On September 1, 2003, about 1720 Pacific daylight time, a Bell 47D-1, N64580, main rotor struck the tail boom while the pilot was attempting a run-on landing at Chino Airport, Chino, California. Zemlock Helicopters was operating the helicopter under the provisions of 14 CFR Part 91. The student helicopter pilot, who possessed an airplane private pilot certificate, was not injured. The helicopter sustained substantial damage. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot reported in a written statement that he was practicing run-on landings. During the second landing, the right skid dug into the dirt and the main rotor made contact with the tail boom. The pilot did not report any mechanical problems prior to the accident. The pilot had an estimated 2,024 hours of total flight time; approximately 58 of those hours were in helicopters, with 7 logged as pilot-in-command. The Safety Board investigator-in-charge interviewed the helicopter operator. The operator stated that the pilot was practicing run-on landings. During the accident landing, he touched down on the heels of the skids. The helicopter rocked forward and the pilot pulled back on the cyclic. The main rotor blades made contact with the tail boom. The operator also noted that the student was not allowed to practice run-on landings without an instructor on board.