On May 4, 1999, approximately 1000 mountain daylight time, a Piper J3C-65, N6563H, owned by Cub Air, LLC, and operated by The Pilot Center, was substantially damaged when it nosed down while turning at Downtown Airpark, Fort Collins, Colorado. The commercial pilot and his passenger were not injured. Visual meteorological conditions prevailed for the local personal flight that was to be conducted under Title 14 CFR Part 91, and no flight plan had been filed. The flight had not yet originated. The pilot said the wind was from 290 degrees at 10 knots with gusts to 20 knots "or less." After completing the pre-takeoff checklist, the pilot turned the airplane 360 degrees to check for traffic before taxiing onto the active runway. When the airplane had made a 180 degree turn (tail directly into the wind), an "unexpected strong gust of wind" lifted the tail and the airplane nosed down. Another wind gust caused the airplane to nose over onto its back. At 0955, five minutes before the accident, the following weather observation was recorded at Fort Collins-Loveland Municipal Airport (FNL), located 11 miles south of the Fort Collins-Downtown Airpark: Wind, 290 degrees at 14 knots, gusts to 21 knots; sky condition, clear; visibility greater than 10 miles; temperature 11 degrees C. (51.8 degrees F.); dew point -4 degrees C. (24.8 degrees F.); altimeter, 29.37 inches of mercury.