On April 21, 1995, at 1702 central daylight time, a Piper PA-25-235, N9740P, was substantially damaged during a forced landing near San Antonio, Texas. The airline transport rated pilot received minor injuries. The aircraft was being operated by Petra Aviation, under Title 14 CFR Part 91. The flight originated from Geronimo Field near Seguin, Texas, at 1530 CDT. Visual meteorological conditions prevailed for the banner towing flight and a flight plan was not filed. During a personal interview with local police and the investigator-in-charge, the pilot reported that he performed an airborne pick up of the banner at the Bill Dean Ranch private grass airstrip near the north end of Randolph Air Force Base. After completing his banner towing flight, he was en route back to the ranch to drop the banner off when he "ran out of fuel." He released the banner and initiated a forced landing, subsequently landing "flat" and structurally damaging both wing spars. The pilot stated on his enclosed Pilot/Operator report that he "developed a leak in fuel line." In a telephone interview with the NTSB investigator-in-charge he stated that "a fuel leak was found near the carburetor at a connecting joint."