On October 19, 2004, about 1630, Atlantic standard time, a Robinson R-22, N2314T registered to and operated by a private individual, as a Title 14 CFR Part 91 personal flight, had a dynamic roll over during landing in a open field near Fernando Luis Ribas Dominicci Airport, San Juan, Puerto Rico. Visual meteorological conditions prevailed and no flight plan was filed. The private-rated pilot reported minor injuries, one passenger received serious injuries, and the airplane incurred substantial damage. The flight originated from Fernando Luis Ribas Dominicci Airport, San Juan, Puerto Rico, earlier that day, about 1330. The pilot stated that he selected a landing spot in an open field to drop off his passenger. After the approach to the landing area, he hovered about 5 feet and descended slowly to make contact with the ground. Due to the height of the vegetation in the area he could not see the actual ground. Once the helicopter got close to the vegetation, the passenger believed the helicopter had come to a full landing and disconnected his seat belt. The helicopter continued to sink and the pilot decided to abort the landing by raising the collective. One of the skids became tangled on the vegetation, causing a dynamic roll over. The pilot stated there were no mechanical failures or malfunctions to the helicopter or any of its systems prior to the accident.