Accident Overview
The accident involved a homebuilt helicopter that had departed from an unspecified location and transited to an area approximately 8 miles from its departure point. A witness observed the helicopter making a low pass along a 5-mile trail. It then flew to a point about midway along the trail, where trail maintenance was taking place, and began maneuvering at an altitude of about 50 feet above 50-foot trees.
Maneuvering and Impact
The helicopter entered a steep turn, at which point a loud 'bang' was heard. The helicopter then descended almost vertically into the woods. The main wreckage was found upside down, and the tail boom was located about 150 feet away from the main wreckage. Paint transfer marks were found where the tail boom had separated, which matched the paint on the end of a main rotor blade. The blade exhibited downward bending near its inboard end and upward bending near its outboard end. The blade's leading edge had impact marks and paint transfer marks consistent with contact with the tail boom.
Engine and Systems
Fuel was found onboard the helicopter. The engine exhibited scoring marks consistent with a sudden stoppage. There was no evidence of in-flight blade failure or separation. An onboard recording of throttle positions revealed that the throttle had been opened to 29 to 32 percent for the first 4 of the last 5 minutes of flight, consistent with the helicopter transiting the area. From 56 seconds until 6 seconds prior to the last recording, the throttle position was approximately 38 to 40 percent, consistent with the use of added power for maneuvering over the trees. Three seconds before the last recording, the throttle had been closed to 7 percent, before it was returned to 38 percent for the last two seconds of the recording.
Pilot Information
The student pilot had accumulated 64 hours of flight time. He had attended the kit manufacturer's facility three times for training. He had been endorsed for hovering flight, flight through translational lift, and quickstops, provided he remained within 35 feet of the ground at all times. He had previously been involved in an accident while hovering the helicopter. Another builder/pilot, who had flown with the student pilot, stated that his 'ability to maintain proper rotor rpm was a problem.'