On May 15, 2008, about 1510 Pacific daylight time, an Ercoupe 415-C, N99180, sustained substantial damage during a forced landing following a loss of engine power in Penngrove, California. The sport pilot and his passenger were not injured. The airplane was being operated by the pilot under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The local personal flight departed from the Petaluma Municipal Airport, Petaluma, California, about 1450. According to Sonoma County Sheriff's Department personnel, the pilot reported that while in cruise flight he noticed the oil pressure gauge begin to fluctuate erratically. The needle on the gauge "began to bounce up and down," and seconds later, the engine "began to cut out and sputter." The pilot headed back towards Petaluma Airport. However, the engine lost total power, and the pilot executed a forced landing in an alfalfa field about 4.5 miles northwest of the airport. During the landing roll in the 2- to 3-foot-tall grass, the airplane skidded sideways and the tail dug into the ground. The airplane's tail cone was buckled, and the right vertical stabilizer and rudder were bent. The airplane was examined by Federal Aviation Administration (FAA) inspectors. The inspectors found that both magnetos had frayed primary wires ("P" leads) at the magnetos, which could have been shorting out and intermittently killing the ignition system. They noted numerous additional maintenance discrepancies with the airplane; however, none of these would have contributed to a loss of engine power. According to the inspectors, the airplane's most recent annual inspection was completed on March 19, 2008.