Incident Overview
A helicopter was completing a training flight with an instructor pilot and a non-rated, non-certificated student pilot on board. As the aircraft touched down, a severe resonant vibration began. The instructor stated that he attempted to lift off the ground but the collective input gave no response.
Findings
Post-incident examination revealed that the clutch pulley bracket had failed due to overload. Witnesses described the vibration as typical of ground resonance.
Investigation
The investigation focused on the mechanical failure of the clutch pulley bracket, which was found to have been subjected to overload conditions. The exact sequence of events leading to the overload was not specified in the available information. The incident occurred during a routine landing after a training session.