An ADS-B tower in Louisville is one of 794 such structures that will form the NextGen backbone
SURVEILLANCE
Two years after signing a contract to create the surveillance backbone for the next generation air transport system (NextGen), the US Federal Aviation Administration is about to reap early benefits from its $1.8 billion baby.
In test programmes about to get under way in at least four locations, avionics makers, aircraft operators and airlines along with the FAA are set to begin experimenting with critical features of the first online network of automatic dependent surveillance - broadcast stations installed by prime contractor ITT.
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An ADS-B tower in Louisville is one of 794 structures that will form the NextGen backbone |
ITT has completed the first of 28 en route "service volumes" in southern Florida, and is working to complete four "key sites" where the ADS-B positioning information will be used for air traffic control purposes, also known as "critical services".
The Miami air route traffic control centre (ARTCC) service volume, aka SV 168, went operational in August 2008 with 11 ground stations and received the FAA's in-service decision (ISD) in November, an approval certificating its ability to provide "essential services" to ADS-B equipped aircraft.
"Essential" in this case means appropriately equipped aircraft can receive traffic information about other aircraft in the area (traffic information services, or TIS-B) and flight information services (FIS-B), including weather and other aeronautical information.
Those ground stations include redundant multi-channel radios, often collocated with ATT cellular phone towers, but at other times sited at dedicated locations. ATT is a subcontractor to ITT for the programme.
SURVEILLANCE SERVICES
When the network is complete, it will contain about 800 ADS-B ground stations and support equipment in the continental USA, Gulf of Mexico and Alaska to provide "essential" and "critical" surveillance services to the 26 ARTCC zones, more than 200 terminal areas and 35 airport surface zones, including in the near future the international airports at Louisville, Philadelphia and Seattle.
The company is under contract to operate and maintain the system through 2025, with the FAA paying subscription charges.
Set to become the de facto surveillance standard for the USA in 2020 and sooner in Europe, ADS-B pushes out (ADS-B "out") radar-like GPS-generated position reports from an aircraft, but at a higher frequency and with more data about the subject aircraft.
In addition to allowing the FAA to gradually phase out its secondary surveillance radar systems, ADS-B will also enable radar-like coverage in areas where radar today is not practical, including the Gulf of Mexico and vast areas of Alaska. For operators, the true benefits will come with the application of ADS-B "in" functionality, which brings a wealth of information, including TIS-B, FIS-B and other data.
Operational readiness tests and pilot programmes set to begin later this year will put the nascent surveillance network through its most strenuous yet paces yet, enabling a series of FAA-funded demonstrations the agency hopes will convince industry to voluntarily equip with ADS-B "in". By contrast, the FAA plans to issue a final rule next year that will mandate ADS-B "out" equipage by 2020 (see sidebar).
At two-month intervals starting in October, ITT expects to go operational for ADS-B critical services at Louisville International airport, in the Gulf of Mexico, at Philadelphia International airport and in the en route area around Juneau, Alaska, respectively, says John Kefaliotis, vice-president of next generation air transport systems for ITT. After a period of testing by the FAA, the sites are expected to receive final certification by September 2010.
With initial operating capability of the critical services, some persuasive pilot programmes will begin.
In the Gulf of Mexico, where ITT is testing the network of nine ground stations on the shore and one on an oil platform, helicopter operators in the oil and gas industry are keen to begin using the surveillance services to boost capacity in instrument weather conditions, not to mention giving operators visibility as to where hundreds of helicopters are at any one time. Without the equivalent of radar coverage in the area, the FAA today has to reduce flight activity in such weather to very conservative levels.
Ground stations in general include sectorised antennas and higher-power, multi-channel internally redundant systems that gather the airborne data and send it to localised ITT control centres, where software platforms fuse the ADS-B data from all participants with radar data obtained from ARTCCs and terminal radar control facilities.
After formatting the FIS-B weather and aeronautical data for broadcast, the stations compute the minimum set of ground stations that should broadcast the information to reduce frequency congestion. TIS-B messages are only sent to traffic inside a 28km (15nm) radius cylinder of virtual airspace 3,500ft (1,065m) above and below a participating ADS-B aircraft.
Along with the more rigorous software load needed for critical services, ground stations at airports require a slightly different hardware approach. Whereas ITT was required to keep ground stations at least 30km from the secondary surveillance radar (SSR) sites to eliminate the potential for interference (SSRs transmit on1030MHz but receive on 1090MHz, the frequency on which airline-type ADS-B systems operate) for en route and terminal area sites, the buffer was not possible for the 35 airport sites, all of which are or will soon be equipped with ASDE-X airport surveillance radar systems.
As such ITT developed smaller single-channel, lower power radios to reduce potential for interference with ASDE-X. Redundancy for airport the airport systems is achieved through overlapping coverage.
In the terminal area and on the airport itself, the availability of ADS-B will by all accounts offer a boost to capacity and efficiency as well as safety. UPS, a front-runner in demonstrating ADS-B technologies at its Louisville hub, will begin testing its merging and spacing and surface awareness capabilities at Philadelphia, in concert with US Airways, which is installing the ACSS-built software in its Airbus A330s.
In Louisville, Philadelphia and Seattle, ITT is working with ASDE-X provider Sensis to integrate the ADS-B signal into the variety of surveillance technologies, including traditional transponders, multi-lateration systems and airport radar, inputs that ASDE-X fuses together to monitor all airport operations and issue impending collision alerts to controllers.
The coupling of ADS-B to ASDE-X could provide a much needed boost to runway safety and satisfy a perennial request by the US National Transportation Safety Board - to get a real-time alert of an impending collision to pilots as well as controllers.
In addition to US Airways' test at Philadelphia, Alaska Airlines will test runway safety ideas using ADS-B at Seattle, with Honeywell, both projects paid for by the FAA.
Source: Flight International