The Transportation Safety Board released its investigative report earlier this week on the accident that claimed the lives of four Hydro One employees near Tweed, Ontario on December 14, 2017.

The lengthy, 46-page report reveals that the cause of the accident was the separation of a piece of equipment that was not properly secured to the helicopter’s external platform that struck the helicopter’s tail rotor, causing it and the tail rotor’s transmission and tail fin to separate from the aircraft. The TSB investigation also revealed that the three power line technicians (PLTs) were wearing neither the lap belts not the shoulder belts which the helicopter was equipped with.

The TSB reports that the shoulder harness straps were found rolled up and taped. This was admitted by the operator to be standard practice as there had previously been complaints of the shoulder straps interfering with the PLT’s safety harnesses. The operator interpreted the CARs to mean that only the use of lap belts was mandatory, with the use of shoulder harnesses being optional.

This has led the TSB to release this recommendation: “[that] the Department of Transport amend the Canadian Aviation Regulations to remove any ambiguity associated with the definition of ‘safety belt.’”

The occurrence aircraft, an Airbus Helicopters AS 350 B2, was being used to carry personnel to and from job sites. It was equipped with an external platform, known as an Air Stair, that permits PLTs to conduct work outside of the helicopter on powerline transmission towers and to facilitate the transfer of PLTs to the towers themselves. However, due to the low temperature on the day of the accident, the Air Stair was not being used and the PLTs were transferred to and from the base of the tower where they needed to intervene. It was on the return flight and during the descent to the staging area the accident occurred.

See below for the complete TSB report.

Photos by the TSB