On December 21, 2006, about 1510 central standard time, a single-engine Eurocopter EC120B turbine powered helicopter, N171AE, was substantially damaged during a hard landing following a practice autorotation at the Grand Prairie Municipal Airport (GPM), near Grand Prairie, Texas. The flight instructor and student pilot were not injured. The helicopter was registered to Wells Fargo Bank Northwest of Salt Lake City, Utah, and was operated by American Eurocopter of Grand Prairie, Texas. Visual meteorological conditions prevailed and no flight plan was filed for the 14 Code of Federal Regulations Part 91 instructional flight. The local flight originated from GPM approximately 1430. In a written statement, the 5,943-hour flight instructor reported that during the instructional flight, the student pilot had completed multiple autorotations prior to the accident. On previous landings, the flight instructor noted that "the ground was soft and the aircraft demonstrated a propensity to pitch nose forward on two of the previous touchdowns". The student pilot was executing his fourth 180-degree autorotation to the west grass landing area parallel to Runway 17 when the accident occurred. According to the flight instructor, the student pilot made an appropriate autorotational entry and started his 180-degree turn for a final heading of between 220-degrees and 270-degrees. The flight instructor noted that as they passed through a heading of 200-degrees, the approach became steeper as the helicopter turned into the wind. Passing through approximately 70-feet above the ground (agl), the flight instructor observed that the student pilot would not make the landing area and that there was "no time to power-recover." The flight instructor added that he took over the helicopter controls and elected to land in the grass near the runway. According to the flight instructor, "[the helicopter] touched down with low rotor energy and what seemed like a higher touchdown speed than during runway touchdowns." The helicopter proceeded to skid on the soft grass before digging in and rolling forward on its nose. The rotor blades subsequently impacted the ground before the helicopter rolled and came to rest on its right side. Both pilots were able to exit the helicopter unassisted. An inspector from the Federal Aviation Administration (FAA) responded to the accident site. According to the inspector, the helicopter's tail boom and horizontal stabilizer sustained structural damage. The pilot did not report any abnormalities with the helicopter's flight controls. At 1455, the weather observation facility at GPM reported, wind from 260-degrees at 6 knots, visibility 10 statute miles, clear of clouds, temperature 59 degrees Fahrenheit, dew point 32 degrees Fahrenheit, and a barometric pressure of 29.98 inches of Mercury.