Defining terms

Airport surface detection equipment (ASDE): digital radar that is used to track planes and other vehicles on airport runways and at up to 60 meters (200 feet) in altitude.

Automated surface observing system (ASOS): a system intended to reduce the cost of weather data collection at airports; it employs a Motorola 68000 to collect inputs from weather sensors that monitor such conditionsas temperature, humidity, visibility, winds, and cloud cover.

Airport surveillance radar (ASR): a short-range radar (typically 55 nautical miles), used for tracking aircraft in the terminal environment. The current version, ASR-9, is the first to use ICs. The next radar, the ASR-11, will be the first fully digital radar.

Air route surveillance radar (ARSR): a long-range radar (typically 200 nautical mile), used for tracking aircraft at high altitudes under observation by the en route centers. The latest version, ARSR-4, is the second digital system.

Automatic dependent surveillance (ADS): a system that uses the airplane's own navigation information (possibly derived from the Global Positioning System)to calculate an aircraft's position and transmit that information to ground-based control facilities, replacing or augmenting radar surveillance. ADS-B, a broadcast version of ADS, would provide position information that could be read by nearby aircraft as well.

Center-Tracon Automation System (CTAS): software, at present running on networked Sun UltraSparc workstations, which provides tools to controllers to advise or automate some operations, including runway assignments and landing sequences in Tracon airspace and arrival schedules and delay calculations in en route airspace.

Display system replacement (DSR): IBM RS/6000 workstations running the IBM AIX operating system with software written in Ada and C. The system is being developed by Lockheed Martin for installation in the en route centers.

Global Positioning System (GPS): a network of 24 satellites that provides navigational signals for use in determining position, including altitude and time.

Host computer system: a systemused in the 20 U.S. en route centers to track aircraft locations, maintain a database of flight plans, and issue conflict alerts and minimum safe altitude warnings. Host currently runs on IBM 3083 computers, with software containing more than one million lines of Jovial code, only about 200 000 lines of which are actually used for real-time operational functions.

Standard terminal automation replacement system (Stars): a system of networked Sun workstations and Sony high-resolution monitors, being developed by Raytheon, which will replace the radar processing system and displays currently being used in Terminal Radar Approach Control facilities, beginning in 1998.

Traffic alert and collision avoidance system (TCAS): an on-board tool for pilots that identifies traffic within 5­40 miles of the aircraft (depending on pilot settings), warns pilots of impending conflicts, and recommends action (only climb or dive in current systems due to poor bearing information) to avoid such conflicts.

Voice switching and communications systems (VSCS): digital switches with a touch-screen interface for changing radio frequencies and opening phone links that automatically route communications between controllers and pilots or among controllers.

Wide-area augmentation system (WAAS): a network of Global Positioning Satellite reference stations that send information to a master station, where corrections are determined and transmitted by synchronous satellite to the users, enhancing their accuracy, integrity, and availability.