Occurrence
On 14 December 2017, a Hydro One Networks Inc. Airbus Helicopters AS 350 B2 helicopter (registration C-GOHS, serial number 3240) equipped with an external platform was transporting crews of power line technicians between a staging area and transmission towers in an area 8 nautical miles north-northeast of Tweed, Ontario.
At 1144 Eastern Standard Time, the pilot picked up a crew of 3 power line technicians near the bottom of a tower for a return flight to the staging area. It had become common practice for technicians to attach tool bags and other small items to the external platform for flights to and from work sites. In line with this practice, the technicians attached a few items to the platform while boarding the helicopter, and then took their seats in the aft cabin.
Sequence of Events
The practice of carrying external loads attached to the platform was not a formalized procedure at the company, and adequate controls were not in place to ensure that these objects were properly stored or secured. Consequently, an empty canvas supply bag with an attached carabiner that was being carried on the platform was not adequately secured before the helicopter departed for the return flight.
When the helicopter was 0.26 nautical miles from the staging area, the canvas bag separated from the platform and struck the helicopter's tail rotor, causing significant damage, severe imbalance, and intense vibration.
Shortly after, while the pilot was attempting to land, the helicopter's tail rotor, tail rotor gearbox, and vertical fin separated from the helicopter. The helicopter became uncontrollable and collided with terrain. The 3 power line technicians were unrestrained and became separated from the helicopter, either slightly before or during the impact, and received fatal injuries from contact with the helicopter or the surrounding terrain. The pilot was fatally injured on impact. The helicopter was destroyed.
Safety Communications
On 21 December 2017, the Transportation Safety Board of Canada issued Aviation Safety Advisory A17O0264-D1-A1 regarding unsecured cargo and unrestrained passengers in helicopters.