The National Transportation Safety Board (NTSB) is currently investigating the alarming incident involving a Boeing 737 Max 9 aircraft that lost its door plug mid-flight. The NTSB stated that it is still unclear why four critical bolts were missing from the door plug, causing a blowout at 16,000 feet. The preliminary report suggests that the bolts were initially installed but subsequently removed, raising concerns about the possibility of a similar incident occurring again.
This investigation has primarily focused on the four bolts that hold the door plug in place on the side of the fuselage of the Max 9 aircraft. Both Alaska Airlines and United Airlines have reported finding planes in their fleets with loose bolts. However, the NTSB discovered that Alaska Flight 1282 was missing all four bolts. The agency made this determination after recovering the door from a backyard in Portland and conducting a thorough inspection at a Washington D.C. laboratory.
The NTSB observed damage patterns on the door plug that indicated an upward and outward movement, as well as a lack of damage around the bolt holes, indicating the absence of bolts. Additionally, the agency disclosed that the plane flew for two months without the door plug bolts, effectively making it a ticking time bomb since its construction at Boeing's Renton factory in September of the previous year. Boeing had removed the door plug to conduct repair work on nearby rivets and later failed to reinstall the bolts.
Jennifer Hamedi, Chair of the NTSB, expressed her concern, stating that the plane should never have been delivered with such critical bolts missing. The agency is now deepening its investigation not only into Boeing but also into the Federal Aviation Administration's oversight of the company. This incident further amplifies the ongoing FAA audit of Boeing's quality control, as the head of the FAA reported that two dozen inspectors are currently stationed at the 737 factory.
While no findings of blame or probable cause have been announced yet, Boeing's CEO, Dave Calhoun, acknowledged the company's accountability for the incident. He emphasized that such events should never occur on planes leaving their factories. The final report from the NTSB is expected to be issued in 12 to 18 months and may shed more light on the incident. Aircraft operators have already performed inspections on their planes following the end of the 19-day emergency grounding.
One aspect that the final report may clarify is who was responsible for reinstalling the bolts after the door plug was removed at the Boeing factory in September of last year. Whether it falls on Boeing or Spirit Aerosystems, the contractor responsible for building the fuselage, remains unclear at this point in the investigation.
