What happened
In the late afternoon in the Yukon, a Bell 206B helicopter was tasked with transporting a two-person initial attack fire crew to a forest fire located approximately 20 miles away in Northern British Columbia. Shortly after departing from the Watson Lake area, the aircraft's engine lost all power at an altitude of roughly 300 feet.
The pilot attempted an emergency autorotation toward a nearby secondary road. However, the aircraft overshot the intended landing area and struck a stand of spruce and pine trees. The impact destroyed the helicopter and resulted in one fatality and two serious injuries.
The investigation
Investigators examined the circumstances leading up to the engine failure and the maintenance activities performed prior to the flight. It was noted that the pilot had spent several hours washing and grooming the aircraft, specifically attempting to clear a clog in the engine pan drain tube.
Laboratory analysis of the fuel system and physical examination of the airframe revealed scratches inside the fuel cell vent tube, suggesting it had been probed with a wire. The investigation focused on the proximity of the engine drain tube to the fuel vent tube, noting that both tubes are visually similar and lack required external labels on older models.
Findings
- The engine failure was caused by water-contaminated fuel.
- The pilot likely introduced water into the fuel system by accidentally back-flushing the fuel cell vent tube with a water hose while attempting to clean the adjacent engine drain tube.
- The low altitude at the time of the engine failure prevented a successful autorotation to the road.
- The engine pan drain tube is prone to clogging with debris, which prompted the maintenance attempt.
- The fuel cell vent tube was not clearly identified by a label or decal, making it easy to misidentify.
Safety action
Following the accident, the operator issued a technical memorandum requiring all drain and vent lines on their Bell 206 fleet to be clearly identified. The memorandum strictly prohibits the back-flushing of any lines to prevent system contamination. Additionally, Transport Canada has worked to inform operators of the risks associated with improper washing techniques and the potential for vent line contamination.