Automatic dependent surveillance-broadcast (ADS-B) has emerged as what many describe as the surveillance technology of the future, but Asia Pacific air navigation service providers (ANSPs) are already taking advantage of its capability and cost-efficiency.

In fact, the Asia Pacific region stands at the forefront of a global switch from conventional secondary radar (SSR) to the new technology. Thales is deploying a national network in Australia. Fiji is looking for a system to cover the 2.4 million square miles of the Nadi flight information region in the South Pacific. And in October China announced that it was about to embark on its first commercial aviation trial of ADS-B at Chengdu Shuangliu International and Jiuzhai Huanglong airports in preparation for nationwide deployment.

For users of those airports, the cost and practicality benefits of ADS-B compared with today’s system loom as large as the differences in the technology. Conventional SSR broadcasts an interrogation signal that triggers a reply from airplane transponders giving call sign and altitude. That signal combined with range and bearing data from primary radars to give an airplane’s position, altitude and identity, and successive readings build a picture of its past track.

ADS-B relies instead on the airplane’s own GPS-derived position estimate. This is transmitted automatically along with information on its direction, turn rate and climb or descent rate by the 1090 MHz mode-S transponders that were mandated during the 1990s as part of the traffic alert and collision avoidance system.

The transmissions are received by ground stations that cost around one tenth the price of SSRs. They are also much easier and less expensive to install and maintain. So the promise is much better surveillance– letting air traffic controllers know where each airplane intends to go next as well as where it has been–at much lower cost.

Last year the U.S. Federal Aviation Administration awarded a team led by ITT a contract that could be worth as much as $1.86 billion through 2025 to develop, deploy, operate and maintain an ADS-B system covering the U.S. Canada is deploying a system to cover the Hudson Bay as a first step toward providing surveillance over its vast northern territories. Even Europe, where comprehensive primary and secondary radar coverage already exists, is working to introduce the technology.

Another attraction of ADS-B technology is its ability to act effectively as its own backup. Even without the mode-S extended squitter transmissions that carry the position and intent information, transponder squawks can be used to calculate an airplane’s position by multilateration: a ground station can calculate the bearing and distance to a target using the elapsed time between transmission and reception, and combining the calculations from several ground stations gives its location in three dimensions.

Multilateration can be used over a wide area for surveillance of en route traffic, so the same receivers using a different technique constitute an alternative means of tracking air traffic. It can also be used by airports to track both aircraft on the surface and suitably equipped ground vehicles accurately. Suvarnabhumi in Bangkok, Beijing Capital, Kuala Lumpur International and Singapore’s own Changi are among the major regional hubs to have adopted multilateration for airport surveillance.

Ground surveillance relies on ADS-B output, or the signal broadcast by the aircraft. Additional applications are made possible by ADS-B, which requires the aircraft to have a 1090-MHz receiver, a traffic computer and a cockpit display of traffic information (CDTI). The first application facilitated by ADS-B is expected to be airborne traffic situational awareness.

Beyond that, it may be possible for pilots to use the information on other traffic to maintain an assigned distance behind another aircraft, which should help improve airspace capacity and efficiency. Ultimately, pilots may be able to use it to maintain separation from other traffic, the main task of today’s air traffic controllers.

The U.S. ADS-B program includes broadcast traffic information and flight information services (TIS-B and FIS-B) using the ADS-B function. TIS-B provides equipped aircraft with SSR position reports on aircraft not equipped with ADS-B, generating an ATC-like view of traffic on the CDTI. FIS-B transmits graphical charts from the National Weather Service plus information such as temporary flight restrictions and special use airspace.

Surveillance Alliance
To help Asia Pacific ANSPs accelerate the transition to the new technology, Airservices Australia and air/ground datalink service provider SITA have launched an ADS-B surveillance service. Building on ANSP Airservices’ experience of deploying ADS-B technology in Australia and SITA’s global telecommunication infrastructure, the alliance says it can offer a region-wide ADS-B network capability that includes design, planning, implementation and support.

The collaboration developed over the last few years and the two organizations revealed in October 2004 that they were forming a strategic partnership to market ADS-B services in the Asia Pacific region. They formalized the partnership at the end of 2005 and went on to participate, along with Thales, in a trial completed last year demonstrating the possibilities for Indonesia.

Indonesia controls a huge area of airspace occupied by heavy international and domestic air traffic. The trial involved the deployment of Thales ADS-B ground receivers at Denpasar in Bali, Kupang in Nusa Tenggara Timur and Natuna Island in the South China Sea. The SITA communications links and surveillance processors connected the receivers to Indonesia’s control centers in Jakarta and Makassar.

The output was also displayed in the lobby of ICAO’s regional office in Bangkok: part of the impetus behind the move to commercialize the technology came from a specific ICAO regional recommendation that ADS-B surveillance be introduced in the region beginning in January 2006. The goal is to close the many surveillance coverage gaps that exist in the Asia Pacific region and to assist the many developing nations that are faced with ongoing high maintenance costs and costly replacement of radars.

The partners call ADS-B ideal for this region because it eliminates the need for expensive multiple radar sites. They estimate that a region-wide ADS-B network can operate for 10 percent of the cost of radar-only infrastructure.

A region-wide ADS-B network would also enable ANSPs to share data across national and flight information region (FIR) borders. As well as enhancing aircraft surveillance data for ANSPs and airlines, cross-border data sharing would bring immediate operational benefits, including safety, particularly around FIR boundaries.

The region-wide network of ADS-B sites would be linked by SITA’s multi-layered Internet protocol virtual private network architecture. Installing the ground stations on existing SITA VHF datalink ground station sites would speed development.
Alternatively, the ADS-B ground stations could be installed at ANSPs’ sites and integrated into the SITA telecommunication network service. The service offering also includes air traffic controller training and ATC procedure, business case and safety case development.

The alliance offers three levels of service. Tier 1 is based on a highly redundant architecture designed to provide a level of performance high enough to allow an ANSP to separate aircraft using a 5-nm separation standard. It would support vectoring of aircraft, separation of aircraft from other aircraft and separation of aircraft from terrain.

The Tier 2 ADS-B service would enable an ANSP to provide situational awareness to controllers and support safety net alerting. Tier 3 would provide aircraft operators such as airlines with access to the ADS-B service to enhance flight operations. It would typically provide data relating only to the customer’s own aircraft. In all cases, the ADS-B data stream would be delivered to a customer’s premises from a pre-defined set of ADS-B receivers via an IP connection.