Boeing dismissed concerns about a powerful new anti-stall system on the 737 Max for months, insisting that pilots could deal with any problems by following a checklist of emergency procedures.

Now, the preliminary findings from the crash of Ethiopian Airlines Flight 302 have cast doubt on whether those instructions were sufficient, adding to the scrutiny over Boeing’s and federal regulators’ response to two deadly crashes involving the same jet model.

The findings, released Thursday in Ethiopia, suggest that the pilots on the Ethiopian Airlines flight initially followed the prescribed procedures after the anti-stall system malfunctioned. They shut off the electricity that allows the automated software to push the plane’s nose down and took manual control of the jet. They then tried to right the plane, with the captain telling his co-pilot three times to “pull up.”

But they could not regain control. About four minutes after the system initially activated, the plane hit the ground at colossal speed, killing all 157 people on board.