Accident Description
While the aircraft was in level flight, the right wing separated from the airframe. During the separation sequence, fuel from the wing ignited. The accident resulted from a structural failure.
Examination Findings
Laboratory examination of recovered right-side center-wing fragments revealed two fatigue cracks. These cracks had propagated to the point of overstress fractures. One crack was located in the underside wing skin beneath a doubler, while the other was within the doubler itself. Due to damage to the fracture surfaces and a lack of available material, the total size and origin of the fatigue regions could not be determined.
Aircraft History and Operation
The aircraft was originally delivered new to the U.S. Air Force in December 1957 and retired from military service in 1986. In May 1990, the FAA issued a restricted-category special airworthiness certificate authorizing its use for dispensing aerial fire retardant. At the time of the accident, the aircraft had accumulated 20,289 total flight hours, of which 19,547 were acquired during military service.
Maintenance and Inspection Programs
The operator's inspection and maintenance programs were based on military standards. These programs included general visual inspections for cracks but did not incorporate enhanced or focused inspections of highly stressed areas, such as the wing sections where the fatigue cracks were located. The operator did not have the engineering expertise necessary to conduct studies and engineering analysis to define the stresses associated with the firefighting operating environment or to predict the effects of those stresses on the operational life of the aircraft.