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The helicopter sustained a loss of tail rotor control while carrying out a power line inspection. It made approximately 12 to 15 full rotations before landing in a paddock. The pilot and two observers on board received minor injuries. The helicopter sustained minor damage.

Examination of the tail rotor revealed that the loss of control was due to failure of the inner tab of a tang washer. The washer locked the retaining nut holding the drive fork and the tail rotor assemblies onto the transmission output shaft. The failure of the inner tab resulted in looseness of the retaining nut and the split ring becoming dislodged. Consequently, the drive fork and the tail rotor assemblies were allowed to move freely along the transmission output shaft.

The ATSB was advised that at the helicopter rebuild a new tang washer was fitted. To inspect the washer, the retaining nut would have to be removed.

The operator sent the failed tang washer to the helicopter manufacturer to determine nature of the locking tab failure. The report had not been received at the time of writing this report.

A search of the ATSB database, for the 1995 to 2005 period, revealed no records of similar tail rotor control problems. The Civil Aviation Safety Authority Service Difficulty Report database, for the same period, contained only the record of the tail rotor control problem from this occurrence.

The manufacturer advised that they have received two worldwide reports of a broken locking tab since 1988.

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