On May 24, 2007, about 1950 Pacific daylight time, the tail rotor of a Westland Helicopters Wasp HAS MK1, N612VH, struck a tree during a precautionary landing in a dirt field near Ramona, California. Classic Rotors Museum was operating the helicopter under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The private pilot was not injured, and three passengers sustained minor injuries. The helicopter sustained substantial damage. The local personal flight departed Ramona Airport (RMN) about 1830. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot reported that during the flight he felt a severe vibration, and thought there might have been a hydraulic failure. He descended to a lower altitude and was attempting to land in a clearing. During the final portion of the landing, the controls were becoming harder to operate when the tail rotor struck the top of a tree. During the crash sequence, the tail rotor gearbox and tailboom departed the helicopter. After the helicopter was recovered, the National Transportation Safety Board investigator-in-charge (IIC) interviewed the pilot/mechanic for Classic Rotors Museum. He stated that although the damage to the rotor head and associated components were substantially destroyed during the accident sequence, he believes that one of the snubber dampners failed during the flight. He contacted maintenance personnel who were familiar with the accident make and model of helicopter, and they explained that if the snubber dampners failed it would result in the cyclic stirring. The pilot had experienced this prior to impacting the trees.