On August 9, 2007, about 1120 eastern daylight time, a Messerschmitt-Bolkow-Blohm BK-117 A-4 helicopter, N171MU, registered to Chase Equipment Leasing Inc., and operated by Omniflght Helicopters, Inc., as a Title 14 CFR Part 135 aeromedical flight, had the tail rotor contact a tree branch while preparing to takeoff in Ridgeville, South Carolina. Visual meteorological conditions prevailed, and a company flight plan was filed. The commercial-rated pilot, two flight crewmembers, and one passenger were not injured, and the helicopter incurred substantial damage. The flight was originating at the time of the accident. The pilot said that upon landing at the scene he kept the helicopter operating with him at the controls, while the medical crew attended to the patient. According to the pilot, after completing weight and balance calculations, the patient was loaded onto the helicopter, and the paramedic did a walk around inspection prior to entering the helicopter. After the engine run-up, the pilot said that the paramedic called out the before-takeoff-checklist, and issued a warning to be alert for the overhanging trees on the port side of the aircraft. The pilot said he acknowledged, and told the crew that he would pick the helicopter up into a hover, slide to the right, and then perform a left pedal turn to exit the scene to the west. The pilot said the paramedic affirmed what he had heard, and while performing a left pedal turn at a hover, a vibration occurred throughout the airframe. The pilot said he immediately set the helicopter back on the ground, facing west. A paramedic that was aboard the helicopter stated that after they had performed the "slide and pedal turn", he felt a strong vibration and when he queried the pilot the pilot said he lost his tail rotor. Within seconds the paramedic said they were back on the ground with a sort of run on landing, and the pilot said that he was shutting down. The paramedic said he still felt the vibration but he did not know what had happened. After exiting the helicopter the paramedic said he noticed the tail rotor wobbling . After everything had come to a stop the paramedic said he asked fire personnel who had been watching if they had struck something and the fire personnel pointed to a tree on the south side of the highway, saying that the helicopter had barely clipped it. An EMS technician on the ground who had been observing the helicopter, stated that after the patient had been loaded into the helicopter, the helicopter was lifted into about a 3-foot hover, and then began to rotate and face into the direction of the light wind, coming from the west. After the helicopter completed the rotation into the wind, the EMS technician stated that it then began to increase altitude, and as the altitude increased the tail rotor struck a small pine tree limb that stuck out about 1 to 2 feet into, and over the westbound traffic lane closest to the median. He said he heard the change in pitch to the sound of the helicopter's engine, and also saw the tail rotor begin a slight "wobbling." At this point the EMS technician said the helicopter was about 6 to 8 feet off the ground, and he believes that the pilot sensed that something was wrong with the helicopter, and set the helicopter down firmly on the curbside lane, facing west. A postaccident examination revealed that the helicopter had incurred damage that included the tail rotor and tail boom. The examination did not reveal evidence of any preaccident mechanical failure or malfunction to the helicopter or any of its systems.