On January 24, 2004, at 1650 eastern standard time, an Eurocopter EC120B, N125MG, registered to KSB Domestic Holdings, Inc, and operated by the flight instructor, collided with the ground during a practice autorotation at the Clayton County -Tara Field Airport in Jonesboro, Georgia. The instructional flight was operated under the provisions of Title 14 CFR Part 91, and visual flight rules. Visual meteorological conditions prevailed and no flight plan was filed for the local flight. The certified flight instructor (CFI) and the air transport pilot, (dual-student), were not injured and the helicopter sustained substantial damage. The flight originated from Peachtree City - Falcon Field, at 1600 on January 24, 2004. The CFI and the dual-student had completed five practice touchdown autorotations without any incident. However, during the accident autorotation, the CFI stated that the dual-student had placed the helicopter in an autorotative descent and his cross-check showed normal rotor RPM indications. At 50 feet above the ground, the in CFI told the student to "progressive decel" and at six feet above ground to "cushion". The dual student pulled additional rear cyclic and the tail stinger struck the ground. As the helicopter rebounded into a nose low attitude the CFI pulled collective and aft cyclic to level the helicopter for touchdown. However, a loud noise was heard after the tail stinger hit the ground and the helicopter rebounded. According to the CFI, during the touchdown phase of the autorotation, the main rotor blades made contact with and severed the tail boom. The helicopter landed and the CFI shut down the engine. The CFI did not report any mechanical malfunctions with the helicopter prior to the accident. Examination of the helicopter revealed damage to the main rotor blades and the tail boom severed. The FAA Rotorcraft Flying Handbook includes the procedures for a straight-in autorotation. Part of the technique section states that "care must be taken in the execution of the flare so that the cyclic control is not... moved so slowly as to not arrest the descent, which may allow the helicopter to settle so rapidly that the tail rotor strikes the ground." It also states that "extreme caution should be used to avoid an excessive nose high and tail low attitude below 10 feet," to "increase collective pitch, as necessary, to check the descent and cushion the landing," and to "...not try to stop the forward ground run with aft cyclic, as the main rotor blades can strike the tail boom." Two of the common errors that the handbook lists for straight-in autorotation are: (1) application of up-collective pitch at an excessive altitude resulting in a hard landing, loss of heading control, and possible damage to the tail rotor and to the main rotor blade stops and (2) failing to level the helicopter.