The National Transportation Safety Board’s preliminary report on the January 5 incident in which a Boeing 737 MAX 9 jet lost a fuselage panel during flight revealed that four bolts holding the door plug in place were lost in the incident. The “mid-cabin emergency door” (MED) plug is installed during aircraft assembly to fill an open space available as an optional side door.
“Overall, the observed damage patterns and absence of contact damage or deformation around holes associated with the vertical movement arrestor bolts and upper guide track bolts in the upper guide fittings, hinge fittings, and recovered aft lower hinge guide fitting indicate that four bolts that prevent upward movement of the MED plug were missing before the MED plug moved upward off the stop pads,” according to the NTSB preliminary report.
According to NTSB, the door plug had been removed and reinstalled at Boeing’s Renton, Wash., assembly plant prior to the aircraft’s deliver to Alaska Airlines in October 2023. The board did not state whether the panel had been reinstalled by Boeing or the fuselage manufacturer, Spirit AeroSystems.
Both Boeing and Spirit AeroSystems have confirmed that some of the fuselage structures delivered for the 737 MAX 9 aircraft have been found to have nonconforming assembly
In a statement on the NTSB preliminary report, Boeing pledged to “continue to cooperate fully and transparently with the NTSB and the FAA investigations.”
“Whatever final conclusions are reached, Boeing is accountable for what happened,” president and CEO Dave Calhoun stated. “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.”
Among the changes that Calhoun described is a “a control plan to ensure all 737-9 mid-exit door plugs are installed according to specifications”. The OEM also has established new inspections of MED plug assemblies and similar structures, at Spirit AeroSystems and at the Renton assembly line.
Boeing also is implementing plans to improve overall quality and stability for the 737 production system, among its suppliers and at the assembly line.
