The U.S. is close to completing the nationwide deployment of a satellite-based navigation network, which will be by far the largest such system in the world and a key foundation for the NextGen initiative.

Exelis is the prime contractor for the automatic dependent surveillance-broadcast (ADS-B) project, and is installing 660 ground stations to achieve complete surveillance coverage across U.S. airspace. The company expects to deploy the last ground stations in the lower 48 states this month, says John Kefaliotis, vice president for international strategy and business development. Most of the stations required for Alaska, Hawaii and the island territories will also be installed by then.

ADS-B “Out” provides air traffic controllers with GPS-based aircraft positions that are more accurate than radar data. As the network is deployed, ADS-B feeds are being progressively introduced at the FAA's terminal and en route facilities. Data from ADS-B and radar will be fused, which is expected to allow reduced separation in some airspace.

As of late February, 625 ADS-B ground stations were operational, says Kefaliotis. Another 30 will be added during 2014, with most of these in March. There will be 202 delivery points—known as service volumes—where the ADS-B feed is provided to the individual FAA facilities. Of that total, 178 have been completed, and the rest will be finished by year-end—again, primarily in March.

Of the 601 ground stations required to cover the contiguous U.S., 589 were finished by late February, with the remainder due to come on line by the end of this month. Deployment in the U.S. Virgin Islands should also be completed in March, and all but a few of the Hawaiian ground stations will be on line by then. One station in Puerto Rico will be installed soon, and a second will follow in the third quarter.

Most of the remaining sites are in Alaska, where the building season is relatively short. Additional stations will be deployed this summer and the rest in summer 2015.

Kefaliotis says the project has remained within budget, and Exelis has met its contract milestones. The first service volume was completed in 2008, and ADS-B has been performing well since then, he notes.

The FAA has said it “initially expected” deployment to be completed by the end of 2013, but admitted that weather, terrain and land acquisition challenges complicated work at some sites. Kefaliotis says the agency recognized that some of the work would spill into 2014. He stresses that the deployment is well within contract requirements, and is “consistent with FAA expectations.”

After Exelis has deployed each ADS-B service volume, the FAA is then responsible for integrating the feed into its automation systems so it can be used to control traffic. The agency has been gradually testing and bringing ADS-B on line at its centers, terminal control facilities and many towers. The FAA intends to have all 24 en route centers at initial operating capability by September 2015, and all other facilities by 2019.

Exelis is contracted to operate and maintain the ADS-B network through September 2016, with two options that likely will extend it through 2025.

As well as ADS-B Out, the U.S. network is providing some services that are primarily used by general aviation operators—traffic information services-broadcast (TIS-B) and flight information services-broadcast (FIS-B), which provide improved situational awareness and weather information. “As general aviation comes up the equipage curve, [it] is going to experience very substantial benefits from the TIS-B and FIS-B services,” says Kefaliotis.

Aircraft will be required to equip for ADS-B Out in most controlled airspace by 2020. Congress has also asked the agency to mandate ADS-B “In” equipage by that date, but the agency has not yet done so. ADS-B In allows aircraft positions and other information to be displayed in the cockpit.

The airline industry generally does not support an ADS-B In mandate, although it is keen for the FAA to develop applications for carriers that choose to begin using this technology.

Exelis is also marketing its ADS-B system beyond the U.S. The magnitude of the U.S. network “demonstrates that the solution we have deployed has unlimited scalability,” says Kefaliotis.

Meanwhile, the company is involved in developing the next evolution in ADS-B technology. This will see ground stations replaced by receivers hosted on a satellite network. Because it is not tied to a ground network, this space-based system can potentially provide coverage in oceanic airspace that is out of range of current ADS-B networks.

Iridium and Nav Canada formed the Aireon joint venture to build such a system, and Exelis has been contracted to develop the infrastructure to process and distribute the data to Aireon customers.

Kefaliotis notes that space-based ADS-B will complement rather than supplant terrestrial ADS-B systems. While it is ideally suited to cover vast areas of remote airspace, the space-based version is not as effective in dense traffic environment. Some countries may opt for a hybrid where both terrestrial and satellite ADS-B are used in different airspace.