HISTORY OF FLIGHT On February 4, 2011, about 1422 Pacific standard time, a McDonnell Douglas Helicopters 369E (MD500E), N416WC, became entangled with a sock line rope used to string power lines near Elverta, California. Wilson Construction Company was operating the helicopter under the provisions of 14 Code of Federal Regulations (CFR) Part 133. The commercial pilot and one passenger sustained minor injuries; the helicopter sustained substantial damage to the airframe and main rotor blades. Visual meteorological conditions prevailed, and no flight plan had been filed. The operator reported that the helicopter was working on a project to construct 30 miles of high power electrical lines, which are oriented north-south. It is not possible to pull the conductor wire through bundled travelers unless the sock line is actually in contact with the roller. Construction crews install a hold down, which is a temporary block that they secure to a ground anchor. They adjust the anchor rope to force the sock line to rest in the bundle block traveler when in tension. The operator noted that it is standard industry practice to use a helicopter to install a hold down. A lineman was on the skid of the helicopter, which was in position to install a hold down at a power line structure. The pilot positioned the helicopter about 30-50 feet south of the structure; his flagman was facing the west. The pilot believed that he was properly positioned near the sock line so that they could perform the task safely. The lineman on the skid placed the larger of the two hold down ropes over the sock line, and allowed it to fall onto the west side. The lineman allowed the hold down block to hang by the large rope just below and on the east side of the sock line. The large rope tangled as it fell to the ground. The lineman on the ground grabbed the end of the rope, and tried to clear the tangle. The lineman on the skid had one hand on the hold down, and was preparing to release the second, smaller rope downward on the western side of the sock line with the other hand. The main rotor blades made contact with the sock line rope, which wrapped around the mast as the blades pulled it in. The pilot lost control of the helicopter, and it began an uncontrolled descent to the ground. The helicopter came to rest upright about 10 feet south of the power line structure. The lineman on the skid was lying on the ground, but still attached to the helicopter by her fall restraint and positioning belt. The pilot extricated himself from the helicopter. TESTS AND RESEARCH Investigators from the FAA, Boeing, and Rolls-Royce Allison (RR) examined the wreckage at the operator’s facilities at McLellan Airfield, Sacramento, California, on February 9, 2011. The investigators examined the airframe and engine, with no mechanical anomalies identified that would have precluded normal operation.