MYSTERY SOLVED: We Know Now Why Boeing’s Door Plug Bolts Didn’t Do Their Job. “The latest revelation is especially damning: the plane that sparked a new round of questions over Boeing’s ability to ensure its jets’ safety left the factory without the door plug bolts installed. They weren’t just loose — as door plug bolts on other aircraft were found to be upon mandatory post-incident inspections — they weren’t there. . . . If, as the evidence points, Boeing sent the 737 MAX 9 into service with Alaska entirely missing the bolts needed to keep the door plug in place, it seems there’s a lot more oversight necessary to ensure the bare minimum of quality control is achieved on the assembly line.”