Aircraft: Vans RV-6A. Injuries: None. Location: Albany, Ore. Aircraft damage: Substantial.
What reportedly happened: The pilot noted that the propeller assembly had undergone maintenance by its manufacturer on three occasions prompted by his observation of hub grease seeping onto the shank portion of the blades.
The pilot removed the propeller and hub assembly and returned it to the manufacturer for inspection and repair. The manufacturer reportedly performed maintenance and returned the assembly to the pilot, who then reinstalled it on his airplane.
The propeller logbook indicated that the hub was repaired and inspected by a repair station and reinstalled by the pilot/owner three days prior to the accident. At the time of the accident the propeller had 309.1 hours and the replacement hub had 114.2 hours total time.
The pilot reported that a few minutes after takeoff, he heard a loud noise and felt a vibration when an aluminum propeller blade separated from the airplane. He made a forced landing in a grass field north of the departure airport.
The propeller, the two-bladed propeller hub, separated blade, and fracture surfaces were examined. The examination revealed finely spaced striations consistent with high-cycle fatigue. The hub wall had fatigue cracks initiating from shallow oxidized pits. Evidence of rework or repair was found on the hub blade bore.
Probable cause: The in-flight separation of a propeller blade due to fatigue.
NTSB Identification: WPR11LA412
This August 2011 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.