On January 20, 2004, about 0950 mountain standard time, an Eurocopter AS 350 B3, N970AE, landed hard during a practice autorotation at the Falcon Field (FFZ) airport, Mesa, Arizona. The helicopter came to rest on its right side. Petroleum Helicopters, Inc., was operating the helicopter under the provisions of 14 CFR Part 91. The airline transport certificated flight instructor, the commercial pilot undergoing instruction (PUI), and one passenger, were not injured. The airplane sustained substantial damage. The local instructional flight departed Phoenix Sky Harbor International Airport (PHX), Phoenix, Arizona, at 0910, en route to Falcon Field. Visual meteorological conditions prevailed, and no flight plan had been filed. In a written statement, the flight instructor reported that the purpose of the flight was to give the PUI the recurrent flight checks required by 14 CFR Part 135. They entered a landing pattern parallel to 22R. At 500 feet above ground level (agl) and 80 knots indicated airspeed (IAS), the flight instructor initiated an engine failure. The PUI responded appropriately and entered an autorotation with 60 knots IAS and 398 rpm rotor speed (Nr). At 60 feet agl, the PUI began the flare; however, it was more aggressive than necessary for the conditions. The PUI then lowered the nose after being advised by the flight instructor to do so. At 30 feet agl, the PUI began to increase the collective; the Nr dropped to 380. The flight instructor announced, "I am on the controls with you," and then, "I have the controls." The flight instructor leveled the helicopter and reduced the collective. About 5 feet agl, the flight instructor initiated the final collective application. As the Nr decreased, the tail rotor lost effectiveness; the helicopter yawed to the left with full right anti-torque pedal applied. The helicopter touched down and the nose was approximately 15 degrees to the left of the direction of travel. The right skid touched down and the helicopter drifted to the right. The helicopter then rolled to the right despite corrective inputs by the flight instructor. He immediately turned the start switch to the "OFF" position and reached for the emergency fuel shutoff handle. The front portion of the right skid dug into the soft turf and pivoted the helicopter forward and the main rotor blades contacted the ground. No mechanical malfunctions were noted with the helicopter.