On November 25, 1997, approximately 1030 Pacific standard time, a Bell TH-1L rotorcraft, N8160G, registered to Kenneth G. Guthrie, d/b/a Blue Bird Helicopters, and being flown by a commercial pilot, was substantially damaged during an emergency landing in a field following a loss of control while in cruise approximately five nautical miles south of Canby, Oregon. The pilot and six passengers sustained minor injuries. Visual meteorological conditions existed and no flight plan had been filed. The flight, which had been engaged in external long-line operations (slinging Christmas trees), was repositioning with the six member ground crew team. The flight was to have been operated under 14CFR133, and originated from a site near Molalla, Oregon, approximately 1025. The pilot reported that he was repositioning the helicopter to another work site with the 30 foot long-line trailing from the aircraft, and that "the hook (was) trailing smoothly beneath the aircraft as observed by myself in the chin mirror" and that "the hook suddenly became unstable and could no longer be seen in the chin mirror." Shortly thereafter the pilot heard a loud "bang" and felt the aircraft "lurch." The pilot, having been operating the helicopter at 80 knots and approximately 500 feet above ground at the time of the event, attempted to execute a run-on landing to a nearby field. He reported that "as I attempted to roll out on final I realized that I had allowed my airspeed to bleed off beyond the point where I could maintain any directional control with cyclic." The aircraft then began to yaw right, and after approximately 720 degrees of revolution impacted the ground in a near level attitude with a near vertical flight path. An FAA inspector responding to the accident site reported finding fragments of aluminum rotor blade imbedded in the hook at the end of the long-line.