Incident Overview
During a confined area takeoff, the helicopter passed through effective translational lift (ETL) when the pilot noticed a reduction in engine noise. Both the engine and rotor rpm needles were still joined at a position just below the bottom of the green arc.
Pilot Actions
The pilot lowered the collective and rolled the throttle full on without obtaining an increase in engine rpm. He initiated a straight-in autorotation.
Ground Slide and Damage
During the ground slide, a skid contacted a rock and the tail boom yawed. The tail boom then struck a tree and separated from the aircraft.
Post-Incident Examination
The main rotor drive belt was disconnected, and a run-up check was performed on the engine. The engine ran throughout the normal operating range, and magneto checks were within tolerances. The engine air cleaner was removed and exhibited trapped dirt and grass.