On June 5, 1994, approximately 1420 Pacific daylight time (PDT), a Piper PA-38, N9271T, experienced a gear collapse during a forced landing near Sweet Home, Oregon. The private pilot and his passenger were not injured, but the aircraft sustained substantial damage. The personal pleasure flight, which departed Lebanon State Airport, Lebanon, Oregon, about 20 minutes earlier, was being operated in visual meteorological conditions at the time of the accident. No flight plan had been filed, and there was no report of an ELT activation. In a post-accident interview, the pilot said that the engine suddenly quit while he was maneuvering near Sweet Home, and he attempted a forced landing in a nearby field. During the landing roll on the rough/uneven terrain, the aircraft's gear collapsed. No problems with the engine were found in a post-accident investigation, and the engine was started and found to run fine at the scene of the crash. As part of the investigation, the temperature and dew point of the two nearest reporting stations were checked for the time of the accident. A station 27 miles south (Eugene, Oregon) showed a temperature of 62 degrees and a dew point of 48 degrees. A station 30 miles northwest (Salem, Oregon) showed a temperature of 61 degrees and a dew point of 52 degrees. These numbers were used to figure the probability of icing using the carburetor icing probability chart from the DOT/FAA/CT-82/44 publication. The numbers from the Eugene station showed the aircraft to be operating in conditions where carburetor icing could be expected to be serious at glide power. The figures from the Salem station showed the aircraft to be operating in conditions where carburetor icing could be expected to be serious at both glide and cruise power (see attachment #1). Although the pilot applied carburetor heat after the engine had lost power, he had not applied it to check for ice accumulation in the carburetor throat prior to the loss of power.