Ethiopian authorities, in a press conference Thursday disclosing findings from their preliminary crash probe, stopped short of drawing any firm conclusions about the causes of the crash. But they confirmed a flight-control system triggered repetitively during the six-minute flight, pushing the nose down. They recommended Boeing review the system, and said regulators should then test it before lifting a global grounding of the MAX fleet.
A stall-prevention feature on the MAX, called MCAS, has been the subject of intense scrutiny since another deadly crash of a 737 MAX in Indonesia last year. In early findings into that crash, investigators found a faulty sensor caused the system to mistakenly push down the jet’s nose. A similar sequence of events unfolded in the Ethiopian Airlines accident that killed all 157 people aboard.
The Indonesian probe also raised questions about maintenance of a sensor feeding the system, and about whether pilots followed Boeing guidance on how to respond to a fault. In the Ethiopian flight, no such issues were found—at least so far.
The Wall Street Journal previously reported that MCAS, which stands for maneuvering characteristics augmentation system, had been activated on the Ethiopian Air flight, and that the pilots had followed Boeing’s primary emergency response step in trying to manually override the system. Investigators didn’t immediately detail on Thursday what steps the crew took to save the plane.
Ethiopian Airlines Chief Executive Tewolde Gebremariam said “we are very proud of our pilots’ compliance, to follow the emergency procedures and high level of professional performances in such extremely difficult situations.”
Ethiopian authorities declined to immediately make the preliminary report public, saying they had submitted the document to the International Civil Aviation Organization, the United Nation’s air safety arm. ICAO is the global repository for crash reports, though the decision on whether to make interim findings public is left to the country leading the probe.
The findings—which can change in subsequent examinations—puts the ball in Boeing’s court in terms of next steps to fix the system and defend the future safety of the jet. The final report into the Indonesia crash is expected sometime this year. A final report into Ethiopian Flight 302 could take a year to complete.
A Boeing spokesman has said the company will review the report’s findings and comment further later. The company since last year has been working on a fix to improve how MCAS operates. On Wednesday, Boeing Chief Executive Dennis Muilenburg accompanied test pilots on a 737 MAX flight in which they tested the software update.
“Experienced the MCAS software update performing safely in action,” he tweeted.
Ethiopia is leading the probe, aided by international experts, including from the U.S. National Transportation Safety Board and Boeing. Ethiopian Transport Minister Dagmawit Moges said all participants in the probe, including European representatives, agreed on the preliminary report’s findings, which were largely based on data from the plane’s so called black boxes.
The Federal Aviation Administration, the principal regulator for the MAX plane, said it would “continue to work towards a full understanding of all aspects of this accident. As we learn more about the accident and findings become available, we will take appropriate action.”
Similarities between a Lion Air crash in Indonesia and the Ethiopian Airlines flight, which crashed on March 10 after takeoff from Addis Ababa, led investigators to suspect early on an MCAS issue. Citing those similarities, authorities around the world grounded the plane.
The Journal has also reported that accident investigators in Ethiopia had preliminarily concluded the MCAS was triggered by a faulty sensor. That caused the plane’s flight-control computer to erroneously believe the plane was at risk of stalling and pushed the jet’s nose down. Pilots turned off the system but turned it back on when they couldn’t regain control of the plane, investigators have found.
Ethiopian lead crash investigator Amdye Andualem Thursday said there was no evidence of foreign object damage, which could have provided an outside cause for the sensor fault.
A key question for investigators remains why the pilots’ action to circumvent the system didn’t work in preventing the crash. Boeing has said after the Indonesian crash, such actions would have worked.
The initial sequence of events in the Ethiopia crash closely match the findings of Indonesian air accident investigators probing the Oct. 29 loss of another MAX that killed all 189 passengers and crew. In that accident, though, crew failed to disable to faulty anti-stall system that repeatedly pushed the plane’s nose down before the aircraft plunged at high speed into the Java Sea.
The U.S. Department of Justice and others are investigating whether Boeing provided incomplete or misleading information to win the safety approval for the plane. Congress last week also kicked off hearings that will examine the scrutiny the Federal Aviation Administration gave the plane.
The fallout from the two accidents less than five months apart has spread globally. Airlines have been forced to park their MAX planes, cancel flights and scramble for replacement aircraft. Indonesian flag carrier Garuda said it is seeking to cancel its order for 737 MAX planes because customers have lost confidence in the jet. Norwegian Air Shuttle ASA, one of Europe’s biggest customers of the plane, and LOT Polish Airlines are among those seeking compensation for losses linked to the grounding.