On August 5, 2013, at 0915 central daylight time, a Hughes model 369D helicopter, N8688F, was not damaged when its external cargo long-line was severed after colliding with a shield wire suspended between power transmission towers near Ackerly, Texas. The two linemen who were being hoisted on the long-line were fatally injured after falling about 200 feet to the ground after the collision. The helicopter was registered to and operated by Haverfield Aviation Inc., under the provisions of 14 Code of Federal Regulations Part 133 as an external load flight, without a flight plan. Day visual meteorological conditions prevailed for the local flight, which was operating from a landing zone situated near the accident site.According to the operator, the helicopter was equipped with a 100-foot long external cargo long-line that was being used to hoist linemen onto power transmission towers. Shortly after departure, as the helicopter was climbing toward the transmission tower, the long-line collided with a shield wire suspended between transmission towers. The operator reported that the long-line severed about 5 feet above the linemen. The pilot returned to the landing zone and made an uneventful landing. The operator did not report any malfunction or failures with the helicopter that would have prevented normal operation. The pilot reported that during his repositioning flight he noticed that there were multiple power lines and shield cables erected on the tower structures located to the north and west of the tower to be serviced. After landing, he completed a preflight briefing with the two linemen assigned to his helicopter. After the briefing, the helicopter was brought into a 100-foot hover above the landing zone while the two linemen secured themselves to the long-line below. The pilot reported that as he maneuvered toward the tower he briefly noticed a slight kink in the long-line carrying the linemen before it was severed. The pilot stated that the shield wire installed on the tower had not been identified or discussed during the preflight briefing. He reported that the clear sky condition and the morning light made the shield wire impossible to see from the ground. Additionally, he stated that it was uncommon for shield wire to be installed on the upper tower structures before the lower line work had been completed. The nearest aviation weather reporting station was located at Big Spring McMahon-Wrinkle Airport (KBPG), Big Spring, Texas, about 20 miles southeast of the accident site. At 0915, the KBPG automated surface observing system reported: wind from 160 degrees at 11 knots, visibility 10 miles, sky clear, temperature 28 degrees Celsius, dew point 16 degrees Celsius, and an altimeter setting of 30.10 inches of mercury.