In the initial report from U.S. investigators, it was revealed that a door panel detached from a Boeing 737 MAX 9 aircraft during a flight on January 5, and it seems to have been lacking four essential bolts. This report offers the first official insight into the sequence of events that led to this alarming incident. The National Transportation Safety Board oversees airplane accidents and said the bolts were likely missing before the plane departed Portland, Oregon, and lost its door plug at 14,800 feet. That triggered an emergency depressurization and forced the jet to make an emergency landing. No one was hurt. The NTSB’s findings support earlier reports that the missing bolts, which prevent the door plug from moving upward, were removed from the fuselage at a Boeing factory and later reinstalled without them.

The NTSB said a photo from Spirit AeroSystems, which makes the fuselages that Boeing assembles into aircraft, shows three of the four bolts. Investigators say the spot where the fourth bolt should be is covered by insulation. The bolts were installed after the fuselage panel was opened for rivet repair work logged by workers at Boeing’s Renton, Washington, plant on Sept. 1, 2023. Investigators said they are seeking documentation to determine who authorized the panel’s opening for the rivet repairs and why the bolts were not replaced then.

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Lawmakers and the flying public have demanded answers to what caused the panel to fly off a brand-new Alaska Airlines-operated jet in what has turned into a full-blown safety and reputational crisis for Boeing. The FAA is reviewing 737 MAX jet production to ensure quality and safety, and the company’s share price has fallen by more than 10 percent since the crash.

Boeing has insisted that its aircraft has no issue and is “focused on continuing to build the safest planes in the world.” But former company employees, including aviation safety advocate Ed Pierson, have raised concerns about a shift in corporate culture in recent years that prioritizes profits over quality. They point to deep staff cuts and offers of buyouts that have left a shortage of experienced workers.

Pierson says those issues have contributed to a deterioration in the company’s quality control and led to mistakes like the ones that appear to have doomed the 737 MAX 9. “Leadership seems more concerned about getting the airplanes out the door than making sure they are safe,” he said in an interview last week with CNN. He served as a senior manager at the company’s 737 factory and is the executive director of the Foundation for Aviation Safety, a nonprofit group. He is also a former military pilot. The NTSB hasn’t yet determined the cause of the jet’s door plug failure, but it’s possible that corrosion or improper installation of a component called a deflector led to its removal. The NTSB’s final report could take a year or more to complete. The FAA is reviewing the MAX program and its procedures, which could eventually require the airline to upgrade its planes.