The Flight Safety Foundation (FSF) has published a report—Benefits Analysis of Space-Based ADS-B—that highlights how automatic dependent surveillance-broadcast technology could be used to cover remote regions of the world, including oceans, where it is difficult or impossible to place ADS-B ground stations. Space-based ADS-B uses receivers installed in satellites to detect ADS-B signals broadcast from equipped aircraft then retransmits that information to air navigation service providers (ANSPs). “Experts interviewed for this report believe it may introduce a step change in improving the safety of oceanic operations,” according to the FSF.
Currently one company, Aireon, has created the type of space-based ADS-B network discussed in the FSF report, with transceivers installed on Iridium Next satellites, and it is offering its services to ANSPs worldwide. (The FSF report does not specifically mention Aireon.) To send data to ADS-B-equipped satellites, aircraft would need to have an ADS-B antenna installed on the top of the fuselage. Recently Aireon signed agreements with South Africa’s ANSP and Singapore’s Civil Aviation Authority to provide space-based ADS-B services, and other ANSPs have signed on for Aireon services as well.
There is another company that is offering its own version of space-based ADS-B. ADS-B Technologies developed the ADS-B Link Augmentation System (Alas), which uses a special transceiver installed in ADS-B-equipped aircraft to send ADS-B information to GlobalStar satellites, which then retransmit the information to ground stations then to ANSPs or other users. The company has tested Alas—the first flight-tests took place in 2010—and says it is ready for implementation. One difference between the two companies’ systems is that Alas can encrypt the signals sent from the aircraft to the GlobalStar satellite and from there to the ground station. Normal ADS-B signals are unencrypted, and there are concerns that this could raise privacy issues and also open the door to signal spoofing or other types of hacking. Alas equipment would cost “less than $40,000” for a commercial aircraft, according to ADS-B Technologies.
In addition to much faster update rates than radar, space-based ADS-B could allow for reductions in aircraft spacing where there is currently little ability for air traffic controllers to monitor aircraft position in real time. Current spacing over oceans is typically 30/30 nm (lateral and longitudinal spacing). Space-based ADS-B should eventually allow implementation of a 15/15 nm standard, according to the FSF report: “Space-based ADS-B should enhance ATC [situational awareness] significantly because the data-update rate combined with the known accuracy, reliability and integrity of ADS-B will enable ATC to provide enhanced monitoring and separation services over the ocean and over remote (unsurveilled) regions.”
There are other benefits of space-based ADS-B, such as improved flight tracking that would meet upcoming ICAO requirements. “Space-based ADS-B will create a global surveillance ‘blanket’ and, with this, an ability to support [search-and-rescue] services globally in retaining position data,” the report noted. This would include transmission of “time-critical flight data to assist in the reconstruction of some initial parameters of an accident,” which would be helpful in accidents where the location of the wreckage is difficult to pinpoint.
Many other benefits would accrue to aircraft operators and ANSPs using space-based ADS-B, among them improved safety alerts for air traffic controllers, easier rerouting for weather, routing flexibility to take advantage of favorable winds, RVSM height monitoring and NextGen trajectory operations.
“There are a number of regulatory safety performance and certification processes that must be completed; however, the range of ADS-B mandates that must be complied with over the next five to six years should stimulate both equipage uptake and regulatory processes to manage the various risks identified,” the FSF report concluded.
