During inspections, United Airlines claims to have discovered weak bolts on several 737 Max 9 aircraft’s plug doors. It coincides with the Federal Aviation Administration’s (FAA) announcement that all 171 Boeing 737-9 Max aircraft will stay grounded following the mid-air explosion of a window and a section of the fuselage on an Alaska Airlines passenger airliner. According to industry newspaper Air Current, during the weekend accident investigation, United discovered weak bolts on other components on at least five panels. “Since we began preliminary inspections on Saturday, we have found instances that appear to relate to installation issues in the door plug—for example, bolts that needed additional tightening,” United stated in a statement.