Boeing 737 MAX 9

The 737 MAX 9 is the stretched version of the 737 MAX 8 and the direct successor to the Next Generation 737-900. It was born within the MAX programme, which Boeing's board approved on August 30, 2011 in response to record orders for the Airbus A320neo: rather than a new aircraft, Boeing re-engined the 737 with CFM International LEAP-1B engines and refined its aerodynamics, promising 14% lower fuel burn than the 737NG. Within that family the MAX 9 targeted the upper end of the single-aisle market, where its rival was the Airbus A321neo.

The launch customer was the Indonesian airline Lion Air, which ordered 201 of the type in February 2012. The first aircraft rolled out on March 7, 2017 and flew on April 13 that year, taking off from Renton Municipal Airport and landing at Boeing Field after a 2 hr 42 min flight. It was shown at the Paris Air Show the same year. Its test campaign built on that of the MAX 8, repeating about 30% of its tests: aircraft 1D001 was used for autoland, avionics, flutter and mostly stability-and-control trials, while 1D002 tested the environmental control system. Certification came by February 2018, and on March 21 that year Lion Air Group took delivery of the first MAX 9, which entered service with its subsidiary Thai Lion Air.

In 2016 Boeing had planned to improve its range from 3,510 nmi (6,500 km) to 3,605 nmi (6,676 km) after 2021. Commercially the MAX 9 lived in the shadow of the A321neo, which attracted more orders: in 2018 its sale value was the same as a MAX 8's, about $53 million. Like the rest of the family it was grounded worldwide during the MAX crisis that followed the Lion Air and Ethiopian Airlines crashes, and it was recertified together with the MAX 8 before Boeing resumed work on certifying the MAX 7 and MAX 10.

In 2021 a new MAX 9 in a special Alaska Airlines livery served as the ecoDemonstrator, Boeing's flying technology testbed. Its programme focused above all on sustainable aviation fuel in blends of up to 50%, including a flight from Seattle to Glasgow to attend the United Nations COP26 climate change conference.

The event that most marked the type came on January 5, 2024. Alaska Airlines Flight 1282, a MAX 9 that had just taken off from Portland, suffered an uncontrolled decompression when a mid-cabin exit door plug blew out. The MAX 9, like the 737-900ER, has a rear mid-cabin emergency exit on each side behind the wings that is only required with dense seating; on less densely configured aircraft door-shaped plugs are fitted instead, as on this aircraft. The aircraft returned to Portland with no fatalities or serious injuries among the 171 passengers and 6 crew, although personal belongings and cabin trim were sucked out through the opening; according to some passengers, the airflow pulled the shirt off a child while his mother held him.

Alaska Airlines grounded its MAX 9 fleet that night. On January 6 the FAA issued an emergency airworthiness directive mandating inspection of the door plugs, temporarily grounding the 171 aircraft with that configuration, and the next day EASA mandated the same inspection for aircraft under its jurisdiction. Alaska and United Airlines both found loose door plug bolts on some aircraft. On February 6 the NTSB preliminary report found that the four key bolts meant to secure the plug had not been installed on delivery: Boeing had opened the plug at its Renton factory to repair damaged rivets and failed to secure it again. The FAA cleared the plugged MAX 9s to return to service on January 24 once inspections were complete; Alaska resumed flights on January 26 and United on January 27. The Department of Justice considered whether Boeing had violated its January 2021 deferred prosecution settlement, and in June 2024 the NTSB sanctioned the manufacturer for sharing investigation information with reporters without authorization. On June 28 Alaska returned the accident aircraft to Boeing to reduce its storage and maintenance costs.