Federal investigators have determined bad workmanship caused a five-foot roof section of a Southwest Airlines jet to rip en route from Phoenix to Sacramento two years ago, forcing an emergency landing and causing two minor injuries.
In findings published Friday, the National Transportation Safety Board concluded workers at a Boeing Co. plant installed a section of outer skin on a Boeing 737 out of alignment, causing the rivets to be off-kilter, weakening the connections between the planes outer and inner layers.
The hole quality in the crown and left side skin panels was not in accordance with Boeing specifications or standard manufacturing practices and showed a lack of attention to detail and extremely poor manufacturing technique, the report authors concluded.
The rivets held for 15 years, until April 1, 2011, when an 8-inch by 60-inch portion of the jets skin peeled off just after Flight 812 took off from Phoenix. The failure caused the planes cabin air to decompress, and forced an emergency landing in nearby Yuma, Ariz.
A flight attendant and an off-duty airline employee were injured. The flight attendant fainted, causing him to fall and break his nose. Federal transportation board investigators said in their report that the flight attendant was trying to phone for assistance, but should have put on his oxygen mask first.
A 15-page investigation report determined that that section of skin had been replaced at some point by Boeing employees during construction in 1996, but that it was installed improperly. Report authors said Boeing no longer had construction records for the plane in question, so investigators could not determine why the crown skin panel was replaced or how the poor repair was not identified in the (quality assurance) process.
The report indicated that investigators do not believe the problem was systemic. Nevertheless, after the crash, federal officials called for inspections of Boeing 737s and found several other jets with small fatigue cracks along the same rivet row.
None of the airplanes had the extensive fatigue cracking or double-drilled holes evident on the accident airplane, the NTSB reports.
Boeing officials told the NTSB they have upgraded their design and manufacturing process on newer 737s.
According to the report, the current production variant of 737 (next generation as opposed to the accident airplane) has a different design at the lap joint that has an improved fatigue life; more modern manufacturing techniques are used, such as 3D computer design, machine-driven rivets, and laser alignment.
Boeing issued an emailed statement over the weekend, The Associated Press reported, in which the company said it is dedicated to the safety of its planes and said inspections suggest the problem was isolated.
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