Definition

Area of Common Interest. A volume of airspace as agreed between 2 ATS Units, extending into the adjacent/subjacent Areas of Responsibility, within which airspace structure and related activities may have an impact on air traffic coordination procedures.

Source: EUROCONTROL Guidelines - Common Format Letter of Agreement between ATS Units

Description

The area of common interest (ACI) is defined in the Letter of Agreement (LoA) between two ATS units as a volume of airspace where controllers on both sides of the inter-unit border need to be familiar in order to facilitate coordination between them. To this end, controllers must know the airspace structure (e.g. airways, waypoints, nearby aerodromes and TMAs, etc.) and restrictions (e.g. SUAs) existing immediately beyond their area of responsibility. In addtion, ATS systems are designed in a way as to present the flight trajectory within the area of interest (AoI) which often includes the neighbouring part of the ACI. Thus, various functions (such as MTCD) help enhance the controller's situational awareness and support the provision of safe and efficient ATS.

An example of ACI definition is shown in the picture below. Note that while in this partucular case the ACI comprises part of the airspace of ATSU A and the whole airspace of ATSU B, there are no set rules regarding the size of the ACI. It is not uncommon for the ACI to include the whole AoRs of the two adjacent ATSUs and it is also possible for the ACI to only partially include both AoRs.

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The definition of the ACI as well as the extent to which it is described is determined during the development of a particular LoA. According to the EUROCONTOL guidelines for the common format LoA between ATS Units (which is used for most LoAs in the ICAO EUR region) the ACI is described in Annex B and must contain, as a minimum, all of the cross-border ATS Routes. In most cases, however, this part of the LoA includes other elements, such as:

• Airspace classification and organization (e.g. FRA, transition altitude, etc.)
• Sectorisation on both sides of the border
• SUA description
• Non-published coordination points
• Appendices with maps describing sectorisation and SUAs

Other Annexes to the LoAs include provisions related to the ACI, such as:

• Notification for SUA activation in the neighbouring airspace
• Surveillance coverage