NTSB Identification: SEA98FA104.
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Accident occurred Thursday, June 18, 1998 in COUER D'ALENE, ID
Probable Cause Approval Date: 01/11/2000
Aircraft: Garlick UH-1H, registration: N869W
Injuries: 1 Uninjured.
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.
The pilot stated that he heard a loud metallic bang coming from the rear of the aircraft, followed immediately by a loss of power. He elected not to auto-rotate to a landing at the log-landing because of personnel in the vicinity, so he initiated an approach to a logging road adjacent to the log-landing. He landed with skids level, no power, and very low rotor rpm, but felt that he had the road made. After touching down, the helicopter rocked backward and rolled over on its left side. The engine was still running, and the pilot shut it down with the fuel valve. During the course of engine disassembly and inspection, output reduction gearbox damage was found to be consistent with a number one planet gearshaft separation caused by fatigue initiating at the outside diameter of the gear shaft within the shaft/gear web shoulder fillet radius. Laboratory analysis of the remnants of the number one planet gear noted that a cross section through the apparent fatigue origin did not exhibit evidence of material defects; however the fatigue initiation area was obscured as a result of secondary damage. The outer diameter of the planet gear shaft was found to have been plated with chromium or nickel and the case hardness of the carburized case on the planet gear was below that specified by the manufacturer. Investigation determined that none of the three planet gears in this engine were of OEM manufacture. Plating of the planet gear is not an authorized repair procedure, and no military repair procedure was identified authorizing this type of repair.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: Fatigue failure of a reduction drive planetary gear. Factors include an unapproved part and plating process, and uneven terrain at the emergency landing site. Full narrative available
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