Automated Radar Terminal Systems (ARTS) manage air-traffic control at USA airport locations such as New York, Dallas/Fort Worth, Chicago, Southern California, and Atlanta. The Common ARTS program sought to develop a common software baseline at the Nation's Terminal Radar Approach Controls (TRACONs) and incorporate more commercial-off-the-shelf (COTS) products. Common ARTS has evolved into a real-time distributed open-systems architecture that is multithreaded, and which uses a local area network. Thousands of tracks are supported, and so are hundreds of displays. Because Common ARTS is a safety-critical application, a standby system is always ready to take control if any subsystem ever ceases to broadcast its heartbeat on the network.