On August 3, 1999, at 2030 mountain daylight time, a Beech A23-24, N4789J, sustained substantial damage when it was involved in a hard landing during an instructional flight at Wheatland, Wyoming. The certified flight instructor and student pilot were not injured. The flight was a local flight operating under Title 14 CFR Part 91 and no flight plan was filed. Weather at the time was reported by the flight instructor to be bright night visual meteorological conditions. Damage to the aircraft was discovered on June 9, 2000, by an inspector from the Casper, Wyoming, Federal Aviation Administration (FAA) Flight Standards Field Office (FSFO) during a routine inspection. Beegles Aircraft Services, Greeley, Colorado, and Flight Vehicles, Inc., Houston, Texas verified the extent of damage. According to these two repair stations, both wings required replacement or extensive structural repair. According to the flight instructor, the student pilot froze on the controls during flare for landing and he took control. The airplane landed hard and a go around was executed. Following the next landing, which was a full stop, inspection revealed wrinkles in the upper surfaces of both wings. The flight instructor said he thought the damage was "cosmetic" and the aircraft flew at least 20 times before the damage was discovered by the FAA inspector.