Accident Summary
While conducting a patrol mission, the helicopter suffered a major engine failure at approximately 500 feet above ground level. The pilot initiated an autorotation to a vacant parking lot. Upon touchdown, the tail rotor snapped off and the helicopter yawed 180 degrees to the left.
Engine Examination
Post-accident inspection of the engine disclosed that the number two cylinder had separated from the engine block. Additionally, the connecting rod cap bolt was found to be sheared. The investigation also reviewed maintenance records, which indicated that the number one cylinder had been removed and reinstalled at 646.2 hours since overhaul, which was 66.6 hours prior to the accident.
Conclusion
The incident resulted from a mechanical failure of the engine, specifically the detachment of the number two cylinder and the shearing of the rod cap bolt. The pilot's autorotation was executed but the impact caused structural damage to the tail rotor assembly.