Cover Story: ADS-B On The Ground

FAA’s NextGen program to modernize the National Airspace System (NAS) took a great leap forward in late August with the selection of an industry team led by ITT Corp. to provide the ground infrastructure of a nationwide Automatic Dependent Surveillance-Broadcast (ADS-B) network.

Under the 18-year, $1.86 billion contract, won against competing teams headed by Lockheed Martin and Raytheon, ITT, an $8 billion engineering and manufacturing concern based in White Plains, N.Y., will provide 794 ADS-B transmit/receive ground stations across the United States, many installed on cell phone towers.

Other than assuring that those ground stations meet good commercial manufacturing standards and the agency’s performance, reliability and other criteria, FAA certification staff will play a relatively small role in the ADS-B deployment. The contract gives ITT overall responsibility for design and development, testing, production, site selection, installation and technical support of the equipment.

The latter installation and support functions will be facilitated by AT&T, at more than $117 billion in revenue the largest communications holding company in the United States and a major member of ITT’s "ADS-B America" team. AT&T, based in San Antonio, claims to be the nation’s leading wireless carrier, and its widespread communications network reportedly strongly influenced FAA’s contract decision.

ITT’s proposal "was heavily invested in a pre-existing infrastructure, such as (that for) cell phone," Vincent Capezzuto, FAA director of surveillance and broadcast services, said Aug. 30, in a teleconference announcing the contract award.

"Their main subcontractor (is) AT&T. That gives you a sense of where the installations and the radios are going to be," Capezzuto added. "They have a pretty large infrastructure that they are going to leverage off of. They have the telecommunications there already to distribute the information and the operations centers that are really key to maintaining the system and keeping it healthy."

Other members of the ITT team are Thales North America, Science Applications International Corp., based in San Diego; weather information provider WSI Corp., Andover, Mass.; Aerospace Engineering and Research Associates, Lanham, Md.; Sunhillo Corp., West Berlin, N.J.; Comsearch, Ashburn, Va.; MCS, Tampa, Fla.; Pragmatics, McLean, Va.; Aviation Communications & Surveillance Systems (ACSS), Phoenix; Sandia Aerospace, Albuquerque, N.M.; NCR Corp., Dayton, Ohio; PriceWaterhouseCoopers and Washington Consulting Group.

Ground Transceivers

The ADS-B roll-out will begin with a three-year, $207 million design and production phase. The ITT team will build an initial 300 ground stations, known as ground-based transceivers (GBT), destined for installation around the Gulf of Mexico, in Alaska, and in Louisville, Ky., and Philadelphia, both major freight hubs used by ADS-B pioneer UPS. In 2010, FAA will complete system certification and signal-in-space tests.

The period from 2010 to 2013 will see the production and shipment of the balance of GBTs to the remaining sites, providing ADS-B service wherever secondary surveillance radar (SSR) coverage is currently available. Under the NextGen plan, roughly half of FAA’s 300-plus SSRs will gradually be replaced as ADS-B service begins.

The $207 million initial cost is more like a "start-up fee" because, as ground installations enter operation, FAA will pay ITT annual subscription fees proportional to the number of systems that come on line. When all stations become fully operational, the agency’s annual tab will be in excess of $100 million.

In defining its requirement for ADS-B ground stations, FAA followed a "performance-based" approach. In virtually all new procurements by the agency, bidders are requested to offer products incorporating best commercial practices, rather than being held to the previous, rigid production rules. A commonly cited example of these rules was FAA’s strict enforcement of the allowable radius of wiring when it was required to curve.

In its time, the rule was prudent, but newer materials and commercial assembly experience have shown it to be unnecessarily conservative, more space consuming and more costly. In the ADS-B solicitation, bidders were invited to offer approaches that reflected commercial best practices, and innovative solutions were encouraged.

A screening information request was sent to potential ADS-B providers last November to determine which vendors had viable solutions. Three teams — led by ITT, Raytheon and Lockheed Martin — responded and made it through the screening process. A request for offers was issued in March.

"Once the offers were in, our team of experts worked quickly and carefully to evaluate the technical, business and cost areas of each proposal, based on strict criteria," FAA Acting Administrator Robert A. "Bobby" Sturgell told the teleconference. "Five months later, we are here today announcing the team selected to move forward with a key building block of the Next Generation Air Traffic System…. I think you’ll agree, this isn’t the same old foot-dragging FAA you may have written about before."

Dual frequencies

In their responses, all three bidding teams followed FAA’s guidelines to a greater or lesser extent. And each had to find a satisfactory way of handling an unusual design challenge, where two different and incompatible data link frequencies and data formats would be used.

All U.S. and foreign airlines and high-end corporate aircraft carry internationally adopted, ICAO-standard 1090 MHz Mode S transponders that now largely include Extended Squitter (ES) capability. But in the early 1990s, when the potential of ADS-B for general aviation became recognized, private aircraft owners balked at the large, heavy airline units. As a result, FAA funded the development of the Universal Access Transceiver (UAT), a smaller, lighter and somewhat more capable unit operating at around 978 MHz.

The UAT subsequently was recognized by ICAO. While these units proved successful in FAA’s Capstone project in Alaska and at a number of locations in the contiguous United States, UAT never achieved international acceptance. In the United States, this means that 1090ES-equipped aircraft can "see" all other 1090ES aircraft, but not UAT-equipped aircraft, and vice versa.

The GBTs provided by the ITT team will therefore be dual-frequency units which, upon receiving an airliner’s 1090ES squitters, will immediately "translate" them into UAT formats and transmit them back up on the UAT frequency, thereby making the airliner "visible" to UAT aircraft in the vicinity. When UAT signals are received by the GBTs, they will perform a reverse translation process and retransmit these in 1090ES format and frequency.

The United States is not alone in supporting dual ADS-B frequencies. While FAA was developing the UAT concept, engineers in Sweden were investigating VHF data link solutions for ADS-B. Today, 70 percent of Swedish radar airspace is covered by VHF Data Link, Mode 4 (VDL-4) GBTs, which also are ICAO approved. Sweden plans to incorporate 1090ES into this network to assure compatibility for all users since 1090ES and VDL-4 are incompatible.

Thales North America’s Air Traffic Management (ATM) business in Shawnee, Kan., will supply the dual-link 1090 MHz and UAT transceivers and provide life-cycle support. The company said the initial, three-year contract is worth $40 million; with all options exercised it grows to $140 million.

Participation in the FAA contract represents another feather in Thales’s ADS-B cap. The company in March 2004 was awarded a contract from Airservices Australia for the provision of 57 ADS-B ground stations at 28 sites, a deployment completed by December 2005. The air-traffic management corporation owned by the Australian government awarded Thales another contract last November for the provision of 40 additional ADS-B ground stations, a project now underway.

Thales was awarded a contract from Eurocontrol in 2005 under the CASCADE3 program for deployment of ADS-B systems in Europe, including the first multi-channel system, which combines multiple receivers and sectorized antennas in order to improve performance in dense signal environments.

The Thales system includes Traffic Information Service-Broadcast (TIS-B) functionality, and recently completed acceptance testing with Deutsche Flugsicherung (DFS), the German air-traffic-control organization, in Langen, Germany. In July, Thales reported delivering five ADS-B ground stations to Germany, Cyprus, France, Greece and Italy.

Todd Donovan, Thales North America vice president of Air Traffic Management, said the company will supply nearly 1,600 transceivers for the FAA contract, as most of the GBT sites will be redundant. Thales ATM also will provide sensor fusion of radar and ADS-B data, supporting the uplink of TIS-B messages to receiving aircraft.

Prior to the FAA contract award, Thales ATM announced the launch of a new UAT transceiver to augment its modular ADS-B platform, a system capable of ADS-B reception and broadcast services for en route, terminal or surface applications.

"We have configurations for 1090 and UAT ground stations, but we’ve created a very tailored solution for the FAA that really matches their requirement," Donovan said. "Now we’re working closely with ITT to analyze how best to address the service nature of this contract. We have a variety of standard configurations that we’ll be building in order to satisfy this contract, which will be made up essentially of modules that exist or will be modified from existing ones."

Thales, partially owned by the French government, also is involved in the ADS-B contract through ACSS, its joint venture with New York City-based L-3 Communications. Asked if there were any foreign-content issues related to the FAA contract, Paul Kahn, managing director of Thales Global Navigation and Airports, pointed out that Thales ATM evolved from the American radio navigation firm Wilcox Electric. The company has a legacy of providing FAA with DME, VOR and ILS navigation aids.

In 1988, Wilcox was acquired by Thomson Corp. of America, an entity of France’s Thomson-CSF, and later renamed Airsys ATM. Thomson-CSF was renamed Thales in 2000 and Airsys changed to Thales ATM in 2001.

"People don’t realize that Thales is the FAA’s supplier of navaids," Kahn said. "We supply nearly all of the navigation aids and the navigation infrastructure for the FAA already, and we do that from Kansas. So this is a U.S. business that has bid for ADS-B. It’s leveraging Thales’s global technology, but it is very much a U.S. business and a U.S. team that is developing this competence. It’s not been an issue."

While both ITT and Lockheed Martin proposed dual-frequency GBTs, Raytheon offered a very different approach. The company proposed completely replacing UAT with 1090ES which, according to Raytheon, would standardize a single link nationwide and reduce GBT costs by dispensing with the translator and the extra frequency. In a number of ways, this could have been beneficial to general aviation, since UAT ADS-B service is unavailable outside the U.S. border. But while FAA encouraged innovative approaches, Raytheon’s approach was considered "just too innovative" by agency assessors, sources told Avionics.

"Make no mistake, all three vendors were eligible and all three proposed significant innovations for the flying ADS-B services across the National Airspace System," Capezzuto said. "However, we chose ITT because its proposal had the best value solution combined with the least risk to the agency and the entire aviation community."

Proposed Rule Issued For ADS-B Equipage

FAA on Oct. 2 issued a long-anticipated Notice of Proposed Rulemaking (NPRM) setting out performance requirements of the avionics needed to operate in an Automatic Dependent Surveillance-Broadcast (ADS-B) flight regime.

The 100-page NPRM proposes that only ADS-B "Out" broadcast capability be required, deferring a mandate for ADS-B "In" equipage "at this time." Aircraft position accuracy would be provided by the GPS Wide Area Augmentation System (WAAS). The document also provides estimated ADS-B equipment and installation costs, ranging from a low of $4,328 for GA aircraft to a high of $463,706 for turboprops.

The proposed rule was open to public comment for 90 days after publication in the Federal Register, and is scheduled to become final by late 2009. It proposes a compliance date of 2020, giving aircraft operators 10 years to equip.

Under the NPRM, aircraft must be equipped with either 1090ES (Extended Squitter) transponders or Universal Access Transceivers (UAT) conforming to Technical Standard Order (TSO) C166a and C154b, respectively. Aircraft flying at or above FL240 (24,000 feet) must use the 1090ES transponder; aircraft operating below that level can have either the 1090ES or UAT broadcast units.

The draft rule states that top and bottom antennas are required for "optimal link performance." For aircraft already equipped with a TSO-C112 Mode S transponder, no additional antennas would be required for ADS-B Out using 1090ES. For ADS-B installations using UAT, "it may be possible to share the aircraft’s existing bottom ATCRBS (Air Traffic Control Radar Beacon System) transponder antenna through the use of an antenna diplexer, thus only requiring installation of a top antenna."

The use of a WAAS-capable navigation sensor is deemed necessary for the accuracy and integrity of position broadcasts, as measured by NIC (Navigation Integrity Category), NACp (Navigation Accuracy Category for Position) and NACv (Navigation Accuracy Category for Velocity) values. FAA is considering whether other options, such as the Global Navigation Satellite System "with tightly coupled inertial navigation," are capable of meeting performance standards.

The estimated cost of ADS-B equipment and installation ranges from $4,328 to $17,283 for GA aircraft; from $12,906 to $463,706 for turboprops; and from $3,862 to $135,736 for turbojet aircraft, according to FAA. — Bill Carey