The pilots, unable to stabilize the 737 Max 8 plane even after following the emergency procedures recommended by Boeing, tried together the pull the airplane's nose up repeatedly during the last moments of the flight, the preliminary report revealed.
In a statement following the preliminary report from Ethiopian authorities, Boeing said flight data recorder information indicates the airplane had an erroneous angle of attack sensor input that activated a system known as MCAS, similar to the Lion Air disaster.
"We will carefully review the AIB's preliminary report, and will take any and all additional steps necessary to enhance the safety of our aircraft".
Aviation regulators around the world grounded Boeing's 737 MAX last month following the Ethiopian Airways crash, which came less than five months after an October Lion Air crash that killed 189 people.
As NPR's Russell Lewis has reported, the similarities involve an anti-stall system on both jets, the MCAS, created to push the nose of the plane down if flight control systems sense a problem with low air speed.
Thursday's complaint accuses Boeing of putting "profits over safety" and said the U.S. Federal Aviation Administration must also be held accountable for certifying the 737 MAX.
The Ethiopian Airlines flight was headed to Nairobi on a clear morning on March 10 when it plummeted nose-first into a field outside Addis Ababa just minutes after take-off, having reportedly experienced erratic steep climbs and descents.
Boeing also is continuing to work closely with the U.S. National Transportation Safety Board (NTSB) as technical advisors in support of the AIB investigation. Investigations are also looking at the role of the Federal Aviation Administration in the us, which certified the Max in 2017, and declined to ground it after the first deadly crash in October.
"As we learn more about the accident and findings become available, we will take appropriate action", the USA agency said in a statement. A final report is due within a year.
Rosemount makes the angle of attack sensor. Boeing's procedures instruct pilots to leave the MCAS system disconnected and continue flying manually for the rest of the flight. The FAA has said it will review the software before allowing the Max to fly again.
Ethiopian investigators did not address that issue at its press conference, saying only that the pilots had done what they were supposed to.
The pilots shut off the anti-stall system, called the Manoeuvring Characteristics Augmentation System, but switched it back on because they could not regain control, The Journal reported, citing people briefed on the preliminary findings.
Another official said Ethiopian authorities expected the investigation to take up to a year, depending on how complicated it proved, and said there would be no interference from Ethiopian Airlines. Among the areas of focus for criminal investigators are the processes by which Boeing itself certified the plane as safe and the data it presented the FAA about that self-certification, the sources said. This is something that is very rare in aviation. A whistleblower has reportedly told the Senate Commerce Committee that inspectors assigned to the Boeing 737 MAX aircraft did not receive proper training. Instead, the pilots tried to use the backup manual trim wheel to adjust the trim, but the airplane was traveling too fast and the manual trim wheel would have been physically impossible to operate. "It seems likely they've got more things going on at once in a shorter time period". He also would like to know at what point the MCAS system was turned back on and if it was too late to prevent the crash.