Boeing 737 MAX groundings

Boeing 737 MAX groundings
Boeing 737 MAX grounded aircraft near Boeing Field, April 2019.jpg
A parking lot at Boeing Field in Seattle, Washington, filled with undelivered Boeing 737 MAX aircraft
  • between accidents: 4 months and 10 days
  • of grounding: 1 year, 4 months and 27 days since March 10, 2019 (515 days ago)
Cause Airworthiness revoked after recurring flight control failure
Deaths 346:

In March 2019, the Boeing 737 MAX passenger airliner was grounded worldwide after 346 people died in two crashes, Lion Air Flight 610 on October 29, 2018 and Ethiopian Airlines Flight 302 on March 10, 2019. Ethiopian Airlines immediately grounded its remaining MAX fleet. On March 11, the Civil Aviation Administration of China ordered the first nationwide grounding, followed by most other aviation authorities in quick succession. The U.S. Federal Aviation Administration (FAA) publicly affirmed the airworthiness of the airplane on March 11, but grounded it on March 13 after receiving evidence of accident similarities. All 387 aircraft, which served 8,600 flights per week for 59 airlines, were barred from service by March 18, 2019. The groundings have become the longest ever of a U.S. airliner.

In November 2018, Boeing revealed the MAX had a new automated flight control, the Maneuvering Characteristics Augmentation System (MCAS), that can repeatedly push the airplane nose down. Boeing had omitted any mention of the system from the aircraft manuals. On November 6, a week after the first accident, Boeing sent airlines a service bulletin and the FAA followed up November 7 with an airworthiness directive to specify a flight recovery procedure.[1] In December 2018, the FAA privately predicted that an uncorrected MCAS could cause more accidents, but anticipated that Boeing would deliver a software update by April 2019.[2][3]

During the groundings, the U.S. Congress, Transportation Department, FBI and ad hoc panels investigated FAA certification of the MAX, especially the agency's delegation of nearly all approvals to Boeing employees, who were subject to undue pressure by the company. Inquiries also found several systems and manufacturing defects. The Indonesian NTSC accident report faulted aircraft certification, maintenance, and flight crew actions. The Ethiopian ECAA determined that the flight crew had attempted the recovery procedure, and both authorities blamed flaws in aircraft design. The U.S. NTSB said Boeing failed to assess the consequences of MCAS failure and made incorrect assumptions about flight crew response. The U.S. Inspector General said Boeing deliberately misrepresented MCAS to avoid scrutiny. The House of Representatives criticized Boeing's "culture of concealment." The FAA revoked Boeing's delegation to issue airworthiness certificates for individual MAX airplanes.

In January, with 400 aircraft awaiting certification and delivery, Boeing suspended production of the MAX until May 2020. By March 2020, the grounding had cost Boeing $18.6 billion in compensation to airlines and victims' families, lost business, and legal fees. By June 2020, airlines and leasing companies that once struggled without the MAX had cancelled nearly 600 orders during the COVID-19 pandemic. On July 1, Boeing completed several days of certification flights. In August, the FAA announced its final list of design, operation, maintenance and training changes that must be completed before the MAX's return to service, expected no earlier than mid-October 2020.



  • October 29, a 737 MAX 8 operating Lion Air Flight 610 crashed after take-off from Jakarta, killing all 189 on-board.
  • November 6, Boeing issued a service bulletin 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.[1]
  • November 7, the FAA issued an Emergency airworthiness directive requiring revising "the 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".[1]
  • November 10, Boeing referred to MCAS in multi-operator messages.[4] The automated flight control could cause unintended nosedives, but was omitted from crew manuals and training.[5]
  • November 27, the Allied Pilots Association of American Airlines had a meeting with Boeing to express concerns with the MCAS effectiveness, but was unnerved by the airframer responses.[6]
  • December 3, the FAA conducted an unpublished "Transport Aircraft Risk Assessment Methodology” (TARAM) analysis that concluded, "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”; it was exposed by the United States House Committee on Transportation and Infrastructure on December 11, 2019.[7]


  • March 10, another 737 MAX 8 operating Ethiopian Airlines Flight 302 crashed shortly after take-off from Addis Ababa airport, killing all 157 on-board, due to a similar faulty MCAS, initiating a worldwide flight ban for the aircraft, starting with China.
  • March 13, the U.S. FAA was among the last to order the grounding of the 737 MAX, after claiming there was no reason: China had the most aircraft in service, 96, followed by the U.S. with 72, Canada with 39 and India with 21.
  • March 27, Boeing unveiled a software update to avoid MCAS errors, already developed and tested it in-flight, to be certified.
  • April 5, Boeing announced it was cutting 737 production by almost a fifth, to 42 aircraft monthly, anticipating a prolonged grounding, and had formed an internal design review committee.
  • May 13, Rep. Congressman Sam Graves at the House Aviation subcommittee hearing, blamed the 737 MAX crashes on poor training of the Indonesian and Ethiopian pilots; he stated that "pilots trained in the U.S. would have been successful" in handling the emergencies on both jets.[8][9]
  • June 18, IAG signed a letter of intent for 200 737 MAXs at the Paris air show, followed by Turkish SunExpress and Air Astana later in the year.
  • June 26, flight tests for the FAA uncovered a data processing issue affecting the pilots' ability to perform the "runaway stabiliser" procedure to respond to MCAS errors.
  • October 30, Boeing CEO Dennis Muilenburg testified before U.S. Congress committees, defending Boeing's safety culture and denying knowledge of internal messages in which Boeing's former chief technical pilot said he had unknowingly lied to regulators, and voiced its concerns on MCAS.
  • November 22, Boeing unveiled the first 737 MAX 10 flight-test aircraft.[5]
  • November 26, the FAA revoked Boeing's Organization Designation Authorization to issue airworthiness certificates for individual MAX airplanes.[10]
  • December 17, Boeing confirmed the suspension of 737 MAX production from January 2020.
  • December 23, Dennis Muilenburg resigned, to be replaced by board chairman David Calhoun.[5]


  • January 7, Boeing recommended "simulator training in addition to computer based training".[11]
  • January 9, Boeing released previous messages in which it claimed no flight simulator time was needed for pilots, and distanced itself from emails mocking airlines and the FAA, and criticising the 737 MAX design.
  • January 13, David Calhoun became CEO, pledging to improve Boeing’s commitment to safety and transparency, and estimating the return to service in mid-2020.
  • January 21, Boeing estimated the ungrounding could begin in mid-2020.[5]
  • May 27, Boeing resumed production of the MAX at a "very gradual pace".[12]
  • June 28 to July 1, the FAA conducted flight tests with a view to recertification of the 737 MAX.[13]


After the Ethiopian Airlines crash, China and most other aviation authorities preceded the U.S. Federal Aviation Administration (FAA) in grounding the airliner over perceived safety risks. The FAA issued a Continued Airworthiness Notification to the International Community on March 11 and resisted pressure from U.S. lawmakers to ground the aircraft.[14][15] Boeing CEO Dennis Muilenburg called President Donald Trump on March 12 to assure him the airplane was safe.[16] On March 13, 2019, the FAA found similarities between the two accidents and grounded the plane.[17] About 30 MAX aircraft were flying in U.S. airspace at the time and were allowed to reach their destinations.[18] By March 18, regulators grounded all 387 MAX aircraft in service with 59 airlines worldwide and making 8,600 flights each week.[19] Several ferry flights were operated with flaps extended to circumvent MCAS activation.

The grounding subsequently became the longest ever of a U.S. airliner.[20] As of January 2020, another 400 newly-manufactured aircraft await delivery to airlines pending the aircraft's return to service.

Accident investigations

Lion Air Flight 610

PK-LQP, the aircraft involved in the crash of 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 previous flights, 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 just replaced before the accident flight.[21] The report tentatively attributed the accident to the erroneous angle-of-attack (AoA) data and automatic nose-down trim commanded by MCAS.[22][23]

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".[24][25][26]

The final report has been shared with families of Lion Air Flight 610, then published on October 25, 2019.[27][28][29][30]

Ethiopian Airlines Flight 302

ET-AVJ, the Ethiopian Airlines aircraft that crashed as Flight 302

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.[31] 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.[32] This further implicated MCAS as contributory to the crash.[33][34][35]

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."[36] Despite following the procedure, the pilots could not recover.[37]

The Ethiopian Civil Aviation Authority (ECAA) is leading investigations for Flight 302. The United States Federal Aviation Administration will also assist in the investigation.[38] Both the cockpit voice recorder and the flight data recorder were recovered from the crash site on March 11, 2019.[39] The French aviation accident investigation agency BEA announced that it would analyze the flight recorders from the flight.[40] BEA received the flight recorders on March 14, 2019.[41]

On March 17, 2019, the Ethiopia's transport minister Dagmawit Moges 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.[42][43][44] Due to this finding, some experts in Indonesia suggested that the NTSC should cooperate with Flight 302's investigation team.[45] Later on 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.[46]

The Ethiopian Civil Aviation Authority published an interim report on March 9, 2020, one day before the March 10 anniversary of the crash.[47] Investigators have tentatively concluded that the crash was caused by the aircraft's design.[48][49]

United States

Vertical airspeeds of Boeing Max 737s in 2018-2019 crashes
The vertical airspeeds of the Boeing 737 MAX 8s involved in the JT 610 and ET 302 crashes

On November 6, 2018, four days before it identified MCAS by name, Boeing published a supplementary service bulletin prompted by the first crash. The bulletin describes warnings triggered by erroneous AoA data, and referred pilots to a "non-normal runaway trim" procedure as resolution, specifying a narrow window of a few seconds before the system would reactivate and pitch the nose down again.[50] 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.[51][52] On March 11, FAA defended the aircraft against groundings citing these emergency procedures (Continued Airworthiness Notification to the International Community) for operators.

In December 2018, a month after the Lion Air accident, the FAA had conducted an internal safety risk analysis predicted fifteen more crashes with no repairs to MCAS, but that report was not revealed until the U.S. House hearing in December 2019. FAA's administrator, Stephen Dickson, who assumed the position during the accident investigations, said in retrospect that the accident risk was unsatisfactory.

On September 26, 2019, the NTSB released the results of its review of potential lapses in the design and approval of the 737 MAX.[53][54](p1)[55] The NTSB report concludes that assumptions "that Boeing used in its functional hazard assessment of uncommanded MCAS function for the 737 MAX did not adequately consider and account for the impact that multiple flight deck alerts and indications could have on pilots' responses to the hazard". When Boeing induced a stabilizer trim input that simulated the stabilizer moving consistent with the MCAS function, "... the specific failure modes that could lead to unintended MCAS activation (such as an erroneous high AOA input to the MCAS) were not simulated as part of these functional hazard assessment validation tests. As a result, additional flight deck effects (such as IAS DISAGREE and ALT DISAGREE alerts and stick shaker activation) resulting from the same underlying failure (for example, erroneous AOA) were not simulated and were not in the stabilizer trim safety assessment report reviewed by the NTSB."[54][54][56]

The NTSB questioned the long-held industry and FAA practice of assuming the nearly instantaneous responses of highly trained test pilots as opposed to pilots of all levels of experience to verify human factors in aircraft safety.[57] The NTSB expressed concerns that the process used to evaluate the original design needs improvement because that process is still in use to certify current and future aircraft and system designs. The FAA could for example randomly sample pools from the worldwide pilot community to get a more representative assessment of cockpit situations.[58]

Responsible states

ICAO regulations Annex 13, “Aircraft Accident and Incident Investigation”, defines which states may participate in investigations. For the two MAX accidents these are:[59]

  1. Indonesia, for Lion Air Flight 610 as state of registration, state of occurrence and state of operator.
  2. Ethiopia, for Ethiopian Airlines Flight 302, as state of registration, state of occurrence and state of operator.
  3. The United States, as 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 recognised countries are members of the Joint Authorities Technical Review (JATR).

Type certification and return to service

The Boeing 737 MAX needs to be recertified to fly again in commercial airline service

Under a system known as the Organization Designation Authorization, the FAA allowed manufacturers like Boeing to act on its behalf, while the agency retains legal authority to issue a type certificate. The goal for Boeing was to ensure the aircraft retains a compatible type rating with all other aircraft in the 737 family, thus avoiding costly simulator training and the need to learn about new systems like the MCAS.

On March 11, 2019, a U.S. federal grand jury issued a subpoena on behalf of the U.S. Justice Department (DOJ) for documents related to development of the 737 MAX.[60][61][62][63] On March 19, 2019, the U.S. Department of Transportation requested the Office of Inspector General to conduct an audit on the 737 MAX certification process.[64] Over the next several months, The Seattle Times's award-winning[65] coverage of the ongoing crisis revealed how management decisions at Boeing and the FAA pushed for cost-saving solutions, but ultimately produced a flawed design with insufficient oversight. [66] The FAA found that Boeing had violated regulations in deciding to not fix a known defect with the aircraft.[67]

In November 2019, the FAA suspended Boeing's authority to issue individual airworthiness certificates for MAX aircraft. In February 2020, the DOJ was conducting an ongoing investigation into whether Boeing lied to the FAA.[68] In March 2020, the House of Representatives criticized Boeing's culture of concealment and its undue influence over the FAA, as exemplified during certification and in the aftermath of the crashes. In June 2020, the U.S. Inspector General report said that Boeing downplayed MCAS for years, and the FAA missed it.[69]

By convention, aviation regulators worldwide accept the certification of aircraft from the country of manufacture and do not review those certifications in much detail.[70] However, since the fatal accidents and grounding of 737 MAX several aviation authorities, particularly the European EASA,[71] will conduct their assessments and validation tests of the MAX prior to authorizing it in their controlled airspace. As of October 2019 the disagreements over various system revision details, Level of Involvement (LoI) between the two leading aviation authorities, FAA and EASA, as well as Boeing's new recommendation of simulator training could delay the 737 MAX return to service.[72]

Maneuvering Characteristics Augmentation System

The MAX uses an adjustable stabilizer, moved by a jackscrew, to provide the required pitch trim forces. Generic stabilizer illustrated.
Movable horizontal stabilizer on an Embraer ERJ-170

The Maneuvering Characteristics Augmentation System (MCAS) is a flight control law (software) first deployed on the Boeing KC-46 Air Force tanker, where it "moves the stabilizer in a wind-up turn".[73] MCAS adjusts the horizontal stabilizer trim to push the nose down when the aircraft is operating in manual flight, with flaps up, at an elevated angle of attack (AoA), so the pilot will not inadvertently pull the airplane up too steeply, potentially causing a stall. Contrary to descriptions in news reports, however, Boeing claims that MCAS is not an anti-stall system.

On the Boeing 737 MAX, MCAS was intended to mimic pitching behavior similar to aircraft in the previous generation of the series, the Boeing 737 NG. MCAS activated by input from only one of the airplane's two angle of attack sensors, making the system susceptible to a single point of failure. It could not be instinctively disabled by pulling on the control yoke. During aircraft certification, Boeing removed a description of MCAS in the MAX flight manuals, leaving pilots unaware of the system when the airplane entered service.[74]

On November 10, 2018, Boeing publicly revealed MCAS in a discussion with airline operators and other aviation interests twelve days after Lion Air Flight 610 crashed.[75] Yet, a recovery procedure highlighted by Boeing and the FAA failed to prevent the crash of Ethiopian Airlines Flight 302, which led to the global grounding of all 737 MAX aircraft pending investigations and software fixes.

In April 2019, Boeing admitted that MCAS played a role in both accidents. The investigations identified numerous defects with associated systems, including an AoA disagree message that should have prevented MCAS activation. The Wall Street Journal reported that Boeing failed to share information about that issue for "about a year" before the Lion Air crash in Indonesia.[76]


The Boeing 737 MAX groundings drew mixed reactions from multiple organizations. While Boeing initially expressed its sympathy to the relatives of the Lion Air Flight 610 and Ethiopian Airlines Flight 302 crash victims, it defended the aircraft against any faults until rebutted by evidence. Boeing provided several outdated return to service timelines, the soonest of which was "in the coming weeks" following the March 2019 grounding. On October 11, 2019, David L. Calhoun replaced Dennis Muilenburg as chairman of Boeing, then succeeded Muilenburg's role as chief executive officer in January 2020.

Rep. Congressman Sam Graves of the House Transportation Committee had blamed the 737 MAX crashes on substandard-quality training of the Indonesian and Ethiopian pilots; stating that "pilots trained in the U.S. would have been successful" in handling the emergencies on both jets, at the House Aviation subcommittee hearing in Washington D.C.[77][78]

Airbus downplayed that it is "winning" in any way due to the MAX grounding, citing its own logistical and supplier capacity to fulfill orders for the A320 family aircraft.

Pilots and flight attendants opinions are mixed as some expressed confidence in the certification renewal, while others are disappointed as Boeing had hidden an important safety feature to their knowledge. Aviation experts asserted that MCAS is not comparable to a runaway trim stabilizer condition.

Most airlines seek compensation from Boeing to cover costs of the disruption, while the 737 MAX received some support when International Airlines Group (IAG) announced at the June 2019 Paris Air Show it could order 200 jets. Opinion polls suggested most passengers are reluctant to fly again aboard the 737 MAX when it will be reintroduced, while most should be comfortable boarding it again after some time passes to prove its safe operations. Public observers commented upon the "cozy relationship" that exists between the industry and its regulators.

Financial and economic effects

The Boeing 737 MAX groundings have had a deep financial effect on the aviation industry and a significant effect on the national economy of the United States. No airline took delivery of the MAX during grounding. Boeing slowed MAX production to 42 aircraft per month until in January 2020, when they halted until the airplane is reapproved by regulators. Boeing has suffered directly through increased costs, loss of sales and revenue, loss of reputation, victims litigation, client compensation, decreased credit rating and lowered stock value. In January 2020, the company estimated a loss of $18.4 billion for 2019, and it reported 183 canceled MAX orders for the year.

In February 2020, the global coronavirus pandemic and the resulting travel bans created further uncertainty for Boeing. In March 2020, news that Boeing was seeking a $60 billion bailout caused a steep drop in its stock price, though Boeing eventually received $17 billion in funds from the coronavirus stimulus[79]. Its extensive supply chain providing aircraft components and flight simulators suffered similar losses, as did the aircraft services industry, including crew training, the aftermarket and the aviation insurance industry. Its customers, the airlines and aircraft lessors, had their operations and strategic plans severely disrupted.[not verified in body] By May 2020, Boeing's net orders were down by 602 planes in 2020.[80]

See also


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Further reading