ANC11LA099

The pilot reported that, during cruise flight, the engine ran rough for about three engine revolutions before losing total power. The pilot entered an emergency autorotation and landed the helicopter in a shallow bay. Postaccident examination of the helicopter did not reveal any mechanical anomalies that would have precluded normal operation; however, a detailed engine examination was not completed. According to a carburetor icing probability chart, conditions at the time of the accident were conducive to severe carburetor icing at both cruise and glide power settings. Although carburetor icing was a possible initiating event for the loss of engine power, carburetor icing could not be determined.

On August 30, 2011, about 1330 Alaska daylight time, a Robinson R22 Beta II helicopter, N169CW, sustained substantial damage following a loss of engine power and subsequent emergency landing approximately 60 miles southwest of Unalaska, Alaska. The helicopter was registered to Bering Pacific Ranches, LTD, and operated by the pilot as a personal flight under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed for the flight, and no flight plan was filed. The flight originated from the Unalaska Airport, Unalaska, Alaska, about 1230. The pilot reported that approximately 9 miles from his destination, the engine ran rough for about three engine revolutions before losing total power. He entered an emergency autorotation, and landed the helicopter in a shallow bay, approximately 150 feet from the shoreline. After contacting the water, the helicopter rolled to the right, and sank in shallow water. The pilot reported substantial damage to the tail rotor drive system. A Federal Aviation Administration inspector traveled to the operator's hangar, and examined the helicopter. No mechanical anomalies were noted that would have precluded normal operation. The operator stated that the helicopter was going to be sent to a facility for a more detailed inspection, but as of this writing, no further inspection has been performed. At 1358, the nearest weather reporting facility to the accident site was reporting the temperature as 14 degrees Celsius, and the dew point as 9 degrees Celsius. According to a carburetor icing probability chart, serious icing conditions existed at cruise and glide power settings.