Automatic Dependent Surveillance (ADS-B)

Automatic Dependent Surveillance Broadcast (ADS-B) is an air traffic surveillance technology that enables aircraft to be accurately tracked by air traffic controllers and other pilots without the need for conventional radar.While the initial application of ADS-B is to provide high quality surveillance for air traffic control, it also facilitates a number of advanced air-to-air applications that will in future significantly improve safety and performance of aircraft operations.

The technology delivers both environmental and economic benefits through:

  • improved aircraft access to preferred routes and levels,
  • more efficient diversions around restricted areas and weather and,
  • Increased accuracy of navigation.

In addition to delivering radar like surveillance at a fraction of the cost of radar, it also offers considerable safety improvements through:

  • rapid and targeted search and rescue response,
  • reduced collision risks around regional aerodromes, and
  • Improved ATC and pilot situational awareness.

Other ADS-B safety and operational benefits include:

  • Positive ATC identification while within ADS-B coverage
  • No requirement for position reporting while identified
  • Identified aircraft receive priority over non-identified aircraft
  • Route and altitude conformance monitoring
  • ATC safety net alerting functions (e.g. short term conflict alert and dangerous area infringement warning)

ADS-B is a system in which electronic equipment onboard an aircraft automatically broadcasts the precise location of the aircraft via a digital data link.The data can be used by other aircraft and air traffic control to show the aircraft’s position and altitude on display screens without the need for radar.The system involves an aircraft with ADS-B determining its position using GPS. A suitable transmitter then broadcasts that position at rapid intervals, along with identity, altitude, velocity and other data. Dedicated ADS-B grounds stations receive the broadcasts and relay the information to air traffic control for precise tracking of the aircraft.

Automatic - Requires no pilot input or external interrogation.

Dependant - Depends on accurate position and velocity data from the aircraft's navigation system (eg. GPS).

Surveillance - Provides aircraft position, altitude, velocity, and other surveillance data to facilities that require the information.

Broadcast - Information is continually broadcast for monitoring by appropriately equipped ground stations or aircraft.

ADS-B data is broadcast every half-second on a 1090MHz, digital data link.

Broadcasts may include:

  • Flight Identification (flight number callsign or call sign)
  • ICAO 24-bit Aircraft Address (globally unique airframe code)
  • Position (latitude/longitude)
  • Position integrity/accuracy (GPS horizontal protection limit)
  • Barometric and Geometric Altitudes
  • Vertical Rate (rate of climb/descent)
  • Track Angle and Ground Speed (velocity)
  • Emergency indication (when emergency code selected)
  • Special position identification (when IDENT selected)

The ability of a ground station to receive a signal depends on altitude, distance from the site and obstructing terrain. The maximum range of each ground station can exceed 250 nautical miles. In airspace immediately surrounding each ground station, surveillance coverage extends to near the surface.

Working:

However, transmission in the form of 1090MHz Mode-S extended squitter messages has gained significant support and seems to be most likely to become the future standard at least for large commercial aircraft, which typically already carry Mode-S transponders and can easily accommodate this new technology.

Using this technology, aircraft broadcast their position twice per second in the form of 112 bit Mode-S messages.

Such a message contains the unique 24 bit Mode-S address of the aircraft, an encoding of the aircraft position, and, typically, the barometric altitude.

Additional messages can carry further information, including call sign, speed, heading, and geometric altitude.

Figure 1:ADS-B-OUT over 1090 MHz combines existing Mode-S transponder technology with GPS.

Figure 2:ADS-B-IN provides airborne pilots with a visual representation of surrounding traffic.

Functions of TCAS and ADSB

TCAS

TCAS (the Traffic Alert and Collision Avoidance System) is a collision avoidance system designed to operate when normal air traffic management procedures fail to maintain adequate separation between aircraft. TCAS is an airborne system that operates independently of ground systems.

ADS-B

ADS-B (Automatic Dependent Surveillance Broadcast) is the regular transmission of identity, position, velocity and other information by an aircraft. Since ADS-B signals are broadcast, any party that receives the signals can decode the messages to track the position of the transmitting aircraft. The information obtained through ADS-B can be used by air traffic controllers to manage air traffic, and can equally be processed on board other aircraft to determine the identity, proximity, and trajectory of surrounding traffic.

TCAS is a collision avoidance system, while ADS-B may be used to provide the aircraft surveillance required for both air traffic control and airborne applications. ADS-B displays provide more data and more accurate position data than TCAS traffic displays. A number of airborne applications are being developed to take advantage of the surveillance provided by ADS-B.

Automatic Dependent Surveillance (ADS-B) in INDIA

ITT Defense & Information Systems is proposing to play the same systems integration role for automatic dependent surveillance-broadcast (ADS-B) radar in India that it is fulfilling in the U.S., but even as the Indians recognize ADS-B’s superior ability to track and control aircraft, they worry about its costs.
The Airports Authority of India (AAI) is pursuing an ITT system that would cover the entire subcontinent plus the Bay of Bengal and Arabian Sea. As Indian skies become more crowded, AAI says ADS-B’s ability to precisely locate one aircraft’s position in relation to others will greatly enhance the Indian air traffic controllers’ management of takeoff, landing and transit operations. ITT is leads systems integrator on the ADS B ground infrastructure program in the U.S.Under the proposed contract, ITT will be responsible for overall system integration and engineering and will operate and maintain the system after deployment through September 2025. In the U.S., ITT’s contract with the FAA is novel because it calls for an independent company to own and maintain the infrastructure, thereby absorbing the financial risks.. AAI has indicated that the ADS-B system should be in place in India by 2015. That’s faster than the U.S. This has a great potential for future growth in India.But enabling the system will require a survey and analysis of where to establish ground stations, which has not been done. At the FAA’s invitation, he recently traveled to Dallas to observe ITT’s operations control center.

Airports Authority of India has selected Era Corporation, in partnership with the Holland Institute of Traffic Technology (HITT), to provide three multilateration and ADS-B surface surveillance systems for India. The airports covered under this deal include the Chhatrapati Shivaji International Airport in Mumbai, India’s largest and busiest, the Anna International Airport in Chennai, and the Netaji Subhash Chandra Bose International Airport in Kolkata.

India’s airports have seen a staggering rise in demand over the past several years. To compensate, India has invested in new airports, terminals, runways and surveillance infrastructures. In an effort to further increase safety, efficiency and optimization, Airports Authority of India chose to add A-SMGCS (Advanced Surface Movement Guidance and Control Systems) to three of the nation’s busiest airports.

AVT-453 Traffic Collision Avoidance System
Assignment - 4
Pramod Kumar.M
0701AEET001