Plane & Pilot
Saturday, December 1, 2007

Catastrophic Structural Failure

Focusing on maintenance programs

The investigation determined that the right wing separated because of preexisting fatigue fractures and cracks in a stringer, the lower skin and rear lower spar cap. They said that this fatigue damage reduced the residual strength capability of the right wing structure, leading to the failure. Examination of the wreckage disclosed that a major repair had been made to the lower right-wing spar at the location where the wing separated from the fuselage. Maintenance records provided to the Safety Board, however, didn’t contain any entry for this repair.

There had been a history of fuel leaks near the area where the wing failed, and the investigators said these leaks were indicators of structural damage inside of the wing. Had the leaks been properly addressed, the extent of the problem could have been discovered, they said. However, that would not necessarily have made the airplane safe, according to the investigators. Metallurgical examination showed significant fatigue cracks affecting the airplane’s left wing, including one crack on the left-wing front spar lower cap that had extended from an area of corrosion damage and had begun to progress fairly rapidly. The Safety Board said that had the airplane not experienced the catastrophic failure of the right wing, the crack in the left wing likely would have led to a catastrophic failure. The Board said that the company’s maintenance program was ineffective at identifying and correcting the long-standing structural problems that led to the in-flight separation of the right wing. The company’s Director of Operations was quoted in the NTSB’s report as defending the safety of airplanes in its fleet and pointing to the company’s 86-year unblemished safety record before the time of the accident. The NTSB report referenced seven accidents or incidents involving Chalk’s aircraft before the crash of flight 101.

The Safety Board noted that the FAA inspector who was responsible for overseeing the company’s maintenance said it met all FAA requirements, and he was comfortable with the maintenance being performed on Chalk’s airplanes. He had conducted an aging-aircraft inspection and records review only a few weeks before the accident. The Safety Board said he should have raised a red flag about the recurring fuel leaks on the accident airplane.

The Safety Board said there were some other clues that should have caused the FAA to look more closely at maintenance on Chalk’s aircraft. Among these were: paperwork from the Department of Transportation expressing concern about the airline’s financial condition; an incident in November 2004, when an airplane’s elevator cable failed in flight and the airline submitted a Service Difficulty Report to the FAA; and a landing-gear-fatigue failure incident in 2001. The NTSB concluded that the Chalk’s Ocean Airways maintenance program plan was inadequate to maintain the structural integrity of its aircraft fleet.

The NTSB determined that the probable cause of this accident was the in-flight failure and separation of the right wing during normal flight, which resulted from (1) the failure of the Chalk’s Ocean Airways maintenance program to identify and properly repair fatigue cracks in the right wing and (2) the failure of the FAA to detect and correct deficiencies in the company’s maintenance program.

Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, NY 10602-0831.


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