Accident Details
On June 1, 2011, at approximately 1620 Pacific daylight time, a Hiller UH-12E helicopter, registration N68012, executed an emergency autorotation into a grove of cherry trees while conducting low-level agricultural operations near Stockton, California. The flight was operated by Alpine Helicopter under 14 Code of Federal Regulations Part 137. The commercial pilot was not injured, and the helicopter sustained substantial damage. Visual meteorological conditions prevailed for the local area agricultural flight.
Pilot Narrative
The pilot initially reported that during low-level agricultural drying of cherry trees, the tail rotor struck a tree while turning. Later that week, the pilot revised his statement, noting that the skids were at least 10 to 15 feet above the tallest tree when he felt a shake or vibration through the control surfaces. He began looking for a landing area and maneuvered the helicopter toward a road. The helicopter then experienced a full left yaw. The pilot applied full right pedal to counter the yaw and entered autorotation through the trees to the ground. No emergency alarms or cautionary lights accompanied the accident sequence, and the pilot sustained no injuries on impact.
Post-Accident Examination
A post-accident examination by a mechanic and an FAA inspector revealed continuity between the tail rotor and the linkages through the drive train leading 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 blade tip. Tail rotor blade #2 exhibited compression deformation of the trailing edge near the blade root. The sheared portion of tail rotor blade #1 was found in the orchard. Visual inspection showed a circular impact deformation in the leading edge at the blade tip, separation of the blade tip weight from the blade, deformation of the blade's surface area, and compression bending of the blade's trailing edge. The main rotor blade, tail rotor blade, tail boom, front fuselage, skids, and undercarriage of the helicopter were substantially damaged.