Fatal Powerline Human External Cargo (HEC) Flight (Winco H369D N138WH)
On 7 November 2017 Hughes 369D helicopter, N138WH operated by Winco Powerline Services under Part 133 regulations, was lifting two electricity utility linesmen on an external cargo long line. as Human External Cargo (HEC). The long line contacting a shield wire suspended between power transmission towers near Sulphur, Louisiana. The long line severed and the two linesmen were fatally injured when they fell around 100 ft to the ground.
According to the US National Transportation Safety Board (NTSB) investigation report (issued November 2019):
…the purpose of the flight was to install guard ropes between the deenergized 500-kilovolt power transmission lines before the existing braided steel shield wire from the nearby transmission tower was replaced. The east/west power transmission lines, with three sets of bundled conductors (northern, center, and southern), crossed perpendicular over a road.
The pilot reported that, following a preflight safety briefing, he and one of the linemen discussed the expected work tasks. The pilot stated that, following their discussion, he brought the helicopter into a hover to allow the linemen to hook onto the external cargo long line.
Winco Hughes 369D N138WH with Two Linesman as HEC Just Prior to the Fatal Accident (Credit: Witness via Calcasieu Parish Sheriff’s Office and NTSB)
He then repositioned the helicopter to allow the linemen to work on the center conductor bundle. …after the linemen had tied off the guard rope to the center conductor bundle, he repositioned the helicopter to allow work on the northern conductor bundle.
The pilot reported that he saw the long line contact the braided steel shield wire as one of the linemen held onto the northern conductor. The long line severed as the pilot turned the helicopter into the wind and attempted to move the linemen away from the northern conductor. The pilot reported that, immediately before the long line severed, he observed one of the linemen tugging at the conductor to reposition the guard rope perpendicular to the conductors. After the long line severed, the pilot returned to the landing zone and made an uneventful landing.
The 60-ft long line separated about midspan.
The pilot was 71 and had…
…had accumulated 25,090 total hours of flight experience, of which 21,063 hours were logged as pilot-in-command and 11,286 hours were flown in Hughes 369 helicopters.
The helicopter was operating under Part 133 Class B during the flight according to the operator (i.e. with a jettisonable load). The linesmen were considered as crew, not passengers, during powerline construction operations. The operator reported that:
The FAA had approved the helicopter’s hook installation; however, because the flight was conducted under Part 133 Class B, the FAA did not regulate, specify, or approve the long line or the harnesses that was used to hoist the two linemen.
In 2018 the FAA issued Safety Alert for Operators (SAFO) 18013 Updated Rotorcraft External Load Attaching Means and Quick Release Devices for Human External Cargo (HEC). This prohibited Part 133 operators from conducting HEC operations with attaching means not certificated to HEC requirements contained in Parts 27 and 29. This specifically related to a Portable Safety Device (PSD), also known as a Belly Band System or emergency anchor, that serves as a backup system to the primary hook, even if the hook kit is not certified for HEC. This affected MD500/Hughes 369 operators in particular.
The operator reported that the long line was a 7/16 inch Amsteel Blue synthetic rope made of Dyneema SK-75 synthetic fiber that had a break strength of 21,500 lbs. The operator reported that the use of Amsteel Blue synthetic rope had been an industry standard for at least 15-20 years, and that the use of synthetic rope is advantageous for powerline work because it is non-conductive and has a higher break strength than a similarly sized braided steel cable.
The operator stated that the use of an abrasion-resistant cover was typically used to protect a long line from incidental contact with sharp edges on tower structures [but] the use of an abrasion-resistant cover would not offer much protection if the long line had prolonged lateral contact with a braided steel cable. The operator noted that the use of a braided steel long line is not practical when working on powerlines due to the potential for electrocution. The operator reported that the pilot selects the length of the long line for a specific mission after he/she considers the required length to position the lineman at the specified workstation and to keep the helicopter above any wires, structures, or obstacles. The pilot chooses the shortest long line available that ensures obstacle clearance, which increases positive control of the cargo/linemen during the flight.
No safety actions are specifically reported and no recommendations are made in the NTSB report.
Safety Resources
The European Safety Promotion Network Rotorcraft (ESPN-R) has a general helicopter safety discussion group on LinkedIn and a Hoist Operation Safety Promotion LinkedIn group.
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