Incident Overview
During cruise flight, the outboard half of one propeller blade separated from the aircraft. In the subsequent forced landing attempt, the aircraft struck trees, which severed the right wing. The aircraft then crashed and came to rest inverted. The front occupant seats separated from their seat tracks during the event.
Investigation Findings
Examination of the propeller revealed that the blade separation resulted from a fatigue failure. This fatigue failure was caused by corrosion pitting that had developed under a previously installed propeller decal. The corrosion pitting weakened the blade material, leading to crack initiation and eventual fatigue fracture.
Regulatory Context
FAA Airworthiness Directive (AD) 66-23-02 had been issued, which directed the removal of the decal, cleaning of the propeller blade, and inspection of the propeller blade for corrosion pits. The aircraft had undergone an annual inspection on April 29, 1985, prior to the incident.