The helicopter was transporting supplies with a cargo net from one mountain site to another. The sling loads consisted of steel angle iron, which was bagged and secured with velcro, and then placed into the cargo net. After delivering the fourth load, the pilot lifted off with only an empty bag inside the net. The Bell 206B rotorcraft flight manual, in the supplement for external loading, states, "Control movements should be made smoothly and kept to a minimum to prevent oscillation of sling load." According to a witness, as the helicopter departed, the net "floated very close to the propeller [tail rotor], then floated back down." The net, which was attached directly to the helicopter cargo hook without the use of a long line, swung back up again and impacted the tail rotor, cutting the cargo net and releasing the bag. The pilot heard noise and "thumping" sounds, accompanied by vibrations and yawing, and realized that he had a tail rotor strike. The pilot entered an autorotation at "25 miles per hour and 200 feet" above a timbered slope. The pilot selected a small, sloped, clearing as a landing zone, and upon touchdown, the helicopter rolled over, coming to rest on it's right side.