Accident Overview
While initiating a spray run over a field, the pilot reported hearing a loud pop. The airplane subsequently began to roll and pitch nose down before impacting the ground and coming to rest inverted. Post-accident examination revealed that the right wing had separated in-flight.
Findings
Examination of the separated wing identified that the right outboard wing section's forward lower attachment fitting had failed. The failure was due to fatigue cracking, which originated from severe corrosion pitting in the bore of the central lug of the fitting. Additionally, the right side lower expansion mandrel and bolt were found devoid of grease or anti-corrosive material.
Maintenance History
At the time of the accident, the airplane had accumulated 5,898.6 total flight hours. The aircraft's maintenance records contained no indication that the recommended 3,000-hour wing attachment fitting inspection had been performed. According to the service life limit, the airplane was authorized to operate up to 6,000 hours only if that inspection had been completed.
Conclusion
The in-flight wing separation resulted from fatigue cracking of the attachment fitting due to severe corrosion, with the absence of protective lubrication on critical components. The lack of documented compliance with the mandatory 3,000-hour inspection suggests that the corrosion condition may have gone undetected.