MD Helicopter 600 accident near Smethport, Pennsylvania, April 8, 2018

The NTSB's narrative final · quoted from the NTSB record

The pilot of the helicopter was conducting a power line construction flight. The power lines were supported by a series of structures made of either wood (dual-pole, H-frame) or steel (single pole). A static line was affixed to the top of the structures above the power lines. The purpose of the flight was to remove the static line from the wheeled, pulley device (dolly) that temporarily secured the static line and permanently secure the static line to the structures. One lineman completed the task from the skid of the hovering helicopter, and another lineman inside the helicopter passed tools and equipment back and forth to the lineman on the skid. The accident occurred when the crew (the pilot and the two linemen) were working on the second structure, which was constructed of wood. During work on that structure, the helicopter hovered facing westbound adjacent to the wooden structure with the pilot, both linemen, and the structure on the helicopter's left side. The static line sloped upward aft of the helicopter toward the uphill structure and downward and to the right toward the downhill structure. The initial steps taken for the task included wrapping the line with a spiraled wire coating (armor rod) and attaching a safety strap (safety). The lineman on the helicopter skid attached the first half of the armor rod ahead of the dolly and manipulated the line and the dolly to complete the wrap. According to the pilot, the lineman opened the spring-loaded locking gate on the dolly above the static line to wrap the second half of the armor rod, which was "normal" before the attachment of the safety. About that time, the pilot felt the helicopter being "pulled" toward the structure. The pilot stated that he made cyclic and pedal inputs to avoid the structure but reported that "all I remember is rolling over the structure." The pilot stated that he neither felt nor heard anything unusual before the helicopter was pulled toward the structure. Visual examination of the static line, helicopter rotor blades, and visual and metallurgical examination of the dolly revealed that, as the lineman on the skid wrapped the armor rod, and before he attached the safety, the aft portion of the main rotor struck the static line, which broke the locking gate that secured the line inside the dolly. Once free of the dolly, the static line fell between the uphill and downhill structures and over the left front skid of the helicopter, which created the pivot point over which the helicopter rolled inverted. The pilot and the linemen began work without installing a safety. According to the operator's director of safety, the safety strap aboard the helicopter was "not long enough" to install it before work began. The holding company of the subsidiary that hired the operator as an independent contractor had a safety manual for linemen who performed work from helicopters. The manual indicated that "secondary securement systems shall be utilized" when clipping wire (permanently securing a static line to the structures).

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.