20210122000119A

01-22-2021 N60BK, MD600N. Pilot (PIC) obtained aviation weather from foreflight before departing mankato MN (kmkt) airport in the morning enroute to the field site named LZ61. In the morning he flew class b 133 operations in support of power line operations while training another pilot from the right seat. In the afternoon, he was single pilot in the left seat. He departed LZ61 with about 1/2 tank of fuel and flew to pull site #68. He landed and the ground team connected the feeder line (rope) for pulling cable. The ground team informed him the hydraulic brake would not release to allow cable pulling operations. The aircraft was unhooked and the PIC flew back to LZ61. The PIC was then radioed that they had fixed the issue. He departed LZ61 for #68 to continue with 133 operations. About 1/2 way to #68, he was radioed that there were still issues with the ground equipment. The pilot turned around and was returning to LZ61. He was flying at about 250FT AGL with the power pole towers out his right and below him. The pilot stated the towers are about 110FT high. At this time they had 3 cables runs installed on them (3/8 inch steel cables) two on the bottom fixtures and one on the middle. He stated that flying parallel to the wires, like he was, is the common practice as it is part of the right of way for the power company. As he neared LZ61 and began his descent to land the PIC was distracted as he started calculating fuel use during the flight to decide if there was need to refuel (LZ61 contained the refuel truck). Instead of performing a visual scan of the flight path the PIC checked his flight timer and fuel gauge. The aircraft flight timer showed he was 14 minutes into the flight and he checked his fuel which showed 700# remaining. When the PIC looked up from checking the instruments he noticed the aircraft had drifted to the right toward the wires so he made a left cyclic input correction. Out of the corner of his eye he saw the strung cable and heard the loud noise of the main rotor blades striking the middle cable. He believes the aircraft was at about 95FT AGL. He continued his left descent and landed at LZ61 without incident approxametley 5 seconds after impact. From wire strike to landing he stated the aircraft controlability was normal but he did notice the blade track appeared to be different. The aircraft was immediately shut down after landing. Post flight inspection revealed visible damage to 4 of 6 main rotor blades.

The PIC stated he realized the wires and the road made for a smaller area of operations at LZ61, by flying the left side of the wires sw bound, when you arrive at LZ61, it makes for a tight turn to landing because the perpendicular gravel road is at less then 90 degrees to the power lines. When they started this job, this lz was muddy and the support truck would park just off the gravel road at the field access drive which is close to the wires. Now that the field is frozen, the truck and lz could have been moved east down the gravel road further from the wires.