On October 12, 1993, at 1645 eastern daylight time, a Hughes 269A, N7032U, operated by Brooks Aero, Inc., Marshall, Michigan, sustained substantial damage when it had an in-flight structural failure, while in a hover at the Branch County Airport, Coldwater, Michigan. Neither the certified flight instructor, nor the private certificated student pilot were injured. The instructional flight originated at Brooks Field, Marshall, Michigan. No flight plan was filed, and visual meteorological conditions prevailed at the time. The investigation found the left tailboom support strut attachment lug on the left aft cluster fitting (P/N 269A2234) had failed. A witness reported the tailboom was moving up and down just before the accident. The tailboom was hit and severed by the main rotor system. The dual student, who was at the controls, made a successful hovering autorotative landing without additional damage to the helicopter. The helicopter log book shows the last inspection was a 100 hour inspection performed on June 22, 1993. The helicopter has logged 65 hours since the inspection. The log book entry records compliance with Airworthiness Directives 88-17-04 and 76-18-01 which pertain to the cluster fittings. The failed support strut attachment lug was sent to the NTSB Materials Laboratory, Washington, D.C., for examination. The laboratory reported the presence of fatigue fracture features on both ears of the attachment lug.