NTSB Identification: LAX01FA306.
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Nonscheduled 14 CFR
Accident occurred Saturday, September 29, 2001 in Hilo, HI
Probable Cause Approval Date: 06/02/2004
Aircraft: Bell 206B, registration: N206KS
Injuries: 2 Minor,3 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 made a mayday call, shut off the fuel valve, and performed an autorotation into high grass after the single engine helicopter experienced a loss of engine power shortly after takeoff. The pilot had heard a bang followed by illumination of the engine out warning light, and the engine began smoking. During the terminal phase of the autorotation, the pilot assumed the grass height was 3 feet and flared accordingly; however, the grass was at least 6 feet tall. Post-accident examination of the engine revealed that the No. 1 turbine wheel was missing. The No. 8 bearing thrust nut exhibited a locking indentation and a notch on its inside surface. Additionally, indentations were on the threads of the threaded end of the first stage turbine wheel shaft. These marks suggest that the thrust nut was not fully engaged on the first stage turbine shaft. The location of the notch suggests that the edge of the nut protruded beyond the end of the turbine shaft. There were no indications of contact by the shaft threads on the inner surface of the deformed area to suggest that it had been displaced into a groove on the first stage turbine shaft. Review of the maintenance records and interviews with the mechanic, who performed the most recent maintenance work, revealed that the turbine section had been replaced approximately 30 hours prior to the accident. Due to excessive oil consumption, maintenance personnel removed the turbine and replaced the No. 5 carbon seal approximately 14 hours prior to the accident. The maintenance records indicated that the day before the accident, the sump cover had been removed for trouble shooting oil consumption. Though it is not detailed in the maintenance entry, it is interpreted that the "sump cover" referred to is the No. 8 Bearing sump nut since the thrust nut was loose.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The failure of the mechanic to secure the No. 8 bearing thrust nut during maintenance work, which resulted in the total failure of the first stage turbine wheel shaft. Also causal was his misjudgment of his height during the flare resulting in a hard landing. A contributing factor was the high vegetation in the forced landing field, which resulted in a hard landing. Full narrative available
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