Bolts securing a panel to the frame of a Boeing 737 MAX 9 were missing on an Alaska Airlines flight from Portland, Oregon, that sustained a midair blowout last month, investigators with the National Transportation Safety Board (NTSB) found.

The U.S. regulators' preliminary report was released Tuesday about the Jan. 5 incident that took place shortly after takeoff. According to the report, the lack of certain damage around the panel, which is called a door plug, indicates that all four bolts were missing before the plane took off.

The plane — used for Ontario, California-bound Alaska Airlines flight 1282 — was a Boeing 737 MAX 9 jetliner, and the incident put Boeing and the Federal Aviation Administration (FAA) under scrutiny. Criticism of both the company and its regulator goes back to deadly crashes in 2018 and 2019 of MAX 8 jets in Indonesia and Ethiopia that killed 346 people. Shares of the The Boeing Co. were down 20% in 2024.

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"Whatever final conclusions are reached, Boeing is accountable for what happened," Boeing President and CEO Dave Calhoun said Tuesday via statement. "An event like this must not happen on an airplane that leaves our factory. We simply must do better for our customers and their passengers. We are implementing a comprehensive plan to strengthen quality and the confidence of our stakeholders. It will take significant, demonstrated action and transparency at every turn – and that is where we are squarely focused.”

The NTSB did not declare a probable cause for the accident — that will come at the end of an investigation that could last a year or longer.

Separate from the report, new FAA Administrator Mike Whitaker testified before the House Transportation Committee on Tuesday. The FAA is separately investigating whether Boeing and its suppliers followed proper safety procedures in manufacturing parts for the MAX. The FAA has barred Boeing from speeding up production of 737s until the agency is satisfied about quality issues.

Whitaker said Tuesday that his agency is about halfway through a six-week audit of manufacturing processes at Boeing and its key supplier on the MAX, Spirit AeroSystems. He said the agency is confronted with two questions — what’s wrong with the MAX 9, and “what’s going on with the production at Boeing?”

'Loud bang'

The NTSB report Tuesday said while climbing through about 16,000 feet, "there was a loud bang."

"The flight crew said their ears popped, and the captain said his head was pushed into the heads-up display and his headset was pushed up, nearly falling off his head," the report said. "Both flight crew said they immediately donned their oxygen masks. They added that the flight deck door was blown open and that it was very noisy and difficult to communicate."

The flight crew immediately contacted air-traffic control, declared an emergency and requested a lower altitude, the report said. The plane returned to Portland International Airport and landed "without further incident," according to the report.

Over the weekend, it was announced that about 50 Boeing 737 planes would need to be reworked after a nonconformance was flagged in some fuselages by a supplier. The nonconformance was found in some 737 fuselages on Feb. 1, according to Boeing Commercial Airplanes President and CEO Stan Deal. An employee with the supplier informed their manager that two holes may not have been drilled exactly to Boeing's requirements.

Boeing said it plans to dedicate several days at its Renton factory for teams with the 737 program to complete the necessary inspections and rework on the planes. The door that flew off the Alaska jet was improperly installed after a repair at Boeing's Renton plant, The Seattle Times reported.

The plug — primarily constructed of aluminum — was manufactured by Spirit AeroSystems Malaysia on March 24 and was received at Spirit AeroSystems Wichita on May 10, according to the NTSB report. It arrived in Renton on Aug. 31, the report said.

"The door plug is only intended to be opened for maintenance and inspection, which requires removing the vertical movement arrestor bolts and upper guide track bolts," the NTSB said in the report.

Investigators said they were still trying to determine who authorized the Boeing crew to open and reinstall the door plug.

The NTSB said Tuesday its investigation is ongoing.

The Associated Press contributed to this report

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