On December 20, 2003, about 2150 eastern standard time, a Bell 407, N508MT, was substantially damaged while landing in a field near Morehead, Kentucky. The certificated commercial pilot and two crewmembers were not injured. Night visual meteorological conditions prevailed for the flight that departed Saint Clair Hospital, Morehead, Kentucky. A company VFR flight plan was filed for the positioning flight conducted under 14 CFR Part 91. The pilot reported that that he was dispatched to a medical evacuation approximately 8 miles east of the hospital. The helicopter arrived over the landing zone, and the pilot performed a "high recon" to locate obstacles and determine the best way to land. The pilot then completed a "low recon" to confirm obstacles, briefed the crewmembers, and initiated an approach. However, the pilot performed a go-around due to blowing snow. The pilot made another "low recon" and re-briefed the crewmembers before initiating a second approach. During the second approach, the tail rotor struck a standing frost free hydrant. The hydrant was approximately 1 inch in diameter and 3 feet high. The helicopter subsequently spun right and the pilot performed a hovering autorotation to the ground. The pilot further stated that ground personnel had marked the perimeter of the landing zone with lights. However, the ground personnel later stated that they had not walked the interior of the landing zone and were unaware of the obstacle. Examination of the helicopter by a Federal Aviation Administration (FAA) inspector revealed damage to the tail rotor, tail rotor gearbox, and tail boom.