What happened
A McDonnell Douglas MD-900 medevac helicopter was dispatched to attend to a motor vehicle accident located in an area characterized by high terrain and dense trees. Before attempting to land, the pilot contacted ground personnel to inquire about the presence of overhead wires; the personnel reported that no wires were present.
After landing, the pilot conducted a visual inspection of the landing zone and the intended departure path for any potential wire hazards, reporting that none were observed. The departure from the accident site occurred during dusk to dark night conditions. Due to the narrow constraints of the canyon, the pilot initiated a vertical climb. During this maneuver, the helicopter struck unmarked transmission lines at an altitude of approximately 150 feet above the ground.
Following the impact, the pilot determined that the aircraft remained controllable and exhibited no unusual flight characteristics. Consequently, the crew elected to continue the flight to their destination.
The investigation
A post-flight examination of the aircraft was conducted to assess the extent of the damage caused by the strike. The inspection revealed crazing on the windscreen and significant damage to four of the five main rotor blades. The damage to these components was severe enough to require major repair or full replacement.