Air traffic controllers coordinate the movement of aircraft to maintain the safe distances between the aircraft. Their primary concern is safety, but they also must direct aircraft efficiently to minimize delays. They manage the flow of aircraft into and out of the airport airspace, guide pilots during take off and landing, and monitor aircraft as they travel through the skies for security purposes. Air traffic controllers use radar, computers, or visual references to monitor and direct the movement of the aircraft in the skies and ground traffic at airports.