What happened
The helicopter was traveling on an easterly heading in level flight at approximately 20 knots, performing shallow turns as it followed a creek bed. During the flight, the pilot reported that the aircraft lost all power and lift, leading to a descent toward nearby trees. According to the pilot, the anti-torque pedals became ineffective, causing the helicopter to spin to the right before impacting the trees.
The investigation
Investigators examined the engine, noting that minor repairs had been performed previously to allow the engine to run on the aircraft. Prior to the accident, the engine had been started and operated twice for a duration of 18 minutes within a range of 1300 to 2500 RPM. A representative from the engine manufacturer stated that no pre-existing deficiencies were identified in the engine and found no evidence suggesting the engine was incapable of producing power at the time of the accident.
Findings
The environmental conditions present at the time of the accident were found to be conducive to the formation of a tail rotor vortex ring state.