On August 10, 2014, about 1020 Pacific daylight time, a Ryan Navion, N4533K, experienced a partial loss of engine power during approach to land at Sierra Skypark Airport (E79) in Fresno, California. The pilot and two passengers were uninjured and the airplane sustained substantial damage to the left wing. The airplane was registered to, and operated by, the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, and no flight plan was filed. The flight originated from Madera Municipal Airport (MAE), Madera, California at about 0950. The pilot reported that the accident flight was the second flight of the day; the airplane was operating as usual and showed no indications of a potential malfunction. When approaching the destination airport to land, the pilot entered the traffic pattern for the runway. While on short final, the pilot increased power to maintain the glideslope when he heard a "muffled bang or chug" followed by the engine sounding "as if it was drowning." The airplane started to descend, and the pilot executed an off airport landing. During the landing sequence, the left wing impacted a fence, before the airplane traversed across a median, and came to rest against a second fence. A postaccident examination by a Federal Aviation Administration Inspector revealed that the fuel system was intact and evidence of fuel was noted throughout. The spark plugs were removed and no damage was noted. The engine was rotated by hand and compression was evident on all six cylinders, the magneto impulse coupling also fired. The oil filter was removed and found to be clear of debris. The propeller blade tips were curled forward. At the conclusion of the engine examination no preimpact mechanical malfunctions or failures were revealed that would have precluded normal operation.