What happened
On 14 December 2017, an Airbus Helicopters AS 350 B2 helicopter, registered C-GOHS, was performing utility work near Tweed, Ontario. Operated by Hydro One Networks Inc., the aircraft was transporting power line technicians between transmission towers and a staging area. During a return flight, a crew of three technicians boarded the aircraft, attaching small items and tool bags to the helicopter's external platform, a common but informal practice among the crew.
As the helicopter approached its destination, approximately 0.26 nautical miles from the staging area, an unsecured canvas supply bag with an attached carabiner became detached from the external platform. The bag struck the tail rotor, leading to intense vibrations and severe mechanical imbalance. During the subsequent landing attempt, the tail rotor, gearbox, and vertical fin detached from the airframe. The aircraft became uncontrollable and struck the ground. The pilot and the three technicians, who were unrestrained in the aft cabin, sustained four fatalities.
The investigation
The TSB examined the circumstances surrounding the loss of the tail rotor assembly and the separation of the passengers from the aircraft. The investigation focused on the procedures regarding external loads and the lack of formal protocols for securing items attached to the external platform. Investigators also looked into the safety of passenger restraint during utility operations.
Findings
- The primary cause of the accident was the failure to adequately secure a canvas bag to the external platform.
- There was no formalized company procedure governing the attachment of tools or bags to the external platform.
- A lack of adequate controls meant that items could be attached to the aircraft without being properly checked or secured before departure.
- The technicians in the aft cabin were not restrained by seatbelts.