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Enhanced Air and Ground Safety Nets
Deadline: Mar 16, 2016  

 Horizon Europe

Topic Description
Specific Challenge:

When SESAR trajectory-based operations and new separation modes are introduced existing ground safety nets should be effective and provide alerts of actual or potential hazardous situations. Current Airborne Collision Avoidance System (ACAS) performance requirements are based on present modes of separation and will need to be adapted for the future operations identified by the SESAR Concept. The adaptation of ACAS to new separation modes and to new categories of airspace users has to be studied. There is a need to anticipate the required evolution of ACAS for the future operations in Europe and take into consideration potential adaptations. The current strategy is to contribute to ACAS X development and standardisation. ACAS X is a set of FAA collision avoidance systems currently under development: ACAS Xa for normal operations of Commercial Air Transport (CAT), ACAS Xo for specific operations of CAT, ACAS Xu for RPAS operations and ACAS Xp for GA/RC operations. A priority issue is the analysis of the ACAS X systems operational and pilot acceptability.

Currently alerts that occur in the air and on the ground in close time proximity can lead to overlapping decisions by pilots and ATCOs (e.g. reactions to close Short Term Conflict Alert (STCA) alerts and Airborne Collision-Avoidance System (ACAS) resolution advisories). Indeed, existing Ground Safety Nets have been developed independently from airborne Safety Nets (in particular ground-based SNETs have been implemented in a local context while ACAS has been implemented globally) and therefore the operations resulting from their alerts are not always compatible.

Overall, there is a need to adapt the safety nets to the changing environments in order to avoid:

  • lack of capacity to timely identify hazardous situations which will increase with the traffic;

  • Insufficient consideration of the new traffic patterns and of operations with reduced spacing, which could result in undesired alerts.

It is required to address the integration of: GA/ Rotorcraft and Civil Remotely Piloted Aircraft Systems (RPAS).


The Project “Enhanced Air and Ground Safety Nets” aims at delivering the following SESAR Solutions:

  • Enhanced ground-based safety nets adapted to future operations: Adapt ground-based safety nets to future trajectory management and new separation modes through the use of new surveillance means and wide information sharing ensuring the role of last ATC safety layer against the risk of collision and other hazards, while minimising negative operational interactions between ACAS and STCA.

  • Enhanced Airborne Collision Avoidance for Commercial Air Transport normal operations- ACAS Xa: Improve current Airborne Collision Avoidance for Commercial Air Traffic by taking benefit of optimized resolution advisories and of additional surveillance data, without changing the cockpit interface.

  • Airborne Collision Avoidance for Remotely Piloted Aircraft Systems – ACAS Xu: Provide Airborne Collision Avoidance to RPAS taking benefit of optimised resolution advisories and of additional surveillance data, but taking into account the operational specificities of the RPAS. The additional surveillance sources could be ADS-B but also any other sensor installed on the RPAS.

  • ACAS for Commercial Air Transport specific operations– ACAS Xo: Improve Airborne Collision Avoidance taking benefit of optimised resolution advisories and of additional surveillance data while avoiding unnecessary triggering of RAs in new separation modes, in particular if lower separation minima are considered. (new separation modes include ASAS applications but may include other solutions).

  • Airborne Collision Avoidance for General Aviation and Rotorcraft – ACAS Xp: Provide Airborne Collision Avoidance to GA/RC, taking into account the limited capability of GA to carry equipment and its operational specificities.

Expected Impact:
  • The main goal is to increase safety, reducing the number of ATM related accidents and incidents.

  • The project will provide inputs and influence the work on Ground / Airborne Safety Nets at global and regional standardisation level, within ICAO (in coordination with FAA for ACAS), EUROCAE and RTCA.

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