Incident Overview
During a practice missed approach conducted under instruction, a propeller blade separated from the aircraft. The flight instructor, who was supervising the commercial pilot, took control of the airplane after the separation. He shut down the affected engine to prevent additional damage, issued a Mayday call, and glided the aircraft to a successful landing on the runway.
Postflight Examination
A detailed postflight inspection of the propeller revealed that the blade had separated approximately 12 inches from the center of the hub. Metallurgical analysis of the remaining fracture face identified fatigue cracking that originated from an indentation on the blade's leading edge. The fatigue crack extended through about 50 percent of the fracture face, beyond which a band of overstress cracking was present. No evidence of corrosion was found, and chemical analysis confirmed that the blade's hardness and chemical composition met the engineering drawing specifications.
Preflight and Maintenance History
During the preflight inspection, both the flight instructor and the commercial pilot visually inspected the propeller blade and ran their hands along its leading and trailing edges, noting no anomalies. The most recent maintenance inspection of the propeller had occurred approximately one month before the incident.
Conclusion
The investigation determined that the propeller blade failure was caused by fatigue cracking that began from an indentation at the blade's leading edge.