Evergreen Helicopters International Bell BH-212 incident

The airline transport-rated pilot executed a precautionary landing following an uncommanded right yaw and in-flight control anomalies. The operator reported 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 12,900-hour pilot executed a normal approach, touched down at 25 to 30 knots, and controlled the yaw with the collective and throttle. 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.

Verbatim NTSB analysis and probable cause from the NTSB dataset