What happened
On 06 May 2023, an Airbus Helicopters AS 350 B3, registered as C-GUXR, was undergoing ground run operations at Smithers Airport (CYYD) in British Columbia. The aircraft, operated by Mustang Helicopters Inc., was being monitored by a pilot while two maintenance personnel stood near the left cargo door.
During the third of three scheduled maintenance ground runs, the pilot increased the engine power from idle to flight idle. Once the engine reached this power setting, the helicopter experienced an uncommanded rotation to the right. The pilot immediately reacted by reducing the engine control to idle, cutting the fuel supply, and engaging the rotor brake. Despite these emergency actions, the aircraft completed a rotation of approximately 540 degrees.
During the uncontrolled movement, the tail rotor struck both maintenance staff members on the ground. One individual sustained serious injuries, while the other suffered fatal injuries. The pilot remained uninjured, and the helicopter sustained minor damage.
The investigation
The investigation focused on the sequence of events during the power increase and the mechanics of the uncommanded rotation. Investigators examined the aircraft's behavior as the engine transitioned from idle to flight idle, noting that the rotation occurred specifically at the moment the flight idle power was reached, a phenomenon that had also occurred during the two preceding ground runs.