On January 28, 2004, at 0930 central standard time, a Bell 206-L4 helicopter, N207RT, registered to and operated by Rotorcraft Leasing Company, L.L.C., of Broussard, Louisiana, was substantially damaged during a forced landing following a loss of directional control while in cruise flight in the vicinity of Patterson, Louisiana. The airline transport pilot and five passengers were not injured. Visual meteorological conditions prevailed, and a company flight plan was filed for the 14 Code of Federal Regulations Part 135 on-demand air taxi flight. The flight originated from an offshore platform, South Pelto Block 10, located in the Gulf of Mexico, and was destined for the Harry P. Williams Memorial Airport (PTN), near Patterson, Louisiana. The 10,300-hour pilot reported in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2), that he had just made the five mile inbound call for landing at PTN, and the aircraft was in cruise flight at an altitude of 500 feet and 110 knots, when he heard a "loud" bang followed by "severe" and constant vibration. He stated that the pedal inputs "seemed" to have no effect in correcting the yawing of the aircraft. It was apparent to the pilot that continued flight would be impossible, and he elected to perform a forced landing. The pilot began a 180-degree autorotation to the left. While in the turn, the pilot made a "mayday" call, and reduced the throttle, which had no effect. Once the pilot closed the throttle, the "pounding and vibration" lessened. After the aircraft rolled out, and was level at 100 to 150 feet, the pilot realized they were going to hit the levee of the pond. He pulled a little collective to clear the levee, performed a cyclic turn to the right, and cushioned the landing. The landing area was a clear level strip beside the pond. When the helicopter landed, the main rotor blade contacted the tailboom. Once the blade stopped turning, the passengers egressed from the helicopter. Examination of the wreckage by the operator and a FAA inspector, who responded to the accident site, revealed structural damage to the tailboom. Strike marks on the tailboom, corresponding to the main rotor blade top path plane, were found adjacent to the #7 tail rotor drive shaft segment. Additionally, the left horizontal stabilizer winglet device was not found. Further examination revealed a ten-inch crack in the fixture securing the left winglet to the horizontal stabilizer. The right winglet, which was found, also had a pre-existing crack in the same area. The cracks were not visible during a visual inspection, and the crack area is under a line of structural adhesive used during manufacture of the horizontal stabilizer, and can only be seen when the winglet is removed. According to the operator, the 10-inch crack that was discovered on the left winglet appeared to have existed for some time. The operator stated that the winglet could have separated from helicopter in-flight, and struck the tail rotor, resulting in the "loud bang" that was heard by the pilot, and subsequent loss of directional control. Other than the winglet, examination of the helicopter, and its drive and flight control components did not reveal any pre-existing anomalies that could have contributed to the accident.