On March 4, 1999, at 1453 Alaska standard time, an Interstate S-1B1 Arctic Tern, tailwheel equipped airplane, N48027, was substantially damaged during a forced landing about 1/2 mile short of runway 33 at Merrill Field, Anchorage, Alaska. The solo private pilot sustained minor injuries. The airplane was being operated as a local, personal flight under 14 CFR Part 91. The flight departed Merrill Field at 1315. Visual meteorological conditions prevailed at the time of the accident, and no flight plan was filed. The NTSB investigator-in-charge (IIC) interviewed the pilot at the scene at 1530 on March 4. The pilot indicated that as he was returning to Merrill Field, the engine began to run rough, and the engine speed dropped to about 600 rpm. He applied carburetor heat, but did not notice a change in rpm. During the emergency descent, while in a wings level attitude, engine power momentarily returned to normal, then dropped off again. The pilot said he confirmed his fuel selector was on the left tank, which held about five gallons of fuel. He stated that he realized he was not going to reach the runway, and completed a forced landing at slow speed into a snow covered area with small trees. The pilot told the NTSB IIC that during his flight, he intentionally exhausted the fuel in the right tank, and was returning to Merrill on the left tank. Initial inspection of the airplane revealed fuel in the left tank, and a trace amount in the right tank. A steady stream of clear, blue fluid flowed out of each wing tank sump drain with no evidence of water. All engine controls were connected, and moved freely. There was no indication of rotational scratching or bending visible on the propeller. Additional interviews with the pilot, and an inspection of the fuel system, revealed that the left fuel tank has two outlet standpipes which supply the fuel selector valve. The "left main" outlet standpipe is the taller of the two, and loses suction when the fuel level in the left tank drops to about five gallons. The "reserve" standpipe is shorter, and allows the remaining five gallons to be drawn from the left wing tank. The fuel selector valve handle is located between the pilot's legs, and is not easily visible to the pilot. The pilot stated that he was not familiar with the fuel system plumbing, nor that use of the "reserve" position on the fuel selector valve was required to access the remaining five gallons of fuel in the left wing tank. He said he intentionally insured the valve selector was on the left tank position, because he knew there was still five gallons of fuel in that tank.