This was in a Newsday story yesterday:

Lt. Brigadier General Paulo Roberto Cardoso Vilarinho, director of the air traffic control system, said that investigators had stated that controllers in Brasilia tried to contact the Legacy seven times in more than one hour and only made contact after the impact. He added that shortly after the executive jet passed Brasilia, controllers noticed the transponder on the jet was not operating, and it began to operate again after the collision.