NTSB Factual Report

On February 23, 2011, approximately 1620 central standard time, a Hughes 369D, N112AS, registered to and operated by Aerial Solutions, Inc., was substantially damaged when it struck the ground and rolled over 12 miles southwest of Henryetta, Oklahoma. Visual meteorological conditions prevailed at the time of the accident. The external load flight was being conducted under the provisions of 14 Code of Federal Regulations (CFR) Part 133 without a flight plan. The pilot, the sole occupant on board, was not injured. The local flight had originated at 1400 from the landing zone where the accident occurred.

The external load suspended under the helicopter was a patented Aerial Saw, used to cut vegetation along power line right-of-ways. The Aerial Saw consisted of a row of ten 24-inch diameter circular blades mounted on a saw bar channel, driven by belts in the channel, and connected to a gas powered engine. The engine was mounted above the saw bar in a framed cage and was suspended below the helicopter by sections of aluminum tubing. The saw and motor section were hinged to allow the saw to swing fore and aft, but not sideways. The tubular sections were also hinged so that the helicopter could land with the saw stretched out in front of it. The pilot could manage the saw by turning the saw bar left or right, change the saw speed or turn the saw motor on or off. The saw blades are normally pointed in the same direction of the helicopter's travel. The Aerial saw suspended on an 80-foot beam and weighed 822 pounds. At the time of the accident, the saw was idling.

According to the accident report submitted by the operator, the helicopter was facing into the wind and hovering with the external load over an open field adjacent to the work area approximately 120 feet above the ground. The pilot made a 180-degree right pedal turn to enter the work area. While trimming for a left quartering tailwind, reported to be 200 degrees at 11 knots, he heard a loud "pop" and felt a "thump" in his seat. He was unable to move the cyclic control to the left, and helicopter started a right banking turn. The collective control was lowered and aft cyclic control was applied. This lowered the external load to the ground and caused the helicopter to stabilize by the pilot pulling aft on the external load. All efforts to move the cyclic control to the left were unsuccessful. At 5 feet above the ground, as the pilot leveled the helicopter, it rolled sharply to the right and impacted the ground, coming to rest on its left side.

The wreckage was examined and documented by Federal Aviation Administration (FAA) inspectors at the accident site, then transported to Air Salvage of Dallas (Texas) where, on April 12, 2011, it was examined in greater detail by FAA inspectors and representatives of Boeing Helicopters and Rolls Royce. Flight control continuity was established from the cockpit to the control deck. All controls were moved, and no obstructions or binding were noted. The trim actuators were tested. The lateral trim actuator would not operate due to wires being severed during the accidence sequence, but full left lateral trim input was noted. With the wires connected, the lateral trim motor functioned normally. A support on the lower non-rotating portion of the swashplate was fractured in overload during the accident sequence. There was damage on the mating surfaces between the non-rotating and rotating surfaces of the swashplate. The cowling around the swashplate showed evidence of fiberglass debonding and was missing a fastener. The damage to the inlet fairing was a result of the accident sequence from helicopter roll over and the fairing contacting rotating and broken/flailing upper flight control parts. The Boeing Helicopter representatives did not find any anomalies that would cause binding of the controls. Damage to the rotor system was consistent with power being developed. No powerplant discrepancies were noted.

No post-accident examination of the Aerial Saw was performed.

NTSB Probable Cause

Failure of the cyclic control system for reasons undetermined.