On April 30, 1994, at 1415 eastern daylight time, a Piper PA-18-150, N6879B, collided with trees during a simulated forced landing near Bainbridge Airport in Bainbridge, Georgia. The training flight operated under 14 CFR Part 91, with no flight plan filed. Visual weather conditions prevailed at the time of the accident. The airplane sustained substantial structural damage, and the student pilot was not injured. The flight departed Bainbridge, Georgia, at 1345 hours. According to the student pilot, while on final approach to the practice landing area, the rear seat back fell forward and jammed the flight controls. Efforts by the student pilot to free the rear control failed, and the student elected to continue the approach and landing. During rollout, the airplane collided with a small stand of trees. Examination of the airplane failed to disclose a mechanical problem. According to the operator, he has operated the PA-18 type airplane for eleven years and this is the first occurrence of a seat back jamming the flight controls. He further stated that the airplane was not certificated with a seat back locking device. Subsequently the operator has modified his fleet of PA-18 airplanes with seat back locking devices. The operator reported that the pilot completed and mailed a pilot/operator aircraft accident report, NTSB Form 6120.1/2; the form never arrived.