On June 29, 2013, about 1130 central daylight time, a Hiller UH-12A, N6331D, impacted terrain during an attempted landing on a tow trailer near Florence, Alabama. The student pilot was seriously injured. The helicopter was registered to River Cleaning Inc., and operated under the provisions of Title 14 Code of Federal Regulations Part 91, as a positioning flight. Visual meteorological conditions prevailed for the flight and no flight plan was filed. The flight originated from a parking area in the vicinity of the tow trailer just prior to the accident.According to a Federal Aviation Administration (FAA) inspector, who conducted an interview with an eyewitness, the student pilot was attempting to land the helicopter on the trailer in order to transport it to another location. He stated that the helicopter was hovering above the trailer when it started to drift backward. As the helicopter moved back, the nose of the helicopter started to rise and the tail subsequently struck the ground. The helicopter then rolled to the right, the main rotor blades struck the ground, and the helicopter came to rest on the right side of the fuselage, which resulted in substantial damage. According to the FAA inspector, numerous attempts to interview the pilot were unsuccessful as the pilot has no recollection of the events surrounding the accident and that the pilot's flight experience was about 38 total flight hours. Examination of the helicopter at the accident location revealed that it had come to rest on its right side in the immediate vicinity of the trailer. The helicopter sustained substantial damage to the main rotor blades, skids, and fuselage. No mechanical malfunctions or abnormalities were noted that would have precluded normal operation.