What Is Multilateration?

A new surveillance system introduced, called multilateration or Wide Area Multilateration (WAM), is now allowing air traffic controllers to track aircraft along the difficult approach to Juneau, Alaska—a mountainous area where radar was not possible.

Multilateration is a surveillance technology that works by employing multiple small remote sensors throughout an area to compensate for terrain obstructions, and is another tool the SBS program uses to enhance air traffic surveillance. The data from multilateration sensors is fused to determine aircraft position and identification. This data is then transmitted to air traffic control for use in providing surveillance separation services.

Currently, Juneau, Alaska; and several airports in the mountainous regions of Colorado have the first multilateration systems.

Juneau Wide Area Multilateration (WAM) Project

Juneau, Alaska, is one of the most difficult approaches a pilot can make. Mountains make radar impossible and low weather ceilings often require commercial carriers to fly at low altitudes through the narrow valley, along with helicopters and smaller fixed-wing aircraft. Controllers have no radar for surveillance, so they keep aircraft separated by large margins. All of this makes flying in Juneau difficult and much less efficient.

Status of the Juneau Multilateration Project

The new WAM system at Juneau began initial operations on January 25, 2010 and now is tracking all transponder-equipped aircraft, allowing controllers to separate them by only 5 nautical miles. WAM is being used in the near-term while the FAA rolls out Automatic Dependent Surveillance-Broadcast (ADS-B), the satellite-based surveillance system that will be fully deployed nationwide by 2013. WAM will then serve as a backup to ADS-B in case of a GPS outage, and also provide an additional surveillance source for ADS-B traffic broadcasts sent to appropriately equipped aircraft.


ADS-B in Juneau

Colorado Wide Area Multilateration


Increases in air traffic have resulted in growing delays and denied service at the Colorado mountain airports, especially during bad weather. Instrument meteorological conditions can reduce aircraft acceptance rates for these airports from 12 to 17 flights per hour, to only four per hour. From November to April each year, the Colorado Department of Transportation estimates 75 aircraft per airport, per day, are delayed or diverted, resulting in major revenue loss for the state.

In 2005, the FAA, at the request of the State of Colorado Department of Transportation´┐Żs Division of Aeronautics, conducted an analysis of these delays and cancellations. The FAA study determined that the lack of surveillance contributed to reduced capacity during instrument meteorological conditions, and identified multilateration as the preferred solution for providing surveillance to the Colorado mountain airports.

In September 2006, the FAA and the State of Colorado Department of Transportation´┐Żs Division of Aeronautics signed a Memorandum of Agreement for a project to plan, install, test, and commission a surveillance system for the Colorado mountain airports.

Wide-Area Multilateration (WAM), began initial operations on September 12, 2009 at Denver Center serving the Yampa Valley-Hayden, Craig-Moffat, Steamboat Springs and Garfield County Regional-Rifle Airports. The WAM capability provide these airports with improved safety, efficiency and capacity by allowing controllers to see aircraft that are outside radar coverage saving time and money that would otherwise be lost due to flight delays and cancellations or diversions to other airports.

On December 8, 2009, the FAA approved the next phase of the Colorado Wide Area Multilateration (WAM). The phase 2 allows for the development and implementation of air traffic separation services, using Multilateration and ADS-B surveillance, for En Route air traffic operations in and out of the following airports:

  • Gunnison-Crested Butte Regional (GUC)
  • Montrose Regional (MTJ)
  • Telluride Regional (TEX)
  • Durango-La Plata County (DRO)

The system will be an ADS-B 1090 Extended Squittter (ES) and Universal Access Transceiver (UAT) surveillance system with integrated Multilateration surveillance capabilities. The system will also provide additional ADS-B services, including Flight Information Services-Broadcast (FIS-B) and Traffic Information Services-Broadcast (TIS-B) services. The Initial Operating Capability (IOC) of the ADS-B and Multilateration services is expected in Montrose by June 2012 with other sites operational in March 2013.

Denver Center Multilateration