On September 17, 2001, about 1600 mountain daylight time, a Bell 205 helicopter, N458CC, sustained substantial damage following a main rotor blade strike while conducting firefighting operations near Libby, Montana. The helicopter is registered to Billings Flying Service, Billings, Montana, and was being operated by the United States Forest Service (USFS) as a public use aircraft. The commercial pilot, the sole occupant of the helicopter, was not injured. Visual meteorological conditions prevailed, and USFS VFR flight following procedures were in effect. In a written statement dated September 26, 2001, the pilot reported that he was maneuvering near a shoreline in an effort to get a full bucket of water. "I made 40-50 bucket drops on the fire and flew out my fuel cycle before breaking off from the fire and returned to Troy Airport. On the return flight to Troy airport, I noticed a vertical vibration at approximately 90 knots (forward airspeed)." He continued to Troy airport at a slower speed to avoid the vibration. After landing without incident, the pilot noted damage to the helicopter's main rotor blades. He also noted that pine needles had been ingested into the aircraft's induction system. The pilot did not recall coming into contact with anything during the flight. Personnel from the USFS reported that the helicopter was conducting external load long-line (100 feet) operations when the helicopters main rotor blades contacted trees. Postaccident examination of the helicopter, by a certified mechanic, revealed that both main rotor blades sustained substantial damage. The pilot stated that the weather was clear with more than 20 miles visibility, with the sky partially obscured by occasional smoke. The pilot reported no mechanical failure or malfunction of the aircraft.