Two medical helicopters collided in midair Sunday afternoon near an Arizona hospital, killing at least seven people and critically injuring three, a federal official said. All three people on one of the helicopters were killed in the Flagstaff collision, including a patient and the pilot, said Ian Gregor, spokesman for the Federal Aviation Administration. Four others were killed and three critically wounded, Gregor said. He wasn't sure if they were all on the second helicopter or whether some were on the ground. The cause of the collision is being investigated. Two news helicopters collided while covering an auto chase last summer near Phoenix, killing all four people on board.