2019 Boeing 737 MAX groundings

2019 Boeing 737 MAX groundings
Boeing 737-8 MAX N8704Q rotated.jpg
Boeing 737 MAX 8 aircraft in Boeing livery (July 2016)
DateMarch 11, 2019 (2019-03-11) – ongoing (9 days)
CauseCrashing of Ethiopian Airlines Flight 302 and Lion Air Flight 610, causing 346 fatalities within five months.

In March 2019, the Boeing 737 MAX passenger airliner was grounded by airlines and governments worldwide following two crashes of the aircraft within five months that killed all 346 people aboard both flights. On October 29, 2018, Lion Air Flight 610 crashed into the Java Sea twelve minutes after takeoff with 189 passengers and crew. On March 10, 2019, Ethiopian Airlines Flight 302 crashed six minutes after takeoff with 157 passengers and crew.

On March 11 Ethiopian Airlines announced it had grounded its 737 MAX 8 fleet "effective yesterday March 10".[1][2] On March 11, the China Civil Aviation Administration, citing its zero-tolerance policy for any safety hazards, became the first government authority to ground its 737 MAX 8 aircraft.[3][4] Shortly after, the aircraft was grounded in Indonesia, Mongolia, Singapore and other countries, either voluntarily by airlines or by order of government.[5]

In the U.S., the Federal Aviation Administration initially stated it had not received any evidence to justify taking action against the 737 MAX. On March 13 President Trump announced the U.S. would ground the aircraft, and the FAA explained that new information about the similarity of the two crashes supported the government's decision. The agency said there was a "possibility of a shared cause" for the accidents.[6][7][8] Panama's aviation authority became the last to ground their fleet. Several countries not served by the 737 MAX fleet imposed an airspace ban on the aircraft, effectively barring newly produced aircraft from leaving the factory.[9][10][11][12][13][14][15] The worldwide fleet of 737 MAX aircraft at the time of the FAA grounding was 387.[16]

In each accident, the aircraft involved was less than four months old. The FAA and Transport Canada Civil Aviation stated that satellite tracking data showed similar flight profiles, indicating that both aircraft had experienced extreme cycles of upward and downward speed fluctuations shortly after takeoff, with the pilots struggling for control, before crashing. Both pilots had radioed their intention to return to the airport.[citation needed] Attention quickly focused on an automated anti-stall flight control system ("MCAS") newly introduced on the 737 MAX.

The U.S. Department of Transportation (DOT) Inspector General opened an investigation into the FAA's approval of the Boeing 737 MAX aircraft series; the probe focuses on potential failures in the FAA's safety-review process. The day after the Ethiopian Airlines crash, a federal grand jury issued a subpoena on behalf of the U.S. Justice Department for documents related to development of the 737 MAX.[17]


737 MAX design

The Maneuvering Characteristics Augmentation System (MCAS) was developed for the 737 MAX to prevent stalls in flaps-retracted, low-speed, nose-up flight.[18] The MCAS uses airspeed and other sensor data to make an attempt at computing when a dangerous condition has developed and then trims the aircraft nose down.[19]

Boeing 737 MAX aircraft have engines mounted higher and further forward than previous 737 models. According to The Air Current, "the relocated engines and the refined nacelle shape" cause an upward pitching moment. In order to pass Part 25 certification requirements, Boeing employed the MCAS to automatically apply nose-down trim when the aircraft is in steep turns or in low-speed, flaps-retracted flight. When the angle of attack (AOA) exceeds a limit that depends on airspeed and altitude, the system activates without notice to the pilot. The system is temporarily deactivated when a pilot trims the aircraft using a switch on the yoke.[19]

The system is sensitive to failure of AOA sensors mounted outside the aircraft.[19] The FAA and Boeing made the AOA Disagree alert an optional feature for the 737 MAX, deciding it was not critical for safe operation.[20] Following the crashes of Lion Air Flight 610 and Ethiopian Airlines Flight 302 soon after takeoff, for which several technical experts implicated the MCAS,[21] Boeing announced a planned software upgrade that notifies pilots of a sensor failure.[22][23] It will be deployed to aircraft operators "in the coming weeks", the company said on March 11, 2019.[22]

Lion Air Flight 610 crash

PK-LQP, the aircraft involved in the crash of Flight 610

On October 29, 2018, Lion Air Flight 610, a scheduled domestic flight operated by the Indonesian airline Lion Air from Soekarno–Hatta International Airport in Jakarta to Depati Amir Airport in Pangkal Pinang, crashed into the Java Sea 12 minutes after takeoff. All 189 passengers and crew were killed in the accident.[24][25][26][27]

The preliminary report tentatively attributed the accident to the erroneous AoA data and automatic nose-down trim commanded by MCAS.[28][12]

Ethiopian Airlines Flight 302 crash

ET-AVJ, the aircraft involved in the crash of Flight 302

On March 10, 2019, Ethiopian Airlines Flight 302, a scheduled international passenger flight operated by Ethiopian Airlines from Addis Ababa in Ethiopia to Jomo Kenyatta International Airport in Nairobi, Kenya, crashed six minutes after takeoff near Bishoftu, killing all 157 passengers and crew aboard the aircraft.[29][30][30][31][32]

Initial reports indicated that the Flight 302 pilot struggled to control the airplane in a manner similar to circumstances of the Lion Air crash.[33] A stabilizer trim jackscrew found in the wreckage of Ethiopian flight 302 was set to put the aircraft into a dive.[34] Experts suggested this evidence further pointed to MCAS as at fault in the crash.[35][36] After the crash of flight ET302, Ethiopian Airlines spokesman Biniyam Demssie said in an interview that the procedures for disabling the MCAS were just previously 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."[37] Ethiopia’s transportation minister, Dagmawit Moges said that initial data from the recovered flight data recorder of Ethiopian flight 302 shows "clear similarities" with the crash of Lion Air flight 610.[38]

Pilot complaints

In addition to the crashes in Indonesia and Ethiopia, Boeing 737 MAX pilots in the United States registered several complaints about the way the jet performed in flight, including reports that pilots in the United States may have experienced similar issues to what happened in the Lion Air crash.[39] Several reports were filed in the Aviation Safety Reporting System in November 2018, including one where the captain "expressed concern that some systems such as the MCAS are not fully described in the aircraft Flight Manual."[40]

On March 13, 2019, it emerged that pilots on at least two 2018 flights in the U.S. filed safety concerns after the nose of a 737 MAX pitched down suddenly when they engaged the autopilot.[41] In response, the FAA made a statement, "Some of the reports reference possible issues with the autopilot/autothrottle, which is a separate system from MCAS, and/or acknowledge the problems could have been due to pilot error."[42] MCAS only activates if the autopilot is turned off.[43] Boeing had advised pilots to disengage autopilot in nose-down incidents, though MCAS initiates nose-down in response to stall incidents.[44][45]

Certification Concerns

On 17 March 2019, the Seattle Times stated that they had raised concerns about the flawed certification of the MCAS system already on 6 March 2019, five days before the Air Ethiopia crash. The Seattle Times also stated that they had still been awaiting an answer to these concerns, when the Air Ethiopia crash occurred. Boeing responded that “there are some significant mischaracterizations” in the description. The concerns (of unnamed current and former engineers directly involved with the evaluations or familiar with Boeing's safety analysis) were that:[46]

  • The FAA had delegated the certification of the system to Boeing themselves. While not unusual per se, the delegation of certification over such a system was felt to be dubious. Anonymous sources at the FAA had reported that they were repeatedly pressured to delegate to Boeing, which was under commercial pressure and needed the 737 to become certified quickly.
  • The system had potentially been mis-rated - it was rated as "hazardous" (capable of causing hazard upon malfunction) rather than "catastrophic" (potential catastrophic consequences of failure).
  • The system relied on a single sensor, which was unusual and inappropriate for a system rated "hazardous", and certainly incorrect if the system should have been rated catastrophic.
  • The system was certified for corrections of up to 0.6 degrees. But by the time the 737 MAX was operational, it was discovered that larger corrections were needed, and the system was modified in production to allow 2.5 degrees of control of the vertical tail. This was 50% of its maximum 5-degree correction and a range over 4 times as large as that certified. As well as being an uncertified range, this meant that the system could quickly impose a vertical correction to the same 5 degree vertical extent that the pilots could. There was no scope for human control beyond this.
  • Regulators and airlines were only informed of the greatly increased range after the Lion Air crash. Until that time, it had been understood that the system limit was 0.6 degrees of correction. An FAA engineer is quoted as stating that "The FAA believed the airplane was designed to the 0.6 limit, and that’s what the foreign regulatory authorities thought, too. It makes a difference in your assessment of the hazard."
  • Boeing's certification appeared to overlook the fact that the system could reset, and then reapply further repeated corrections.
  • The MCAS system was only supposed to operate in "extreme" situations, and therefore pilots were not specifically trained on it or informed much about it. The report states that "Boeing decided that 737 pilots needed no extra training on the system — and indeed that they didn’t even need to know about it. It was not mentioned in their flight manuals [...] Minimizing MAX pilot transition training was an important cost saving."