What happened
On 15 February 2018, an Aerospatiale AS-350-B2 was performing an engine warm-up procedure on a helipad located on a hilltop, roughly three nautical miles west-north-west of Tulita, Northwest Territories. The aircraft was operated by Sahtu Helicopters.
During the warm-up, once the engine reached 70% gas generator speed (Ng), the helicopter experienced vibrations, began to bounce, and started yawing to the left. In an attempt to stabilize the aircraft, the pilot increased the Ng. As the engine speed approached 100%, the pilot raised the collective to lift the helicopter from the pad. However, the main rotor speed dropped below the governing range, resulting in a loss of control. The aircraft struck the ground and tumbled approximately 140 feet down the side of the mountain. The pilot, the sole occupant of the aircraft, suffered serious injuries. Although the pilot was wearing a lap and shoulder harness, no helmet was in use. The aircraft's emergency locator transmitter (ELT) failed to activate during the event.
The investigation
The TSB conducted a Class 4 investigation into the collision with the terrain. The investigation focused on the sequence of events during the engine warm-up and the subsequent loss of rotor speed and control.