On January 2, 2013, about 1810 eastern standard time, a Robinson R22 Beta, N345VH, was substantially damaged following a practice autorotation to runway 22 at Peter O Knight Airport (TPF), Tampa, Florida. The flight instructor and a student pilot were not injured. The helicopter was operated by Helicopter Academy under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed and no flight plan was filed. The flight originated at Clearwater, Florida (PIE) about 1715. The flight instructor reported that she landed at PIE to pick up her student and proceeded to TPF for approaches and practice autorotations. The first three approaches were uneventful. During the fourth approach to runway 22, the student entered a practice autorotation at 500 feet above ground level (agl) and at 70 knots. About 40 feet agl, the student bled off airspeed by making “baby flares.” She reported that the student rolled on the throttle, but the governor did not catch and the rpm started to decay. The instructor had her hands on the controls and added throttle to arrest the rpm decay. When the rpm continued to decay, she took the controls and performed a hovering autorotation. The helicopter impacted a grassy area next to the runway, bounced, and rolled over, coming to an immediate stop. A Federal Aviation Administration (FAA) inspector responded to the accident site and examined the wreckage. The inspector confirmed substantial damage to the airframe. Both main rotor blades were bent in several places. The engine firewall was buckled. The tail boom was crushed at the fuselage attachment point and the horizontal stabilizer was bent about 90 degrees. The flight instructor reported to the inspector that there was excessive “play” in the left throttle and she had reported the condition to the operator’s maintenance personnel twice previously, and was informed that the play was normal. On January 8, 2013, the FAA re-inspected the helicopter throttle system with the assistance of a technical representative from Robinson Helicopter Company. The inspector reported that, based on the description of the throttle rigging provided to the technical representative, the throttle was in an airworthy condition. Recorded weather at PTF at the time of the accident included calm surface wind.