Helicopter Tail Rotor Failure and Hard Landing in Mountainous Terrain (N1089N)

Incident

A helicopter pilot was operating in mountainous terrain with three doors removed, positioning survey personnel to re-mark survey sites. During departure from the mountainous terrain, the pilot briefly noticed something in his skid mounted mirror. At that point, the pilot and three passengers heard a loud 'whump' followed by a loss of tail rotor control. The pilot maneuvered the spinning helicopter over some power lines and onto a downward sloping ridgeline. The helicopter landed hard and rolled down the mountain approximately 100 to 150 feet.

Investigation Findings

Investigators were unable to recover the tail rotor blades along with half of the severed gear box. The left rear seat passenger was missing a sweat jacket. An abundance of 12-inch reinforced marker tape was found at the accident site. Metallurgical analysis revealed that a high strain rate crack growth had occurred as in a one-time overload on the tail rotor gearbox casting.