In November 2018, after the Lion Air accident, Boeing instructed pilots to take corrective action in case of a malfunction in which the airplane entered a series of automated nosedives.

In April 2019, the Ethiopian preliminary report stated that the crew had attempted the recommended recovery procedure, and Boeing confirmed that MCAS had activated in both accidents.

[5] FAA certification of the MAX was subsequently investigated by the U.S. Congress and multiple U.S. government agencies, including the Transportation Department, FBI, NTSB, Inspector General and special panels.

The Indonesian NTSC and the Ethiopian ECAA both attributed the crashes to faulty aircraft design and other factors, including maintenance and flight crew actions.

[9] On January 5, 2024, Alaska Airlines Flight 1282 suffered a mid-flight blowout of a plug filling an unused emergency exit, causing rapid decompression of the aircraft.

[10] In July 2024, Boeing took ownership of the Alaska Airlines jet, pleaded guilty to criminal charges regarding the fatal accidents; and was ordered to allocate funds towards execution of an independently monitored safety compliance program,[11] though the plea was later rejected by a federal judge due to conditions imposed in the deal regarding the selection of the independent monitor.

[13] In response to increasing domestic and international pressure to take action,[14][15][16] the U.S. Federal Aviation Administration (FAA) grounded the aircraft on March 13, 2019, reversing a Continued Airworthiness Notice issued two days prior.

[18] By March 18, every single Boeing 737 MAX plane (387 in total) had been grounded, which affected 8,600 weekly flights operated by 59 airlines across the globe.

Australia and Singapore also offered technical assistance, shortly after the Lion Air accident, regarding data recovery from the new generation flight recorders (FDR).

[needs update] With the exception of Ethiopia, the officially recognized countries are members of the Joint Authorities Technical Review (JATR).

"[35] While the pilots initially followed the correct procedure to disable runaway trim, they did not complete the checklist fully, and consequently, the recovery effort did not succeed.

Boeing wanted the FAA to certify the airplane as another version of the long-established 737; this would limit the need for additional training of pilots, a major cost saving for airline customers.

During flight tests, however, Boeing discovered that the position and larger size of the engines tended to push up the airplane nose during certain maneuvers.

To counter that tendency and ensure fleet commonality with the 737 family, Boeing added MCAS so the MAX would handle similar to earlier 737 versions.

[150] In September 2020, the House of Representatives concluded its investigation and cited numerous instances where Boeing dismissed employee concerns with MCAS, prioritized deadline and budget constraints over safety, and where it lacked transparency in disclosing essential information to the FAA.

[152] Various system, maintenance and training requirements are stipulated, as well as design changes that must be implemented on each aircraft before the FAA issues an airworthiness certificate, without delegation to Boeing.

Other major regulators worldwide are gradually following suit: In 2021, after two years of grounding, Transport Canada and EASA both cleared the MAX subject to additional requirements.

MCAS on the 737 MAX was designed to mimic the pitching behavior of the previous generation of the series, the Boeing 737 NG, by pushing down the aircraft nose from an elevated angle of attack (AoA) by automatically adjusting the horizontal stabilizer and trim tab.

During certification of the MAX, Boeing requested and received permission from the FAA to remove a description of MCAS from the aircraft manual, leaving pilots unaware of the system when the airplane entered service in 2017.

[155][156] Boeing had also knowingly withheld knowledge, for at least a year before the Lion Air crash, that a system to warn of a possible AoA malfunction did not work as advertised.

[158] The FAA issued an emergency airworthiness directive, 2018-23-51, on November 7, 2018, requiring the bulletin's inclusion in the flight manuals, and that pilots immediately review the new information provided.

One important line of enquiry was how Boeing "tricked" regulators into approving sub-standard pilot training materials, especially the deletion of mentioning the critical flight stabilization system MCAS.

[169] A Texas court ruled in October 2022 that the passengers killed in two 737 MAX crashes are legally considered "crime victims", which has consequences concerning possible remedies.

Retired pilot Chesley Sullenberger criticized the aircraft design and certification processes and reasoned that relationship between the industry and its regulators had been too "cozy".

Boeing suffered directly through increased costs, loss of revenue, reputational damage, victim litigation, client compensation, reduced credit rating, and decreased stock value.