On February 13, 1999, at 1645 central standard time, a Eurocopter BK 117 B-1 helicopter, N220HH, was substantially damaged when it impacted power lines during takeoff climb near Hockley, Texas. The commercial pilot, the two medical crewmembers, and the two previously injured patients did not receive any injuries. Visual meteorological conditions prevailed and a company flight plan was filed for the Title 14 CFR Part 135 air medical transport flight destined for the Hermann Hospital of Houston, Texas. The helicopter was registered to Memorial Hermann Hospital System of Houston, Texas, and operated by Hermann Hospital, Life Flight. The operator reported that the helicopter was part of a two aircraft team that was dispatched to the scene of an automobile accident near Hockley, Texas. During the approach for landing on highway 6, the pilot noticed power lines running parallel to the road; however, he did not consider them to be an unusual hazard at the time. After the patients were loaded in the helicopter, the pilot took off and impacted the power lines. The pilot mentioned that he felt a light shutter but no loss of control and set the helicopter back down in a field adjacent to the road. Another helicopter was dispatched to the scene of the accident to transport the patients to the hospital. The pilot of the other helicopter at the automobile accident scene witnessed the accident. The witness stated that he performed a "safety walk around" for the departing helicopter and signaled that everything was O.K. He noticed the helicopter lift up and drift towards the power lines where the main rotor blades contacted the wires. In the enclosed Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) the pilot stated that during takeoff he noticed "trash blowing around," and that "the sun was shining directly into the windscreen." The pilot added that at the time the aircraft impacted the wires, he didn't see them, nor did he remember making any control input to cause the helicopter to move toward the wires. Inspection of the helicopter by a certified aircraft mechanic revealed that the undersides of the main rotor blades were damaged and that two of the tail rotor blades were destroyed. Notification from the Houston Electric Company revealed that four primary distribution cables 5/8ths of an inch in diameter were severed, interrupting electrical power to the local area. At the time of the accident, the pilot had accumulated approximately 3,026 hours in the BK 117 helicopter.