Pilot Heard A Loud "Bang" -- Followed By The Low Rotor RPM

On April 6, 2020, about 1410 Pacific daylight time, a Robinson R44 Raven II helicopter, N725GT, was substantially damaged following a forced landing at Portland-Hillsboro Airport (HIO), Portland, Oregon. The pilot was not injured. The helicopter was registered to and operated by the Horizons Unlimited Air Inc. as a Title 14 Code of Federal Regulations Part 91 flight. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight destined for Warren, Oregon. The pilot reported that, during takeoff, about 30 to 40 ft above ground level, he heard a loud "bang", followed by the low rotor RPM. In response, he lowered the collective and performed an autorotation on