The pilot reported that, during the approach to landing, the RV-9A’s propeller stopped spinning, but that the engine continued functioning normally. He subsequently made a forced landing to a field near Apopka, Fla.
During the landing, the plane flipped over and came to rest inverted, which resulted in substantial damage to the wings and vertical stabilizer, as well as one serious injury and one minor injury.
Post-accident examination of the engine revealed that the spline shaft had uncoupled from the drive disk adapter. The splines of the spline shaft, the drive disk adapter, and the propeller speed reduction unit (PSRU) input spline exhibited signs of severe wear consistent with fretting corrosion.
Research revealed that several spline shaft failures had occurred on other airplanes. Some of the failures resulted in a loss of engine power and subsequent forced landings, while some of the failures were identified during inspection.
The manufacturer issued guidance to users to apply a nickel or copper antiseize compound on the spline shaft during installation of the PSRU to decrease wear, however, the manufacturer did not provide users with any instructions or recommendations to routinely inspect and lubricate the spline components.
The pilot/builder reported that the PSRU and spline shaft had not been removed, lubricated, or inspected since it had been installed about 325 hours before the accident.
The NTSB determined the probable cause as the failure of the propeller spline shaft, the drive disk adapter, and the PSRU input spline due to a lack of inspection and lubrication, which resulted in a total loss of propeller drive and a subsequent forced landing. Contributing to the accident was the lack of manufacturer guidance for inspecting and lubricating the PSRU gearbox spline components.
NTSB Identification: ERA14LA130
This February 2014 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.