On September 21, 2000, at 1100 mountain daylight time, a Bell 206-L4, N3310, registered to Air Resources Helicopters, and operated by the United States Forest Service as a public use external load operation, collided with trees during descent to the landing zone near Atlanta, Idaho. Visual meteorological conditions prevailed at the time and a company flight plan was in effect. The helicopter was substantially damaged and the commercial pilot, the sole occupant, was not injured. The flight originated from a forest service strip near Graham, Idaho, at an unknown time. In a written statement, the pilot reported that he performed an aerial survey of the drop points (one and two) and determined that there was sufficient room to belly hook the loads in lieu of using a long line. The pilot then returned to Graham to pick up the cargo that was pre-rigged in cargo nets. The pilot reported that as he was descending to drop point two, a ground crew member was talking to him on the radio and giving him distance to the ground information. The load was released and the pilot began a vertical climb to clear trees, and then transitioned to forward flight. The pilot reported that at approximately 40 knots, he felt a one-to-one vertical vibration. Due to the lack of an acceptable landing site, the pilot elected to return the 3.5 miles back to Graham. After landing and upon inspection of the helicopter, it was found that the main rotor blades were damaged. The pilot stated that he was unaware of the collision. Two ground crew members present at the drop point reported that they expected the load to be dropped via a long line, and were surprised when the helicopter approached with the load attached at the belly hook. The drop point was a clearing surrounded by dead (burned) lodge pole pine trees. The ground crew reported that as the helicopter descended, the main rotor blades struck two of the approximate 1-3 inch diameter trees that were located at about the pilot's nine o-clock position. The helicopter continued to the drop spot where the load was released. After the release, the helicopter lifted away to the south of the clearing to return to Graham. The ground crew member who was in contact with the pilot reported that she was "awestruck" when the collision occurred, but allowed the drop to continue and did not notify the pilot of the collision at the time. She later stated, "HINDSIGHT: I should have notified the pilot sooner of strike. Also, I should have discussed using the long line as an option further."