If you were walking, driving or just sitting comfortably in your home Saturday morning, chances are you had a Henry Hill moment. For the better portion of the morning and early afternoon, members of the Massachusetts State Police, FBI and the U.S. Department of Energy were conducting training drills over the city making several low passes just above rooftops in a Bell Rotorcraft Survey helicopter measuring natural ground radiation levels. Several people were caught by surprise as the aircraft would appear out of nowhere over rooftops and tree lines. At one point the aircraft made an extremely close pass by the Chelsea Street Bridge about 150 feet off the ground. The training exercises were being conducted over several cities in the Metro Boston area.