Software designed to stop an aerodynamic stall activated four times as Ethiopian Airlines pilots struggled to control their Boeing 737 Max 8 shortly before the jet slammed into the ground on March 10, 2019.
That's one of many findings in an interim report on the crash released Monday by Ethiopia's Aircraft Accident Investigation Bureau. The report came out just a day before the one-year anniversary of the crash, which killed all 157 people on board.
The report makes safety recommendations and gives clues to the cause, but an analysis won't be done until the final report, which is expected later this year.
The software called MCAS pushes the nose of the plane down. That touched off the pilots' desperate struggle to regain control of the plane.
The report also blames a faulty sensor reading that led to the cascading events that brought the plane down. And it says that pilots should have received simulator training on what to do if the flight-control system malfunctions.
One of Boeing's biggest selling points for the Max was that it was essentially the same as older 737s and therefore no simulator training was needed to switch to the new aircraft.
Boeing said in a statement Monday that it is providing technical assistance to support the probe.
"We look forward to reviewing the full details and formal recommendations that will be included in the final report from the Ethiopian Accident Investigation Bureau,” it said.
According to the report, the pilots de-activated MCAS and tried to control a stabilizer on the tail manually to point the nose back up. But their air speed was 575 miles per hour (925 kilometers per hour), which some experts believe put too much force on the stabilizer, making manual movement nearly impossible.
About five minutes and 43 seconds after takeoff, the pilots apparently reactivated MCAS, and the plane descended despite the pilots exerting force to bring the nose up.
“The descent rate increased from minus 100 feet per minute to more than 5,000 feet per minute,” the report said.