On January 6, 2001, approximately 1500 Pacific standard time, a Cessna 170A, N1703D, collided with trees during an attempted forced landing after experiencing a complete loss of power while in the landing pattern at Eastsound Airport, Orcas Island, Washington. The airline transport pilot and his passenger received serious injuries, and the aircraft, which was owned and operated by the pilot, sustained substantial damage. The local 14 CFR Part 91 personal pleasure flight, which had been in the air for about 15 minutes, was being operated in visual meteorological conditions. No flight plan had been filed. The ELT, which was activated by the impact, was shut off at the scene. According to the pilot, he took off from Eastsound Airport and climbed to an altitude of about 1,000 to 1,500 feet. He then flew out over the water to the north of Orcas Island for approximately 10 minutes. Upon his return, he approached the airport from the north and entered a right downwind for a VFR pattern and landing back at Eastsound. From when he first started maneuvering over the water until he entered the downwind, the aircraft's engine was set at full-rich cruise power, and the pilot did not apply the carburetor heat in order to check for any possible build-up of ice in the carburetor throat. As he entered the pattern, he applied the carburetor heat at the same time as he reduced the power to idle. In a telephone interview after the accident, he said that while on final, he advanced the throttle, but the engine did not respond. He tried to restart the engine by pumping the throttle and switching the fuel selector from the "BOTH" position to the left tank, but was not successful. He attempted to reach the end of the runway, but found it necessary to put the aircraft down in a wooded area about 700 feet short of the south end of the runway. As the aircraft settled into the wooded area, the right side of the fuselage impacted a large coniferous tree. The 1453 surface weather observation (METAR) taken at Friday Harbor Airport, which is located about 12 miles south of Eastsound, indicated a temperature of 43 degrees Fahrenheit and a dew point of 37 degrees Fahrenheit. Plotting these data points on the Carburetor Icing Probability Chart (attached) shows that operations under these conditions may result in serious icing at climb, cruise, or glide power. According to the pilot, he was not aware of the minimal temperature-dew point spread, or that he was operating in conditions that may cause carburetor icing at cruise power. A post-accident teardown inspection of the engine and carburetor indicated fuel was present in those systems, and did not reveal any evidence of anomalies or malfunctions that would have contributed to a loss of engine power.