On April 16, 1996, at 1600 hours Pacific daylight time, a Bell 206B III helicopter, N2750F, landed hard on uneven terrain while practicing touchdown autorotations at Montgomery Field, San Diego, California. The helicopter sustained substantial damage. The certified flight instructor (CFI) and the certificated commercial pilot student were not injured. The helicopter was being operated as an instructional flight under 14 CFR Part 91 when the accident occurred. The local flight originated from Montgomery Field. Visual Instrument meteorological conditions prevailed. The CFI indicated that the commercial pilot was demonstrating an autorotation with a turn from 200 feet above ground level to runway 23. As the commercial pilot completed the turn and was aligning with the runway, the helicopter rotor rpm dropped to 70 percent. According to the CFI, halfway into the maneuver he realized the helicopter was too low and slow to accomplish a power recovery. The flight instructor took control of the helicopter. The helicopter touched down short of the intended point on the runway in rough uneven terrain. Post-flight inspection of the helicopter revealed wrinkles in the tail boom. The commercial pilot under instruction held a rotorcraft helicopter rating. The surface winds at Montgomery Field at the time were reported from 240 degrees at 11 knots.