The Ethiopian Air Boeing 737 Max crash had similarities to the Lion Air plane that went down off the coast of Indonesia about five months ago, the nation’s transport minister said, as scrutiny of one of the aircraft’s flight control systems continued to build.

A preliminary study of the flight data recorders show clear similarities between Ethiopian Airlines flight 302 and Indonesian Lion Air Flight 610, Dagmawit Moges said on Sunday at a press conference in Addis Ababa. The findings will be subject to further investigation, and a preliminary report will be released within 30 days, she said.

The Ethiopian Airlines plane crashed March 10 minutes after it took off from Ethiopia’s capital, killing all 157 people on board. The accident prompted most of the world to ground Boeing Co’s 737 Max 8 aircraft on safety concerns. Much of the attention focused on a specific flight-control system known as MCAS that may have thwarted pilots’ efforts to keep the plane from falling into a catastrophic nose dive.

In one of the most detailed descriptions yet of the relationship between Boeing and the Federal Aviation Administration during the 737 Max’s certification process, the Seattle Times reported on Sunday that the US regulator delegated much of the safety assessment to Boeing and that the analysis the planemaker, in turn, delivered to the authorities had crucial flaws.

The newspaper’s report was based on interviews with current and former engineers directly involved or familiar with the evaluations, all of whom asked not to be identified, and was under way even before the Ethiopia crash.

Boeing told the newspaper on Saturday the FAA had reviewed the company’s data on the plane and concluded that it met all certification and regulatory requirements, and repeated that comment on Sunday in a statement to Bloomberg News. The planemaker, which is based in Chicago, but designs and builds commercial jets in the Seattle area, had also told the newspaper there were some significant mischaracterisations in the engineers’ comments, the Seattle Times reported.

In a separate statement on Sunday, Boeing Chief Executive Officer Dennis Muilenburg made his fullest public comments to date, reiterating the company’s sympathies for the affected families and support for the investigation.

While investigators continue to work to establish definitive conclusions, Boeing is finalising its development of a previously announced software update and pilot training revision that will address the MCAS flight control laws behaviour in response to erroneous sensor inputs, Muilenburg said in the statement.

The airline’s shares declined about 10 per cent last week, closing at $378.99 on March 15.

Safety Analysis

Boeing’s System Safety Analysis of the flight control software — suspected to have contributed to the Lion Air jetliner crash in October and also under the spotlight in the Ethiopia accident — understated the power of the system, the engineers told the Seattle Times. The newspaper said the analysis also failed to account how the system could reset itself each time a pilot responded — in essence, gradually ratcheting the horizontal stabiliser into a dive position.

FAA technical experts told the newspaper that as the agency’s certification of the 737 Max proceeded, managers prodded them to speed up the process as development of the MAX was nine months behind that of rival Airbus’s A320neo.

The Seattle Times said the safety analysis ranked a potential failure of the Manoeuvering Characteristics Augmentation System, or MCAS, as hazardous, one step below catastrophic. But even that designation should have been enough to prod reliance on more than just one input sensor, the engineers told the newspaper.

The FAA’s aircraft certification processes are well established and have consistently produced safe aircraft designs, the agency said in a statement Sunday. The 737 Max certification programme followed the FAA’s standard certification process.

As far as MCAS goes, the FAA said, the periodic training required of all US commercial pilots includes how to handle events where there are unexpected movements of the horizontal stabilizer. A nose-down scenario resulting from an issue with the MCAS system would have the same characteristics as a runaway stabilizer trim scenario, the safety regulator said. A proper response to a runaway stabilizer trim scenario would resolve a situation resulting from either a stabilizer trim issue or an MCAS issue.