On May 16, 1998, about 1418 eastern daylight time, a Cessna 172P, registered to American Flyers Schools, Inc., nosed over during a landing in a field near Fort Myers, Florida. Visual meteorological conditions prevailed at the time and a VFR flight plan was filed for the 14 CFR Part 91 instructional flight. The airplane was substantially damaged and the private-rated pilot, the sole occupant, was not injured. The flight originated about 1318, from the Pompano Beach Airpark, Pompano Beach, Florida. The pilot stated that while in contact with Fort Myers Approach Control, the aircraft's radios began to malfunction. She advised the controller of this and was provided a vector to the La Belle Municipal Airport. She recognized that she had flown past the airport and elected to land in a field adjacent to an airstrip. After touchdown during the landing roll, she applied the brakes and the airplane nosed over. Examination of the airplane by an FAA airworthiness inspector revealed a loose electrical connection at the avionics master switch. According to the pilot, another pilot had noted that the avionics master switch would not activate the radios. According to flight school personnel, the avionics switch was turned on and the problem was not duplicated. No further test or examination was accomplished.