A door panel that blew off of an Alaska Airlines plane while it was flying over Oregon last month appears to have been missing four bolts, according to a preliminary report released Tuesday by the National Transportation Safety Board.
The bolts that secure the panel to the fuselage had been removed from the Boeing 737 Max 9 during repair work at Boeing’s factory in Renton, Washington, and apparently were not replaced, the report says.
Photos taken during the repair work in September show no evidence that the bolts were replaced before the panel, called a door plug, was closed by workers, the report states.
Plastic sheeting covers the fuselage plug area of the Boeing 737 Max 9 jetliner after the Jan. 5 mid-flight incident.
The report notes that a pressurization light in the plane came on during three flights following the repair work. The NTSB previously said that these alerts, on Dec. 7, Jan. 3 and Jan. 4, resulted in the aircraft being restricted from making long flights over water in case it needed to make an emergency landing.
The panel blew off the jetliner shortly after takeoff on Jan. 5, leaving a gaping hole in the side of the plane. There were 177 people on the aircraft, including passengers and crew members, but no major injuries were reported.
Boeing on Tuesday said it will “expeditiously” review the NTSB’s findings.
“Whatever final conclusions are reached, Boeing is accountable for what happened,” Boeing President and CEO Dave Calhoun said in a statement.
Boeing 737 Max 9s were immediately grounded in the U.S. by the Federal Aviation Administration following the mid-air scare. During this grounding, Alaska Airlines and United Airlines, which are the only two U.S. airlines using the Max 9 jets, reported finding loose bolts and other installation issues on some of its grounded planes.
The FAA on Monday said that nearly 94% of the Alaska and United planes have returned to service following inspections.