The aircraft was performing external load flights with delivering of concrete to a powerline fundament. During delivery of concrete to powerline mast number 49, the pilot experienced severe vertically vibrations. The pilot took immediate action, released the external load and was capable to manoeuvre the helicopter away from the construction area. During this operation the helicopter lost altitude and hit some threes. The helicopter stopped laying on the right-hand side about 50 meters from the construction area. No persons were seriously injured.