4 bolts missing from Alaska Airlines door plug before blow-out: NTSB report

Four bolts designed to prevent the door plug from falling off the plane were missing before the plug blew off during an Alaska Airlines flight last month, the NTSB said.

Four bolts designed to prevent the door plug from falling off the Boeing 737 Max 9 plane were missing before the plug blew off during an Alaska Airlines flight last month, the National Transportation Safety Board said in a preliminary report of the incident released on Tuesday.

Boeing records reviewed by the NTSB showed that damaged rivets on the edge frame forward of the plug were replaced by Spirit AeroSystems employees at Boeing's factory in Renton, Washington, on Sept. 19, 2023, according to the agency's report. Boeing had to open the plug by removing the two vertical movement arrestor bolts and two upper guide track bolts for the rivets to be replaced, but photo documentation obtained from Boeing showed evidence that the plug was closed with no bolts in three visible locations, according to the NTSB report.

One bolt area is obscured by insulation in the photo, though the NTSB said it was able to determine in its laboratory that that bolt was also not put back on.

After examining damage to the recovered plug, the NTSB determined that the "four bolts that prevent upward movement of the MED plug were missing before the MED plug moved upward off the stop pads," the preliminary report stated.