What happened
On a morning flight near Alice Arm, British Columbia, an MD Helicopter 369D, registered C-GZIO, crashed during its initial departure of the day. Operated by Prism Helicopters for mining exploration support, the aircraft was carrying one pilot and three passengers toward a drill site in the Kitsault River valley.
As the helicopter began a shallow left-hand climb, an unusual noise was heard. Upon reaching approximately 150 feet above the ground, the aircraft suddenly banked 90 degrees to the right and descended rapidly. The helicopter struck a fallen tree and broke apart upon impact. The main section of the aircraft and all occupants fell into the Kitsault River, where they remained largely submerged. All four occupants sustained fatal injuries during the crash. A small fire ignited on the riverbank following the impact but extinguished without intervention.
The investigation
The investigation examined the maintenance and pre-flight procedures of the aircraft and the pilot's recent activity. The pilot, an experienced aviator with over 11,000 flight hours, was fully qualified and well within his duty time limits. The aircraft was found to be maintained and equipped according to all regulatory requirements.
Investigators focused on the presence of a synthetic heavy material cover, known as a "doghouse cover," which is used to protect the engine intake and main rotor control system during storage. While an apprentice engineer was on-site to assist with securing the aircraft at night, the investigation determined that the cover had not been removed prior to takeoff.
Findings
- The doghouse cover remained installed during the flight, causing it to wrap around the flight control linkage and damage the mechanism.
- The binding effect of the cover between stationary and rotating parts of the swashplate assembly likely caused a loss of rotor RPM.
- The failure to remove the engine cover rendered the helicopter uncontrollable.
- The lack of physical barriers or visual cues to alert the pilot to the cover's presence, combined with potential distractions during passenger loading, contributed to the oversight.
- The practice of having another individual install the cover may have reduced the pilot's mental awareness of the task's necessity.
Safety action
Following the accident, Prism Helicopters updated its procedures to require that blade tie-downs be used whenever the doghouse cover is installed. Additionally, the covers have been modified with straps that hang into the front doors to serve as a visual reminder. The manufacturer, Aerospace Filtration Systems Inc., has also implemented modifications to the cover design.