The U.S. FAA has confirmed that not one, not two, not three, but four bolts used to hold a door plug on a Boeing 737 MAX 9 jet belonging to Alaska Airlines were missing, allowing the door panel to fall off during a flight in January.
The U.S. Safety Board investigating the incident said that evidence released this week shows bolts were missing from the door plug, which had been removed to fix rivets that were damaged in the production process.
The NTSB had previously remained silent on the cause for the panel to rip off during a flight operated by Alaska Airlines, but now it has confirmed that "The investigation continues to determine what manufacturing documents were used to authorize the opening and closing" of the plug during the rivet rework," The troubled aircraft had recently experienced pressurisation warnings on previous flights had climbed to around 16,000 feet following departure from Portland, Oregon.
The NTSB said it had been focused on how this panel or door plug which is fitted into a number of Boeing 737 MAX 9 models as a replacement for an optional emergency exit - detached from the Alaska Air plane. The report indicates that the plug is held down by four bolts, and then secured by "stop fittings" at 12 different locations along the side of the plug and the door frame.
According to the report, the door plug was manufactured by Spirit AeroSystems, a former subsidiary of Boeing and had been installed in the fuselage before being delivered to Boeing. The preliminary report confirmed the door plug was later removed by Boeing staff in the factory due to damage that had occurred during the production process. Photographic evidence suggests that when the plug was reinstalled, at least three of the four locking bolts were not put back in place. The report highlights that damage to the door plug and its hinges, as well as a lack of damage to the areas where the bolts should have been, suggests that the bolts were missing before the door moved out of its normal position.
This is a further condemnation of production quality in Boeing's factories due to the ramping up of aircraft production, increased demands and pressure on staff, combined with a corporate culture focused on cutting costs and losses from previous groundings of the 737 MAX family of planes.
Inspections of other 737 MAX 9 jets were hastily ordered and those investigations found loose/missing bolts and fixings on a number of other aircraft of the same specification. Many in the industry have raised questions about the way the planes are put together and the safety of various components now that the supply lines have been pressurized to provide more items to keep up with production schedules.