Accident Hughes OH-6 N66372, 08 Feb 2008
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ASN Wikibase Occurrence # 286309
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Time:11:15 LT
Type:Silhouette image of generic H500 model; specific model in this crash may look slightly different    
Hughes OH-6
Owner/operator:Customs And Border Protection
Registration: N66372
MSN: 67-16595
Fatalities:Fatalities: 0 / Occupants: 1
Aircraft damage: Substantial
Location:Valentine, Texas -   United States of America
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Departure airport:Marfa Municipal Airport, TX (KMRF)
Destination airport:
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
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.

Probable Cause: 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.



Accident investigation:
Investigating agency: NTSB
Status: Investigation completed
Duration: 7 months
Download report: Final report

Revision history:

03-Oct-2022 08:49 ASN Update Bot Added

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