What happened
During a period of level flight, the right wing of the aircraft detached from the fuselage. As the separation occurred, the fuel within the wing ignited. The aircraft, which had been operating under a restricted-category special airworthiness certificate for aerial firefighting since 1990, suffered this catastrophic structural failure while performing its duties.
Findings
Laboratory analysis of fragments recovered from the right-side and center-wing areas identified two distinct fatigue cracks that had progressed into overstress fractures. One crack was located in the wing skin on the underside, situated beneath a doubler, while the second crack was found within the doubler itself. Due to the extent of the damage to the fracture surfaces and the limited amount of material available for study, investigators could not establish the exact origin or the total dimensions of the fatigue regions.
- The aircraft had been in service since 1957, having been originally delivered to the U.S. Air Force.
- At the time of the incident, the airframe had accumulated a total of 20,289 flight hours.
- The operator's maintenance protocols, which followed military-based standards, utilized general visual inspections for cracks but lacked specialized or focused inspections for high-stress components.
- The operator lacked the necessary engineering expertise to perform the complex analyses required to understand the specific stresses imposed by firefighting operations or to predict how such environments would impact the structural lifespan of the aircraft.