On November 15, 2000, at 1030 hours mountain standard time, a Eurocopter AS-350-B3, N972AE, was substantially damaged during a hard landing at Falcon Field, Mesa, Arizona. The airline transport certificated instructor pilot and the certificated commercial pilot under instruction were not injured. No flight plan was filed for the local area instructional flight, which departed from Falcon Field about 1000. The flight was operated under 14 CFR Part 91 by Petroleum Helicopters, Inc. Visual meteorological conditions prevailed. The pilot reported that he had demonstrated an autorotation landing and then turned control of the helicopter over to the student to perform the next autorotation landing. The student's entry was abrupt resulting in first, high rotor rpm, then low rpm; however, the rpm was proper prior to initiating the landing flare. The student's initial pitch application during the flare was a little too high but okay. As the aircraft neared the landing, additional collective was applied, but it was insufficient to check the sink rate and the heels of the skids made ground contact, rocking the helicopter first forward onto the toe of the skid and then back down on the full skid. The pilot heard a metallic sound and, on external inspection, found the tail boom was bent down. The pilot noted that a ballast installation in the tail boom might have contributed to the accident. The helicopter was configured for EMS (Emergency Medical Service) use with a stretcher installation. Part of the EMS modification moved the 48-pound battery into the tail cone forward of the stabilizer and installed a ballast station rated for up to 19.22 pounds of lead ballast in the tip of the tail cone. Both the battery relocation and the ballast installation were installed in accordance with an American Eurocopter Supplemental Type Certificate (STC). The accident helicopter was carrying 18.3 pounds of lead ballast in addition to the relocated 48-pound battery.