On December 3, 2003, approximately 0825 central standard time, a Bell BH-212 helicopter, N5017H, registered to Evergreen Equity, Inc., of McMinnville, Oregon, and operated by Evergreen Helicopters International, Inc., of Galveston, Texas, was in cruise flight when it experienced an uncommanded right yaw and in-flight control anomalies. The pilot executed a precautionary landing at South Lafourche Airport (L49), near Galliano, Louisiana. The airline transport-rated pilot, co-pilot, and nine passengers were not injured. Visual meteorological conditions prevailed and a company visual flight rules (VFR) flight plan was filed for the 14 Code of Federal Regulations Part 135 domestic, non-scheduled, on-demand air taxi flight. The flight originated from Ship Shoal 358 (SS358) offshore platform, Gulf of Mexico, at 0750, and was destined for Evergreen Fourchon Heliport (OLS2), near Golden Meadow, Louisiana. The operator stated in the Pilot/Operator Aircraft Accident Report (NTSB form 6120.1/2), that approximately 35 minutes into flight, the aircraft suddenly yawed "violently" to the right with slight nose tuck. The tail rotor pedals were simultaneously driven to near full right position. The co-pilot immediately reduced collective and IAS, corrected with left pedal while canceling the Flight Director. The aircraft oscillated twice at medium intensity and relatively small magnitude. Control of the aircraft was then passed to the pilot-in-command who reestablished straight and level flight at reduced power, with full right pedal required. Cruise power at this time was approximately 60 percent. The crew reviewed the prescribed emergency procedures and notified company dispatch. In-flight troubleshooting revealed no remedial effect from securing one or both Helipilot SAS systems. Hydraulic systems not cycled, but pressure was noted as "normal" on both systems. Hydraulic boost to pedals appeared "normal." Slight left pedal input confirmed tail rotor control input. Controlled slow flight ability was confirmed down to 40 knots with resultant increasing right yaw. The pilot consulted with Base Maintenance and determined to proceed to the nearest airport for run-on landing. The co-pilot briefed the passengers on the situation and safety procedures. The 12,900-hour pilot-in-command executed a normal approach to L49, touched down on Runway 36 at 25 to 30 knots, and controlled the yaw with the collective and throttle. The shutdown and evacuation were uneventful and the helicopter was not damaged. Examination of the aircraft by the operator revealed that the upper/left bolt that secures the tail rotor pitch control bellcrank support was bent and loose in the nutplate. The lower/left bolt had sheared just below the bolt head, and the lower/right bolt was sheared in the threaded area in the nutplate. Control movement was checked with no binding, lost motion or unusual noises. No additional anomalies were noted in the tail rotor control system.