Preliminary Report Shows 737 Fuselage Bolts Were Missing Before Alaska Airlines Flight

NTSB investigators examine the door plug from Alaska Airlines flight 1282, a Boeing 737-9 MAX.

The National Transportation Safety Board (NTSB) published its preliminary report on the cause of the in-flight structural failure that occurred during Alaska Airlines flight 1282, where the left mid exit door (MED) plug of a Boeing 737-9 departed the airplane at 16,000 feet. According to the report, four of the bolts that attach the plug to the fuselage were missing before the flight took off, and safety investigators are still trying to determine the initial cause.

Several NTSB structures and materials specialists, along with representatives from parties to the investigation, examined the MED plug and associated components removed from the accident airplane in the NTSB Materials Laboratory. The MED plug was mostly intact with some damage from the event and appeared to be manufactured in accordance with the engineering drawings, according to the preliminary report.

Contact damage was noted on the lower sides of the 12 stop pins and fittings on the MED plug. Corresponding contact damage was noted on the 12 stop pads and fittings attached to the fuselage. Overall, the damage was consistent with the MED plug translating upward, outboard, and aft during the separation.

“The Manufacturing Records Group traveled to Boeing’s Renton, Washington, facility to review manufacturing records for the accident airplane specific to the left MED plug area. According to records, the accident fuselage arrived at Boeing’s Renton facility by rail on August 31, 2023. During the manufacturing process, if any defects or discrepancies were found, a NonConformance Record (NCR) or a disposition required NCR were generated,” NTSB states in its report.

On September 1, 2023, a review of the records showed that an NCR report was created noting five damaged rivets on the edge frame forward of the left MED plug. Documents and photos show that to perform the replacement of the damaged rivets, access to the rivets required opening the left MED plug.

To open the MED plug, the two vertical movement arrestor bolts and two upper guide track bolts had to be removed.

“Records show the rivets were replaced per engineering requirements on Non-Conformance (NC) Order 145-8987-RSHK-1296-002NC completed on September 19, 2023, by Spirit AeroSystems personnel. Photo documentation obtained from Boeing shows evidence of the left-hand MED plug closed with no retention hardware (bolts) in the three visible locations (the aft upper guide track is covered with insulation and cannot be seen in the photo). This image was attached to a text message between Boeing team members on September 19, 2023. These Boeing personnel were discussing interior restoration after the rivet rework was completed during second shift operations that day,” NTSB writes in the report.

NTSB’s investigation is ongoing and continues to determine what manufacturing documents were used to authorize the opening and closing of the left MED plug during the rivet rework process.