LAX94LA043

The pilot lost control of the helicopter while executing a maneuvering turn while loaded with chemical at about 35 feet above the ground. The main rotor head paddle assembly fractured and separated before the loss of control. Metallurgic examination of the fracture revealed an overload failure mode.

On November 13, 1993, at 0940 hours Pacific standard time, a Hiller UH-12E, N149HA, lost control while applying chemicals to a field and collided with level terrain near Salinas, California. The pilot was conducting a visual flight rules aerial application flight under Title 14 CFR Part 137. The helicopter, operated by Helicair Ag, Inc., Salinas, was destroyed by impact forces and postimpact fire. The certificated commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed. The flight originated at Salinas at 0850 hours.

The pilot reported that while executing a maneuvering turn at about 35 feet above the ground he lost control of the helicopter and crashed. Examination of the wreckage by the operator revealed a component of the main rotor head fractured and separated before the pilot lost control of the helicopter.

The part, a main rotor paddle assembly, was fractured at the cuff and found about 200 feet from the fuselage. The fractured part held the main rotor stabilizer paddle on the main rotor hub. According to the operator, the paddle sustained minor damage that was not consistent with ground impact forces sufficient to fracture the cuff before the separation.

The main rotor head cuff and trunnion assembly were examined by the National Transportation Safety Board, Material Laboratory. According to the Safety Board's metallurgist, there was no evidence of preexisting fracture areas found. The fractured cuff assembly exhibited a 45 degree shear plane, indicative of an overstress separation. The main rotor hub cuff assembly was also bent opposite the direction of main rotor rotation.