Accident Hughes OH-6A N6188L, 25 Oct 2004
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ASN Wikibase Occurrence # 134807
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Type:Silhouette image of generic H500 model; specific model in this crash may look slightly different    
Hughes OH-6A
Owner/operator:Tucson Sector Air Operations
Registration: N6188L
MSN: 891257
Fatalities:Fatalities: 0 / Occupants: 2
Other fatalities:0
Aircraft damage: Written off (damaged beyond repair)
Location:Tucson, AZ -   United States of America
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Departure airport:Ajo, AZ
Destination airport:Tucson, AZ (TUS)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
The engine spooled down during a law enforcement surveillance flight, and the pilot made a hard forced landing in uneven terrain. The crew was performing surveillance at low altitude above an uneven wash, and the pilot was in slow sideward flight. He pulled the collective to gain altitude and airspeed to make another pass. Then he heard and felt the engine spool down. He said that it quit producing power completely, and he attempted to autorotate to the ground. He said that he had insufficient airspeed and altitude to complete a successful autorotation. The helicopter hit the ground hard in a near level attitude. It bounced backwards, and rotated 45 degrees to the right. Metallurgical examination revealed that the governor tee to fuel control PC line fractured as a result of fatigue. The tubes were bent with contours differing from the original manufactured shape, indicative of handling/assembly damage. Disassembly and inspection of the starter/generator revealed conditions indicative of wear and misassembly, including the wrong bearings being installed, which would cause the unit to operate in an out-of-balance condition and induce vibrations.
Probable Cause: The loss of engine power due to a fatigue fracture of the PC line from the governor to fuel control, resulting from fretting damage induced by excessive vibration, which was due to the failure of maintenance personnel to install the proper bearings in the starter/generator. A contributing factor was the loss of power at low altitude and airspeed (height/velocity limitation) which diminished the possibility of a successful autorotation.




Revision history:

21-Dec-2016 19:26 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
07-Dec-2017 18:29 ASN Update Bot Updated [Other fatalities, Nature, Departure airport, Destination airport, Source, Narrative]

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