Investigators into a Boeing 737 MAX crash in Ethiopia that killed 157 people have reached a preliminary conclusion that an anti-stall system was activated before the plane hit the ground, the Wall Street Journal reported.
Citing people briefed on the matter, the newspaper on Friday also reported the preliminary findings from the "black box" recorders were subject to revisions.
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The plane crashed on March 10 shortly after take-off from Addis Ababa.
Investigators into a deadly 737 MAX crash in Indonesia in October have focused on the new anti-stall system, called MCAS.
Boeing on Wednesday said a planned software fix would prevent repeated operation of the system that is at the centre of safety concerns.
The manufacturer said it had developed a training package that 737 MAX pilots are required to take before a worldwide grounding of the aircraft can be lifted.
The amount and quality of training that Boeing and airlines provided to 737 MAX pilots is one of the issues under scrutiny.
On Thursday, a lawsuit was filed against Boeing by the family of Rwandan citizen Jackson Musoni, who died in the Ethiopian Airlines crash.
The lawsuit alleges that Boeing had defectively designed the automated flight control system. Boeing said it could not comment on the lawsuit.
The US Department of Justice is investigating Boeing's development process and what Boeing disclosed about MCAS.
US and European regulators knew at least two years before the Indonesian crash that the usual method for controlling the 737 MAX's nose angle might not work in conditions similar to those in two recent disasters, Reuters reported on Friday, citing a document.
The European Aviation and Space Agency (EASA) certified the plane as safe in part because it said additional procedures and training would "clearly explain" to pilots the "unusual" situations in which they would need to manipulate a rarely used manual wheel to control the plane's angle.
Boeing declined to comment on the EASA document.