At about 0730 Eastern time, the airplane experienced a stuck throttle control and was substantially damaged during a subsequent forced landing. Visual conditions prevailed. The certified flight instructor (CFI) and observer were not injured; the student pilot sustained a minor injury. The operator later reported the throttle was reduced to begin a descent, but could not be advanced by either the student or CFI when the flight was close to the target altitude. An emergency was declared with ATC, the airplane was trimmed to maintain best glide airspeed, and the flight proceeded to the nearest airport. While descending near the airport, the airplane clipped tree tops, then impacted soft ground and nosed over. The occupants broke a rear cabin window using the emergency egress hammer and exited the inverted airplane. Preliminary examination of the engine compartment revealed an electrical cable from the No. 2 (standby) alternator had chafed, and arched against the throttle control cable housing and throttle cable.
