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 theFlag staff collision, including a patient and the pilot, said Ian Gregor, spokesman for the US 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.