On November 29, 1998, approximately 1756 mountain standard time, a McDonnell Douglas MD-900 helicopter, N977LF, registered to Alvac, Inc., operated by Idaho Helicopters, Inc., and being flown by a commercial pilot, sustained substantial damage when it collided with unmarked transmission lines. The collision occurred during the initial climb immediately following takeoff approximately eight miles south-southwest of Idaho City, Idaho (refer to CHART I). The pilot, nurse, EMT, and patient were uninjured. Visual meteorological dusk to dark night conditions prevailed, and a company flight plan was in effect. The flight, which was an unscheduled medevac pickup of a car accident victim, was to have been operated under 14CFR135, and was destined for the St. Alphonsus hospital heliport, Boise, Idaho. The pilot reported that the helicopter was dispatched to the accident site and "prior to landing the ground crew was asked about wires and the[y] said there were none" and "no wires were observed by the front passenger crew member, pilot or ground personnel." He also reported that the approach to the landing site was steep with high trees and terrain, and that after landing he "took [a] flashlight and surveyed obstructions and looked for wires ahead in [the] direction of takeoff" with "none seen other than trees." He further reported that he "elected to do a vertical takeoff since due to the narrowness of the canyon" and that "the vertical takeoff was initiated and at approximately 150' I rotated forward and at approx[imately] 20 kts a loud noise similar to equipment falling in the back and a bright white light flashed." The pilot assessed the controllability of the helicopter and determined that there were no unusual vibrations or instrument readings, and an onboard crew member reported that "he had seen or thought we had hit wires." "Due to no adverse flight characteristics and all instruments reading normal and no safe landing area available" the pilot elected to continue to his destination. Post-flight examination revealed crazing of the windscreen and damage to four of the five main rotor blades requiring major repair/replacement.