A linchpin in the FAA's long-term plan to upgrade the nation's air traffic control system is Automatic Dependent Surveillance-Broadcast, or ADS-B, which provides data of unprecedented precision and timeliness on the whereabouts of aircraft in the air and on the ground. Plans call for the ADS-B system to replace the 60-year-old, radar-based traffic control system nationwide by 2013. ADS-B is being deployed in a growing number of areas, including Juneau, Alaska; Louisville, Ky.; and Philadelphia. Because it employs GPS, ADS-B extends capabilities to new areas of coverage. ADS-B ground stations were deployed on oil rigs in the Gulf of Mexico and, in November 2009, service was turned on, making helicopters and other aircraft over the Gulf visible to air traffic controllers for the first time. The system makes for improved "situational awareness" in the cockpit, too, because pilots receive real-time data on aircraft that are in close proximity to their own planes.