The pilot reported that during a mustering operation he had descended to tree top height to force out a mob of cattle. He then turned downwind towards some other animals, and increased power. The helicopter did not respond as he had expected and began to lose height. The pilot stated that that there was insufficient room to recover and he guided the helicopter into the only clearing available. The aircraft landed heavily, and the main and tail rotor blades struck trees. The pilot reported that the wind was gusting to 15 knots at the time of the accident. The pilot stated that he did not notice any symptoms of engine malfunction and was unsure if the sink was due to insufficient power or overpitching. No engine defects were evident during examination after the accident. The reaction of the helicopter was most likely due to the combined effects of turning downwind and possible overpitching.
