N929JVEurocopter SA315B · 1973

On March 30, 2012, about 0943 central daylight time, the pilot of a Eurocopter SA315B, N929JV, made a forced landing in an open field about 25 miles northwest of Alva, Oklahoma, after the engine lost power. The pilot, the sole occupant on board, was not injured. The helicopter was substantially damaged. The helicopter was registered to Roberts Aircraft Company, Cheyenne, Wyoming, and operated by Trans Aero, Ltd., of Longmont, Colorado, under the provisions of 14 Code of Federal Regulations (Part 133 as an external load operation. Visual meteorological conditions prevailed at the time of the accident, and no flight plan had been filed. The local flight originated from Alva, Oklahoma, about 0830.

According to the pilot's statement, he was flying at 300 feet above the ground with an external load. He 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. The helicopter tilted up on its nose then settled back on its skids.

The engine was removed from the airframe and shipped to Turbomeca in Tarnos, France, where it was disassembled and examined under the oversight of the Bureau d’Enquêtes et d’Analyses (BEA), the French aircraft accident investigation bureau. According to Turbomeca's report, which was endorsed by BEA, 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.

Turbomeca Procedure 72-40-01, page 203, describes how sand deposits were to be eliminated. There was nothing in the helicopter's engine maintenance records to indicate that this procedure had been performed.