The 737 MAX is based on earlier 737 designs, with more efficient CFM International LEAP engines, aerodynamic changes including distinctive split-tip winglets, and airframe modifications.

The 737 MAX series has been offered in four variants, with 138 to 204 seats in typical two-class configuration, and a range of 3,300 to 3,850 nautical miles [nmi] (6,110 to 7,130 km; 3,800 to 4,430 mi).

Contributing to the accidents was the Maneuvering Characteristics Augmentation System (MCAS), which activated unexpectedly due to erroneous angle of attack data.

The FAA immediately mandated a grounding and inspections of all 737 MAX 9 with a similar configuration; affected aircraft were returned to service starting at the end of that month.

[28] 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.

[35] On August 13, 2015, the first 737 MAX fuselage completed assembly at Spirit Aerosystems in Wichita, Kansas, for a test aircraft that would eventually be delivered to launch customer Southwest Airlines.

[68] Contributing to the accidents was the Maneuvering Characteristics Augmentation System (MCAS), which activated unexpectedly due to erroneous angle of attack data, and inadequate pilot training.

When erroneous data from that sensor was fed into flight computers, it caused repeated uncommanded activation of MCAS, which applied nose-down trim to the horizontal stabilizer.

[72] Before the crash of Lion Air Flight 610, pilots were not informed by Boeing of the existence of MCAS and were not required to undergo simulator training on the difference between the 737 MAX and earlier 737 versions.

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.

[77] The FAA curtailed Boeing's delegated authority and invited global aviation stakeholders to comment on pending changes to the aircraft and to pilot training.

[84] After the announcement, Moody's cut Boeing's debt ratings in December, citing the rising costs due to the grounding and the production halt including financial support to suppliers and compensation to airlines and lessors which could lower the program's margins and cash generation for years.

[85] The rating agency also warned that the production halt would have wide and harmful impact to the whole aerospace and defense supply chain and the ramp-up would be slower than previously anticipated.

[citation needed] 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.

[103] In late January 2020, production was expected to restart in April and take a year and a half to clear the inventory of 400 airplanes, ramping up slowly and building over time: Boeing might have delivered 180 stored jets by year-end and produce an equal number.

[111] On March 4, Boeing reportedly had preliminary plans to ramp up production of the 737 MAX aircraft to about 47 a month by the end of 2023 as the company looked to extend its recovery from successive crises.

[114][115] However, after the January 2024 Alaska Airlines Flight 1282 accident in which a door plug became detached (after not being bolted in place by Boeing) and resulted in an uncontrolled decompression of the aircraft, the FAA announced it would not grant any production expansion of the 737 MAX until it is satisfied that more stringent quality control measures have been enacted.

[131] The 737 MAX uses a split-tip winglet, designed to reduce vortex drag, which improves fuel efficiency[132] by maximizing lift, while staying in the same ICAO aerodrome reference code letter C gates as current Boeing 737s.

[31] 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.

[31] Rockwell Collins was selected to supply four 15.1-inch (380 mm) liquid-crystal displays (LCD), as used on the 787, for the glass cockpit to improve pilots' situation awareness and efficiency.

MCAS was to automatically mitigate the pitch-up tendency of the new flight geometry due to the engines being located farther forward and higher than on previous 737 models.

[168] It reached 250 knots (460 km/h; 290 mph) and 25,000 ft (7,600 m), performed a low approach, systems checks and an inflight engine restart, and landed at Boeing's flight test center in Moses Lake, Washington.

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.

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.

[201] 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 (140 kN) LEAP-1B that could be available by 2019 or 2020, and would likely require a landing-gear modification to move the rotation point slightly aft.

[216] At the time, 531 MAX 10s were on order, compared to the 3142 Airbus A321neos sold, capable of carrying 244 passengers or to fly up to 4,700 nautical miles (8,700 km; 5,400 mi) in its heaviest A321XLR variant.

[217] The MAX 10 has similar capacity as the A321XLR, but shorter range and much poorer field performance, greatly hindering its potential to service smaller airports as compared to the A321XLR.

[224] 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, though this did not happen.

[239] In November 2021, during the Dubai Airshow, Boeing received 72 firm orders from a new 737 MAX customer, India based Akasa Air,[240] to be fulfilled over a 4-year period with first delivery in June 2022.

Following the Lion Air crash, Boeing issued an operational manual guidance, advising airlines on how to address erroneous cockpit readings.