Four bolts designed to prevent the door plug from falling off the Boeing 737 Max 9 plane were missing before the plug blew off during an Alaska Airlines flight last month, the National Transportation Safety Board said in a preliminary report of the incident released on Tuesday.
Boeing records reviewed by the NTSB showed that damaged rivets on the edge frame forward of the plug were replaced by Spirit AeroSystems employees at Boeing's factory in Renton, Washington, on Sept. 19, 2023, according to the agency's report. Boeing had to open the plug by removing the two vertical movement arrestor bolts and two upper guide track bolts for the rivets to be replaced, but photo documentation obtained from Boeing showed evidence that the plug was closed with no bolts in three visible locations, according to the NTSB report.
One bolt area is obscured by insulation in the photo, though the NTSB said it was able to determine in its laboratory that that bolt was also not put back on.
After examining damage to the recovered plug, the NTSB determined that the "four bolts that prevent upward movement of the MED plug were missing before the MED plug moved upward off the stop pads," the preliminary report stated.
Boeing said Tuesday it would review the NTSB's findings "expeditiously" in a statement following the release of the report.
"Whatever final conclusions are reached, Boeing is accountable for what happened. An event like this must not happen on an airplane that leaves our factory," Boeing president and CEO Dave Calhoun said in a statement Tuesday. "We simply must do better for our customers and their passengers."
Boeing said it is taking "immediate action to strengthen quality," including implementing a plan to ensure all mid-exit door plugs on 737-9s are installed properly and adding inspections further into the supply chain.
Spirit AeroSystems said in a statement Tuesday that it is reviewing the NTSB's report and "remain focused on working closely with Boeing and our regulators on continuous improvement in our processes and meeting the highest standards of safety, quality and reliability."
The door plug fell off a few minutes after Alaska Flight 1282 took off from Portland International Airport on Jan. 5. Passengers captured footage showing a hole where the door plug came loose on the Boeing 737 Max 9 plane. The plane safely made an emergency landing and no one was seriously injured.
The Federal Aviation Administration grounded approximately 171 Max 9s worldwide following the incident. Alaska Airlines resumed flying the Boeing 737 Max 9 following fleet inspections on Jan. 26.
Alaska Airlines said Tuesday it remains "in close contact" with the NTSB.
"Safety is always our top priority," the airline said in a statement. "As this investigation moves forward, we have full confidence in the safety of our operation and aircraft."
The FAA is increasing its oversight of Boeing and began an audit of the company's production and manufacturing in the wake of the door plug blow-out.
Boeing said Tuesday it will "fully and transparently support the FAA's investigation, audit and oversight actions."
"This added scrutiny -- from ourselves, from our regulator and from our customers -- will make us better. It's that simple," Calhoun said.
The CEO took responsibility for the incident in the company's fourth quarter earnings call last week, saying the company is "accountable for what happened."
This is a developing story. Please check back for updates.
4 bolts missing from Alaska Airlines door plug before blow-out: NTSB report originally appeared on abcnews.go.com