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Economic Impact Sustainability Flexibility Safety July 2014

Wide AreaMultilateration (WAM)Wide AreaMultilateration(WAM) is a NextGeneration AirTransportationSystem (NextGen)surveillancecapability thatenables air traf ccontrollers to track

aircraft ying intoand out of airportsin mountainousareas with no radarcoverage.

WAM providessurveillancethrough a networkof small sensorsdeployed in remoteareas. WAMsensors areinexpensive compared to multi-million dollar radarinstallations and much easier to install around airportsin mountainous areas and even on mountain tops. Ahalf-dozen sensors can cover a wide swath of previouslyunobserved airspace.

The sensors send out signals that interrogate aircrafttransponders which, in turn, transmit a response.Computers analyze those responses and triangulatethe precise location of aircraft. Aircraft position andidenti cation information are then transmitted to air

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Wide Area Multilateration (WAM)

traf c controllers, who use the surveillance data tosafely separate aircraft.

Today, controllers are using WAM to control traf cin Juneau, Alaska, and at several airports in themountainous regions of Colorado.

The rugged terrain that makes Colorado a popular skidestination in winter also makes it impossible toprovide radar surveillance in certain areas. In theseareas, inclement weather can reduce the pace ofoperations. Prior to WAM, arrivals and departures atremote Colorado airports could drop from 12 to 17 anhour to just four when bad weather set in.

In 2009, the FAA began using WAM to providesurveillance at four remote Colorado airports, enablingcontrollers to maintain 12 to 17 arrivals and departuresper hour, even during reduced visibility. The systemwent operational at four more airports in 2013.

WAM is also enabling air traf c controllers to trackaircraft along the dif cult approach to Juneau. Themountainous terrain and the lack of radar meant that in

the past, controllers had to keep aircraft separated bylarge margins. The airports single runway sits at theend of the Gastineau Channel, surrounded by steepmountainous terrain.

The Juneau WAM system began initial operations in2010, and is now tracking all transponder-equippedaircraft. Air traf c controllers are now able to safelydecrease the separation to ve nautical miles.

WAM technology is allowing more aircraft to y intoJuneau and it has given air traf c controllers the tools

they need to safely and ef ciently handle these ights.

WAM improves safety, ef ciency and capacity. It savestime and money that would otherwise be lost due to ightdelays and cancellations or diversions to other airports.

WAM surveillance alsotranslates into moreef cient ight paths,saving time and burningless fuel.

WAM is being used toprovide near-termsurveillance until

Automatic DependentSurveillance-Broadcast(ADS-B) becomes theprimary means ofsurveillance in theNational Airspace System.

At that point, WAM willserve as a backup in caseof a GPS outage. ADS-B

ground stations are nowdeployed nationwide andaircraft operating in mostcontrolled airspace mustbe equipped to broadcastposition information to the

ADS-B network by 2020.

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