A 24-year-old Salem woman driving a 1998 Volkswagen Jetta on the Lowell Connector was killed yesterday when a utility trailer connected to a tow truck broke free, became airborne, and landed on her car, which was heading in the opposite direction. According to State Police, the accident occurred at about 3:45 p.m. The trailer was being hauled by Patrick Sheehy, 27, of Lowell, police said. Sheehy had picked up the trailer a few minutes before the crash, said Trooper Thomas Ryan. The crash is under investigation, police said. No charges have been filed. The woman was pronounced dead at the scene. Her name was withheld pending family notification.