NTSB Identification: IAD05LA046.
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Accident occurred Saturday, March 19, 2005 in Leet, WV
Probable Cause Approval Date: 08/29/2006
Aircraft: Schweizer 269C, registration: N61193
Injuries: 1 Serious,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.
While investigating a fire, the pilot noticed an "unusual vibration," and a "needle split" on the rpm gauge. The rotor speed began to decay and the engine speed began to increase. The pilot then entered an autorotation. The helicopter, impacted terrain, was substantially damaged, and a passenger was seriously injured. Examination of the drive train revealed that the main drive pinion, which drove both the main rotor assembly and the tail rotor drive shaft, had failed in fatigue that had initiated in the root of the first (most forward) engaged pinion thread. The failed pinion had been in service for 4,055.4 hours. Including the accident pinion, 10 instances of pinion failures were identified during the investigation. Times in service ranged from 261.5 to 4,243 hours. According to the manufacturer, life limits for the pinion ranged from 6,000 to 8,000 hours depending on application. As a result of this investigation, The FAA issued an SAIB alerting owners and operators of pending revisions to the inspection procedures for the pinion. The manufacturer revised its Handbook of Maintenance Instructions, to include the revised inspection procedures, and submitted design revisions to the FAA to make the part more robust.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: A fatigue fracture of the main transmission drive pinion. Also causal was the manufacturer's failure to remove the affected pinions from service during the period that transpired between the initial failures and the accident flight. Full narrative available
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