Reports of high-level briefing with US regulators come as lawsuit is filed against Boeing

Investigators believe Boeing’s controversial anti-stall system on its 737 Max aircraft was activated before Ethiopian Airlines flight ET302 crashed, killing all 157 people onboard, according to reports of a high-level safety briefing with US regulators.

The apparent findings, reported in the Wall Street Journal, would be the strongest indication yet that the same software problem could have contributed to the crash and that of Lion Air flight 610, which killed 189 people in Indonesia in October.

Investigators in the Lion Air case highlighted how pilots battled to keep the plane pointing upwards as the system automatically forced the nose down.

Ethiopian Airlines officials and Ethiopia’s transport minister have already said their 737 jet appeared to fly in a similar pattern to the Lion Air plane, both of which displayed erratic altitude during their short time in the air after takeoff.

A preliminary report into the latest crash could be released by Ethiopian authorities within days. US officials at the Federal Aviation Administration (FAA) had been briefed, Reuters said, on the contents of the black box recorders, which are being analysed in Paris by French air crash investigators.

Boeing also faces legal action from relatives of those who died when the Nairobi-bound plane crashed on 10 March soon after taking off from Addis Ababa.

The family of Jackson Musoni, a Rwandan citizen, filed in Chicago what appeared to be the first lawsuit related to the crash. It claims Boeing had defectively designed the automated flight control system and failed to warn the public, airlines and pilots of the plane’s allegedly erroneous sensors.

Boeing said it could not comment on the lawsuit. Similar claims have already been brought in relation to the Lion Air crash.

More legal action is expected to follow, with relatives considering a class action.

Antonis Mavropoulos, who narrowly missed the flight, said: “I know that many of them are in contact with lawyers. I think that most of them will want to take this further.”

The Greek engineer, who was turned away at the departure gate two minutes after it closed, is now spearheading a campaign to uncover why the plane went down. He said it was vital European authorities also became involved in the investigation.

“This should be a turning point for the aviation industry,” Mavropoulos said. “The European parliament must also play a role. Everything points to fatal safety flaws and the problem lying with Boeing, deregulation of the industry and the way the 737 Max got approved by the FAA.”

Mavropoulos, 53, said he had been deluged with thousands of messages, many from retired pilots and aviation experts, who he said expressed concerns that market competition was downgrading safety. He said he felt a moral obligation to find out why the plane crashed, adding: “Yes, I was lucky, but I now know I was not the only one. Thousands who have travelled with the plane were lucky too.”

Boeing outlined this week steps it would take to restore its bestselling latest model to the air, including a planned software fix that would prevent the anti-stall system, known as Mcas, from repeatedly operating.

Cockpit alerts to warn of potentially incorrect data from sensors will also be fitted as standard. While investigators found sensors had given wrong information about the angle of the plane before the Lion Air crash, neither the Indonesian nor Ethiopian planes displayed warnings, a safety feature sold as an optional extra.

Boeing said it had also developed a mandatory training package for 737 Max pilots to undergo before the worldwide ban on flying the model is lifted. But it still proposes that qualified 737 pilots would not need time on flight simulators to safely operate the aircraft.

The US Department of Justice is investigating Boeing’s development process, while the government is to review how the FAA certifies new aircraft, with questions being asked about the extent of self-certification by manufacturers.

It appears US and European regulators were aware at least two years before the first 737 Max crash that the method for controlling the plane’s nose angle might not work in certain conditions.

According to Reuters, European Aviation Safety Agency documents from 2016 certified the plane as safe, partly because training would “clearly explain” to pilots the “unusual” situations in which they would need use a manual wheel on the flight deck to adjust the angle. But those situations were not listed in the flight manual used by American Airlines, Reuters said.