NTSB Identification: DFW05FA032.
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Accident occurred Thursday, December 09, 2004 in Zachary, LA
Probable Cause Approval Date: 10/27/2005
Aircraft: Hughes 369D, registration: N7148Z
Injuries: 1 Serious.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

While performing aerial side-trimming of trees and bushes for a pipeline right-of -way using an external saw at an altitude of about 200 feet, the 14,000-hour pilot experienced a left yaw and what he perceived to be an engine failure. The pilot released the external load as he attempted an autorotation from an out-of-ground effect hover at 200 feet agl. Crushing damage to the airframe was consistent with a ground impact at a high rate of descent. A detailed examinations of the engine confirmed the reported loss of engine power. The engine examination revealed the Rolls-Royce manufactured compressor adapter coupling, which had been installed approximately 414 hours earlier, had disconnected the compressor assembly from the turbine assembly as a result of fatigue cracking initiated by fretting on the pilot diameter.

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

The loss of engine power as a result of fatigue cracking of the compressor adaptor coupling initiated by fretting on the pilot diameter and subsequent disconnection of the compressor from the turbine assembly. A contributing factor was the low operating altitude of the helicopter, which made a successful autorotation by the pilot imposible.

Full narrative available

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