On August 31, 1996, at 1428 hours Pacific daylight time, a Cessna 305A, N5277G, experienced a total loss of engine power while towing a banner about 3 miles northwest San Diego, California. The pilot made a forced landing on a hillside's rough terrain. The airplane was substantially damaged, and the airline transport pilot received minor injuries. Visual meteorological conditions prevailed at the time, and no flight plan was filed. The flight originated from San Diego at 1108. According to the pilot, he had operated the airplane's 225 HP engine for about 3:08 hours since beginning the first of two flights. The first flight lasted about 1 hour. No fuel was added after the first flight. The pilot reported anticipating that the engine would burn approximately 10 or 10.5 gallons per hour, and the fuel tanks held about 37.8 gallons of usable fuel. When the engine first sputtered, the left (main) fuel tank indicator was still indicating that the fuel level was in the takeoff range. The pilot further stated that he switched to the right (auxiliary) tank, the engine instantly regained full power, and then after a few seconds all power was again lost. Other than the erroneous indication presented by the fuel gauge, the pilot did not report experiencing any malfunction in the airplane. The pilot stated that, in general, the airplane's fuel gauges were neither accurate nor reliable. The owner of Southern Cal Aircraft, a repair station located in El Cajon, California, verbally reported that during the postaccident examination of the airplane no evidence was found of any rupture to the airplane's fuel tanks, and no fuel was found in them. The fuel tank caps were found secured to the airplane. No fuel was found in the main fuel line to the carburetor. The carburetor's finger screen was removed, and it was found clean. The airplane's owner verbally reported that his airplane generally burned fuel at a rate of between 10 and 10.5 gallons per hour. The owner stated that in his opinion, no mechanical malfunctions occurred during the accident flight. The pilot reported that his total flying experience in the accident airplane was about 1,212 hours. His total piloting time was about 19,157 hours. Most of his flight time was accrued flying turbojets.