On March 5, 2012, about 1136 central standard time, a Sikorsky Aircraft Corporation 269C helicopter, N1099N, impacted terrain during a precautionary landing following an in-flight pop sound and torque pedal vibrations near Staples, Texas. The private pilot and passenger reported no injuries. The helicopter sustained substantial tailboom damage. The helicopter was registered to and operated by Xotic Aviation LLC. under the provisions of 14 Code of Federal Regulations Part 91 as personal flight. Day visual flight rules (VFR) conditions prevailed for the flight, which did not operated on a VFR flight plan. The flight originated from Fentress Airpark, near Fentress, Texas, about 1121, and was destined for Bulverde Airpark, near San Antonio, Texas. According to the pilot's accident report, about 15 minutes into the flight, he heard a "pop" sound "like metal breaking." He felt a violent vibration and loss of torque pedal response. The pilot reported that there was no change in "RPM" and he performed a precautionary landing due to the vibration. The helicopter impacted terrain hard and the main rotor blades impacted the tailboom. The engine was shut down by the pilot after the landing. The pilot held a private pilot certificate with ratings for rotorcraft-helicopter. His last Federal Aviation Administration (FAA) second-class medical was issued on August 24, 2011, with no limitations. The pilot reported that he had accumulated 143 hours of total flight time, of which 100 hours were in same make and model as the accident helicopter. He indicated flying 21 hours in the last 90 days and 10 hours in the last 30 days. FAA inspectors and a manufacturer's safety investigator examined the helicopter. The helicopter wreckage debris field was approximately 100 yards long. The cockpit mounted Hobbs meter indicated 479.9 hours. The cockpit flight controls exhibited continuity. The tailboom was partially separated at its middle section just forward of the center attach fitting. The left tailboom support strut tube was separated at the tailboom end through the bolt holes attaching the tube to its end fitting. Tail rotor controls exhibited continuity up to the separated points of the tailboom and its rod ends safety wired hardware was intact. Drive system rotation was confirmed at the lower pulley shaft, the overrunning clutch, and up to the separated end of the tail rotor drive shaft. A main rotor damper assembly with blade grip attachment bracket and its hardware was retained for further examination. Maintenance records showed that the helicopter's total time at its last maintenance work on February 8, 2012, was 10,037.2 hours and its Hobbs meter indicated 460.2 hours. The last maintenance in the logbook was the installation of a repaired main rotor blade. The last annual inspection was performed on January 24, 2012. A National Transportation Safety Board senior materials engineer examined the retained damper items. A manufacturer's periodic extension-under-load test was applied to the damper and the damper met the test's specifications. Separation surfaces present on the damper assembly were consistent with overload and no evidence of preexisting cracks were observed. No anomalies were detected that would have precluded normal operations. The reason for the pop and subsequent vibration was not determined.