What happened
At approximately 06:15, a pilot with 450 hours of experience departed on the return leg of a personal cross-country flight. At about 08:05, witnesses observed the helicopter traveling north along a highway at a normal height. Shortly thereafter, witnesses reported seeing the aircraft lose altitude very quickly. One witness, traveling in the opposite direction, observed the aircraft flying extremely low over the highway median, approximately 20 to 30 feet above the ground and below the tree line. The witness noted that the pilot appeared to be working the controls with fast, vigorous motions while concentrating on the center gauges and console.
The investigation
Investigators from the FAA and the Department of Public Safety observed that the aircraft struck power lines before hitting the ground. Evidence of a wire strike was found on the top and forward sections of both the left and right landing skids. While the fuel tank was breached near the top, approximately 3 quarts of fuel remained after being drained through the gascolator.
An examination of the rotor system showed that the blades lacked leading-edge gouges. One blade was bent upward, while the other two were bent downward; one of these blades exhibited scuffing and paint marks consistent with contact with the tail rotor boom, along with slight buckling on the trailing edge. The main rotor drive shaft and housing were broken from the transmission, with the shaft bent at a 45-degree angle without evidence of twisting. The tail rotor drive shaft had separated into two pieces without twisting motion at the break, though it showed longitudinal scuffing and paint transfer.
Mechanical inspections revealed that the metal mixture control cable clamp on the fuel servo lacked a rubber cushion, allowing the cable to move freely. Additionally, while control continuity through the cyclic and collective was established, three bolts connecting the cyclic controls were missing their safety cotter pins, and one castled nut had backed off nearly to the point of falling off. The bottom set of spark plugs were found to be heavily worn and lead-fouled. A post-accident engine run showed no abnormalities during operation, though fuel was observed leaking through the servo and out of the induction system when the mixture was left in the full-rich position.