CHI01LA119

The pilot said that he was using an aerial saw to side trim trees along a powerline right-of-way. The pilot said, "At the end of the tree line at approximately 150' (feet) agl (above ground level) I applied power to climb, immediately the low rotor rpm horn sounded. I tried to increase N2/Nr (engine and rotor rpm) with the governor 'beep switch' and checked N2/Nr. There was no response from trying to increase N2/Nr and N2/Nr was in the low 90's. I lowered the collective, released the saw and radioed my ground crew that the engine had stopped. At this point I had low airspeed, low N2/Nr and approximately 100' agl. I aimed the aircraft at an open field and tried to gain airspeed to attempt a running landing." The pilot said the helicopter "impacted the field in a near horizontal attitude." An examination of the helicopter at the accident site showed the helicopter resting on its left side in a corn stubble field approximately 300 feet south of east-west running power lines, and approximately 730 feet from a clearway of trees where the helicopter was cutting prior to the accident. An examination of the helicopter revealed no anomalies.

On April 18, 2001, at 1430 central daylight time, a Hughes 369D helicopter, N713HT, operated by Aerial Solutions, Incorporated, and piloted by a commercial pilot, was destroyed when it impacted the terrain during an emergency landing after experiencing a loss of engine power. Visual meteorological conditions prevailed at the time of the accident. The tree-trimming operation was being conducted under the provisions of 14 CFR Part 133, Rotorcraft External Load. The operation entailed using an aerial saw suspended beneath the helicopter to trim trees in the vicinity of power lines. There was no flight plan on file. The pilot on board sustained minor injuries. The local flight departed from a landing zone approximately 5 miles northwest of Du Quoin, Illinois, at 1330.

In his written statement, the pilot said that he was using an aerial saw to side trim trees along a powerline right-of-way. The pilot said, "At the end of the tree line at approximately 150' (feet) agl (above ground level) I applied power to climb, immediately the low rotor rpm horn sounded. I tried to increase N2/Nr (engine and rotor rpm) with the governor 'beep switch' and checked N2/Nr. There was no response from trying to increase N2/Nr and N2/Nr was in the low 90's. I lowered the collective, released the saw and radioed my ground crew that the engine had stopped. At this point I had low airspeed, low N2/Nr and approximately 100' agl. I aimed the aircraft at an open field and tried to gain airspeed to attempt a running landing." The pilot said the helicopter "impacted the field in a near horizontal attitude."

A Federal Aviation Administration (FAA) inspector examined the helicopter at the accident site. The helicopter was resting on its left side in a corn stubble field approximately 300 feet south of east-west running power lines, and approximately 730 feet from a clearway of trees where the helicopter was cutting prior to the accident. Both of the helicopter's skids were broken outward and aft. The bottom of the helicopter was crushed upward. All four main rotor blades were bent upward approximately 12 inches outboard of the rotor head. One blade was broken aft near mid-span. The tail boom was broken downward approximately 30 inches aft of the engine section. The boom remaining with the helicopter fuselage was bent and broken downward in several places and crushed upward immediately aft of the exhaust opening. The aft portion of the boom was crushed inward, bent to the right, and broken downward. Black paint similar to the paint on the broken rotor blade was found on the tail boom where it was crushed inward. Control continuity was established to the control pedals and the collective. Fuel samples were taken from the helicopter and a nurse truck used to refuel the helicopter. The helicopter's engine was retained for further examination.

The fuel samples were examined at the FAA Flight Standards District Office, Springfield, Illinois on May 1, 2001. The fuel samples were consistent with type Jet A and showed no water or sediments in suspension.

The helicopter's engine was examined at Rolls-Royce Corporation, Indianapolis, Indiana, on May 2, 2001. The engine was mounted on a test stand and run as received. The first engine run resulted in limited N2, the loss of 100 percent power turbine governor control, and speed oscillations. A Rolls-Royce test mechanic determined that the 3-inch in line accumulator installed on the engine was a post factory shipping modification and requested the test be conducted with the 6-inch accumulator that is in accordance with the current standard C20B new production shipping configuration. The 6-inch accumulator was installed and the engine run was repeated. The engine was able to maintain 100 percent N2 speed at 188 foot-pounds of torque. A new 3-inch accumulator was installed on the engine and the test was run again with similar results from the first engine run. A fourth engine run involving the original 3-inch accumulator that came with the engine produced the same loss of turbine power governor performance as was observed in the first engine run. The governor (part number 23065121, serial number BR37539) and fuel control unit (part number 2524644-29, serial number BR53162) were removed from the engine and retained for further examination. Rolls-Royce On-site and engine test report is attached as an addendum to this report.

The fuel control unit and governor were examined at Honeywell Engine Systems and Accessories, South Bend, Indiana, on September 6, 2001. Visual inspections and flow testing of both components revealed no anomalies. Honeywell's test report is attached as an addendum to this report.

The FAA, Rolls Royce Corporation, and Honeywell Engine Systems and Accessories were parties to the investigation. All wreckage was released and returned to representatives of the helicopter's owner.