NTSB Identification: CHI07IA042.
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Nonscheduled 14 CFR
Incident occurred Monday, December 11, 2006 in Raytown, MO
Probable Cause Approval Date: 03/31/2008
Aircraft: Bell 407, registration: N302LE
Injuries: 4 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
The air ambulance helicopter executed an emergency landing on an elementary school parking lot following a loss of engine power. Night visual meteorological conditions prevailed at the time of the incident. The pilot stated that he heard a bang and got a low frequency vibration during cruise flight. The helicopter received minor damage due to internal engine components exiting the engine collector and exhaust stack. Examination of the third stage turbine wheel noted high cycle fatigue features on the fracture surface of one of the blades. The fatigue initiated at the trailing edge of the airfoil and propagated 0.515 inch before a fast fracture separation. Although a small area of porosity was observed in the microstructure adjacent to the fracture, it did not intersect the fracture surface, and no evidence of porosity was observed on the fracture surface. Chemistry and hardness were as specified. Given the high cycle features, good material properties, and lack of a stress-concentrating defect at the origin, the fatigue could be secondary to some other event that produced unusual loading or vibrations in the blade.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The loss of engine power during cruise flight due to third stage turbine wheel blade fatigue and subsequent separation, which resulted in an emergency landing. Full narrative available
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