The Boeing 737 MAX passenger airliner was grounded worldwide between March 2019 and December 2020 after 346 people died in two similar crashes in less than five months, and briefly in January 2024 following a dangerous in-flight incident.
The accidents leading to the earlier, 2019–2020 grounding were Lion Air Flight 610 on October 29, 2018 and Ethiopian Airlines Flight 302 on March 10, 2019. The Federal Aviation Administration initially affirmed the MAX's continued airworthiness, following these, claiming to have insufficient evidence of accident similarities. On March 13, following grounding decisions by 51 other regulators, the FAA grounded the aircraft. All 387 aircraft delivered to airlines were grounded by March 18.
In 2016 the FAA had approved Boeing's request to remove references to a new Maneuvering Characteristics Augmentation System (MCAS) from the flight manual. 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. Boeing avoided revealing the existence of MCAS until pilots requested further explanation. In December 2018, the FAA privately predicted that MCAS could cause 15 crashes over 30 years. 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.
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. Engineering reviews uncovered other design problems, unrelated to MCAS, in the flight computers and cockpit displays. The Indonesian NTSC and the Ethiopian ECAA both attributed the crashes to faulty aircraft design and other factors, including maintenance and flight crew actions. Lawmakers investigated Boeing's incentives to minimize training for the new aircraft. The FAA revoked Boeing's authority to issue airworthiness certificates for individual MAX airplanes and fined Boeing for exerting "undue pressure" on its designated aircraft inspectors.
In August 2020, the FAA published requirements for fixing each aircraft and improving pilot training. On November 18, 2020, the FAA ended the 20-month grounding, the longest ever of a U.S. airliner. The accidents and grounding cost Boeing an estimated $20 billion in fines, compensation, and legal fees, with indirect losses of more than $60 billion from 1,200 cancelled orders. The MAX resumed commercial flights in the U.S. in December 2020, and was recertified in Europe and Canada by January 2021.
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. The FAA grounded some 171 Boeing 737 MAX 9s with a similar configuration for inspections. The Department of Justice believes Boeing might have violated its January 2021 deferred prosecution settlement.
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, though the plea was later rejected by a federal judge due to diversity, equity, and inclusion requirements imposed in the deal regarding the selection of the independent monitor.
The Boeing 737 MAX passenger airliner was grounded worldwide between March 2019 and December 2020 after 346 people died in two similar crashes in less than five months, and briefly grounded in January 2024 following a dangerous in-flight accident.
The accidents leading to the 2019–2020 grounding were Lion Air Flight 610 on October 29, 2018 and Ethiopian Airlines Flight 302 on March 10, 2019. On March 11 the Federal Aviation Administration said it did not yet have data to take action. On March 13 the FAA said evidence showed "similarities" between the two crashes and grounded the aircraft, an action already taken after the second crash by 51 other regulators. All 387 aircraft delivered to airlines were grounded by March 18.
Official investigations concluded that a new automated flight control feature—the Maneuvering Characteristics Augmentation System (MCAS)—contributed to both crashes. During development of the airplane in 2016, the FAA approved Boeing's request to remove references to MCAS from the aircrew flight manual. 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. Boeing avoided revealing the existence of MCAS until pilots requested further explanation. In December 2018, the FAA privately predicted that MCAS could cause 15 crashes over 30 years. 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.
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. Engineering reviews uncovered other design problems, unrelated to MCAS, in the flight computers and cockpit displays. The Indonesian NTSC and the Ethiopian ECAA both attributed the crashes to faulty aircraft design and other factors, including maintenance and flight crew actions. Lawmakers investigated Boeing's incentives to minimize training for the new aircraft. The FAA revoked Boeing's authority to issue airworthiness certificates for individual MAX airplanes and fined Boeing for exerting "undue pressure" on its designated aircraft inspectors.
In August 2020, the FAA published requirements for fixing each aircraft and improving pilot training. On November 18, 2020, the FAA ended the 20-month grounding, the longest ever of a U.S. airliner. The accidents and grounding cost Boeing an estimated $20 billion in fines, compensation, and legal fees, with indirect losses of more than $60 billion from 1,200 cancelled orders. The MAX resumed commercial flights in the U.S. in December 2020, and was recertified in Europe and Canada by January 2021.
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. The FAA grounded some 171 Boeing 737 MAX 9s with a similar configuration for inspections. The Department of Justice believes Boeing might have violated its January 2021 deferred prosecution settlement. 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, though the plea was later rejected by a federal judge due to diversity, equity, and inclusion requirements imposed in the deal regarding the selection of the independent monitor.
Groundings
After the Ethiopian Airlines crash, China and most other civil aviation authorities grounded the airliner over safety concerns. Other jurisdictions, including the U.S., followed suit as new evidence revealed similarities between both crashes. The groundings were ordered despite Boeing CEO Dennis Muilenburg's public assurances that the airplane was safe and a phone conversation with President Trump in which he "reiterated to the President our position that the MAX aircraft is safe", according to a Boeing statement. In response to increasing domestic and international pressure to take action, the U.S. Federal Aviation Administration (FAA) grounded the aircraft on March 13, 2019, reversing a Continued Airworthiness Notice issued two days prior. About 30 MAX aircraft were flying in U.S. airspace at the time and were allowed to reach their destinations. 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. Several ferry flights were operated with flaps extended to prevent MCAS activation.
Accident investigations
ICAO regulations Annex 13, "Aircraft Accident and Incident Investigation", defines which states may participate in investigations. For the two MAX accidents these are:
Indonesia, for Lion Air Flight 610 as the state of registration, state of occurrence, and state of the operator.
Ethiopia, for Ethiopian Airlines Flight 302, as the state of registration, state of occurrence, and state of the operator.
The United States, as the state of manufacturer and issuer of the type certificate.
The participating state or national transportation safety bureaus are the NTSB for the US and the NTSC for Indonesia. Australia and Singapore also offered technical assistance, shortly after the Lion Air accident, regarding data recovery from the new generation flight recorders (FDR). With the exception of Ethiopia, the officially recognized countries are members of the Joint Authorities Technical Review (JATR).
Lion Air Flight 610
Preliminary investigations revealed serious flight control problems that traumatized passengers and crew on the aircraft's previous flight, as well as signs of angle-of-attack (AoA) sensor and other instrument failures on that and the accident flight, tied to a design flaw involving the Maneuvering Characteristics Augmentation System (MCAS) of the 737 MAX series. The aircraft maintenance records indicated that the AoA sensor was replaced two days before the accident flight. The report tentatively attributed the accident to the erroneous angle-of-attack (AoA) data and automatic nose-down trim commanded by MCAS.
The NTSC final report, published on October 23, 2019, was prepared with assistance from the U.S. NTSB. NTSC's investigator Nurcahyo Utomo identified nine factors to the accident, saying:
The nine factors are the root problem; they cannot be separated. Not one is contributing more than the other. Unlike NTSB reports that identify the primary cause of accidents and then list contributing issues determined to be less significant, Indonesia is following a convention used by many foreign regulators of listing causal factors without ranking them.
The final report was shared with families of Lion Air Flight 610, then published on October 25, 2019.
Ethiopian Airlines Flight 302
On March 11, the FAA defended the MAX against groundings by issuing a Continued Airworthiness Notice to operators. The initial reports for Flight 302 found that the pilots struggled to control the airplane in a manner similar to the Lion Air Flight 610 crash. On March 13, 2019, the FAA announced that evidence from the crash site and satellite data on Flight 302 suggested that it might have suffered from the same problem as Lion Air Flight 610 in that the jackscrew controlling the pitch of the horizontal stabilizer of the crashed Flight 302, was found to be set in the full "nose down" position, similar to Lion Air Flight 610. This further implicated MCAS as contributory to the crash.
Ethiopian Airlines spokesman Biniyam Demssie said that the procedures for disabling MCAS had just been incorporated into pilot training. "All the pilots flying the MAX received the training after the Indonesia crash," he said. "There was a directive by Boeing, so they took that training." 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.
The Ethiopian Civil Aviation Authority (ECAA) led investigations for Flight 302, and the United States Federal Aviation Administration assisted in the investigation. Both flight recorders (voice and data) were recovered from the crash site on March 11, 2019. The French aviation accident investigation agency BEA announced that it would analyze the flight recorders from the flight. BEA received the flight recorders on March 14, 2019.
On March 17, 2019, Dagmawit Moges, Ethiopia's transport minister, announced that the black box had been found and downloaded, and that the preliminary data retrieved from the flight data recorder show a "clear similarity" with those of Lion Air Flight 610 which crashed off Indonesia. Due to this finding, some experts in Indonesia suggested that the NTSC should cooperate with Flight 302's investigation team. Later in the evening, the NTSC offered assistance to Flight 302's investigation team, stating that the committee and the Indonesian Transportation Ministry would send investigators and representatives from the government to assist with the investigation of the crash.
The Ethiopian Civil Aviation Authority published an interim report on March 9, 2020, one day before the March 10 anniversary of the crash. Investigators tentatively concluded that the crash was caused by the aircraft's design. On December 23, 2022, the Ethiopian Aircraft Accident Investigation Bureau published its final report on the crash, concluding the probable cause was "Repetitive and uncommanded airplane-nose-down inputs from the MCAS", due to false input from the angle of attack (AoA) sensor.
Timeline
2016
March 2016, The General Manager of Boeing's 737 MAX program and the former Chief Project Engineer on the 737 MAX program both approved a redesign of MCAS to increase its authority to move the aircraft's stabilizer at low speed, in order to address "stall characteristics" requirements necessary for FAA certification. Just hours after the approval for MCAS's redesign was granted, Boeing sought, and the FAA approved, the removal of references to MCAS from Boeing's flight crew operations manual (FCOM). The FAA officials who authorized this request remained unaware of the redesign of MCAS until after the crash of the Lion Air flight.
2018
January 10, The Operational Evaluation Report of the National Civil Aviation Agency of Brazil (ANAC) mentions the MCAS. The FAA had approved Boeing's request to remove MCAS from differences tables and quick reference handbook (QRH); The Operational Evaluation Report prepared by Transport Canada contained the same table as ANAC's, except the reference to MCAS.
October 29, a 737 MAX 8 operating Lion Air Flight 610 crashed after take-off from Jakarta, killing all 189 on board. Boeing started redesigning the MCAS system right after the accident.
November 6, Boeing issued an Operations Manual Bulletin (OMB), describing a MAX-specific feature of the pitch trim system, warning that with "erroneous AoA data, the pitch trim system can trim the stabilizer nose down in increments lasting up to 10 seconds" which "can be stopped and reversed with the use of the electric stabilizer trim switches but may restart 5 seconds after" and instructed pilots to counteract it by running the Runaway stabilizer and manual trim procedure. The background introduction of the bulletin states: "This bulletin directs flight crews to existing procedures to address this condition", and reminds operators to use the "existing procedures in the Runaway Stabilizer NNC [Non-Normal Checklist]" when the MAX reacts to a false stall detection. This was Boeing's first public announcement about MCAS, albeit not by name.
November 7, the FAA issued an Emergency airworthiness directive to owners and operators, requiring revising the aircraft flight manual (AFM) "to provide the flight crew with runaway horizontal stabilizer trim procedures" when "repeated nose-down trim commands" are caused by "an erroneously high single AoA sensor", reinforcing the Boeing bulletin. The FAA directive warned that the problem was an "unsafe condition" that could result in "impact with terrain". The directive informs pilots of a new function specific to MAX models : "Note: The 737-8/-9 uses a Flight Control Computer command of pitch trim to improve longitudinal handling characteristics. In the event of erroneous Angle of Attack (AoA) input, the pitch trim system can trim the stabilizer nose down in increments lasting up to 10 seconds." The FAA had removed reference to MCAS from its draft EAD.
November 10, Boeing referred publicly for the first time to the MCAS by name in a Multi Operator Message to operators. The MCAS control law, a few lines of software code in the FCC, could autonomously command nosedives, when even a single sensor failure resulted in bad data; MCAS was omitted from aircraft manuals and training, therefore flight crews had no knowledge of its existence or functioning until Boeing published a bulletin on November 6.
November 27, the Allied Pilots Association of American Airlines had a meeting with Boeing to express concerns with the MCAS effectiveness, and was unnerved by the airframer's responses. Union president Daniel Carey later said, "The huge error of omission is that Boeing failed to disclose the existence of MCAS to the pilot community. The final fatal mistake was, therefore, the absence of robust pilot training in the event that the MCAS failed". The Boeing officials acknowledged that they were considering some changes, for example preventing MCAS's repetitive activation to ensure that it only triggers once.
December 3, the FAA Seattle Certification Office reviewed an unpublished quantitative risk assessment analysis of the MAX, prepared using the "Transport Aircraft Risk Assessment Methodology" (TARAM). The U.S. House Committee on Transportation and Infrastructure made the report public just over a year later, on December 11, 2019. In the committee's words, the report concluded that "if left uncorrected, the MCAS design flaw in the 737 MAX could result in as many as 15 future fatal crashes over the life of the fleet", predicting 2900 deaths over 30 years.
December 17, in a presentation to the FAA, Boeing deflected blame and continued to assert that appropriate crew action would save the aircraft.