On June 21, 2009, about 0120 eastern daylight time, a Robinson R-22 Beta helicopter, N2306T, collided with trees while executing an emergency autorotation in Del Ray Beach, Florida. The certificated flight instructor (CFI) and student pilot received minor injuries and the helicopter sustained substantial damage. The flight was operated as an instructional flight under the provisions of 14 Code of Federal Regulations (CFR) Part 91, with an instrument flight rules (IFR) flight plan filed. Night visual meteorological conditions prevailed at the time of the accident. The flight originated from the Palm Beach County Park Airport (LNA), Lantana, Florida, at 0105, and was enroute to Kendall-Tamiami Executive Airport (TMB), Miami, Florida, when the accident occurred. According to the CFI, they had taken off from LNA and just opened their flight plan with Miami Center. They were at 3000 feet with an airspeed of 65 -70 knots when he felt a low frequency vibration throughout the helicopter. He described the vibration as being a lateral vibration as if coming from the tailrotor. He did not remember feeling the vibration in the pedal or cyclic, but more of an overall vibration. He took over the controls from the student and lowered the collective, but could not remember if he rolled the throttle off or not. He decided on a spot to autorotate into. He noticed the clutch light was on and one other light, but wasn’t sure which light it was, it’s color or location on the panel. He said the vibration did not get any better or any worse as he reduced power and he never attempted to add power. He was confident there was no overspeed of the engine or the rotor and he did not recall hearing the low rotor RPM warning horn. As they approached the chosen spot, he saw wires and decided on a second spot closer to some trees. The helicopter made contact with the trees and the ground. According to the student pilot, during a change in cruise altitude from 3,500 feet mean sea level (MSL) to 4,000 msl, they felt an airframe vibration. The vibration increased in intensity to a point where they could not read the instrument panel and they both observed the rotor brake light and clutch light illuminate. The CFI took control of the helicopter and initiated an emergency autorotation. During flare/touchdown the low rotor rpm light and horn came on as the helicopter stuck some trees and rolled onto its right side. Examination of the helicopter by a Federal Aviation Administration (FAA) Inspector found the leading edge of the main rotor blades had no impact damage and other than being bent, the blades were intact. The pitch control rod to one blade was broken on impact. The temperature tape on the main gearbox was within normal range. The tail rotor blades or gearbox showed no impact damage. The right side of the horizontal stabilizer was bent from impact with the ground on the right side of the helicopter. The tail section was broken and bent downward and to the left. The vibration dampener inside the tail cone was not damaged. Both main drive vee belts were off their pulleys. The forward vee belt left black residue on the front side of the pulley and shaft. The rear vee belt was broken in two and also had breaks in the center between the two v sections. Other than the breaks, the belts had no evidence of deterioration. There was no indication that the belts had visible damaged prior to the flight. A review of the helicopters logbooks found no entries as to when the drive vee belts were last changed. The was last engine overhauled 430.5 hours prior to the accident. The total time on the helicopter at the time of the accident was 6,630.6 hours.