NTSB Factual Report

On June 29, 2000, at 0935 hours Pacific daylight time, a Garlick HH-1K helicopter, N896RP, was destroyed by impact with the ground following the separation of the tail boom and an uncontrolled descent at Live Oak, California. The certificated commercial pilot was fatally injured. The agricultural application flight was operated by Rick Patterson, Inc., under 14 CFR Part 137, and departed from Yuba City about 0900. Visual meteorological conditions prevailed and no flight plan was filed.

An inspector from the Federal Aviation Administration (FAA) Sacramento Flight Standards District Office reported that the helicopter was being operated in restricted category, and the pilot radioed his ground crew words to the effect that he was experiencing a structural failure. Witnesses near the accident location 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 southwest of the fuselage wreckage.

The wreckage was examined by an FAA inspector with technical assistance provided by Bell Helicopters. There were no wire or other external object impact marks observed on the wreckage.

The main rotor blades remained attached to the main rotor hub. The white blade was intact, and the red blade was broken about 3-feet outboard of the root doubler but remained attached. The hub and mast remained attached to the transmission, which was with the forward fuselage wreckage. Fracture surfaces in the blade pitch control linkages exhibited a shiny, uniform appearance.

The tail boom separated from the forward fuselage about 6 feet forward of the horizontal stabilizer in proximity of the second tail rotor drive shaft coupling aft of the main rotor transmission. 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 skin thickness on the left side was 0.025 and on the right side was 0.050. According to the Bell Helicopter representative, this was the correct skin thickness specified in production drawings. 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). The tail rotor gearboxes turned freely when rotated by hand and the overrunning clutch engaged when turned clockwise and released when turned counterclockwise.

An autopsy was conducted on the pilot by the Sutter County Coroner's Office, with specimens retained for toxicological testing. No alcohol or drug substances were detected.

NTSB Probable Cause

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.