On October 8, 1994, at 0735 hours Pacific daylight time, an Enstrom F-28C helicopter, N5697D, was substantially damaged during a hard landing approach near La Verne, California. Visual meteorological conditions prevailed for the instructional flight and no flight plan was filed. Neither the certified flight instructor (CFI) nor the dual student were injured. The flight originated at La Verne about 0720 hours. The instructor stated that they were to practice pinnacle landings. They flew about 5 miles north to a practice area. The elevation was 2,500 feet mean sea level. A go-around was made during the first approach. During the second approach, the CFI stated that the site picture had steepened, so he started assisting on the controls to regain the proper angle. The CFI stated: "Within seconds, it became obvious that the wind had reversed and was now behind the helicopter which was settling with power." The CFI attempted a recovery; however, there was not enough altitude, and the helicopter landed hard. The instructor stated that they had planned their approach into the prevailing wind which was near calm at the time of the accident. He stated that there may have been a wind shear at the time of the approach. On the pilot/operator accident report form, the CFI reported the winds as variable at 10 knots with gusts to 20 knots. There were no formal wind direction indicators at the accident site.