On April 20, 2002, at 1444 eastern daylight time, a Robinson R-22, N8414H, was substantially damaged when it impacted the ground while hovering at the Long Island Mac Arthur Airport (ISP), Islip, New York. The certificated flight instructor received serious injuries, and the student pilot was not injured. Visual meteorological conditions prevailed for the local instructional flight. No flight plan was filed, and the flight was conducted under 14 CFR Part 91. According to the instructor, he boarded the helicopter, along with the student, started the engine, and departed the airport area to conduct some level flight training. After approximately 20 minutes, they returned to the airport, and began doing some hover training to the southeast of the approach end of runway 24. About 40 minutes later, while hovering into the wind at 5 to 10 feet agl, the instructor felt a gust of wind push the helicopter to the left and down. The helicopter impacted the ground, rolled onto its left side, and then slid several feet before coming to a stop. The instructor secured the electrical master, and pulled the mixture control to the "OFF" position, (he could not remember if the engine was running). He released his and the student's restraint harness, opened the door on the student's side, and both egressed the helicopter. About 2 minutes later airport emergency vehicles arrived. It was determined the instructor had injured his shoulder and would require medical attention. He was taken to a local hospital, and diagnosed with a broken clavicle. The instructor added that when the accident happened, he was in the left seat, and making about 70 percent of the control inputs, and the student was making about 30 percent. The wind was approximately 220 degrees and 8 to 10 knots. Other than during the accident sequence, the instructor identified no change in the wind, either before or after the accident, nor did he recall any airplanes taking off or landing on runway 24 or 15. He also stated that he did not experience any preimpact failures or malfunctions with the helicopter. In addition, the student had approximately 5 hours of flight experience in helicopters. According to the student, they had just turned the helicopter into the wind, and were hovering approximately 15 feet agl, when he felt a gust of wind from the right. The helicopter started to settle and drift left. The next thing the student knew, the helicopter was on its left side, and the accident sequence was over. The student also did not remember any airplanes taking off or landing on runway 24 or 15 at the time of the accident. A weather observation taken at the airport about 12 minutes after the accident recorded the weather as wind 280 degrees at 8 knots, visibility 10 miles, thunderstorms in the vicinity with light rain, temperature 57 degrees Fahrenheit, dew point 54 degrees Fahrenheit, and an altimeter setting of 29.86 inches Hg.