What happened
On September 24, 2006, a Heli-Lift International Inc. Bell 204B helicopter, registration C-GSHK, was performing external load operations near Stony Rapids, Saskatchewan. The mission involved transporting drill rods between sites using a long-line method. Approximately three minutes into the flight, the pilot reported that the left-side bubble window door had opened and was difficult to secure.
In an effort to prevent the door from being lost, the pilot released the sling load and attempted to hold the door in place with his hand. This action prevented him from using the collective control. The aircraft was observed climbing in an increasingly steep, nose-up attitude. As the helicopter reached approximately 1,000 feet, the nose dropped sharply. During the subsequent descent, an explosion occurred, and the aircraft struck the ground approximately 22 nautical miles southwest of Stony Rapids. The impact and a resulting post-crash fire destroyed the aircraft, and the pilot was killed.
The investigation
Investigators examined the wreckage and found that the main rotor mast had fractured and separated from the helicopter. The damage pattern, specifically the symmetrical distortion of the mast, was consistent with a phenomenon known as mast bumping. The investigation also reviewed the maintenance history of the Bell 204B, finding that the aircraft had been properly maintained and was within weight and balance limits at the time of the accident.
Regarding the cockpit door, investigators found that the latches were in the unlatched position. While a ground worker had attempted to secure the door prior to takeoff, it is believed the pilot failed to fully engage the mechanism upon re-entering the cockpit. A review of the pilot's experience showed significant flight time, though the investigation noted that recent company training did not specifically cover the hazards of mast bumping.
Findings
- The left-side bubble door opened during flight, likely because it was not properly latched.
- While preoccupied with the door, the pilot allowed the helicopter to enter a low-g condition.
- The lack of collective control prevented the pilot from applying the necessary aft cyclic to recover from the nose-high attitude, leading to mast bumping and the subsequent in-flight structural breakup.