avoid letting the MCAS cause similar problems. These advisories were not fully implemented, however, and it would take another crash for the situation to be taken seriously.

PT Lion Mentari Airlines, operating as Lion Air, is an Indonesian low-cost airline. Based in Jakarta, Lion Air is the country's largest privately run airline, the second largest low-cost airline in Southeast Asia (after AirAsia) and the largest airline of Indonesia. With Wings Air and Batik Air, Lion Group is the country's largest airline's group. The airline operates domestic as well as international routes, which connects different destinations of Indonesia to Singapore, the Philippines, Malaysia, Thailand, Australia, India, Japan and Saudi Arabia, as well as charter routes to Mainland China, Hong Kong, South Korea and Macau, with more than 630 flights per day.

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ETHIOPIAN AIRLINES FLIGHT 302

The accident aircraft, ET-ALI, of Ethiopian Airlines

Crash-site of Ethiopian Flight 302 just outside Addis Ababa

The second and ultimate crash was that of Ethiopian Airlines Flight 302 was a scheduled international passenger flight from Addis Ababa Bole International Airport in Ethiopia to Jomo Kenyatta International Airport in Nairobi, Kenya. On the 10th of March, 2019, the Boeing 737-MAX 8 aircraft which operated the flight crashed near the town of Bishoftu just six minutes after takeoff, killing all 157 people aboard.

Flight 302 is Ethiopian Airlines's deadliest accident to date, surpassing the fatal hijacking of Flight 961 resulting in a crash near the Comoros in 1996.

This was the second MAX 8 accident in less than five months after the crash of Lion Air Flight 610. Both crashes prompted a two-year worldwide long-term grounding of the MAX and an in-depth investigation into how the aircraft was approved to service. The aircraft was manufactured in October 2018 and delivered on 15 November 2018, making it around four months old at the time of the accident. This aircraft had flown from Johannesburg, South Africa as flight ET858 the night prior.

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BACKGROUND & ORIGIN

In 2006, Boeing started considering the replacement of the 737 with a "clean-sheet" design that could follow the successful long-haul widebody, 787 Dreamliner.

On December 1, 2010, Boeing's competitor, Airbus, launched the Airbus A320neo family to improve fuel burn and operating efficiency with new engines: the CFM International LEAP and the Pratt & Whitney PW1000G turbofan. In February 2011, Boeing's CEO Jim McNerney maintained "We're going to do a new airplane."

Initial Concept of the MAX

In March of 2011, Boeing Commercial Airplanes (BCA) President James Albaugh told participants of a trade meeting the company was not sure about a 737 re-engine, like Boeing Chief Financial Officer (CFO) James A. Bell stated at an investor conference the same month. The Airbus A320neo gathered 667 commitments at the Paris Air Show of June 2011, for a backlog of 1,029 units since its launch, setting a record for a new commercial airliner order.

On July 20, 2011, American Airlines announced an order for 460 narrowbody jets including 130 A320ceos (Current Engine Option), 130 A320neos, 100 737NG and intended to order 100 re-engined 737s with CFM LEAPs, pending Boeing confirmation. The order broke Boeing's monopoly with the airline and forced Boeing into a re-engined 737.

As this sale included a Most-Favoured-Customer Clause, Airbus has to refund any difference to American Airlines if it sells to another airline at a lower price, so the European manufacturer was unable to offer it at a price which United Airlines deemed to be "competitive" leaving the airline with a Boeing-skewed fleet.

On August 30, 2011, Boeing's board of directors approved the launch of the re-engined 737, expecting a 4% lower fuel burn than the Airbus A320neo. Studies for additional drag reduction were performed during 2011, including a revised tail cone, natural laminar flow nacelle, and hybrid laminar flow vertical stabilizer were conducted during this time. Boeing then abandoned the development of a new design. Boeing expected the 737 MAX to meet or exceed the range of the Airbus A320neo. Firm configuration for the 737 MAX was scheduled for 2013.

In March 2010, the estimated cost to re-engine the 737, according to Mike Bair, Boeing Commercial Airplanes' vice president of business strategy and marketing, would be US$2–3 billion, including the CFM engine development. During Boeing's Q2 2011 earnings call, former CFO James Bell said the development cost for the airframe only would be 10–15% of the cost of a new program estimated at US$10–12 billion at the time. Bernstein Research predicted in January 2012, that this cost would be twice that of the A320neo.

The MAX development cost could have been well over the internal target of US$2 billion, and closer to US$4 billion. Fuel consumption is reduced by 14% from the 737NG. Southwest Airlines was signed up as the initial United States-launch customer in 2011.

On August 13th of 2015, the first 737-MAX fuselage completed assembly at Spirit Aerosystems in Wichita, Kansas, for a test aircraft that would eventually be delivered to US-launch customer Southwest Airlines. On December 8, 2015, the first 737 MAX—a MAX 8 named Spirit of Renton, See below—was rolled out at the Boeing Renton Factory.

MAX PRODUCED

Boeing 737-MAX 8 at Initial Rollout, Renton, Washington. Aircraft named “Spirit of Renton”

Because GKN Ltd. could not produce the titanium honeycomb inner walls for the thrust reversers quickly enough, Boeing switched to a composite part produced by Spirit Aerosystems to deliver 47 MAXs per month in 2017. Spirit supplies 69% of the 737 airframe, including the fuselage, thrust reverser, engine pylons, nacelles, and wing leading edges.

As an aside and to give context, GKN Ltd. As mentioned above, is a British multinational automotive and aerospace components business headquartered in Redditch, England, UK. It is a long-running business known for many decades as Guest, Keen and Nettlefolds, hence GKN.

Boeing 737-MAX 9, illustrating raked wings, chevroned engine nacelles and contoured “Scimitar” winglets.

For the 737, a new spar-assembly line with robotic drilling machines was expected to increase throughput by 33%. The Electroimpact automated panel assembly line sped up the wing lower-skin assembly by 35%.

Boeing planned to increase its 737-MAX monthly production rate from 42 planes in 2017, to 57 planes by 2019. The new spar-assembly line is designed by Electroimpact. Electroimpact has also installed fully automated riveting machines and tooling to fasten stringers to the wing-skin.

The rate increase strained the production and by August 2018, over 40 unfinished jets were parked in Renton, awaiting parts or engine installation, as CFM engines and Spirit fuselages were delivered late. After parked airplanes peaked at 53 at the beginning of September, Boeing reduced this by nine the following month, as deliveries rose to 61 from 29 in July, and a further 48 in August.

On September 23rd of 2015, Boeing announced a collaboration with Comac to build a completion and delivery facility for the 737, in Zhoushan, China, the first outside the United States. This facility initially handles interior finishing only, but will subsequently be expanded to include paintwork. The first aircraft was delivered from the facility to Air China on December 15th, 2018.

The first flight took place on January 29, 2016, at Renton Municipal Airport, nearly 49 years after the maiden flight of the original 737-100, on April 9, 1967. The first MAX 8, 1A001, was used for aerodynamic trials: flutter testing, stability and control, and takeoff performance-data verification, before it was modified for an operator and delivered. 1A002 was used for performance and engine testing: climb and landing performance, crosswind, noise, cold weather, high altitude, fuel burn and water-ingestion.

The 737-MAX gained FAA certification on March 8, 2017, and in the same month was approved by EASA on March 27th, 2017. After completing 2,000 test flight hours and 180-minute ETOPS testing requiring 3,000 simulated flight cycles in April 2017, CFM International notified Boeing of a possible manufacturing quality issue with low pressure turbine (LPT) discs in LEAP-1B engines. Boeing suspended 737 MAX flights on May 4, and resumed a week later on May 12.

It must be noted here that during the official certification process, the FAA delegated many evaluations to Boeing, allowing the manufacturer to review their own product. It was widely reported that Boeing pushed to expedite approval of the 737-MAX to compete with the Airbus A320neo, which hit the market nine months ahead of Boeing's competitive model, the 737-MAX.

The first delivery was a MAX 8, handed over to Malindo Air (a small subsidiary of Lion Air) on May 16th, 2017; it entered service on May 22. Norwegian Air International was the second airline to put a 737-MAX into service, when it performed its first transatlantic flight with a MAX 8 named Sir Freddie Laker on July 15, 2017, between Edinburgh Airport in Scotland and Bradley International Airport in the United States, in the northeast New England state of Connecticut.

Boeing aimed for 737 MAX to match the 99.7% dispatch reliability of the 737 Next Generation (NG). Southwest Airlines, the US-launch customer, took delivery of its first 737-MAX on August 29, 2017. Boeing planned to deliver at least 50 to 75 aircraft in 2017, 10–15% of the more than five hundred 737s to be delivered throughout the year in 2017.

Following the recertification of the MAX 8 and MAX 9, Boeing resumed work to certify the MAX 7, the smallest version, and the MAX 10, the largest version.

In March of 2022, there were rumors that Boeing would request an exemption from the U.S. Aircraft Safety and Certification Reform Act of 2020, a safety reform law passed in response to the MAX crashes. The act requires airliners to be fitted with an engine-indicating and crew-alerting system (EICAS) if type certificated after December 31, 2022. Adding this feature would make the MAX 10 different from other MAX variants, necessitating additional training for pilots.

In November of 2022, Boeing announced expected delays to the certification of the MAX 7 and MAX 10, now expected in early 2023 and early 2024 respectively. In December, two proposals to exempt the MAX 7 and MAX 10 from the new requirements were considered for inclusion in a U.S. defense spending bill—one a simple two-year extension to the deadline, the second an exemption for aircraft whose certification applications were submitted before the law was enacted, combined with some equipment changes—but neither proposal was included in the final spending bill.

In December of 2022, the U.S. Congress agreed on a bill allowing Boeing to certify the MAX 7 and MAX 10 without EICAS, but it must install a third angle-of-attack sensor in all 737-MAX types as previously demanded by European and Canadian regulators.

The company also must install a switch to disable the stick shaker, which distracted pilots during the MAX crashes; the stick shaker indicated an imminent aerodynamic stall. Boeing would have to retrofit these design changes to all 737-MAXs already delivered in Canada, Europe, and the U.S. within three years of MAX 10 certification.

DESIGN SPECIFICATIONS AND GOALS

In mid-2011, one design objective was matching fuel burn of the 737-MAX to that of the Airbus A320neo's 15% fuel-burn advantage. The initial 737 MAX reduction was 10–12%; it was later enhanced to 14.5%. The fan was widened from 61 inches (150 cm) to 69.4 in (176 cm) by raising the nose gear and placing the engine higher and forward. The split tip winglet added 1–1.5% fuel burn reduction and a re-lofted tail cone another 1%. Electronically controlling the bleed air system improved efficiency. The new engine nacelle included chevrons, similar to those of the Boeing 787 Dreamliner, which also helped to reduce engine noise.

The new "split-tip" Advanced Technology (AT) winglet is designed to reduce vortex drag, improving fuel efficiency and maximizing lift. It traces its design to the McDonnell Douglas MD-12 1990s twin-deck concept, proposed for similar gate restrictions before the merger with Boeing.

In essence, a 737-MAX 8 with 162 passengers on a 3,000 nautical miles (5,600 km; 3,500 mi) flight is projected to have a 1.8% better fuel burn than a blended-winglet-equipped aircraft and 1% over 500 nmi (nautical miles) at Mach 0.79. The new winglet has a total height of (2.90 m).

Other improvements include a re-contoured tail cone, revised auxiliary power unit inlet and exhaust, aft-body vortex generators removal, and other small aerodynamic improvements.

The engines on the 737-MAX were also repositioned, the top of the new engine slightly higher than the top surface of the wing, resulting in a change to the aerodynamic characteristics of the airframe. Due to the aircraft's close proximity to the ground, the larger and more fuel efficient engines did not have enough clearance. As a result, the engines were mounted higher and further forward on the wings, changing the aerodynamic characteristics. The MCAS software-based flight control law was implemented to account for the undesirable aerodynamic changes.

The 20-cm taller (as opposed to the 737-NG) nose-gear strut maintains the same 43-cm ground clearance of previous 737-series engine nacelles. New struts and nacelles for the heavier engines add bulk, the main landing gear and supporting structure have been reinforced, and fuselage skins are thicker in some places—thus adding 6,500 pounds (2,900 kg) to the MAX 8's empty aircraft weight. To preserve fuel and payload capacity, its maximum takeoff weight (MTOW) is 3,200 kg heavier.

Rockwell Collins Aerospace was selected to supply four 380 mm landscape liquid crystal displays (LCD), as used on the 787, to improve pilots' situation awareness and efficiency. Boeing plans no major modifications for the 737 MAX flight deck, as it wants to maintain commonality with the 737 Next Generation family. Boeing Commercial Airplanes CEO Jim Albaugh said in 2011 that adding more fly-by-wire control systems would be "very minimal". However, the 737-MAX extended spoilers are fly-by-wire controlled. Most of the systems are carried from the 737-NG to allow for a short differences-training course to upgrade flight crews from the Next Generation 737 to the MAX.

In addition to the Speed Trim System (STS), the automatic stabilizer control system has been enhanced to include MCAS. Compared to STS, MCAS has greater authority and cannot be disengaged with the aft and forward column cutout switches. The center console stabilizer-trim cutout switches have been re-wired. Unlike previous versions of the 737, the automatic stabilizer trim control functions cannot be turned off while retaining electric trim switches functionality.

As was production standard, the 737-MAX features the Boeing Sky Interior with overhead bins and LED lighting based on the Boeing 787's interior.

Chosen engines for the 737-MAX, the CFM International LEAP-1B Turofans with Chevroned engine nacelles

In 2011, the CFM LEAP-1B engine was initially 10–12% more efficient than the previous 156 cm CFM56-7B of the 737NG. The 18-blade, woven carbon-fiber fan enables a 9:1 bypass ratio (up from 5.1:1 with the previous 24-blade titanium fan of the 737-NG) for a 40% smaller noise footprint. The CFM56 bypass ranges from 5.1:1 to 5.5:1. The two-spool design has a low-pressure section comprising the fan and three booster stages driven by five axial turbine stages and a high-pressure section with a 10-stage axial compressor driven by a two-stage turbine. The 41:1 overall pressure ratio increased from 28:1, and advanced hot-section materials enabling higher operating temperatures permit a 15% reduction in thrust-specific fuel consumption (TSFC), along with 20% lower carbon emissions, 50% lower nitrogen-oxide emissions, though each engine weighs 849 kilograms; 385 kg more at 2,780 kg.

CFM-LEAP-1B Fan Blade

In November 2011, Boeing selected the larger 68-cm fan blade diameter, necessitating a 15–20 cm longer nose landing gear. In May 2012, Boeing further enlarged the fan to 176 cm, paired with a smaller engine core within minor design changes before the mid-2013 final configuration.

The nacelle features chevrons for noise reduction like the 787. A new bleed air digital regulator will improve its reliability. The new nacelles being larger and more forward possess aerodynamic properties which act to further increase the pitch rate. The larger engine is cantilevered ahead of and slightly above the wing, and the laminar flow engine nacelle lipskin is a GKN Aerospace-made one-piece, spun-formed aluminum sheet inspired by the 787 Dreamliner.

OPERATIONAL ENDURANCE

After one year of service, 130 MAXs had been delivered to 28 customers, logging over 41,000 flights in 118,000 hours and flying over 6.5 million passengers. Flydubai observed 15% more efficiency than the NG, more than the 14% promised, and dependability reached 99.4%. Long routes include 24 over 2,500 nautical miles including a daily Aerolíneas Argentinas service from Buenos Aires to Punta Cana over 3,252 nmi.

PROFIT LOSSES

Costs have since risen significantly for Boeing and the operating profit margin reduced following the two MCAS-caused crashes, the FAA grounding, and the severe disruption to production. Boeing estimated it would cost an additional $6.3 billion to produce the remaining 737 MAX program, $4 billion for "future abnormal costs" as production restarted, plus an estimated $8.3 billion for concessions and compensation to customers and their families.

OPERATING VARIANTS

The 737-700, -800 and -900ER, the most widespread versions of the previous 737NG, are succeeded by the 737 MAX 7, MAX 8 and MAX 9, respectively. The 737-MAX 8 entered service in May 2017, and the MAX 9 entered service in March 2018. Deliveries for MAX 7 and MAX 200 (a higher-density version of the MAX 8) were initially expected to begin in 2021, and the MAX 10 in 2023.

737-MAX 7

Boeing 737-MAX 7 Variant

Originally based on the 737-700, Boeing announced the redesign of the MAX 7, derived from the MAX 8, at the July 2016 Farnborough Air Show, accommodating two more seat rows than the 737-700 for 138 seats, up by 12 seats. The redesign uses the 737-8 wing and landing gear; a pair of over-wing exits rather than the single-door configuration; a 46-inch longer aft fuselage and a 30-inch longer forward fuselage; structural re-gauging and strengthening; and systems and interior modifications to accommodate the longer length. It is to fly 1,000 nmi farther than the -700 with 18% lower fuel costs per seat. Boeing predicts the MAX 7 to carry 12 more passengers 400 nmi (740 km; 460 mi) farther than A319neo with 7 percent lower operating costs per seat. In 2016, Boeing planned to improve its range from 3,850 nmi to 3,915 nmi after 2021.

Entry into service with US-launch operator Southwest Airlines was originally expected in January 2019. WestJet also converted its order for MAX 7s, originally due for delivery in 2019, into MAX 8s, not expecting to take any MAX 7s until at least 2021. In March 2021 Southwest placed an order for 100 MAX 7s, and exercised options for another 34 in 2021, bringing their total orders to 234; WestJet had 22. In July of 2022, Southwest announced that it did not expect to receive any MAX 7 aircraft until 2023 due to the ongoing certification delays and that it would instead take delivery of MAX 8 aircraft in the interim.

737-MAX 8

Boeing 737-MAX 8 Launch Variant

The first variant developed in the 737-MAX series, the MAX 8 replaces the 737-800 with a longer fuselage than the MAX 7. In 2016, Boeing planned to improve its range from 3,515 nautical miles to 3,610 nmi after 2021. On July 23, 2013, Boeing completed the firm configuration for the 737-MAX 8. The MAX 8 has a lower empty weight and higher maximum takeoff weight than the A320neo. During a test flight conducted for Aviation Week, while cruising at a true airspeed of 832 km/hr and a weight of 140,500 pounds or 63,700 kg, at a lower than optimal altitude (flight level or FL350 vs. the preferred FL390) and with an "unusually far forward" center of gravity, the test aircraft consumed 2,020 kg of fuel per hour.

The Boeing 737-MAX 8 completed its first flight test in La Paz, Bolivia. The 13,300-foot (4,100 m) altitude at El Alto International Airport tested the MAX's capability to take off and land at high altitudes. Its first commercial flight was operated by Malindo Air on May 22, 2017, between Kuala Lumpur and Singapore as Flight OD803.

737-MAX 200

Boeing 737-MAX 200 of launch customer low-cost carrier Ryanair

In September 2014, Boeing launched a high-density version of the 737 MAX 8, the 737 MAX 200, named for seating for up to 200 passengers in a single-class high-density configuration with “slimline” seats; an extra pair of exit doors is required because of the higher passenger capacity. Boeing states that this version would be 20% more cost-efficient per seat than current 737 models, and would be the most efficient narrow-body on the market when delivered, including 5% lower operating costs than the 737 MAX 8. Three of eight galley trolleys are removed to accommodate more passenger space. An order with Ryanair for 100 aircraft was finalized in December 2014.

NOTE ON SLIMLINE SEATS

Simline seats have less padding in the back. Seat pitch and width in economy class have also been decreasing, In 1985 none of the main four US carriers offered a seat less than 19 inches wide. Since the beginning of the 21st Century until 2018 average seat width decreased from 18.5 to 17 inches, and sometimes as low as 16.1 inches.

Slimline seats weigh less than full-size seats, and are claimed to allow airlines to increase capacity without significantly affecting passenger comfort. Many passengers however, have expressed displeasure with these seats. Moreover, the US Department of Transportation (DOT) has begun to explore the safety issues associated with increased aircraft capacity and reduced seat pitch that results from the installation of "slimline" seats. In an 14 April 2015 hearing of the DOT's Advisory Committee for Aviation Consumer Protection, Cynthia Corbett, an investigator for the US Federal Aviation Administration (FAA) Civil Aerospace Medical Institute, discussed concerns regarding the emergency evacuation of higher capacity aircraft.

Example of extra-padded “Slimline” seats. A340 long-haul jetliner. This aircraft is a widebody and would never be used by a low-cost carrier.

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As of ordered in 2018 by Ryanair, 135 of the MAX-200 variant rolled out in a 197-seat configuration. It was first flown from Renton on January 13, 2019, and was due to enter service in April 2019, with another four MAX 200s expected later in 2019, though certification and deliveries were deferred while the MAX was grounded. In November 2019, Ryanair informed its pilots that, due to an unspecified design issue with the additional over-wing exit doors, it did not expect to receive any MAX 200s until late April or early May 2020. In 2020, at the height of the covid slump, Ryanair renegotiated its order for 135 and ordered 75 more at one-third of the list price.

This high-density variant was certified by the FAA on March 31, 2021. Ryanair took delivery of its first 8–200 in June 2021. Besides launch customer Ryanair, other customers include International Airlines Group and low-cost airlines Akasa Air of India, Allegiant Air of the United States, Arajet of the Dominican Republic and Vietnam's VietJet.

737-MAX 9

Boeing 737-MAX 9 Variant

The 737-MAX 9 will replace the 737-900 and has a longer fuselage than the MAX 8. In 2016, Boeing planned to improve its range from 3,510 nautical miles to 3,605 nmi after 2021. Lion Air was, ironically, the launch customer with an order for 201 in February 2012. It made its roll-out on March 7, 2017, and first flight on April 13, 2017; it took off from Renton Municipal Airport and landed at Boeing Field after a 2 hr 42 min flight. It was presented at the 2017 Paris Air Show.

Boeing 737-9 flight tests were scheduled to run through 2017, with 30% of the -8 tests repeated; aircraft 1D001 was used for auto-land, avionics, flutter, and mostly stability-and-control trials, while 1D002 was used for environment control system testing. It was certified by February 2018. Asian low-cost carrier Lion Air Group took delivery of the first on March 21, 2018, before entering service with Thai Lion Air. As the competing A321neo attracts more orders, the sale value of a 737-9 is the same as a 2018 737-8 at $53 million.

737-MAX 10

To compete with the Airbus A321neo, loyal customers, such as Korean Air and United Airlines, pressed Boeing to develop a variant larger than the MAX 9, of which Boeing revealed studies in early 2016. As the Airbus A321neo had outsold the MAX 9 five-to-one, the proposed MAX 10 included a larger engine, stronger wings, and telescoping landing gear in mid-2016.

In September 2016, it was reported that the variant would be simpler and lower-risk with a modest stretch of 6–7 feet (1.83–2.13 m) for a length of 143–144 ft (43.6–43.9 m), seating 12–18 more passengers for 192–198 in a dual-class layout or 226-232 for a single class, needing an uprated 31,000 pounds-force LEAP-1B engine module that could be available by 2019, or 2020, and would likely require a landing-gear modification to move the rotation point slightly aft.

In October of 2016, Boeing's board of directors granted authority to offer the stretched variant with two extra fuselage sections forward and aft with a 3,100 nautical miles (5,700 km; 3,600 mi) range reduced from 3,300 nmi (6,100 km; 3,800 mi) of the MAX 9. In early 2017, Boeing showed a 66 inches (1.7 m) stretch to 143 ft (44 m), enabling seating for 230 in a single class or 189 in two-class capacity, compared to 193 in two-class seating for the A321neo.

The modest stretch of the MAX 10 enables the aircraft to retain the existing wing, and the Leap 1B engine from the MAX 9 with a trailing-link main landing gear as the only major change. Boeing 737 MAX Vice President and General Manager Keith Leverkuhn said the design had to be frozen in 2018, for a 2020 introduction.

Boeing hopes that 737 operators and 737-MAX customers like United Airlines, Delta Air Lines, Alaska Airlines, Air Canada, Lion Air, and Chinese airlines will be interested in the new variant. Boeing predicts a 5% lower trip cost and seat cost compared to the A321neo. Air Lease Corporation wants it a year sooner; its CEO John Pleuger stated "It would have been better to get the first airplane in March 2019, but I don't think that's possible". AerCap CEO Aengus Kelly is cautious and said the -9 and -10 "will cannibalize each other".

The 737-MAX 10 was launched on June 19, 2017, with 240 orders and commitments from more than ten customers. United Airlines was the largest 737-MAX 10 customer, converting 100 of their 161 orders for the MAX 9 into orders for the MAX 10. Boeing ended the 2017 Paris Air Show with 361 orders and commitments, including 214 conversions, from 16 customers, including 50 orders from Lion Air.

The variant configuration was firmed up by February 2018, and by mid-2018, the critical design review was completed. As of August 2018, assembly was underway with a first flight planned for late 2019. The semi-levered landing gear design has a telescoping oleo-pneumatic strut with a down-swinging lever to permit 9.5 inches (24 cm) taller gear. Driven by the existing retraction system, a shrink-link mechanical linkage mechanism at the top of the leg, inspired by carrier aircraft designs, allows the gear to be drawn in and shortened while being retracted into the existing wheel well. Entry into service was slated for July 2020 but has been pushed back. In November 2022, Boeing Commercial Airplanes CEO Stanley Deal told investors at a conference that the MAX 10 was expected to enter service in 2024.

On November 22nd, 2019, Boeing unveiled the first MAX 10 to employees in its Renton factory, Washington, scheduled for the first flight in 2020. At the time, 531 MAX 10s were on order, compared to 3,142 Airbus A321neos sold, capable of carrying 244 passengers or to fly up to 4,700 nautical miles in its heaviest A321XLR variant.

As of February 2022, the five largest operators of the Boeing 737 MAX were Southwest Airlines (69), Ryanair (55), American Airlines (42), Air Canada (32), and China Southern Airlines (24).

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