On August 9, 1999, approximately 1345 Pacific daylight time, a Cessna 182G, N2492R, registered to and being operated by a private pilot, was substantially damaged during an on-ground collision with a fence and ditch following an emergency landing in an open field approximately three miles east of Freeland, Washington. Visual meteorological conditions existed and no flight plan had been filed. The pilot was uninjured and the passenger sustained minor injuries. The flight, which was personal, was to have been operated under 14CFR91, and originated from Port Townsend, approximately 10 minutes prior to the accident. The pilot reported in a telephonic interview with the investigator-in-charge that while en route to Everett he noticed a degradation of engine RPM and attempted to correct for the condition without success. Application of carburetor heat merely aggravated the RPM loss, and the pilot, unable to maintain altitude, maneuvered the aircraft to a field for a forced landing. During the landing roll the aircraft impacted a barbed wire fence and then a ditch during which the nose gear assembly separated from the airframe (refer to photographs 1,2 and 3). The pilot also provided a written statement in which he stated that "during the cruise portion of the flight while reaching over to lean the mixture I noticed that the EGT was already at full lean (the six o'clock position on my gauge). As this was unusual I thought I would check with a mechanic at Paine prior to my return flight to Bellingham. I checked all gauges to see if there was any other anomaly and seeing none, proceeded with the flight." Additionally, he reported that "as we flew over the southwest corner of Useless Bay at 1800 feet AGL the engine began to run rough. Within a few seconds the RPM's dropped noticeably and we began to lose altitude." The pilot also reported to an inspector with the Federal Aviation Administration's (FAA) Flight Standards District Office (Renton FSDO) that he was "at 1800 feet when he started losing RPM, [he] tried to apply carb[uretor] heat - no good." A maintenance inspector from the FAA's Renton FSDO examined the aircraft's fuel and air intake system, as well as the engine aircraft recovery from the site. The inspector reported the following findings: 1. Fuel in both fuel tanks. 2. The gascolator bowl contained fuel and no water. 3. The carburetor was broken off the engine. 4. The carburetor fuel line had fuel in it. 5. The "Brackett" air filter was found unobstructed and its seal was intact. 6. The alternate air intake was unblocked. 7. The crankshaft was rotated and compression was verified on all six cylinders as well as crankshaft/accessory drive continuity. 8. The magnetos were rotated and generated a spark to all six cylinders. 9. The carburetor heat box was intact. 10. There was no visible blockage of the exhaust system. 11. The fuel selector was in the "OFF" position (placed there by the pilot following the accident). The aviation surface weather observation taken at 1353 at Paine field (nine nautical miles east of the site) reported a surface temperature and dew point of 21 and 16 degrees Centigrade respectively at an airport surface elevation of 606 feel above mean sea level. The average atmospheric lapse rate is approximately 2 degrees Centigrade per 1000 feet. A carburetor icing probability chart (Transport Canada), which provides carburetor icing probability as a function of temperature and dew point, is provided as ATTACHMENT CI-I.