What happened
During a firefighting operation, the crew was performing a right-hand turn onto final approach toward a dam. As the sun moved low in the west, shadows from the surrounding steep terrain obscured the visibility of the wind conditions. The crew observed a glassy surface on the water, leading them to believe winds had lightened, though a light tailwind was actually present.
Satellite data indicates the approach involved a 1-50 m radius turn with a 30° bank angle. While flight parameters remained within operational limits, the final approach was significantly shorter than previous maneuvers. This shortened path necessitated a steeper than normal flare to arrest the descent. As the aircraft descended below the tree line, it lost lift and struck the water. The crew reported that the aircraft likely entered a vortex ring state (VRS), a condition exacerbated by the high rate of powered descent and the steep flare used to compensate for the short approach.
The investigation
The investigation examined the flight path and the environmental conditions at the time of the accident. Investigators found that the topography of the dip site, characterized by steep sides and a narrow, tapered shape, left the crew with insufficient space or time to maneuver the aircraft sideways to recover from the VRS.
Furthermore, the investigation looked into the presence of the Crew Chief on board. While the operator's manual allowed for essential crew only, the Crew Chief was present during this mission. Investigators noted that while his presence was not required, it exposed him to the specific hazards of underwater egress.
Findings
- The aircraft's approach was much shorter than usual, requiring a steep flare that reduced airspeed and contributed to the vortex ring state.
- The terrain and the narrow shape of the dam prevented effective recovery maneuvers.
- The presence of the Crew Chief during specialized firefighting operations increased the risk of injury during the submersion.
- The crew's survival was directly attributed to their proficiency in Helicopter Underwater Escape Training (HUET).
- The ability to release helmet cord extension cables easily was a critical factor in the crew successfully exiting the flooded cockpit.