Incident Details
A medical evacuation helicopter, after arriving at its designated landing zone at 6,500 feet mean sea level (MSL), performed an out-of-ground-effect hover to verify aircraft performance. The power check was satisfactory and a positive rate of climb was noted. After landing and crew egress, the pilot departed to locate a landing zone closer to the patient pickup point. A landing zone at 6,600 feet MSL, 3/8 mile nearer to the patient, was selected.
While awaiting the patient, the pilot assessed takeoff performance using the aircraft's data. Following an in-ground-effect power check, the pilot initiated a vertical climbout and confirmed the helicopter would clear a 100-foot tree line as it began forward transition. After clearing the tree line, the pilot detected a complete loss of lift, and the helicopter began to settle toward the trees. Applying remaining power triggered a rotor RPM warning, prompting the pilot to reduce collective. However, the helicopter continued descending toward obstacles. Right pedal was applied to return to the departure point, but rotor RPM had not fully recovered, and the descent continued.
The aircraft impacted a boulder, after which rotor RPM fully recovered, causing the helicopter to jump back into the air. The helicopter then rotated 180 degrees before the pilot executed a hover autorotation. During the maneuver, the tail rotor struck a tree branch, resulting in an 8-inch chordwise gash to one tail rotor blade.
Environmental Conditions
A weather reporting station 7 miles west-northwest of the accident site reported wind variable at 3 knots. The density altitude was calculated to be 8,898 feet. The pilot believed that as the helicopter cleared the tree line, it entered an unanticipated downwind condition, which reduced the power margin available to overcome the loss of lift.
No Mechanical Issues
The pilot did not assert any mechanical malfunctions contributed to the accident.