NTSB Identification: IAD04LA013.
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Accident occurred Saturday, February 28, 2004 in Media, PA
Probable Cause Approval Date: 04/28/2005
Aircraft: Schweizer 269C, registration: N75070
Injuries: 1 Uninjured.
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 student pilot was flying the helicopter in cruise flight, at 800 feet, when a loss of tail rotor thrust occurred, with a "sharp metallic-sounding squeal." The student pilot then performed an autorotation which resulted in a hard landing. Examination of the tail rotor drive shaft, forward fitting teeth, revealed smearing and rubbing in the middle of the tooth surfaces. A wear/rubbing failure mechanism had been previously seen on other helicopters, that resulted from insufficient lubrication. Although the forward fitting had a significant amount of grease on it, it could not be confirmed whether grease had always been present. No significant manufacturing defects were found. With over 3,000 helicopters in service, only two similar events had been attributed to insufficient lubrication, and both occurred on same helicopter model within the previous year. Shaft loading, which was "relatively light," only required minimal lubrication to a design that had remained essentially unaltered since the 1960s. The shaft, which required an inspection every 300 hours, had last been inspected 180 hours before the accident.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: A lack of previous lubrication to the tail rotor drive shaft forward fitting teeth, which resulted in their gradual wear, the eventual slippage of the shaft, and the subsequent loss of tailrotor thrust and forced landing. Full narrative available
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