Collision avoidance validation platform

At EUROCONTROL, we use our validation expertise to ensure that collision avoidance systems are built to be effective and operationally acceptable in Europe’s airspace.

An encounter consists of two or more short aircraft trajectories (up to 4 minutes long) that are likely to trigger airborne collision avoidance systems (ACAS), short term conflict alerts (STCA) or other collision avoidance or separation systems. Stress testing these systems exposes them to various generic encounters to establish whether they are fit for purpose in a particular airspace.

Testing needs to take into account airspace particularities using representative encounter sets, where very close encounters are hard to find due to aviation’s obsession with safety. Thus, when radar encounters are too few to measure safety performance, we develop and use encounter models which generate sufficiently large artificial encounter sets with realistic distributions of physical characteristics.


At EUROCONTROL we have developed and are constantly upgrading our Europe-wide encounter models and ACAS simulator. We make them available to our research partners as part of the Single European Sky ATM Research (SESAR) programmes.


As part of our collision avoidance fast-time evaluator project we collected recent European radar data and upgraded our encounter modelling tools, developed by QinetiQ, Egis Avia, and Polytechnic University of Catalonia. The result of combining data and tools was our revised encounter model for Europe.

An initial version of our encounter model has contributed to the latest development changes of ACAS Xa.


We developed the EUROCONTROL Collision Avoidance Validation and Evaluation Tool (CAVEAT) to simulate and analyse airborne collision avoidance systems (ACAS) in aircraft encounters.

CAVEAT, developed by NLR and Everis, handles the complex socio-technical system dynamic of the ACAS environment using state-of-the-art agent-based modelling.

Our tool offers advanced random behaviour simulation and sensitivity analysis through the use of stochastic simulations.

Our tool is in development, but we welcome any users who would like to test it out and help us improve it.

Drone operations

In preparation for the next set of integration and safety challenges for airspace users – drones – at EUROCONTROL we are evolving our encounter models and CAVEAT simulator to explore the implications of integrating remotely piloted aircraft systems (RPAS) with ACAS Xu’s detect and avoid (DAA) functionality in Europe.


Validate your collision avoidance systems.