Accident Sequence
During cruise flight, a portion of a propeller blade separated from the right engine. The resulting vibration partially separated the engine from its airframe mounts, causing the airplane to roll inverted and dive into a private residence. The house was severely damaged, and the airplane was destroyed.
Blade Failure Examination
The separated 2.5-foot-long span of the failed blade was found approximately 1 mile from the main wreckage. Examination by the NTSB's Metallurgical Laboratory revealed that the blade failed due to fatigue cracking initiated by corrosion pitting in the pilot tube bore. A fatigue crack had initiated at two corrosion pit sites in the bore, which had been painted over without the corrosion being dressed out during the overhaul. Additional corrosion pits were located circumferentially in line with the origin area. The blade's bore was also contaminated with glass beads.
Overhaul Irregularities
The propeller was overhauled about 3 years and 5 operational hours before the accident flight. The conditions found during the examination were contrary to the procedural steps in the manufacturer's overhaul instructions, establishing that the blade was reassembled with an incomplete and improper overhaul.
Inspection Findings
The FAA inspector assigned to oversee the overhaul company reported that he did not observe any repair station deficiencies during his surveillance inspections. However, a Safety Board inspection after the accident disclosed that the repair station's personnel were not following prescribed manufacturer overhaul procedures, did not have the required chemicals for blade treatment, and did not possess required procedure manuals. Additional inspections of other propellers overhauled by the company revealed that propellers overhauled as early as 1997, when the company commenced business, showed evidence of corrosion in the pilot bores and were unairworthy.