On April 29, 2000, at 1810 central daylight time, a Bell 206L3 helicopter, N17237, sustained substantial damage during an emergency landing in the Gulf of Mexico near the Salt Marsh Island 61C offshore platform. The commercial pilot and his passenger were not injured. The helicopter was owned and operated by Chevron USA Inc., of New Orleans, Louisiana, under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and a company VFR flight plan was filed for the local business flight. The helicopter departed the Salt Marsh Island 78B offshore platform at 1735. The 15,672-hour pilot reported that the helicopter lost tail rotor response when turning final to 61C. The pilot reported the problem to the operator and was informed that a rescue boat was dispatched to their area for assistance. After circling in the area for about 25 minutes, the pilot elected to make an autorotative emergency landing to the water. According to witnesses, the helicopter began the autorotation and proceeded to rotate to the left and "pitch nose down." The helicopter entered a steep descent, and the pilot reported that he could not control the helicopter. At approximately 100 feet above the ocean, the helicopter assumed level flight, the emergency floats deployed, and the helicopter subsequently impacted the water. Upon impact, the right float "broke," and the helicopter rolled to the right, coming to rest inverted in the water. According to the FAA inspector, a main rotor blade severed the tailboom. Both main rotor blades were shattered, and the fuselage sustained minor damage. According to the operator's maintenance superintendent, the loss of tail rotor control was a result of "a bolt falling out of a control rod in the tail rotor control system." The bolt (part number 20-057-4-22D) connected the control rod assembly to the control lever located at the rear of the tail rotor gearbox. The cotter key and castellated nut were not recovered. The bolt was recovered and showed no signs of distress. The helicopter underwent an approved aircraft inspection between March 21st and April 1st, 2000, 63 hours prior to the accident. During the inspection, the bolt was removed to facilitate the removal of another control tube for repair. During the re-assembly process, the cotter key was either not properly installed or was accidentally omitted. The discrepancy was not noticed by the mechanic, who was working the inspection, or the supervisor, who was inspecting the mechanic's work.