On February 25, 2006, between 1330 and 1400, a Schweizer 269C-1, N61466, impacted power lines and crashed into a dry wash area of the Santa Clara River about 40 feet below the lines. The accident occurred about 2 miles south-southwest of Valencia, California. The helicopter was operated by Group 3 Aviation, Inc., Van Nuys, California, and it was destroyed. The certified flight instructor (CFI) held a commercial pilot certificate, and he was seriously injured. The student pilot was fatally injured. Visual meteorological conditions prevailed at the time of the instructional flight, and no flight plan was filed. The maneuver (phase of flight) performed at the time of impact was not determined. The flight was performed under the provisions of 14 CFR Part 91, and it originated from Van Nuys about 1230. Representatives from the Southern California Edison Company reported to the National Transportation Safety Board investigator that its unmarked power lines were impacted and severed by the accident helicopter. The lines had been supported from poles located to the north and south of the Santa Clara River. The Federal Aviation Administration coordinator reported that the helicopter crashed onto the near level ground an estimated 200 feet from the lines. The helicopter came to rest on its right side. The student pilot was located in the right seat. The right side Plexiglas canopy (bubble) was shattered. The tail boom was intact. All of the helicopter's principal components were located in the vicinity of the main wreckage. Evidence of wire strike striations was apparent on a main rotor blade. No evidence of any preimpact mechanical malfunction was noted with the airframe. A representative from Lycoming Engine similarly reported that no evidence of any preimpact mechanical malfunction was noted with the engine assembly. During the accident flight the CFI was providing primary flight instruction to the student, and the student had about 6 hours of total flying experience. The student had not soloed. According to the CFI's employer (operator), the CFI had acquired part time employment as an instructor in December 2005. The accident student was the first student for which the CFI had been assigned to provide flight instruction. No witnesses reported observing the accident. The accident pilot provided a written statement to the Safety Board investigator in which he stated having no memory of the accident flight. In March 2006, the CFI's employer issued specific instructions to its employees regarding the location where off airport flight training was to be accomplished. The accident site area was excluded from the authorized training area.