WPR16LA045

On January 1, 2016, about 1530 Pacific standard time, a Piper PA18-150, N2684A, was substantially damaged during a precautionary landing to a private dirt airstrip following a partial loss of engine power near Newman Lake, Washington. The private pilot, the sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed for the local flight, which was being operated in accordance with 14 Code of Federal Regulation Part 91, and a flight plan was not filed. The local flight departed Felts Field (SFF), Spokane, Washington, about 1500, with the destination being a private airstrip about 13 nautical miles northeast of SFF. In a statement submitted to the National Transportation Safety Board investigator-in-charge, the pilot reported that after departing SFF, his intention was to make several slow, low passes over the private airstrip, which was located about 13 nautical miles northeast of SFF. He initially climbed to 6,000 ft mean sea level, cycled the carburetor heat while on descent to the airstrip, then made an initial low pass with full flaps and carburetor heat applied, followed by a go-around with carburetor heat off. The pilot opined that he subsequently made a second low pass in the same configuration, but during the go-around experienced engine roughness, a loss of power, the engine backfiring, and a loss of engine rpm from 2,400 to 2,200. He then applied carburetor heat, but there was no increase in rpm. Unable to maintain altitude, the pilot elected to make a precautionary landing on the private airstrip, which was covered with what the pilot described as covered with snow. Upon touchdown the airplane nosed over, which resulted in substantial damage to both wing struts and the rudder. A postaccident examination of the airplane and engine overseen by a Federal Aviation Administration aviation safety inspector, which included an engine run, revealed no preimpact malfunctions or failures that would have precluded normal operation. During the examination the inspector noted that the carburetor heat/air box had full continuity, the butterfly valve reached full travel, and full continuity of control was confirmed from the throttle and mixture controls in the cockpit to the carburetor. At 1450, the weather reporting facility located at SFF reported wind calm, visibility 10 miles, sky clear, temerature -7 C, dew point -9 C, and altimeter reading of 30.52 inches of mercury. The carburetor icing probability chart from the FAA Special Airworthiness Information Bulletin (SAIB), CE-09-35 Carburetor Icing Prevention, indicated that the airplane was operating in an area associated with a serious risk of carburetor ice accumulation at descent power.