Four "missing" bolts appear to be the cause of the Jan. 5 door-plug blowout on Alaska Airlines Flight 1282, according to a preliminary report released Tuesday by the U.S. National Transportation Safety Board. The incident led to a grounding by the U.S. Federal Aviation Administration of 171 Boeing 737 Max 9 aircraft in the U.S., which was only recently lifted after approved inspections were completed.
Manufacturing records reviewed by the NTSB showed that Spirit AeroSystems Malaysia manufactured the middle exit door plug on March 24, 2023, and it was received by Spirit AeroSystems Wichita on May 10. The MED plug was installed and rigged on the fuselage before it was shipped to Boeing on Aug. 20. The fuselage arrived at Boeing's Renton, Wash., facility on Aug. 31.
There was work done on Sept. 19 to repair five damaged rivets "on the edge frame forward of the left MED plug," according to the report. Removal of the bolts was needed to repair the rivets. The repair was completed by Spirit AeroSystems personnel.
A photo obtained from Boeing that was attached to a text message between Boeing staff on Sept. 19 "shows evidence of the left-hand MED plug closed with no retention hardware (bolts) in the three visible locations" of where the bolts should have been, according to the report. The ongoing investigation will work to determine what manufacturing documents were used to authorize the opening and closing of the left MED plug during the rivet rework.
"Whatever final conclusions are reached, Boeing is accountable for what happened," Boeing president and CEO Dave Calhoun said in a statement. "An event like this must not happen on an airplane that leaves our factory. We are implementing a comprehensive plan to strengthen quality and the confidence of our stakeholders."
The aircraft manufacturer has implemented new inspections of Boeing 737 Max 9 door-plug assembly and similar structures at its supplier's factory and on Boeing's production line. The company also is implementing plans to improve the overall quality and stability across the 737 production system, according to Boeing.
The NTSB report was released the same day FAA administrator Michael Whitaker made a statement before the aviation subcommittee of the House of Representatives Committee on Transportation and Infrastructure, saying that "our findings during inspections of those aircraft showed that the quality issues at Boeing were unacceptable and require further scrutiny. That is why we are increasing oversight activities."
The agency also has increased its oversight activities, including capping expanded production of new Boeing 737 Max aircraft, launching an investigation scrutinizing Boeing's compliance with manufacturing requirements, having increased floor presence at all Boeing facilities, closely monitoring data to identify and mitigate significant safety trends and risks in the system, and launching an analysis of potential safety-focused reforms around quality control and delegation.