During a mustering operation at 100 feet above ground level the pilot noticed an unusual vibration in the aircraft. He decided to land in a nearby clear area to investigate the source of the vibration. As the pilot commenced the approach the engine suddenly oversped and the pilot immediately commenced an autorotational descent. The aircraft touched down while still moving sideways and rolled over. Inspection of the aircraft found that the short drive shaft from the engine to the transmission had failed. The failure was the result of the shaft overheating due to a lack of lubrication when the grease retaining boot on the drive shaft adaptor fell off. The clamp that held the boot in position was not found and the reason the boot was lost could not be determined. This accident was not the subject of an on-site investigation.
