On August 20, 2005, approximately 0750 mountain daylight time, a single-engine Alon A-2A airplane, N5467F, sustained substantial damage following a forced landing after experiencing a loss of engine power near Helena, Montana. The airplane was registered to and operated by a private individual. The certificated private pilot and his sole passenger sustained minor injuries. Visual meteorological conditions prevailed for the local flight, which was operated in accordance with 14 CFR Part 91, and a flight plan was not filed. The flight was originating at the time of the accident. In a written statement the pilot reported that he spent 5 to 10 minutes in the run up area prior to departing; carburetor heat and magneto checks were normal. The pilot stated that after taking off the engine was performing normal, but after reaching an altitude of approximately 100 to 150 feet above ground level (agl) he noticed that the engine was running rough and rpm dropping. The pilot applied carburetor heat, which resulted in a further loss of rpm, prompting him to return the carburetor heat control to OFF. The pilot reported that after informing the control tower operator of the rough running engine, he was cleared for a 180-degree turn to the left for a landing on Runway 9. The pilot reported that his decision to land on Runway 9 was prompted by the reduced engine power available, the lack of runway remaining, and the obstacles at the end of the runway; a fence and a road. The pilot stated that he applied carburetor heat, but due to the additional loss of power, he returned the control to its normal position. The pilot reported that the airplane touched down on the pavement near the departure end of runway 27, bounced once and again contacted the [pavement]. The pilot stated that the airplane then rolled about 10 to 15 feet before leaving the asphalt. The nose gear subsequently collapsed, resulting in the airplane nosing over and coming to rest inverted. The pilot reported no anomalies with the airplane or engine prior to the flight. The temperature and dew point recorded at the airport about the time of the accident were 52 and 31 degrees respectively. A review of a carburetor icing probability chart placed the reported temperature and dew point in the "serious icing - descent power" area of the chart. A Federal Aviation Administration (FAA) airworthiness inspector, who examined the airplane, reported that both magnetos exhibited proper timing, all spark plugs appeared normal, with the exception of the #4 spark plug, which was fouled. Flight control continuity was found at all control surfaces. Damage to the airplane included both propeller blades bent aft, the nose gear collapsed aft, damage to the firewall, the left wing root area and aft spar damaged, and the horizontal stabilizer being bent downward.