ERA13LA344

The pilot reported that, after trimming the top portion of a tree during helicopter tree-trimming operations, the engine experienced a gradual loss of power. The rotor rpm then began to decrease, and the "engine out" alarm illuminated and sounded. The pilot maneuvered to avoid power lines; however, during the descent, the rotor blades struck a power line pole, and the helicopter impacted the ground, which resulted in substantial damage to all five main rotor blades and the left landing skid. Postaccident examination of the engine and airframe and the air, fuel, and oil systems revealed no anomalies that could have contributed to the loss of power.

On July 29, 2013, about 1140 eastern daylight time, a McDonnell Douglas 369D helicopter, N31HM, impacted a power pole during descent following a total loss of engine power during tree trimming operations near Center Point, West Virginia. The commercial pilot sustained minor injuries and the helicopter received substantial damage. The helicopter was owned and operated DAH Aircraft, LLC, under 14 Code of Federal Regulations Part 133, as an external load flight. Visual meteorological conditions prevailed and no flight plan was filed for the flight. The flight originated from a remote landing zone (LZ) about 1.5 nautical miles to the northwest and was destined back to the same LZ.According to the pilot, after trimming the top portion of a tree that was overhanging a power line, he noticed a gradual loss of power with no noticeable yaw. The rotor rpm began to decrease, causing the "Engine Out" alarm to illuminate and sound. The pilot lowered the collective to preserve rotor RPM, and nosed forward and to the right to avoid landing directly onto the power line. During the descent, the rotor blades struck the power line pole. The helicopter impacted the ground on its right side in a dense wooded area. Initial examination of the helicopter by a Federal Aviation Administration (FAA) inspector revealed that the helicopter sustained substantial damage to all five main rotor blades and to the left landing skid. Further examination of the helicopter revealed substantial damage to the right side of the cabin section frame, landing skids, main rotor system, and to the tail boom. According to the helicopter engine logbooks, the engine had a recorded total time of 19,082.8 flight hours with a recorded 29 hours since last annual inspection, and a recorded 4,266.4 hours since overhaul. The helicopter was powered by a Rolls-Royce 250-C20B turbo-shaft engine, serial number CAE-821945F. Review of the helicopter's airframe logbooks revealed that its most recent annual inspection was complete on September 27, 2013, at a total airframe time of 10,446 hours. A fuel vacuum check was completed on the engine and airframe fuel supply system with no discrepancies. A check of engine air, fuel and oil systems was found to have no anomalies. Flight control continuity from the flight controls to all surfaces was completed with no discrepancies noted. The engine was removed and sent to the manufacturer for further testing. The engine was placed in a test cell and run through several power settings with no anomalies noted. A detailed report from the engine manufacturer is contained in the NTSB public docket. A review of the helicopter weight and balance revealed that the pilot was operating the helicopter within the manufacturer's designated weight limits. A review of the 1153 recorded data from North Central West Virginia Airport; Clarksburg, West Virginia (KCKB), revealed winds variable at 5 knots, visibility 10 statute miles, few clouds at 3,900 feet above ground level,temperature 21 degrees Celsius, dew point 12 degrees Celsius, and an altimeter of 30.15 inches of mercury.