Accident Details
On January 2, 2011, at approximately 1315 mountain standard time, a Piper PA-18-180, registration N6774B, sustained substantial damage during a forced landing about 10 miles southeast of Shoshoni, Wyoming. The commercial pilot and his passenger were not injured. The aircraft was owned by STP Aviation LLP and operated by the United States Department of Agriculture. The flight was a local Public Use wildlife aerial observation mission, which had departed Riverton Municipal Airport, Riverton, Wyoming, about four hours earlier. Visual meteorological conditions prevailed, and no flight plan had been filed.
Forced Landing
According to the pilot, during the aerial observation flight, the engine suddenly stopped producing power. He checked the fuel selector, applied carburetor heat, ensured the magneto switch was set to both, and attempted to restart the engine. The engine did not restart, prompting the pilot to execute a forced landing on rough, brush-covered terrain. Although the touchdown was successful, during the landing roll, the airplane went off a low bank. Upon contacting the terrain at the bottom of the bank, the main landing gear support structure failed, causing both gear struts to fold outward. The left wing lift strut was bent to the extent that it required replacement.
Postaccident Investigation
A postaccident examination of the airplane's fuel system revealed that more than one hour of fuel (10+ gallons) remained. The engine was test run for several minutes with no anomalies detected. The investigation also determined that the ambient temperature (10 degrees Fahrenheit) and dew point (1 degree Fahrenheit) were outside the range at which carburetor icing would be expected in maneuvering flight. No other fuel system or engine anomalies were found, and the reason for the loss of engine power could not be determined.