Eurocopter SA315B N929JV accident near Alva, Oklahoma

Probable cause

Failure of the current and previous operators to comply with the manufacturer's maintenance procedures for operation in sandy environments, which resulted in turbine case erosion and the subsequent uncontained engine failure.

NTSB analysis

The helicopter was flying at 300 feet above the ground with an external load when the pilot heard a loud noise from the engine and the rotor rpm began to decay. He jettisoned the load and entered an autorotation. During the flare, the helicopter's main rotor blades contacted the tail rotor drive shaft. Engine disassembly and examination revealed that the turbine casing was deeply eroded by particles that had accumulated in the casing as a result of operating in dusty environments. The erosion caused a crack to develop, and non-uniform overheating of the engine led to the partial melting of the nozzle guide vanes and the rupture of the blade tips in all three turbine stages. Uncontained debris then punctured the turbine casing and shroud. According to the helicopter's maintenance records, the helicopter had operated 68 hours past a 100-hour inspection. The erosion in the engine was likely preexisting since it had been purchased second hand. Further, the records contained no entries pertaining to compliance with the manufacturer's maintenance procedures, by either the current or previous owner, for operations in sandy environments. The current operator reported that they have since complied with the manufacturer’s procedures.

Text from the NTSB. Open the NTSB docket for CEN12LA235 for the full record.