NTSB Identification: CEN10LA431
14 CFR Part 137: Agricultural
Accident occurred Saturday, July 24, 2010 in Rochester, MN
Probable Cause Approval Date: 03/07/2014
Aircraft: BELL 47G-4A, registration: N124SH
Injuries: 1 Fatal.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

A witness reported that the agricultural helicopter was refueled and that the hopper was loaded with chemical before departure. He reported that he saw the helicopter depart, that the engine sounded normal, and that the helicopter’s departure and flightpath appeared normal. He then saw a "brown puff of smoke" come from the helicopter, and it subsequently descended and impacted a hill. A postaccident engine examination revealed that the compressor rotor assembly had failed. The metallurgical examination of the compressor rotor assembly revealed that a single first-stage compressor blade had fractured in high-cycle fatigue. The microstructure, hardness, and chemistry of the first-stage compressor wheel conformed to the requirements of the engineering drawing. No evidence of corrosion was found near the fracture origin. The engine was installed on the helicopter during the last annual maintenance inspection conducted 3 days before the accident. Evidence indicated that the engine was installed properly. The reason for the fracture could not be determined.

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

The total loss of engine power due to a high-cycle fatigue fracture of a first-stage compressor blade. The reason for the fracture could not be determined during postaccident examination.

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