CHI07IA042

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.

On December 11, 2006, at 2217 central standard time, a Bell 407, N302LE, operated by CJ Systems Aviation Group (dba Life Flight Eagle), as an air ambulance helicopter, executed an emergency landing on an elementary school parking lot near Raytown, Missouri. 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. The air ambulance flight was operating under Title 14 CFR Part 135. The pilot, two paramedics, and patient were uninjured. The flight last departed from Golden Valley Hospital, Clinton, Missouri, at 2154, for a patient transfer to St. Lukes Hospital, Kansas City, Missouri.

The National Transportation Safety Board Materials Lab review of the Rolls Royce Metallurgical Investigation Report focused on damage to the third stage turbine wheel where high cycle fatigue features were observed 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.

Parties to the investigation were Bell Helicopter, CJ Systems Aviation Group, FAA, Life Flight Eagle, Standard Aero, and Rolls Royce.