What happened
At 0820 mountain daylight time, an MDHI 369D helicopter, registration C-GNMG, was conducting a mission near Doctor Lake, Northwest Territories. Operated by Sahtu Helicopters, the aircraft was tasked with scouting a water supply for a new drilling site. While the pilot was performing a lateral hover at approximately 75 feet agl to identify a landing pad, the aircraft began an uncommanded rotation to the right.
In an attempt to stabilize the aircraft, the pilot applied left pedal input and sought forward airspeed to regain directional control. Following standard procedures for low-speed flight, the pilot reduced engine power and lowered the collective, which temporarily stabilized the rotation. However, when power was re-applied, the rotation resumed. The helicopter struck the ground before the pilot could recover control. The impact and subsequent fire caused substantial damage to the airframe. The crash resulted in one fatality and one serious injury, while a second passenger escaped the wreckage before the fire spread.
The investigation
Investigators examined the wreckage and the mechanical state of the aircraft. The engine was found to have been running at a low power setting at the moment of impact. While the engine and main rotor were functional, the tail rotor showed no signs of rotation during ground contact. The investigation focused on the tail section, where a break was identified in the aft boom, resulting in significant bending of the flight control tubes and the drive shaft.
Maintenance records showed the aircraft was fully compliant with all regulatory requirements, and there were no known mechanical deficiencies prior to the flight. Weather conditions at the site were favorable, with light winds and good visibility. The investigation also ruled out airflow effects, as the relative wind was not within a critical azimuth that would induce such a rotation.
Findings
- The primary cause of the accident was the failure of the tail rotor drive shaft.
- This failure prevented engine power from being transferred to the tail rotor, leading to the uncommanded rotation.
- The aircraft was at an altitude too low to allow the pilot to recover from the loss of anti-torque control.
- The post-crash fire destroyed critical evidence regarding the forward section of the drive shaft.