The U.S. National Transportation Safety Board (NTSB) has revealed that four missing bolts led to a mid-air door incident on an Alaska Airlines-operated Boeing 737 Max 9. The preliminary investigative report, released on Tuesday, highlights a critical oversight that resulted in the aircraft’s door panel blowing off on January 5, prompting a 19-day grounding of all Boeing Max 9 models.
According to the NTSB report, the bolts that prevent upward movement of the mid-exit door (MED) plug were absent before the incident occurred. “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… indicate that four bolts… were missing before the MED plug moved upward off the stop pads,” the report stated.
The MED plug was initially installed by contractor Spirit AeroSystems in Kansas. Upon arrival at Boeing’s assembly plant in Renton, Washington, damaged rivets were discovered, necessitating repairs that involved opening the door plug. After the repair work was completed by Spirit AeroSystems personnel at the Boeing facility, the critical bolts were not reinstalled—a fact corroborated by photographic evidence provided to the NTSB by Boeing.
Boeing has acknowledged the findings and expressed commitment to addressing the issue. “We will continue to cooperate fully and transparently with the NTSB and the FAA investigations,” the company said in a statement. Boeing President and CEO Dave Calhoun emphasized the company’s accountability: “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. We simply must do better for our customers and their passengers.”
In response to the incident, Boeing is implementing a comprehensive plan to enhance quality control across its production systems. The company has established a control plan to ensure all 737-9 mid-exit door plugs are installed according to specifications. Measures are also being taken to improve overall quality and stability in the 737 production line.
“In addition to these actions, we are opening our factory to 737 customers to conduct their own additional reviews, and will fully and transparently support the FAA’s investigation, audit, and oversight actions,” Calhoun noted. “This added scrutiny—from ourselves, from our regulator, and from our customers—will make us better. It’s that simple.”
The incident underscores the critical importance of meticulous quality control in aviation manufacturing—a sector where even minor oversights can have significant safety implications. The grounding of Boeing Max 9 models not only affected airlines but also had ripple effects across the global aviation industry, including markets in Asia where Boeing aircraft are extensively used.
The aviation community awaits further findings from the NTSB and the FAA. Meanwhile, Boeing’s proactive steps aim to restore confidence among airlines, passengers, and regulatory bodies worldwide.
(With input from Xinhua)
Reference(s):
U.S. regulator says 4 missing bolts led to Boeing door incident
cgtn.com
