On May 18, 2001, at 1000 central daylight time, a Robinson R22 helicopter, N7087X, was substantially damaged when it impacted trees and terrain following a loss of main rotor rpm while maneuvering near Raymondville, Texas. The commercial helicopter pilot and his pilot-rated passenger were not injured. The helicopter was registered to and operated by the pilot. Visual meteorological conditions prevailed and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 personal flight. The local flight departed a private ranch approximately 5 minutes prior to the accident. During a telephone interview conducted by the NTSB investigator-in-charge and in a written statement, the pilot reported that the helicopter had been in flight for approximately 5 minutes before the main rotor rpm began to decrease. The pilot stated that the "clutch light" illuminated and the "low rotor horn sounded." The pilot initiated an autorotation to an open field; however, he did "not have enough altitude" to clear some trees. The helicopter contacted the trees and impacted the ground "hard." According to the pilot and the FAA inspector, who responded to the accident, the helicopter sustained structural damage to the tail boom, the landing skids, and the horizontal stabilizer. The main rotor blades also sustained damage. The main rotor drive belts were found separated from the drive wheels. According to a written statement provided by an aircraft mechanic and the FAA inspector, the drive belts were found "frayed and ripped." No anomalies were noted with the rest of the drive system. The helicopter (serial number 2829) was issued an airworthiness certificate on May 27, 1998. Review of the helicopter's maintenance records revealed that it had undergone its last annual inspection on February 10, 2001, at an aircraft total time of 409.2 hours. At the time of the accident, the helicopter had accumulated a total of 488 hours. There was no record of the drive belts being replaced during the life of the helicopter. According to Robinson Helicopter Company, the drive belts should be replaced on condition, and there is no scheduled life limit for the belts; however, the belts usually get replaced during the helicopter's 2,200-hour overhaul.