History of Flight
On April 8, 2018, about 1711 eastern daylight time, an MD Helicopters 600N helicopter, registration N602BP, was destroyed when it collided with a wooden power line support structure and terrain in Smethport, Pennsylvania. The commercial pilot was seriously injured, and two linemen were fatally injured. The helicopter was operated by High Line Helicopters, Inc., under 14 CFR Part 133 as an external load flight. Visual meteorological conditions prevailed, and no flight plan was filed. The flight departed from an unimproved landing zone adjacent to the accident site.
The purpose of the flight was to remove a static line from a wheeled pulley device (dolly) and permanently secure it to support structures, a process known as "clipping wire." The linemen worked from the helicopter skid and inside the cabin. The crew had completed one structure and repositioned to the next. According to the pilot, the helicopter was hovering "inside the bite," a triangular area formed by the wires and poles.
While the lineman on the skid was wrapping armor rod, he opened the spring-loaded locking gate on the dolly. Shortly after, the pilot felt the helicopter being "pulled" toward the structure. He applied full right cyclic and left pedal inputs but stated he remembered "rolling over the structure." A witness reported the helicopter's nose turned away from the pole, then the helicopter "was violently forced back to the pole." The tail section struck the pole, the helicopter "broke in two," and descended vertically. The engine "continued to surge" after impact.
Personnel Information
The pilot held a commercial pilot certificate with rotorcraft-helicopter and instrument-helicopter ratings. His most recent FAA second-class medical certificate was issued April 5, 2017. He had accrued about 6,200 total flight hours, including 250 hours in the MD 600N and an estimated 3,000 hours performing power line operations.
Aircraft Information
The helicopter was manufactured in 1998 and powered by a Rolls-Royce/Allison 250-C47 turboshaft engine. At the time of the accident, the Hobbs meter showed 5,203.6 hours. The most recent 100-hour inspection was completed February 4, 2018, at 5,120.8 hours. An FAA airworthiness inspector noted numerous record-keeping errors but overall compliance with inspections and airworthiness directives.
The helicopter was modified with aluminum diamond-plate flooring, which required removal of the left cabin door, and a 6061-T6 aluminum pipe. No FAA approval or documentation for these modifications was found. The MD 600N flight manual allowed left door removal but prohibited right seat removal, which resulted in a left-seat command configuration. The cabin had no passenger seats installed, contrary to 14 CFR 91.107(a)(3). Weight and balance computations for three fuel states indicated the helicopter was likely within limits.
Wreckage and Impact
The accident site was at about 1,600 ft elevation. The wreckage was concentrated at the base of the wooden H-frame structure. The six main rotor blades separated at the hub and were scattered south of the power lines; one blade traveled about 300 ft west. The tailboom separated and was found 70 ft west. Striations on the left skid were consistent with wire contact. One rotor blade had a concave dent 2.25 inches from the tip, consistent with static line dimensions.
The dolly was found on the structure with its locking gate fractured due to overstress. The safety strap and hoist were undamaged. Examination revealed no preimpact mechanical anomalies. The dolly locking gate latch fracture surfaces indicated overstress from outward movement of the pulley wheel.
Additional Information
High Line Helicopters was contracted by J.W. Didado Electric, a subsidiary of Quanta Services, for power line construction. The operator's director of safety stated that the safety strap aboard was "not long enough" to remain attached during armor rod installation and a "choker safety" should have been used. Quanta Services' safety manual recommended secondary securement systems for clipping wire. The operator had been involved in two other accidents in early 2018, but no probable cause was determined for this accident. Following the investigation, the company mandated safety strap installation before work on each structure.