On March 19, 1997, at 1730 central standard time, a Hiller UH-12E helicopter, N136HA, was substantially damaged when it impacted wires while maneuvering near Donna, Texas. The commercial pilot, sole occupant of the helicopter, was seriously injured. The helicopter was being operated by the pilot under Title 14 CFR Part 137. Visual meteorological conditions prevailed for the aerial application flight for which a flight plan was not filed. The helicopter's time of departure is unknown. According to local law enforcement personnel, the helicopter impacted a set of north-south aligned power lines at the mid point between two poles during an aerial application flight. The helicopter came to rest on its side in an onion field approximately 400 feet east from the point of impact with the wires. Authorities further reported that wires were found wrapped around the helicopter's tail rotor assembly. According to the FAA inspector, the helicopter approached the dark green onion field to be sprayed from the east, while flying over a fleshly plowed field which exhibited a light tan/sandy shade of color. The FAA inspector added that the poles and the power lines that the helicopter impacted lay directly between light and dark colored fields. Examination of the helicopter revealed that the lower portion of the fuselage structure sustained structural damage, the skid landing gear collapsed and the fertilizer tank was intact. Imprints of the electrical wires were found on the front landing gear cross tubes. The pilot was interviewed by an FAA inspector at the hospital. The result of the interview is enclosed in the attached inspector's statement. Numerous attempts, albeit unsuccessful, were made by the NTSB investigator-in-charge to obtain a Pilot/Operator Report (NTSB Form 6120.1/2) from the pilot/operator of the helicopter.