Event
The helicopter was on a ferry flight from Oedheim to Dattenberg. Approximately 30 minutes after departure, the pilot heard a loud bang, noticed a right turn about the vertical axis, and observed smoke in the cockpit. The pilot initiated an autorotation and switched off the electrical system. After a short time, the smoke dissipated, and the pilot realized the aircraft was in a steep approach to a cemetery. The engine had stopped, the rotor rpm was very low, and the helicopter had only limited controllability.
The emergency landing on the cemetery was performed with forward speed and a high descent rate. After contacting gravestones, the helicopter tipped over.
Technical Investigation
Technical investigation revealed a fracture of the piston pin of the second cylinder. Metallurgical examination of the fracture surfaces demonstrated a fatigue fracture, although its cause and origin could not be determined. A possible technical cause for the low rotor speed could not be identified due to heavy damage in the area of the cyclic and periodic main rotor controls.
Assessment and Conclusions
The accident was initiated by the sudden engine failure. The pilot reacted correctly, but the smoke development in the cockpit worsened the emergency. Due to the low rotor rpm and resulting limited controllability, the pilot could not avoid the emergency landing on the cemetery. A damage-free landing was not possible there, and the accident was unavoidable.
Conclusions
The accident was caused by the sudden engine failure as a result of a piston fracture. The terrain of the cemetery was unsuitable for an emergency landing.