The National Transportation Safety Board (NTSB) said Tuesday that four bolts meant to help secure the door plug of a Boeing 737 Max 9 jet were missing before an Alaska Airlines flight experienced a midair blowout last month.
NTSB investigators have been looking into what may have led to last’s month incident when a fuselage panel on the Boeing 737 Max 9 aircraft blew off minutes after taking off from Portland, Ore. The federal investigators released their preliminary report Tuesday, about a month after the midair accident.
The report detailed the NTSB’s findings into the fuselage panel, which is called a door plug, after investigators dissembled it in their laboratory. The fuselage panel was recovered in Oregon after falling 16,000 feet from the Alaska Airlines flight.
The report included a photo from Boeing, taken in September 2023, that investigators say shows that three of the four bolts on the door were missing. The location of the fourth bolt is covered by insulation in the photo.
Investigators noted that the bolts were meant to prevent the door plug from moving upward. The report notes that the bolts were likely missing before the midair blowout due to the lack of damage surrounding the holes where the bolts should have been.
“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 the four bolts that prevent upward movement of the MED [mid exit door] plug were missing before the MED plug moved upward off the stop pads,” the report states.
Boeing President and CEO Dave Calhoun said the company takes responsibility for the accident in a statement released after the preliminary report was published.
“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,” Calhoun said.
“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,” he continued.
Alaska Airlines and United Airlines, the only other airline to fly the 737 Max 9 jets, said last month that they found loose parts in door panels in some of those 737 Max 9 jets. The NTSB said last month it was looking into whether key four bolts were missing before the midair incident, The Associated Press reported.
The incident resulted in the grounding of the Boeing 737 Max 9 jets for weeks, but the aircraft have since started returning to the skies. The Federal Aviation Administration (FAA) is conducting its own, separate investigation into the incident to determine whether Boeing and its suppliers failed to met quality control measures.
The NTSB’s investigation into the Alaska Airlines flight remains ongoing.
Alaska Airlines deferred any questions on the investigation to the NTSB in an update posted after the release of the preliminary report.
“Safety is always our top priority. As this investigation moves forward, we have full confidence in the safety of our operation and aircraft,” the statement read.
Updated at 5:11 p.m. ET