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ADS-B

Wide Area Multilateration (WAM)

What it is

WAM is a distributed surveillance technology that works by deploying multiple sensors throughout an area to provide coverage of the desired airspace. WAM can be installed in areas of challenging terrain which limits the use of secondary radar. It can also be used as a replacement for secondary radar or complementary surveillance to ADS-B.

Benefits

  • Provides flexibility in surveillance coverage for any desired airspace
  • Provides an additional layer of cooperative surveillance, where needed
  • Improves safety, efficiency, and capacity
  • Reduces flight delays, cancellations, and diversions to other airports

How it works

WAM is comprised of a network of sensors that are deployed throughout a desired coverage area or potentially deployed on satellites in space. WAM capabilities are typically combined within ADS-B receivers to provide a complementary surveillance overlay to ADS-B.

WAM sensors receive signals from aircraft avionics based on ADS-B squitters or transponder replies. WAM ground sensors can also interrogate transponders to elicit replies that are then received and processed by the WAM system. WAM system applications multilaterate on those signals to determine the precise location of aircraft while utilizing the data in the squitters and replies for aircraft identification and barometric altitude information. This surveillance data is delivered to air traffic management systems and presented to air traffic control to safely provide aircraft separation services.

Availability

Under a partnership with the Colorado Department of Transportation, the FAA installed WAM at a number of airports in the Rocky Mountains. WAM has been providing surveillance at these locations for a number of years, helping to keep flights operating safely and spaced efficiently. This system is especially useful during the busy winter ski season in reducing capacity constraints that occur when weather might otherwise cause diversions or flight cancellations.

WAM is also operational at Juneau, Alaska. Juneau is another mountainous area without radar, which has a notoriously difficult approach. Flights into Juneau are now safer and more efficient with WAM surveillance providing a traffic situational awareness picture to ATC.

In Charlotte, N.C., WAM was added to correct coverage deficiencies and tracking anomalies from the airport's limited radar input. With WAM in place, Charlotte fuses it with radar and ADS-B data to provide a comprehensive surveillance picture to ATC which readily supported fully transitioning to ADS-B as the preferred surveillance service.

The FAA most recently installed WAM services at the Southern California Terminal Radar Approach Control Facility (SCT) to mitigate interference to existing radars that resulted from the construction of the National Football League's new SoFi Stadium.

Additional WAM services in the Atlanta and the New York metropolitan areas are planned for activation after 2021 to mitigate spectrum congestion on surveillance frequencies and potentially replace existing radar assets.

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This page was originally published at: https://www.faa.gov/nextgen/programs/adsb/atc/wam/