Incident Description
While cruising at 2,000 feet altitude with the engine at 2,000 RPM, a sudden loud noise and vibration occurred. The pilot reduced power and executed an emergency landing. Examination after landing revealed that approximately six inches of one propeller blade had separated from the propeller.
Propeller Examination
The propeller, a Sensenich Corporation fixed-pitch aluminum model 76EM8S5-0-60, was sent to the Safety Board's Materials Laboratory for metallurgical examination. The examination found a flat, chordwise fracture area with crack arrest positions and radial marks characteristic of fatigue cracking. Microscopy identified the origin area within a notch at the leading edge on the flat side of the blade. The notch was about 0.008 inch deep.
Repair Marks
The leading edge of the blade contained sanding marks typical of a blend repair near the notch. However, these sanding marks did not extend into the deepest part of the notch directly adjacent to the fracture surface at the origin area.
Relevant Guidance
FAA Advisory Circular 43.13-1A, Section 3 'Repair of Metal Propellers,' paragraph 585(a) addresses procedures for repairing aluminum propellers. It advises that when rounding out nicks, scars, cuts, etc., care should be taken to remove the deepest point of the injury.
Additional Information
The total time on the propeller was not available, and the party that performed the propeller dressing procedure was not identified.