AUTOMATIC DEPENDENT SURVEILLANCE
Introduction
Radar measures the range and bearing of an aircraft. Bearing is measured by the position of the rotating radar antenna when it receives a response to its interrogation from the aircraft, and range is measured by the time it takes for the radar to receive the interrogation response. The antenna beam becomes wider as the aircraft gets further away, making the position information less accurate. Additionally, detecting changes in aircraft velocity requires several radar sweeps that are spaced several seconds apart. In contrast, a system using ADS-B creates and listens for periodic position and intent reports from aircraft. These reports are generated and distributed using precise instruments, such as the global positioning system (GPS) and Mode S transponders, meaning integrity of the data is no longer susceptible to the range of the aircraft or the length of time between radar sweeps. PSR is robust in the sense that surveillance outage failure modes are limited to those associated with the ground radar system. SSR failure modes include the transponder aboard the aircraft. Typical ADSB aircraft installations use the output of the navigation unit for navigation and cooperative surveillance, introducing a common failure mode that must be accommodated in air traffic surveillance systems
There are two commonly recognized types of ADS for aircraft applications:
· ADS-Addressed (ADS-A), also known as ADS-Contract (ADS-C), and · ADS-Broadcast (ADS-B). ADS-B is inherently different from ADS-A, in that ADS-A is based on a negotiated one-to-one peer relationship between an aircraft providing ADS information and a ground facility requiring receipt of ADS messages.
For example, ADS-A reports are employed in the Future Air Navigation System (FANS) using the Aircraft Communication Addressing and Reporting System (ACARS) as the communication protocol. During flight over areas without radar coverage (e.g., oceanic, polar), reports are periodically sent by an aircraft to the controlling air traffic region. ADS-B consists of three components:
· A transmitting subsystem that includes message generation and transmission functions at the source. · The propagation medium. · A receiving subsystem that includes message reception and report assembly functions at the receiving vehicle or ground system.
The source of the state vector and other transmitted information as well as user applications are not considered to be part of the ADS-B system.
Automatic Dependent Surveillance (ADS)
It came under Future Air Navigation System (FANS) introduced by ICAO (International Civil
Aviation Organization).It has overcome the difficulties faced by the conventional navigational aids and communication systems especially in oceanic regions where installation as well as maintenance of the conventional navigational aids and communication systems where difficult if not impossible. Moreover , since it uses mainly Satellite Communication,the usable range of the system is not restricted by the Radio Horizon.
Though introduced earlier,CPDLC (Controller Pilot Link Communication) is still very important & kept as part and parcel with ADS. Through this data-link,Air Traffic Controller(ATCO) can
communicate with the Pilot. It outcasts the conventional voice communication in the sense that in the latter,several types of noise,fading and inclusion of personal linguistic accent often make the messages unreadable.
Currently there is a divergence of government and industry positions concerning concepts,
applications, costs and benefits for automatic dependent surveillance broadcast (ADS-B) development, deployment and regulatory status. Most of the potential controversy exists because there is no integrated systems approach that addresses a direct benefits driven transition plan for ADS that enables transformation of the National Airspace System from a ground centric to an airborne centric system.
Description of ADS ground equipment
It comprises of a Local Area Network (LAN) with
1. Redundant Input/Output cum Database Servers (IOS) having separate disk storage system
for database and data required for replay of different events occurred over a time period.
2. A dedicated Terminal Work Station (TWS) through which the system communicates with
the outer world using PSTN (SITA) service provider and private WAN (AMSS) owned by
Airports Authority of India.
3. A few Workstations placed at different ATC user positions (TWR,MCD,A-W,A-E etc.)
and Air Force user position (MLU) for liaison purpose.
Data input/output to the ground station
1. ADS data through SITA (Society of International Telecommunication Aeronautical), from the
different aircrafts.
2. Flight Plan data from AMSS (Automatic Message Switching System).
Generation of ADS Data airborne ADS Equipment
Different flight data prepared by the Flight Management Computer (FMC) of the Aircraft (viz. Call Sign, Co-ordinate in terms of latitude and longitude, Altitude, Azimuth i.e angular position with respect to the magnetic north , speed etc) are sent to the Ground Station by the aircraft airborne ADS equipment when data link with link with ground station is established.
Radar measures the range and bearing of an aircraft. Bearing is measured by the position of the rotating radar antenna when it receives a response to its interrogation from the aircraft, and range is measured by the time it takes for the radar to receive the interrogation response. The antenna beam becomes wider as the aircraft gets further away, making the position information less accurate. Additionally, detecting changes in aircraft velocity requires several radar sweeps that are spaced several seconds apart. In contrast, a system using ADS-B creates and listens for periodic position and intent reports from aircraft. These reports are generated and distributed using precise instruments, such as the global positioning system (GPS) and Mode S transponders, meaning integrity of the data is no longer susceptible to the range of the aircraft or the length of time between radar sweeps. PSR is robust in the sense that surveillance outage failure modes are limited to those associated with the ground radar system. SSR failure modes include the transponder aboard the aircraft. Typical ADSB aircraft installations use the output of the navigation unit for navigation and cooperative surveillance, introducing a common failure mode that must be accommodated in air traffic surveillance systems
There are two commonly recognized types of ADS for aircraft applications:
· ADS-Addressed (ADS-A), also known as ADS-Contract (ADS-C), and · ADS-Broadcast (ADS-B). ADS-B is inherently different from ADS-A, in that ADS-A is based on a negotiated one-to-one peer relationship between an aircraft providing ADS information and a ground facility requiring receipt of ADS messages.
For example, ADS-A reports are employed in the Future Air Navigation System (FANS) using the Aircraft Communication Addressing and Reporting System (ACARS) as the communication protocol. During flight over areas without radar coverage (e.g., oceanic, polar), reports are periodically sent by an aircraft to the controlling air traffic region. ADS-B consists of three components:
· A transmitting subsystem that includes message generation and transmission functions at the source. · The propagation medium. · A receiving subsystem that includes message reception and report assembly functions at the receiving vehicle or ground system.
The source of the state vector and other transmitted information as well as user applications are not considered to be part of the ADS-B system.
Automatic Dependent Surveillance (ADS)
It came under Future Air Navigation System (FANS) introduced by ICAO (International Civil
Aviation Organization).It has overcome the difficulties faced by the conventional navigational aids and communication systems especially in oceanic regions where installation as well as maintenance of the conventional navigational aids and communication systems where difficult if not impossible. Moreover , since it uses mainly Satellite Communication,the usable range of the system is not restricted by the Radio Horizon.
Though introduced earlier,CPDLC (Controller Pilot Link Communication) is still very important & kept as part and parcel with ADS. Through this data-link,Air Traffic Controller(ATCO) can
communicate with the Pilot. It outcasts the conventional voice communication in the sense that in the latter,several types of noise,fading and inclusion of personal linguistic accent often make the messages unreadable.
Currently there is a divergence of government and industry positions concerning concepts,
applications, costs and benefits for automatic dependent surveillance broadcast (ADS-B) development, deployment and regulatory status. Most of the potential controversy exists because there is no integrated systems approach that addresses a direct benefits driven transition plan for ADS that enables transformation of the National Airspace System from a ground centric to an airborne centric system.
Description of ADS ground equipment
It comprises of a Local Area Network (LAN) with
1. Redundant Input/Output cum Database Servers (IOS) having separate disk storage system
for database and data required for replay of different events occurred over a time period.
2. A dedicated Terminal Work Station (TWS) through which the system communicates with
the outer world using PSTN (SITA) service provider and private WAN (AMSS) owned by
Airports Authority of India.
3. A few Workstations placed at different ATC user positions (TWR,MCD,A-W,A-E etc.)
and Air Force user position (MLU) for liaison purpose.
Data input/output to the ground station
1. ADS data through SITA (Society of International Telecommunication Aeronautical), from the
different aircrafts.
2. Flight Plan data from AMSS (Automatic Message Switching System).
Generation of ADS Data airborne ADS Equipment
Different flight data prepared by the Flight Management Computer (FMC) of the Aircraft (viz. Call Sign, Co-ordinate in terms of latitude and longitude, Altitude, Azimuth i.e angular position with respect to the magnetic north , speed etc) are sent to the Ground Station by the aircraft airborne ADS equipment when data link with link with ground station is established.
Flight Plan
Before a flight starts, the details of the Air-Route to be followed including many other information needed for safe navigation is prepared and delivered to the pilot. This is called Flight-Plan.Flight plans are plans filed by pilots with the local Aviation Authority (e.g. FAA in the USA) prior toflying. They generally include basic information such as departure and arrival points, estimated time,alternate airports in case of bad weather, type of flight whether instrument flight rules or visual flightrules, pilot's name and number of passengers. Flight plans are required for flights under IFR. UnderVFR, they provide a way of alerting rescuers if the flight is overdue.
Process of using ADS/CPDLC
As a beginning , the pilot initiates a ' Log On' procedure which established the link with the ground station with consent of ATCO. When the aircraft is 'connected' to the ground station, ATCO configures his configures his computer for downloading the selected flight data from the aircraft, periodically at a selected interval. This constitutes ADS Data.
In this process , an embedded but separately recognized CPDLC link is also initialized by ATCO.
Through this link pilot and ATCO can exchange required messages mostly of pre-formatted type. The message appear in the screens at both the ends.
Displaying of dynamic situation information of the aircrafts in front of ATCO
ADS data and flight plan data received by TWS is sent to IOS. The relevant software present in IOS and other workstation process those data and make a central data storage at IOS . Using ADS software at some dedicated user positions (ADS & MNT) the positional situation of the aircrafts are displayed on a separate 29 inch color monitor dynamically , in the form of 'blips' like that of a RADAR screen.
These blips show the actual positions of the aircrafts.
1. Video maps of the relevant air-routes with positions of Aeronautical Fixes and positions of
different Nav-aids on them , Flight Information Region (FIR) , geographic
territories/boundaries etc. are super imposed on the display . The aircraft 'blips' also
accompany a data block which displays some selectable parameters of the aircrafts (viz.Call
Sign , azimuth, altitude etc.). since the ADS uses Satellite Communication , there is no bar of any range. Surveillance over a far bigger chunk of earth, including oceanic regions becomes easier of ATCO
Associated Hardware and Software
Servers and workstations use SPARC Processors from Sun Microsystems Inc.
All the Hard disks/Tape drive used are SCSI type.
Operating System used in SUN OS version 5.4
LAN established is in star topology , use 100 MBPS Ethernet switches.
Applications are provided by Electronics Corporation of India Ltd.
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