On November 14, 1996, at 1040 hours mountain standard time, a homebuilt experimental Moody RV-6, N12033, collided with the ground during a forced landing near the Cottonwood, Arizona, airport. The forced landing was precipitated by a loss of engine power in the airport traffic pattern. The aircraft was owned and operated by the pilot. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft was substantially damaged in the ground collision sequence. The certificated private pilot, the sole occupant, sustained serious injuries. The flight originated at the Cottonwood airport about 1000 on the day of the accident for a local area personal flight and made an en route stop at the Montezuma airport. The pilot stated in his written report that after returning from a brief flight to the Montezuma airport, he entered the Cottonwood airport traffic pattern for a landing on runway 32. Carburetor heat was pulled on and an initial power change was made from cruise power to 2,200 rpm. After further reducing the power to 1,800 rpm, the engine began to run roughly. The pilot attempted to increase engine power; however, the engine continued to run rough until it finally stopped producing power altogether. While the engine problems were occurring, the pilot declared mayday and attempted to land on runway 14, but had insufficient altitude and collided with the ground 200 yards short of the pavement. The pilot reported that both fuel tanks had been topped off the day before the accident flight by Cottonwood Air Service, and a preflight check showed no signs of moisture. Additionally, the pilot reported that a "RV-6 is hard to slow down - I normally accomplish this by approaching the pattern a bit low and slow down by climbing back to pattern altitude." A postaccident inspection of the engine was conducted by an airframe and powerplant mechanic who reported that "there appeared to be no specific/obvious mechanical reason for the engine failure." His report of the examination is attached. The temperature at the time of the accident was 59 degrees Fahrenheit and the dew point was 34 degrees Fahrenheit. Reference to a carburetor icing probablity chart for the temperature/dew point spread revealed that the points were in an area of the chart delineated "moderate icing cruise power/serious icing glide power."