While on the downwind leg of the traffic pattern for landing, the private pilot of the experimental amateur-built airplane heard a “clunk” sound from the front of the Kitfox, however, the propeller continued to rotate and the engine appeared to be operating normally.
He continued to the base and final legs of the traffic pattern and attempted to add engine power, but the engine “overreved.” The airplane lost altitude as it neared the runway at the airport in Escanaba, Michigan, and touched down on the parking apron, then continued into a ditch, where it nosed over and came to rest inverted. The pilot sustained minor injuries.
A post-accident examination revealed that the propeller gearbox had failed in flight. All of the drive gear and propeller drive teeth were either worn or destroyed, and the gearbox drive gear displayed discoloration and heat signatures consistent with oil starvation.
Additionally, there was no usable oil present in the gearbox, and no evidence of an oil leak.
Although the airplane owner stated that he had added oil to the gearbox before the flight, it is likely that the flight departed with an insufficient oil supply in the propeller gearbox, which resulted in subsequent oil starvation. When the gearbox failed, the engine continued to operate, however it ceased to drive the propeller, which resulted in a loss of thrust.
Probable cause: The airplane owner’s inadequate maintenance and servicing of the propeller gearbox, which resulted in oil starvation, failure of the gearbox in flight, and a subsequent loss of propeller thrust. Contributing to the outcome was the airplane’s low altitude at the time of failure, which precluded the airplane from reaching the runway.
NTSB Identification: CEN16LA035
This November 2015 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.