The Alaska Airlines Boeing crash, in which a door panel exploded in flight earlier this year, could have been prevented. Boeing’s production problems with the 737 Max 9 should have been noticed and addressed years ago, says Jennifer Homendy, head of the U.S. regulator NTSB.

“This incident should never have happened. It should have been noted years ago,” Homendy said on the second day of the hearing into the Jan. 5 incident. She cited “numerous” reports and assessments showing a history of work that did not follow the rules. There is no guarantee, Homendy said, that the problems will not happen again.

An Alaska Airlines passenger jet lost a door panel about 35 minutes after takeoff from Portland, Oregon. The plane, carrying 171 passengers and six crew members, made an emergency landing safely and no one was injured. The NTSB later determined that four bolts were missing from the door panel.

Boeing has been under fire for other incidents involving the planemaker’s aircraft. As a result of two fatal crashes involving the 737 Max in Indonesia and Ethiopia, Boeing reached a settlement, which put the company on a steep decline.

It was announced Tuesday that the aircraft manufacturer would make changes to the aircraft’s design to prevent such an incident from happening again. Board member Elizabeth Lund said the changes should be made within a year.