Aircraft Accident/Incident Report

Milan, New Hampshire 03588
Saturday, October 30, 1999 15:30 EDT

After transiting to an area about 8 miles from its departure point, the homebuilt helicopter was observed 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 about 50 feet, over 50-foot trees. It entered a steep turn, there was a loud 'bang', and the helicopter descended almost vertically into the woods. The main wreckage was found upside down, and the tail boom was located about 150 feet away. There were paint transfer marks where the tail boom had separated, which matched the paint on the end of a main rotor blade. That 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 from the tail boom. There was no evidence of in-flight blade failure or separation. Fuel was found onboard the helicopter, and the engine exhibited scoring marks consistent with a sudden stoppage. The student pilot had 64 hours of flight time, and had been to 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 had 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.' 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.

The pilot's failure to maintain proper rotor rpm while maneuvering, which resulted in main rotor blade flapping, and its subsequent impact with the tail boom. A factor was the pilot's lack of experience in maneuvering flight.