What happened
While cruising at altitude, the pilot detected a loud knocking noise emanating from the engine accompanied by a noticeable decrease in oil pressure. In response to the mechanical failure, the pilot executed an emergency landing in a nearby field. Upon touchdown, the landing gear collapsed under the stress of the uncontrolled descent and impact. Following the collapse, the aircraft ground looped, resulting in significant structural damage.
The investigation
A thorough examination of the engine was conducted to determine the root cause of the failure. The inspection revealed that the hydraulic lifters for three of the four cylinders had failed completely. This mechanical defect prevented the corresponding intake and exhaust valves from opening properly during engine operation, leading to the loss of power and the subsequent knocking sound reported by the pilot.
Findings
The primary factor contributing to this accident was the failure of the hydraulic lifters in three cylinders. This component failure caused the valves to malfunction, which directly resulted in the engine's inability to operate correctly. The resulting loss of power necessitated an off-airport landing, where the landing gear collapse and subsequent ground loop occurred.