What happened
A chartered Bell 206 helicopter was conducting hydrometric measurements near the Snare River, approximately 110 miles north of Yellowknife, when it broke through the surface of an ice-covered bay. The flight, operated for Environment Canada, had diverted to this secondary location because high water levels had flooded the primary landing site.
After the pilot hovered the aircraft near the shore, two technologists exited to inspect the ice. Following a signal from the crew that the surface was stable, the pilot attempted to shut down the engines to conserve fuel. As the pilot reduced power to ground idle and transitioned the full weight of the Bell 206 onto the ice, the surface gave way. The aircraft plunged into the four-foot-deep water. During the descent, the tail rotor gear box separated and the main rotor blades struck the ice, causing a blade to fracture. One technologist was fatally struck by the breaking rotor blade, while the pilot and the second technologist were able to evacuate the submerged aircraft. Both survivors were treated for hypothermia following a rescue facilitated by a portable satellite phone.
The investigation
The investigation focused on the structural integrity of the ice and the sequence of the aircraft's descent. Investigators examined the ice characteristics, noting that the bay was fed by a small, obscured stream that likely compromised the ice thickness. The ice was grey in color and measured approximately three inches thick at the point of failure.
Technical analysis of the aircraft revealed that the tail rotor blades struck the ice surface as the helicopter broke through, leading to the loss of tail rotor control and subsequent rotation and roll. The investigation also reviewed the pilot's decision-making process, noting that while the crew had successfully used similar procedures in the past, there was no reliable way to determine ice thickness from the air. The investigation confirmed the aircraft, its maintenance, and the pilot's qualifications were all in compliance with existing regulations.
Findings
- The load-bearing capacity of the ice was insufficient to support the weight of the helicopter, its equipment, and the personnel.
- A hidden stream flowing under the surface likely reduced the thickness and quality of the ice.
- The pilot's decision to transition from a hover to a full weight-on-ice shutdown exceeded the ice's strength.
- The fracture of the main rotor blade, which caused the fatality, occurred as the blades struck the ice surface during the accident.