On September 9, 1999, at 1030 central daylight time (cdt), a Bell 206B, N4010G, piloted by a private pilot, sustained substantial damage when it impacted terrain and objects near Nekoosa, Wisconsin. The pilot and passenger reported minor injuries. The 14 CFR Part 91 aerial observation flight was not on a flight plan. Visual meteorological conditions prevailed during the flight. The local flight departed near Nekoosa, Wisconsin at 1025 cdt. In a written statement, the pilot said that he took off from the southeast side of the Pacific International building, near Nekoosa, Wisconsin, and flew to the west end of the building. He stated that he turned north and flew to the far north end of the property line. The pilot said that he turned right and flew to the east. He said that he "...experienced a hard gust of wind on my tail, causing the aircraft to enter a right spin." The pilot stated that he applied full left rudder and the helicopter did not stop its spinning. He said that he lowered "the nose in an attempt to fly out of the spin, but to no avail again." The pilot stated, "I would need to attempt an auto-rotation to a safe landing." He said that the "landing was hard and the tail spun and hit two cars in the parking lot." The pilot stated that the pass was done in slow cruise and he reported no preimpact mechanical failures or malfunctions. He said that on the way to the building, he checked wind by looking at windsocks approximately 1 to 2 miles southwest of the building. At 1054 cdt, the Wisconsin Rapids, Alexander Field South Wood County Airport, Wisconsin Rapids, Wisconsin observation was: Wind 270 degrees at 15 knots, visibility 10 statute miles, sky condition scattered 2,900 feet broken 4,300 feet; temperature 13 degrees C; dew point 8 degrees C; altimeter 29.81 inches of mercury.