On February 11, 2010, about 1605 Alaska standard time, a tailwheel equipped Piper PA-18-150 airplane, N278Z, sustained substantial damage when it collided with terrain during an emergency descent and off airport landing, about 3 miles northwest of King Cove, Alaska. The airplane was being operated by the U.S. Fish and Wildlife Service, as a visual flight rules (VFR), public use flight under Title 14, CFR Part 91, when the accident occurred. In a written statement dated February 18, the pilot wrote that he and his passenger were doing an aerial observation/survey at a reduced airspeed and engine rpm. He said he further reduced the rpm to 1900, and shortly thereafter the engine lost power. He reported he thought that carburetor ice might be responsible, and he immediately added carburetor heat, full throttle, and full rich mixture. He said some power was restored, but then the engine lost all power. He wrote that he checked the fuel selector, tank gauges, and the ignition. The pilot said the engine did not respond, and he turned his attention to landing the airplane. The pilot reported he elected to land straight ahead on a rough, unimproved, winding road. During the landing roll he was unable to maintain directional control, and the airplane ran into a ditch on the right side of the roadway, where both wings struck the ground. The pilot said prior to the loss of engine power there were no mechanical problems with the airplane. He said during the accident, the airplane sustained substantial damage to both wings and the fuselage. Additional Information Due to the remote location of the airplane the NTSB did not examine the airplane. On February 14, an engine run was done at Cold Bay, Alaska, by the operator's certificated aircraft mechanics. The engine started and ran normally. The carburetor was removed and sent to an independent maintenance shop where it was determined that the carburetor functioned normally, and all wear was within the serviceable limits. According to a carburetor icing chart, (see attached) the conditions in which the airplane was operating, temperature 3 degrees C, dew point -1 degree C, were conducive to serious icing at any power setting.