Four key bolts were missing from the door that caused an Alaska Airlines plane to explode in mid-air in January, according to a preliminary report from a US regulator.
The initial report said the door panel, known as the plug, was removed to repair screws damaged during production.
She added that those screws were removed at Boeing's factory in Washington and appear to have not been replaced.
Text messages sent in September between employees at the aircraft manufacturer show a discussion about interior restoration after the rivet was reworked. The photo attached to one of the text messages formed part of the investigation.
The report added that there was no evidence that the door opened again after it left the Boeing factory, increasing pressure on one of the world's two largest aircraft manufacturers.
The investigation was launched by the National Transportation Safety Board (NTSB) in early January after a mid-flight explosion in which a Boeing 737 MAX 9 door flew off. Alaska Airlines planes.
The door plug is secured by four screws and is secured by stop fittings in 12 different locations on the side of the plug and door frame.
The NTSB said in January that all 12 stop fittings separated during the flight.
“The investigation is continuing to determine manufacturing documentation that was used to allow the plug to be opened and closed while the rivet was being reworked,” the report said.
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Records from September showed five screws were damaged in the door's plug frame.
“Whatever final conclusions are reached, Boeing is responsible for what happened,” Boeing President and CEO Dave Calhoun said Tuesday. “An event like this should never happen on an airplane leaving our factory.”
The manufacturer added that it “implemented a control plan to ensure all 737-9 center exit door seals were installed in accordance with specifications.”
Federal Aviation Authority (FAA) temporarily All grounded 171 Max 9 aircraft were placed in an unprecedented location Prohibition of increased production Volumes within the entire 737 MAX fleet.
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Boeing CEO: “We fly safe planes”
Thousands of flights were canceled by Alaska Airlines and United Airlines, users of the Boeing 737 MAX 9, as a result of the grounding order, which was lifted on January 24.
Both Alaska Air and United Airlines said in the days following the explosion that they had found dismantled parts on several grounded Max 9 planes.
The Federal Aviation Administration said 94% of the planes were back in service.
The regulator has restricted production of Boeing's ambitious MAX plans indefinitely, raising questions about the company's manufacturing future.
Federal Aviation Administration head Mike Whitaker told US politicians on the Transportation and Infrastructure Committee on Tuesday that the current safety system is not working.
“I certainly agree that the current system is not working, because it does not provide safe aircraft.”
