NTSB Identification: LAX00LA245.
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Accident occurred Thursday, June 29, 2000 in LIVE OAK, CA
Probable Cause Approval Date: 07/17/2001
Aircraft: Garlick HH-1K, registration: N896RP
Injuries: 1 Fatal.

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

The restricted category helicopter was operating on an agricultural application flight. The pilot radioed his ground crew words to the effect that he was experiencing a structural failure. Witnesses heard the helicopter make a loud noise and when they looked up it was falling straight down from about 100 feet agl. The tail boom and tail rotor assembly were found together about 300 feet from the fuselage wreckage. The main rotor blades remained attached to the main rotor hub. The tail boom separated from the forward fuselage about 6 feet forward of the horizontal stabilizer in proximity of one of the tail rotor drive shaft couplings. The tail boom skin sections were separated at right angles to the tail boom axis, and exhibited tension tearing on the left side and compression buckling on the right side. The skin separation surfaces exhibited a shiny, uniform, bright gray appearance. The tail boom skin thickness in the area of the separation matched the manufacturer's drawing specifications. The separation surfaces of the anti-torque control tube were collapsed and exhibited a uniform shiny appearance. Circumferential scrape marks and paint transfer on the drive shaft near the coupling resembled marks on the top of the tail boom adjacent to the point of separation. The star spline gear teeth of the coupling were worn at a 45-degree angle, accompanied by circumferential gouging about 1/8-inch deep on the adjoining collar. When compared with other couplings on the drive shaft, the interior cavity of this coupling appeared dry and did not exhibit appreciable lubricant (grease). No wire or other external object impact marks were observed on the tail boom.

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

The inadequate lubrication of the tail rotor drive shaft coupling by unknown maintenance personnel that resulted in the in-flight failure and separation of the helicopter's tail boom.

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