On March 17, 2004, approximately 1130 Pacific standard time, a Piper PA-18, N2553S, collided with trees during an attempted forced landing in forested terrain near Sisters, Oregon, after experiencing a loss of engine power. The private pilot and his passenger received minor injuries, and the aircraft, which is owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 personal pleasure flight, which departed Corvallis, Oregon, about 45 minutes earlier, and was en route to Prineville, Oregon, was being operated in visual meteorological conditions. No flight plan had been filed. According to the pilot, who had been cruising at 7,500 feet en route, he had been in a gradual descent for about 10 minutes as he proceeded toward Prineville for landing. During the descent, he realized that the engine had lost power, so he switched fuel tanks, applied carburetor heat for about 20 seconds, and moved the throttle in and out. Since these actions did not restore power to the engine, he looked for a place to execute a power-off forced landing. Because there was no suitable smooth terrain in the area upon which to land, he slowed the aircraft and flew it onto the forested terrain in a landing attitude. During that sequence the aircraft collided with several trees. A post-accident inspection of the aircraft by a Federal Aviation Administration Inspector from the Hillsboro, Oregon, Flight Standards District Office, revealed that the wire from the carburetor heat control knob was no longer attached to the bolt in the fitting where it was attached to the carburetor heat box actuation lever. Although the wire had come out of the hole in the bolt, the crush washer, the castle nut, and the cotter pin were all still attached to the bolt. The carburetor heat control wire housing was also found to be disconnected from its mounting point. According to the pilot, he always performed a carburetor heat check during his pre-takeoff check, and he stated that during the check performed at the beginning of this flight there was a significant rpm drop when the carburetor heat was activated.