NTSB Identification: DFW08TA066.
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Accident occurred Friday, February 08, 2008 in Valentine, TX
Probable Cause Approval Date: 09/26/2008
Aircraft: Hughes OH-6, registration: N66372
Injuries: 1 Minor.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this public aircraft accident report.

The commercial pilot/air interdiction agent was engaged in a United States Custom and Border Patrol (CBP) mission in a single-engine turbine equipped helicopter when the engine stopped producing power and the helicopter descended rapidly from a height of 30-50 feet above the ground. The pilot maintained directional control and made a hard landing in a wash-out. The helicopter remained upright, but the skids were completely spread, the tail rotor blades were damaged, and the fuselage sustained structural damage. Further examination of the engine revealed that a castellated nut used to secure the governor lever control rod to the idler bell crank had come completely loose, and the cotter pin that secured the nut was missing. The engine had been replaced 5.1 hours prior to the accident by a contract maintenance facility. The mechanic stated that during the first engine run-up, he discovered an oil leak on the left side of the engine. As a result, the engine was shut down and the linkages on the left side of the engine were disassembled, including the governor level control rod assembly. During the reassembly, he got distracted by a phone call, which delayed him from completing the repair. As a result, when he returned to complete the repair, he got "tunnel vision" and forgot to install the cotter pin during the reassembly process, which would have kept the castellated nut that secured the attachment bolt for the governor level control rod from loosening. According to CBP, their agency was responsible for the oversight of this maintenance and the helicopter was returned to service in accordance with the military technical manuals. However, there were no established inspection procedures to properly accept an aircraft that had just undergone a major repair. In addition, a review of the OH-6A Technical Manuals revealed that only a standard castellated nut and cotter pin was needed to properly install the governor lever control rod, while the more recent Hughes 500 repair manual and an FAA Airworthiness Directive required a castellated nut with fiber inserts to prevent the nut from backing off.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The contract mechanic's failure to properly secure the castellated nut that attached the governor lever control rod to the idler bell crank. Contributing to the accident was the lack of maintenance oversight by the operator.

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