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Communication Navigation Surveillance / Air Traffic Management (Cns / Atm) Beyond 2012
3.4.c Satellite Based Augmentation System (SBAS)
The GBAS will not be able to provide coverage for all phases of flights because of its range limitations. An effective means of overcoming this limitation has been devised, using Geo-stationary earth orbiting satellites (GEOS) to transmit messages to correct GNSS signals on a wide geographic area. There are five SBAS service providers in the world i.e. Wide Area Augmentation System (WAAS) - USA, European Geo-stationary Navigation Over-Lay Service (EGNOS) – European Community, Multifunctional transport satellite Augmentation system (MSAS) – Japan, GPS and Geo Augmentation Navigation (GAGAN)- India, Ground Regional Augmentation System (GRAS) – Australia.
3.4.c.1 Wide Area Augmentation System (WAAS) (USA)
WAAS is designed and under implementation by US as an augmentation to GPS which includes integrity broadcasts, differential corrections and additional ranging signals. It provides the accuracy, integrity, availability and continuity required to support all phases of flight through CAT-I precision approach ( PA). WAAS consists of one integrated system providing all SBAS functionality. The delivery schedule will be accomplished in three phases by delivering an initial operating system and then upgrading the system through preplanned product improvements. Phase–I WAAS will also provide the initial operating system which consists of two WAAS master stations (WMS’s), 25 WAAS Reference Stations (WRS,s) leased GEOSs and ground uplinks to achieve a primary en-route guidance through non-precision approach ( NPA) capability, as well as enable GPS /WAAS to be used as a supplemental navigational-aid for CAT-I PA’s. Shortly after the completion of contract of Phase–I, the FAA will commission the WAAS for operational use in the US national air space (NAS). WAAS has been commissioned in the year 2003 for limited use as a sole means of navigation.
3.4.c.2 European Geo-Stationary Navigation Overlay System (EGNOS) (EUROPE)
EGNOS is the joint venture of European institutions and space industries to show their strong commitment in the development and system operations of satellite navigation.. European’s EGNOS ensures international cooperation as well as European independence. The European Tripartite Group comprising the European Space Agency (ESA), the European Community, EUROCONTROL and the European organization for safety of air navigation, manages EGNOS.
In view of the operational implementation to come, the following seven major European air traffic service providers are on the way to form a legal entity. They are the EGNOS operator and infrastructure group (EOIG), France DGCA, German DFS, Italian ENAV, NAV-EP of Portugal, Spanish AENA, Swiss control of Switzerland and NAST of United Kingdom. In addition the CNES (French Space Agency), the Norwegian Mapping Authority and major European air traffic management service providers actively contribute to the development and the future operation of EGNOS. All of them are working under collaborator framework of the EGNOS program. The EGNOS service augments the GPS and GLONASS signals. The two satellite systems send a positioning signal to the user. The ranging and monitoring stations network acquire, firstly the ranging signal generated by two constellations, GEOS and secondly generate the required atmospheric data.
3.4.c.3 Multi Functional Transport Satellites (MTSAT) Satellite - Based Augmentation System (MSAS) (JAPAN)
The MTSAT Satellite-Based Augmentation System (MSAS) is the wide area augmentation system being developed by Japan Civil Aviation Bureau (JCAB) for civil Aviation. This space-based augmentation system will provide en-route information through PA navigation services for all the aircraft within Japan airspace. The MSAS employs a ranging function to generate GPS like signals and enable aircraft to use MTSAT as a 25th GPS satellite. The MSAS is similar in function to the WAAS (US). Information on real-time conditions of the GPS constellations transmitted to each aircraft via the integrity function of MSAS provides satellites location, while the differential corrections function provides ranging error data to each aircraft. MSAS uses advanced technologies such as satellites orbit ranging, ionospheric and tropospheric delay estimation to ensure the reliability of these functions.
3.4.c.4 GPS /GLONASS And Geo-Stationary Augmented Navigation (GAGAN) (INDIA)
GAGAN system uses two-core constellation of medium orbiting satellites i.e. GPS and GLONASS. The positioning services offered by these two constellations for civilian use including civil aviation fall short of accuracy, integrity, availability and continuity requirements of air navigation services. Indian air space, coming in between Europe on the West and Japan on the East, occupies a very critical position and hence there is a need to have a system to bridge the gap between the coverage of EGNOS and MSAS and to facilitate seamless navigation of the aircraft from East to West and vice versa. GAGAN will provide the coverage over Indian airspace to the users. Indian augmentation with Indian payloads on GSAT-4 satellites, which are controlled by India, will offer some amount of control and flexibility on the position accuracies available to strategic users. India will be able to play an important role in providing seamless SBAS in the world. In years to come, India may well become a SBAS service provider to the neighboring countries in Asia-Pacific region. The national plan envisages implementation of a full operational capability SBAS in three phase and will be operational in the year 2008.
3.4.c.5 Ground Regional Augmentation System (GRAS):
The Ground-based regional augmentation system (GRAS) is a system providing GNSS augmentation service by which the user receives information directly from ground-based transmitters, allowing continuous reception of the service over a large geographical area of approximately 370 Km (200NM). The ground component may be interconnected in a network. GRAS supports GNSS (GPS, GLONASS, and GALILEO) operations in the all phases of the flight including en-route, terminal and instrument approach with vertical guidance (APV) operations. GRAS should be viewed as complementary to SBAS (such as EGNOS, WAAS, GAGAN and MSAS) and GBAS. GRAS is made up of multiple ground station with overlapping coverage. However the service provider will have to ensure that the topology of the ground infrastructures meets the operational requirements. The use of the locally valid augmentation makes it possible to use a subset of the GBAS message elements. A GRAS solution must include an auto-tuning functionality for seamless use of different ground station as the flight progresses.
4.0 Surveillance:
Surveillance is the eye of the ATC. For effective ATC to be possible, people or systems on the ground must know the position of the aircraft on a continuous basis and be able to estimate their future position. Surveillance provides the controller with the information necessary to insure specified separation between aircraft, to manage the airspace efficiently and to assist the pilot in the navigation. The surveillance systems presently in use can be divided into two main types: dependent surveillance and independent surveillance. In dependent surveillance systems, the aircraft position is determined on board and then transmitted to ATC. As far independent surveillance such as primary radar is a system that measures aircraft position from the ground. The current surveillance is based on either voice position reporting or radar, which measures range and azimuth of aircraft from the ground station. The secondary surveillance radar augmented with Mode-S when traffic conditions so warrant will continue to be used, especially in high traffic density airspaces. In other places, where coverage of SSR is not possible, such as oceanic airspaces and remote areas over the earth, surveillance will be provided using automatic dependence surveillance (ADS).
4.1 Automatic Dependent Surveillance (ADS)
In this, the aircraft automatically transmits, via data links, its identification and 3-D position to the ATC unit. It allows controllers to observe on a pseudo-radar display, the position of aircraft and possible deviations from the assigned flight paths. The design of the ADS should allow the implementation without disrupting ATS. It should also be sufficiently flexible to adaptability to local requirement and ATS special requirements, expandability, integration with new technology, provide sufficient safety and switch over to other forms of ATS in case of failure or degradation. It should also have the capability to provide a minimum service to all duly equipped aircraft and become finally part of ATS infrastructure that derives full advantage of the ADS.
4.1.a Automatic Dependent Surveillance ADS-A (Addressed)
This system operates only in the air-ground mode and at the request of the ATC unit. It is the controller who determines which reports are necessary for controlling each aircraft. The basic principle is given as: Communication contracts must first be established between airborne equipment and ground systems before being able to receive any ADS report. The controller determines which report is necessary to control each aircraft in the flight segments under the control of a given ATC unit. The issuance of basic ADS report at periodic intervals is defined by the ground system with one or more blocks of additional data containing specific information. ADS report may contain geographically defined points, such as waypoints and intermediate points, in addition to reports triggered by specific occurrence. Certain types of airborne equipments have the capability to maintain contracts with four or five ATC unit simultaneously. These aircraft will also send automatic position reports, in keeping with ADS contracts made by ground system. At given time or distance before reaching the boundaries of the FIR, which can vary depending on the ground system. The latter will immediately prepare and transmit ADS reports addressed to the grounds system in keeping with the pre-established contracts. In some system, the controller has the capability to replace the ADS contracts if necessary. The ground system will issue the appropriate message to start the modification of exiting contracts.
Automated ground systems can use the ADS position reports and other data groups from the ADS message to provide automated flight tracking in accordance with flight plan. Most automated ground system compares the aircraft position reported by the ADS with the position foreseen by the ground system, taken from the flight plan. The ground system will prepare and show the controller the appropriate message in the event that the ADS report does not match the position foresee by the ground system. This monitoring capability makes it possible to verify whether the flight is proceeding according to flight plan. Further more, aircrafts are equipped with FAN-1A capable of doing their own monitoring and of making an automatic report in case of significant flight variations, when so required by an appropriate occurrence contract. The ground system will include, together with the request for an ADS occurrence contract, the value that triggered these reports.
4.1.b Automatic Dependent Surveillance Contracts ( ADS-C) :
There are three types of contract, each of them operating independently of the others. They are periodic contract, occurrence contracts & demand contracts. A request for a periodic contract defines the contract requirements to be included in the reports and reporting frequency. Through an uplink, an ATS unit initiates the periodic report request. This request allows an ATS unit to include the optional data groups in the basic ADS reports, also specifying the frequency of inclusion. The controller can modify the periodic reporting average up and down in order to accommodate special situations, such as traffic density. Information about the minimum reporting averages recommended for each type of aircraft can be obtained from the manufacturer’s manual. Only one periodic contract can be established. if another is to be established , then the previous contract will be replaced . This periodic contract will remain in force until modified or cancelled.
The occurrence contract specify a report request to be sent by the aircraft if certain occurrence takes place e.g. variation in ascent or decent regime, lateral deviation in flight path, change in altitude, change in reporting point. Only one occurrence contract may be established each time between the aircraft and the ground system even so, the contract may contemplate different type of the occurrence. The demand contracts request is a single request from the ground system for the airborne equipment to send an ADS report containing the data specified in the request. A demand contact may be requested by the ground system at any time. A request for such contract will not affect any other that exists.
The emergency mode is activated or cancelled by the pilot only. Once activated, the emergency mode connects the aircraft with all ground systems that have established periodic or occurrence contracts with it. When pilot cancels the emergency mode, the on board equipment will send a cancellation message to each ground station that received this message.
4.2 Automatic Dependence Surveillance- Broadcast (ADS-B)
ADS-B is a new aeronautical surveillance concept by virtue of which the aircraft transmits its position through data link. The position information is received by near-by aircraft, which enables all users to be informed about their own position and the position of all other nearby traffic. The position information may be displayed in the cockpit of aircraft thus equipped to allow for new possibility of detecting traffic. Ground vehicle and facilities can also be equipped to receive and transmit position data, making it possible to monitor all types of traffic through two-way data links. In addition to position data, other data like aircraft identification and speed (obtained from GNSS receiver) may be also transmitted. ADS-B will play important role in the cockpit environment, and it will keep the pilot informed about all the traffic vicinity of the airports. The cockpit display is used to show the position and intentions of all aircrafts within a 200-NM radius. This equipment is called cockpit display of traffic position (CDTI) or traffic situation display (TSD).
However ADS-B allows keeping a visual display of all surrounding traffic. On the ground, the ADS-B will offer ATC new surveillance capabilities at a fraction of the cost of a conventional SSR. An ADS-B ground station is a transmitter / receiver station without the complex and costly rotary antenna radar systems. An ADS-B ground station does not need to make high-precision measurements of the aircraft position, thus reducing the cost of the ground equipment considerably. The ADS-B concept is independent of the type of link used for data transmission. The information can be relayed by VHF or satellites or SSR mode-S. Therefore ADS-B will be an advanced and relatively low cost-system that will provide high quality flight surveillance information, Low cost, flexibility in surveillance reporting, more precise data capability to support new application,, identical surveillance information to the all users, surveillance available for all phases of flight. The ADS-B will also send a message to ground control unit within a radius of 95 NM around the transmitting aircraft.
ADS messages contain the data like position, time, track, ground speed , vertical situation, magnetic heading, Mac number ( speed of the aircraft), next route reporting point, estimated altitude at next reporting point, second to the next reporting point, upper wind direction, upper wind velocity and temperature. Moreover ATC using ADS information must have the capability to automate the function like flight data validation, automatic tracking, and direction of potential conflict, conflict resolution and display of relevant processed data.
5.0 Air Traffic Management (ATM):
ATM is the aggregation of airborne functions and ground-based functions required to ensure the safe and efficient movement of aircraft during all phases of operation. ATM also is used to describe airspace and air traffic management activities that are carried out jointly by aeronautical authorities concerned with the planning and organization for the effective use of airspace and its movements within their regions of responsibility. The ATM operational concept must have a visionary scope and be referred to the concept of endurance of flight, shared separation assurance and situational awareness in the cockpits. The general objective of the ATM is to allow aircraft operators to comply with the estimated times of departure and arrival and to follow preferred flight profiles with a minimum of limitations and without jeopardizing agreed level of safety. ATM consists of an air and a ground component, both closely integrated through well-defined procedures and interfaces. The ground component is made up of air space management (ASM), air traffic flow measurement (ATFM) and Air traffic services (ATS).
5.1 Air Space Management (ASM):
Its purpose is to maximize use of available airspace within a given airspace structure. In designing the future airspace structure, its boundaries and divisions should not impede the effective use of automated conflict detection and resolution technique or the use of the advanced avionics equipment with which modern aircraft are equipped. The purpose of dividing the airspace into sector is to develop an optimum configuration, combined with use of other appropriate methods for enhancing ATC capabilities. When using the airspace, close co-ordination and supervision are essential in order to meet the contrasting and legitimate requirements of all users and minimize any restriction on operations.
5.2 Air Traffic Flow Measurement (ATFM):
Although ATM is designed to accommodate the maximum traffic demand and can be expanded to respond to predicted growth, it should be borne in mind that it may not be possible to meet excessive maximum air traffic demands. For that reason, ATM has a coordinated sub-system called ATFM. In order to develop, the data on probable future demand forecasts, based on available background, are collated with the development foreseen by airports and airlines, aircraft manufacturer’s order books and macroeconomic trend forecasts of the domestic and other State economics. The ATFM function is to balance traffic demand and ATC capacity. The task of AFTM focuses on a general picture of traffic and on the planning strategy required to ensure efficient use of airport and airspaces in specific area that are prone to “bottlenecks”. ATS units must provide the AFTM with information about traffic management capability. The AFTM should also have access to the airline flight database to obtain up-to-date information about long and short time programming. Common databases are needed to provide a consistent AFTM service. Finally, AFTM units should plan for the introduction and start-up of automated systems.
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