Pilot Debrief

BELL 47G-4A near Rochester, MN — 2010-07-24

Final reportCEN10LA431
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Date
2010-07-24
Location
Rochester, MN, USA
Aircraft
BELL 47G-4A
Registration
N124SH
Category
Helicopter
Highest injury
Fatal
Fatalities
1
Phase of flight
Climb

Probable cause

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.

NTSB narrative

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.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have aborted the flight after engine issues were detected.

NTSB coding

Evidence available

  • ADS-B / radar
  • Photos
  • 44 docket documents
View NTSB final reportView NTSB docket

Docket documents44

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