On April 20, 2009, at 1634 Pacific daylight time, a Cessna 152, N48259, experienced a partial loss of engine power while in the traffic pattern. The pilot subsequently landed the airplane short of the approach end of runway 24 at McClellan-Palomar Airport (CRQ), Carlsbad, California. Orion Aviation operated the airplane as a personal flight under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91. The private pilot, the sole occupant, was not injured. The airplane sustained substantial damage to both wings and the fuselage. Visual meteorological conditions prevailed for the local area flight, and no flight plan had been filed. The flight originated from CRQ about 1530. In the pilot’s written statement to the Federal Aviation Administration (FAA), he stated that he had been performing touch-and-go takeoffs and landings for about 1 hour. On the departure climb, the airplane reached an altitude of 800 feet. As the pilot initiated the crosswind turn, the engine began to run rough. As the airplane was already at established pattern altitude, the pilot continued the flight and contacted Palomar tower, declaring an emergency. Due to humid conditions the pilot thought the engine might be experiencing carburetor icing and activated the carburetor heat; however, he ascertained that was not the problem after there was no change in engine performance. Tower personnel cleared the flight to land on runway 6 or 24. At this point the flight was downwind for runway 24, and the pilot reported that he was committed to the landing. He observed a road on his flight path, but due to traffic congestion, he did not feel it was the best place to land; he also felt that a turn back to runway 6 was not possible. The pilot stated that the engine rpm was 2,100, and the airplane's altitude was 700 feet. He felt that he had enough power to make the runway, and that he was in control of the airplane. The flight was still on the downwind when the pilot trimmed the airplane for best glide, at which point there was a further drop in rpm to 1,700, with an increase in engine roughness. When he turned the airplane onto final, he believed there was a further drop of rpm. The pilot stated that he knew that he was not going to make the runway. The airplane landed on its nose short of the threshold for runway 24. The engine was inspected by Crownair Aviation, Carlsbad, under the auspice of the FAA. Maintenance personnel reported carbon fouling of the number 2 cylinder bottom spark plug, which they reported could have caused a loss of engine rpm and a rough running engine. There were no other defects noted with the engine inspection.