NTSB confirms missing bolts, defective rivets preceded 737 Max 9 door plug incident

In its preliminary report issued Tuesday, the National Transportation Safety Board detailed a host of documentation and process errors by both Boeing and Spirit Aerosystems that preceded the failure of a plug exit aboard an Alaska Airlines 737 Max 9 aircraft while in flight.

The initial conclusion by the U.S. transportation safety watchdog was the plug exit was not properly secured with the four required retaining bolts when the single-aisle jet went through final assembly at Boeing’s Renton, Washington facility. 

As first reported by The Air Current, the report confirms that supplier Spirit Aerosystems delivered a fuselage to Boeing with defective rivets around the plug door exit. It details how, while the plug exit was opened to conduct repairs on those rivets, the bolts that are meant to “prevent upward movement of the [plug exit]” were missing entirely from the assembly once the door was closed. The NTSB released photos that showed the “left hand [plug exit] closed with no retention hardware (bolts) in the three visible locations.”

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This confirmation comes following previous reports by both United Airlines and Alaska, the only U.S. operators of the Max 9, that they had found loose bolts and other components on other aircraft during inspections that were required by the Federal Aviation Administration as a part of the mandatory grounding last month.

“We are implementing a comprehensive plan to strengthen quality and the confidence of our stakeholders,” said Boeing CEO Dave Calhoun in a statement addressing the preliminary report. The company says that it is requiring new inspections “of the door plug assembly and similar structures,” in addition to “signage” and other protocols to properly document the opening, closing and removal of the plug.