On April 25, 2004, about 1400 Pacific daylight time, a Piper PA-28R-200, N169JP, made a hard landing at Franklin Field Airport, Galt, California. Ahart Aviation Services was operating the rental airplane under the provisions of 14 CFR Part 91. The certified flight instructor (CFI) and the commercial pilot undergoing instruction (PUI) were not injured; the airplane sustained substantial damage. The cross-country instructional flight departed Livermore Municipal Airport, Livermore, California, about 1300. Visual meteorological conditions prevailed, and no flight plan had been filed. In a written report, the PUI stated that the purpose of the flight was to practice short-field takeoff and landings on runway 27 at the Franklin Field Airport. While on short final, the PUI noted that the airplane appeared to be slow, indicating an airspeed of about 80 mile per hour. As he flared, the airplane touched down hard on the main landing gear. He initiated a go-around and attempted to return to the Livermore. While en route, he cycled the landing gear and noted that it would not lock in the retracted position. The landing gear was able to lock in the down position and the airplane landed uneventfully. The PUI further stated that both he and the CFI were not aware that the airplane sustained structural damage to several wing ribs until maintenance personnel examined the airplane the following morning. In a written report, the CFI stated that after completing several landings uneventfully the PUI was attempting another practice landing. The PUI maintained a slow airspeed on short final, and the airplane landed hard, touching down on the left main landing gear first. The PUI immediately initiated a go-around. On upwind, both pilots noticed that the landing gear transition light stayed illuminated. The light remained illuminated after several attempts to recycle the landing gear. On two separate Pilot/Operator Aircraft Accident Reports (NTSB Form 6120.1/2), both pilots indicated that there were no mechanical malfunctions or failures with the airplane or engine prior to the hard landing.