WPR11TA087

According to the pilot, during a wildlife aerial observation flight, the engine suddenly stopped producing power. The pilot checked the fuel selector and magnetos and applied carburetor heat. Because he was unable to get the engine started again, he executed a forced landing on rough/uneven terrain. During the landing roll, the airplane went off a low bank, contacted the terrain at the bottom of the bank, and sustained substantial damage. At the time of the accident, the airplane had about one hour of fuel remaining, and the postaccident inspection, which included a successful engine run, did not find any anomalies that would have contributed to a loss of power. The ambient temperature and dew point were outside of the range at which carburetor icing would be expected to occur.

On January 2, 2011, about 1315 mountain standard time, a Piper PA-18-180, N6774B, experienced a gear collapse during a forced landing about 10 miles southeast of Shoshoni, Wyoming. The commercial pilot and his passenger were not injured, but the airplane, which was owned by STP Aviation LLP, and operated by the United States Department of Agriculture, sustained substantial damage. The local Public Use wildlife aerial observation flight, which departed Riverton Municipal Airport, Riverton, Wyoming, about four hours prior to the accident, was being operated in visual meteorological conditions. No flight plan had been filed. According to the pilot, during the aerial observation flight, the engine suddenly stopped producing power. He therefore checked the fuel selector, applied carburetor heat, made sure the magneto switch was on both, and tried to restart the engine. Because the engine did not restart, he made the decision to make a forced landing on the rough, brush-covered terrain. Although the touchdown was successful, during the landing roll, the airplane went off a low bank, and upon contacting the terrain at the bottom of the bank, the main landing gear support structure failed allowing both gear struts to fold outward. During the accident sequence, the left wing lift strut was bent to the extent that it had to be replaced. A postaccident examination of the airplane's fuel system determined that it had more than one hour of fuel remaining (10+ gallons). As part of the examination process, the engine was test run for several minutes with no sign of any anomaly. The investigation also determined that the ambient temperature and dew point (temperature of ten degrees F/dew point of one degree F) were outside the range at which carburetor icing would be expected in maneuvering flight. At the end of the investigation, no other fuel system or engine anomalies had been found, and the reason for the loss of engine power was not able to be determined.