The pilots of a 737 Max jetliner that crashed in Ethiopia last month couldn’t recover from an uncommanded and persistent nose dive, according to a report on the disaster that killed 157 people and sparked a crisis for the planemaker Boeing Co. and U.S. aviation regulators.

“Pilots tried to control the plane repeatedly but were not able to do so,’’ said Ethiopia’s transportation minister, Dagmawit Moges, on Thursday at a press conference to present the findings. “All those responsible need to take actions that would assure the elimination of the said flight control issues.’’

The crew followed all the correct procedures and the system should be reviewed, she said. The plane appeared “very normal” on takeoff and then suffered “repetitive uncommanded nose-down.”

The findings add to pressure on Boeing to prove its best-selling 737 Max jet is safe after Ethiopian Airlines Flight 302 flew about six minutes on March 10 before smashing into the ground. The disaster was the second crash of the new narrow-body model in five months after a Lion Air plane plunged into the Java Sea in October and killed 189 people. The model is now grounded worldwide as investigators probe its airworthiness and how it gained permission to fly.

The report is “significantly bad news for Boeing,” Michael Hewson, Chief Market Analyst at CMC Markets U.K. said by phone. “They’re saying that the pilots were not to blame. It places much more scrutiny on Boeing’s processes.”

MCAS Focus

Officials at a news conference in Ethiopia’s capital Addis Ababa didn’t mention an automated system in the 737 Max that sometimes pushes the aircraft’s nose down. While regulators have stopped short of saying the plane has structural issues, the Ethiopia report underscores the focus on the so-called Maneuvering Characteristics Augmentation System, known as MCAS that also played a role in a Lion Air crash.

The 737 Max is the fourth generation of the world’s best-selling commercial aircraft and the new feature—a computerized anti-stall system that can push the plane’s nose—was activated on the fatal Lion Air flight.

In response to Thursday’s press conference, Ethiopian Airlines said its pilots could not recover from the “persistence of nose diving” despite having followed an emergency protocol mapped out by Boeing and approved by the U.S. Federal Aviation Administration.

Boeing Review

Boeing has said it’s reviewing the report and the FAA said it’s working to understand what happened. Boeing shares, which initially rose in premarket trading, fell back as the press conference wore on. The stock was trading at $384 in early New York trading, little changed from Wednesday’s close.

The investigation, staffed by Ethiopian, U.S. and European experts, has pitted Boeing’s reputation for technical quality against a successful, modern African airline that’s a symbol of pride for Ethiopia. Importantly, Dagmawit said there were no dissenting voices among investigators who worked on the preliminary report. The full report is expected to be published within one year.

Boeing and aviation regulators made a point of telling airlines worldwide how to disarm the MCAS system following the Lion Air disaster.

The crash has raised questions about the aircraft’s approval to fly. In the U.S., the Transportation Department has ordered a full audit of the FAA’s 2017 certification of the Max and the Justice Department is also investigating.

Refining Software

Boeing has spent months refining the 737 Max’s software since data from the Lion Air crash indicated the stall-avoidance system had repeatedly tipped the nose down before pilots lost control. Boeing was close to a software fix when the Ethiopian Airlines jet went down.

Planes usually climb steadily to get safely away from terrain and to reach altitudes where engines burn more efficiently.

Instead, the Ethiopian aircraft twice descended briefly during the first two and a half minutes after liftoff, according to tracking data provided earlier by The plane’s “vertical speed was unstable after take off,” the company said in a tweet.

Ethiopian Airlines earlier said that the plane’s pilots completed training recommended by the manufacturer and approved by the U.S. Federal Aviation Administration before the Max fleet was phased in.

Captain Yared Getachew, in command of the Ethiopian Airlines flight, had amassed more than 8,000 flight hours, according to the airline, while first officer Ahmed Nur Mohammod had spent about 200 hours aloft.

There were people from 35 nations on board, including 32 Kenyans, 18 Canadians, nine Ethiopians and eight Americans. The United Nations, which was hosting an environmental conference in Nairobi, said it lost 19 staff members in the crash.

While Africa has a generally poor aviation safety record compared with global norms, Ethiopian Airlines is known for operating a modern fleet that features Boeing 787 Dreamliners and the latest Airbus SE A350, as well as the 737 Max.

Read Max Disaster Pits Boeing Against Ethiopia’s Prized Carrier

The state-owned airline, Africa’s only consistently profitable carrier, has built Addis Ababa into a major hub feeding travelers from around the world into dozens of African cities in competition with rivals such as Dubai-based Emirates. Ahead of the report, some Ethiopians expressed pride in the airline, and a conviction that any blame would lie with Boeing.

“The mistake is in the software,” retired Colonel Tilahun Nebro, a former jet fighter pilot, said in an interview on a shaded veranda of an aviators’ club beside Bole International Airport, where the fatal flight took off.

Boeing designed the 737 Max to deliver a 14 percent fuel-savings to compete with the A320neo from the company’s European rival, Airbus SE. The use of new, bigger engines required Boeing’s designers to mount the units farther forward on the wings in order to give them proper ground clearance when taking off or landing. That changed the flying characteristics in a way that the engineers thought required the additional system to prevent stalls.