From: http://trainers.hitechcreations.com/radio/radio.pdf"Channel 3 (Room) - This channel sends messages only to those who are nearby. If you are in the tower, hangar, or O Club, only people in the same location can see messages on this channel. If you are in a plane, GV, or PT Boat, only people who took off from the same field as you can see messages on this channel. Messages on this channel show up as purple text. "