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Airport Surface Detection Equipment, Model X, or ASDE-X, is a runway-safety tool that enables air traffic controllers to detect potential runway conflicts by providing detailed coverage of movement on runways and taxiways. By collecting data from a variety of sources, ASDE-X is able to track vehicles and aircraft on airport surfaces and obtain identification information from aircraft transponders.
Originally the FAA installed 38 ASDE-3A radar systems at the nation's busiest airports. The cost-effective alternative to the ASDE-3/AMASS capability, referred to as ASDE-X, is one of the first new runway safety program technologies aimed at improving ATCS situational awareness by providing tools to supplement their tasks (McAnulty, Doros, & Poston, 2001). The data that ASDE-X uses comes from a surface movement radar located on the airport traffic control tower or remote tower, multilateration sensors, ADS-B (Automatic Dependent Surveillance-Broadcast) sensors, terminal radars, the terminal automation system, and from aircraft transponders. By fusing the data from these sources, ASDE-X is able to determine the position and identification of aircraft and vehicles on the airport surfaces, as well as of aircraft flying within 5 miles (8 km) of the airport (selectively up to 60 nmi).
Controllers in the tower see this information presented as a color display of aircraft and vehicle positions overlaid on a map of the airport's runways/taxiways and approach corridors. The system essentially creates a continuously updated map of all airport-surface operations that controllers can use to spot potential collisions.
Consisting largely of commercial off-the-shelf products, ASDE-X was designed as a solution for the smaller of the top-tier airports, and is especially helpful to controllers at night or in bad weather when visibility is poor. The Federal Aviation Administration has also begun the process of deployment of visual and audio alarms, known as Safety Logic, that will assist ASDE-X by alerting controllers to possible collisions or runway incursions.
Pilots normally select their transponders to on just prior to take off and will turn it to standby or off after landing. When ASDE-X is available at an airport, that fact will be included in the recorded ATIS (Automatic Terminal Information Service) to indicate to the pilot to leave his transponder on while taxiing on the ground.
The first ASDE-X was activated for operational use and testing at General Mitchell International Airport in Milwaukee, Wisconsin, in June 2003, and declared ready for national deployment in October 2003.
Airports with ASDE-X installed as of March 2011: