The FAA’s top-level Joint Resources Council (JRC) has called for the estimated cost of a nationwide, GPS-based, automatic dependent surveillance-broadcast (ADS-B) network, according to unofficial reports at a recent GNSS conference. ICAO has recognized ADS-B as offering major contributions to increased safety and airspace capacity, and such programs are already under way or planned in Europe, Australia and some Asian nations.

Until now, ADS-B has seen only limited U.S. implementation, with FAA ground stations in Alaska and other states serving aviation schools in North Dakota, Arizona and Florida, plus a cluster along the northeast coast. A nationwide U.S. program was said to require almost 500 additional ground stations to provide surveillance coverage throughout the National Airspace System (NAS) down to 6,000 feet in en route airspace and down to the surface at airline airports.

The FAA’s Safe Flight 21 organization is reported to have been directed to provide ADS-B budgetary data for the JRC, should it decide to go ahead with a NAS-wide program. According to an industry source, such a decision would be expected late next year, with installations forecast to begin in late 2007 or early 2008 and continue over a four- to six-year period. Industry observers put the acquisition and installation costs of the 500 ground stations–the individual “nerve centers” of ADS-B (see box below)– at close to $1 billion. A public announcement of the JRC’s directive has not been made.

AIN found out that the JRC initiative stemmed from a comprehensive agency review of three potential future ATC surveillance options–radar, multilateration and ADS-B. Of the three, radar was said to be the least preferred option, since not only are many of the FAA’s high-cost secondary surveillance radars due for replacement over the next few years, but continuing with them would merely extend the status quo and would bring little technological advancement to the NAS.

The multilateration technique, which uses ground-based monitoring receivers to triangulate aircraft ATC transponder, TCAS, ADS-B and military IFF signals, has a range equal to radar’s but is much less costly and has a higher update rate and much greater accuracy. But industry experts claim ADS-B offers multilateration’s performance while adding a flight-deck display of local traffic, weather and other flight information, which neither of the other alternatives provide.

FAA Proceeds Slowly

Nevertheless, the FAA is cautious about predicting the outcome of the JRC’s initiative. Greg Martin, FAA assistant administrator for public affairs, told AIN, “It’s premature to make any definitive statements about ADS-B at this time. We recognize its tremendous potential to improve safety and capacity, and the technology has shown its mettle as the backbone of Alaska’s Capstone project. But there’s considerable work to be done if in fact ADS-B is the direction we plan to take. The JRC direction to ‘build the business case’ allows us to begin that work.”

The FAA has evaluated ADS-B in Alaska for several years and now has almost 400 aircraft–mostly commercial singles and twins– using the system around Bethel and Juneau, both of which have FAA-supplied ground stations.

Earlier this year, FAA Alaska officials reported a 47-percent reduction in the accident rate in the test areas, although some have questioned whether this is solely the result of ADS-B, or a combination of ADS-B and the add-on terrain warning system the FAA supplied with its free Capstone avionics packages.

But larger operators have also installed systems. UPS flies 107 fully ADS-B-equipped Boeing 757 and 767 freighters, and 80 to 90 percent of the remainder of the company’s 240-aircraft fleet carries “ADS-B OUT” installations, according to Capt. Jim Walton, UPS supervisor of advanced flight operations. Walton regarded the JRC initiative as “very encouraging,” not only for ADS-B’s surveillance capabilities but also for its potential for developing new applications such as supporting continuous descent arrival procedures and, further into the future, in providing safe “assisted visual separation” in marginal VFR approach conditions.

Yet the UPS installations raise the issue of international standardization of the datalink radio frequencies used between the ground stations and participating aircraft, since three separate but incompatible frequencies have been proposed for ADS-B and are in early datalink use. These are the Swedish VHF-based Mode 4 (VDL-4), the U.S.-developed Universal Access Transponder (UAT) operating around 978 MHz and the international ATC transponder frequencies of 1030 MHz and 1090 MHz, colloquially called “Ten-Ninety.”

Industry specialists speculate that although Sweden and Russia plan to adopt VDL-4, it will probably remain a regional system, as will the UAT, which was designed specifically as a low-cost avionics solution for U.S. general aviation.

Consequently, UPS, along with almost all other U.S. and international airlines, has adopted the Ten-Ninety option. Accordingly, therefore, future U.S. ADS-B ground stations would likely be dual-frequency units, simultaneously uplinking data over both 1090 and the UAT frequency. But outside Sweden, Russia, the U.S. and some other countries, 1090 seems set to become the de facto world standard. Australia’s privatized Airservices Australia has already launched a country-wide, exclusively 1090, ADS-B network, with ground stations currently being installed that will eventually replace its ATC secondary radars.

Yet beside being the world’s pace-setter in ADS-B implementation, Airservices may set another precedent that could delight Aussie private pilots, but could trouble the FAA. In a recent bid request, avionics firms have been asked to quote prices for 1,500 small, low-cost ADS-B units which, it is said, Airservices may simply give to general aviation operators to ensure that all targets are positively tracked at all times by ATC and other aircraft. It seems doubtful whether the FAA could afford to be that generous with the much larger U.S. private aircraft fleet.

The Future of ADS-B

Nevertheless, AOPA is bullish about ADS-B. Association vice president Andy Cebula said, “We are supportive of ADS-B and have been involved from the beginning in the FAA’s testing of the system.” He added that the situational awareness the system offered pilots was clearly a safety benefit, as is its ability to uplink weather and other traffic information.

He also commented that automatic downlinking of the aircraft’s intent–that is, where it was currently headed–could possibly even eliminate the future need for temporary flight restrictions. He also commended the system’s use of discrete individual aircraft IDs, rather than today’s use of a generic transponder code.

On the other hand, Cebula pointed out that equipment cost–currently around $7,800–was a major challenge, and emphasized that this was inextricably linked in the marketplace to the overriding issue of defining ADS-B’s complete future role, which he feels has yet to be resolved. How will it affect ATC, he asked? Is it eventually aimed at a self-separation environment? Will future controllers simply monitor traffic? Will it replace mode-C? How long should the transition be? (Cebula suggested that 10 years is appropriate for the transition.)

NBAA president and CEO Ed Bolen told AIN, “NBAA has been closely following the process under way by the FAA’s Joint Resources Council concerning implementation of ADS-B technology, and the association has been engaged in active dialog with the FAA about the benefits of ADS-B. NBAA supports development of ADS-B, or any other technology that can help modernize our nation’s air traffic system, improve its efficiency and enhance its safety. NBAA will work on behalf of its members with the FAA to ensure that any proposal on the implementation of ADS-B, or other technologies, is compatible with the overall interests of business aviation.”