At about 14:50 PST, a Cessna 172RG suffered a catastrophic engine failure and nosed over during the subsequent off-airport landing. The aircraft departed San Diego at about 13:15 enroute to Camarillo on a cross-country training flight. No one was injured. The instructor said they were cruising at 4,000 feet when he heard a loud bang from the engine compartment and saw flames by the rudder pedals. He turned the fuel off and began a rapid descent. He said the fire went out and he set up to land in a plowed field. After touchdown, he held the nose up as long as possible. When the nose wheel dropped into the soft dirt, it dug in and the aircraft nosed over. An inspector observed that a cylinder had separated from the engine and was missing, along with a section of cowling.