The pilot carried out pre-flight checks on the helicopter, which was parked on an apron in front of a small hangar. The helicopter was facing away from the hanger; to its left was a small portable building and immediately to its right was a parked vehicle. The pilot started the helicopter and initiated lift to the hover by raising the collective lever. As the helicopter lifted off, the pilot felt unusual and severe vibrations which appeared to come from the main rotor. He lowered the collective immediately to land, but as he did so the helicopter yawed to the left. The tail boom struck the parked vehicle, causing damage to both the helicopter and the vehicle.
The helicopter operator reported that an engineering investigation did not reveal any abnormality in the main rotor or its control system which could have accounted for the vibrations reported by the pilot.
Robinson R44 II Raven, G-HECK