NTSB Identification: CHI97LA004.
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Accident occurred Sunday, October 06, 1996 in NUNDA, SD
Probable Cause Approval Date: 09/30/1997
Aircraft: Bell 47G-5, registration: N7925J
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.

During the second agricultural load, a total loss of engine power occurred, and the pilot made an autorotative landing, but the helicopter was damaged during the occurrence. Examination of the engine revealed failure of six bolts that attached the accessory drive gear to the crankshaft. Further examination of the attachment bolts revealed that fatigue cracking had occurred. There was evidence that inadequate pre-load torque had been applied to the assembly. The engine had approximately 400 hours since its last overhaul.

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

failure of maintenance personnel to properly torque the six accessory drive bolts, which resulted in fatigue failure of the undertorqued bolts.

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