On January 12, 2003, about 1220 eastern standard time, a Sikorsky S-61A, N8170V, was substantially damaged when it impacted terrain during a forced landing near Glady, West Virginia. Both certificated commercial pilots sustained serious injuries. Visual meteorological conditions prevailed for the commercial logging flight, and a company flight plan was filed for the flight conducted under 14 CFR Part 133. According to the crew, after the helicopter came out of maintenance, the captain and first officer conducted a test flight, and then ferried the helicopter to the area of operation. On the day of the accident, the first officer flew flights one and three, and the captain flew flights two and four. Each flight lasted about 1 hour 20 minutes, the helicopter was hot refueled between flights, and the flying pilot would occupy the left seat. During the previous flights, no flight control anomalies were identified, and on the accident flight, the captain was in the left seat and flying the helicopter. After completing approximately the seventh load of the flight, the captain maneuvered the helicopter over the ground tenders, and entered a 155-foot out of ground effect hover. The tenders connected the chokers to the cargo hook, and called "clear." About the same time, the helicopter started a slow uncommanded yaw to the right. The captain applied full left pedal, released the load, and the ground tenders called "kick out." With full left pedal applied, the helicopter continued to yaw right. During the first revolutions, the captain identified a small clear area to the north. The area was approximately level with the helicopter, and approximately 150 feet away on a ridgeline. The captain tried to maneuver the helicopter to the clear area, but by the fourth revolutions, the yaw rate had increased drastically, and helicopter controllability became a major issue. The first officer placed his left hand on the throttles, and the captained called for engines to idle. The captain entered an autorotation, and applied full collective before entering the trees. The helicopter impacted the ground, came to rest up right, and both pilots exited with the assistance of one of the ground tenders. The crew estimated they had conducted 75 loads on the day of the accident. In addition, the first officer estimated the winds were approximately 270 degrees at 10 knots. Examination of the tailrotor flight control system revealed that the left tailrotor control cable was broken. The break was in the aft part of the cabin and associated with a pulley assembly. Examination of the cable break revealed that some of the cable strands were bent rearward, and deformed. Examination of the cable fracture surfaces under a stereomicroscope revealed that some of the fractures were irregular and deformed. Examination of the associated keeper pins under a stereomicroscope revealed that both pins displayed wear marks, and light scratches consistent with control cable contact. The associated pulley was intact. The pulley channel contained an oil-based debris, and control cable fragments. Examination of the maintenance records revealed the helicopter had undergone extensive repairs before being returned to service on January 11, 2003. While in maintenance, both tailrotor cables were removed and then reinstalled on January 9, 2003. At the time of the accident, the helicopter had flown 5.3 hours since returning to service, and total flight time was 14,603 hours.