HILLER UH-12E

Full Narrative

On June 1, 2011, about 1620 Pacific daylight time (PDT), a Hiller UH-12E, N68012, performed an emergency autorotation into a grove of cherry trees while performing low level agricultural operations near Stockton, California. Alpine Helicopter's was operating the helicopter under the provisions of 14 Code of Federal Regulations (CFR) Part 137. The commercial pilot was not injured and the aircraft sustained substantial damage. Visual meteorological conditions prevailed at the time for the local area agricultural flight.

The pilot initially reported that he was conducting low level agricultural drying of cherry trees when the tail rotor struck a tree during a turn. Later in the week the pilot revised his statement saying that the skids of his helicopter were at least 10-15 feet above the tallest tree when he felt a shake or vibration through the control surfaces. He looked for a place to land and was maneuvering the helicopter towards a road when the helicopter experienced a full left yaw. The pilot applied full right pedal to counter the yawing motion and entered autorotation through the trees to the ground. The main rotor blade, tail rotor blade, tail boom, front fuselage, skids, and the undercarriage of the helicopter were substantially damaged. The pilot did not report any emergency alarms or cautionary lights accompanying the accident sequence and sustained no injuries on impact.

Post accident examination of the aircraft by a mechanic and a FAA inspector found continuity between the tail rotor and the linkages through the drive train which lead to the main transmission. Control system continuity was also established. The tail boom near the tail rotor transmission was twisted clockwise, shearing the aluminum. Tail rotor blade #1 was sheared off about one quarter of the distance between the blade root and the blade tip, and rotor blade #2 had compression deformation of the trailing edge near the blade root. The sheared off portion of tail rotor blade #1 was located in the orchard. Visual inspection found a circular impact deformation in the leading edge at the blade tip, separation of the blade tip weight from the blade, deformation of the blades surface area, and compression bending of the blade's trailing edge.