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The process of sector definition comprises virtual division of airspace. Thus, the provision of air traffic services is decomposed, in the different sectors, into tasks with manageable workload.
The opening of new sector does not guarantee the arithmetic sum of the capacities of the elementary sectors – the combined capacity is a complex combination of factors such as traffic flow direction, coordination procedures, in-sector flight times, etc. Therefore, a capacity figure is calculated for every sector configuration.
As recently as the mid 1990's, changes to the airspace structure and route network were handled purely as a national responsibility, with international coordination carried out by the International Civil Aviation Organization (International Civil Aviation Organisation (ICAO)). National ATS planning was paramount, and the coordination of airspace and route network developments was limited to the cross-border connections of nationally planned routes.
The ATC sectorisation principles evolved over the years to a complex set of criteria that fit into global concepts. Today, ATC sector definition is an important part of the broader process of airspace design.
A number of factors form the boundaries of a sector, many of them are ATS-oriented, others defined by international relations:
- State boundaries or bilateral agreements for provision of ATS;
- International agreements for provision of ATS over international waters;
- Location of areas of special use – danger, prohibited, temporary segregated;
- Geographical characteristics of the area, type of service that is to be provided, radio and radar coverage;
- Direction of main traffic flow, in-sector flight time, conflict point distribution, etc.
Meeting Capacity Demand
Increased capacity demand is generally met by provision of more sectors. Usually the demand is calculated as short-term operational predictions based on planned flights. Opening/closing of sectors should closely monitor the demand to achieve efficient use of all available resources. For example, dynamic arrangements should be made to ensure the availability of the required air traffic controllers.
Failure to provide the required sector configuration on time may lead to potential risks arising from sector overload, inter-sector miscommunication, etc.
The Network Orientated Development
A significant change in design process is employed in Eurocontrol’s Advanced Airspace Scheme (AAS) Concept. The objective of AAS is to develop airspace capable of greater flexibility and responsiveness that will permit the aircraft operators to plan and fly their preferred route. This choice is supplemented by re-routing schemes that follow pre-defined scenarios that optimise the available capacity when planned routes conflict with Air Traffic Control (ATC) sector capacity limits. In the context of this document, ‘Airspace Structures’ refers to both the ATS Route Network and ATC Sectorisation, which are inextricably linked. AAS proposes an iterative process for the design of new Airspace Structures and introduces the notion of Sector Families and Family Groups built around an ATS route network that includes direct routes.
The Network orientated approach takes an ECAC-wide view and is based upon the need to enhance the overall European Civil Aviation Conference (European Civil Aviation Conference (ECAC)) Air Traffic Management (ATM) capacity. The process progresses from broad proposals towards specific solutions via a number of steps.
- Step 1: Identify current and foreseen problems. The planning work highlights the problem areas and their causes in the airspace structure.
- Step 2: Build generally improved airspace structure proposals (both route segments and Air Traffic Control (ATC) sectors) to accommodate major traffic flows and balance ATC workload.
- Step 3: Within this defined framework, detailed proposals of airspace structure are elaborated with their “modus operandi”, consolidated and validated through regional expert groups.
The result of local studies feeds back into the initial proposals in a dialectical and iterative process.
- Step 4: A phased implementation programme is agreed and carried out.
Advanced Concepts – Dynamic Sectorisation
Dynamic sectorisation is a process in which a number of elementary air volumes are defined. A short-term capacity demand prediction is generated in real time environment using fast time simulation of planned traffic. The ATC sectors are then formed as the most suitable combination of the elementary sectors to meet the capacity demand at a certain moment.
The concept uses reliable planning methods and provides adaptive approach. It offers an efficient way to meet capacity demand and staffing problems at the same time.