On October 6, 1996, a Bell 47G-5 (registration N7925J) was involved in an aviation accident near Nunda, SD. No fatalities were reported. Investigators recorded the probable cause as: Failure of six bolts attaching the accessory drive gear to the crankshaft due to fatigue cracking resulting from inadequate pre-load torque. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced total engine power loss during an agricultural operation. The pilot performed an autorotative landing, resulting in damage. Investigation revealed failure of six attachment bolts due to fatigue from inadequate pre-load torque.
Event Description
During the second agricultural load of an operation, the helicopter experienced a total loss of engine power. The pilot executed an autorotative landing, but the helicopter sustained damage during the occurrence.
Engine Examination
A subsequent examination of the engine revealed that six bolts attaching the accessory drive gear to the crankshaft had failed. Further analysis of the attachment bolts showed evidence of fatigue cracking. Investigators also found indications that inadequate pre-load torque had been applied to the assembly. The engine had accumulated approximately 400 hours of operation since its last overhaul.
Probable cause
Failure of six bolts attaching the accessory drive gear to the crankshaft due to fatigue cracking resulting from inadequate pre-load torque.
What happened in the 6 Oct 1996 Bell 47G-5 accident near Nunda, SD?
A helicopter experienced total engine power loss during an agricultural operation. The pilot performed an autorotative landing, resulting in damage. Investigation revealed failure of six attachment bolts due to fatigue from inadequate pre-load torque.
Were there any fatalities in the 6 Oct 1996 Bell 47G-5 accident?
No fatalities were recorded in this accident.
What aircraft was involved and where did it happen?
The accident on 6 Oct 1996 involved a Bell 47G-5, registration N7925J, at Nunda, SD.
What was the probable cause of the accident?
Failure of six bolts attaching the accessory drive gear to the crankshaft due to fatigue cracking resulting from inadequate pre-load torque.
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