On March 5, 2007, approximately 1600 Pacific standard time, a Piper PA-28-140, N5547F, collided with trees during an attempted forced landing about 10 miles northwest of Crescent Lake, Oregon. The commercial pilot and his passenger received serious injuries, and the aircraft, which was owned by K & J Capital, LLC., and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 personal pleasure flight, which departed Eugene, Oregon, about 45 minutes prior to the accident, was being operated in visual meteorological conditions. No flight plan had been filed. Reportedly, the pilot intended to return to Eugene after flying around the Crescent Lake area. According to the pilot, he was flying between 800 and 1,000 feet above the trees in mountainous/hilly terrain, when, because of rising terrain, he decided to add power and start a climb up the valley he was in. Just as he added power, the aircraft's engine rpm dropped from about 2,300 to about 1,800 to 1,900 rpm. At that point, according to the pilot, he applied full carburetor heat, moved the mixture to full rich, and checked to make sure the fuel selector was in the correct position. According to both the pilot and his passenger, these remedial actions did not help the situation, and the engine rpm stayed near 1,800. Because the terrain was rising and the aircraft could not maintain altitude, and because they were already very low, the pilot made the decision to attempt a forced landing in the densely forested mountainous terrain. While attempting the landing on the snow-covered terrain, the aircraft struck a number of trees, and then impacted the ground in an inverted position. A post-accident inspection of the airframe, systems, and engine did not reveal evidence of any pre-impact anomalies or malfunctions that would have precluded the engine from operating at full power.