Accident Overview
While approaching Moncks Corner Airport for landing, the airplane's engine seized, forcing the pilot to land on tree tops approximately 400 feet from the runway.
Post-Accident Examination
A post-accident examination of the engine assembly revealed four fatigue cracks on the planetary carrier housing. These cracks propagated outboard and caused the housing to fracture into multiple pieces. The teeth around the sun gear in the area corresponding to the planetary gears were fractured and exhibited deformation. The teeth of the planetary gears also showed deformation.
Splined Lock and Gear Inspection
The splined lock was examined and exhibited fretting damage. The width of the fretting/galling damage on the four flat surfaces was wider compared to the thickness of the mating square slot on the cap, consistent with lateral movement between the splined lock and cap. All spine teeth on the splined lock showed deformation.
Previous Maintenance History
Dimensional inspection of the gears was performed on the engine approximately 98 hours prior to the accident. At that time, a new sun gear was installed in the engine. The mating four planetary gears were not replaced and were not required to be replaced.
Wear Analysis
Uneven wear between gear faces caused stresses to be distributed unevenly between the gears, resulting in accelerated wear of the gears. Wear evaluation of the planetary gears is required when the engine is overhauled, but there is no record of a recent engine overhaul.