DSNA (the French air navigation service provider), EUROCONTROL, SESAR JU, EUROCAE, EASA, Airbus and NAVBLUE


Mid-air collisions have occurred throughout modern aviation history with at least 20 in-flight collisions involving commercial aircraft since 1956 (and many more involving purely general aviation aircraft). One of the most high profile accidents in Europe is the 2002 collision between a commercial aircraft and a cargo jet over Überlingen, a southern German town on Lake Constance, near the Swiss border, leading to the death of all 69 passengers and crew members on-board both planes. The official investigation identified among the main causes for the accident ambiguities in the ICAO procedures regarding the use of ACAS and a limitation in the version of the system involved (TCAS II v7.0 at that time). This tragic example is typical of the wide ranging and complex nature of ACAS, requiring studies not only into ACAS systems themselves but also their operational environment, procedures, training and use. Since this accident, a new TCAS version has been developed and deployed in Europe, updated procedures have been implemented and, even today, new concepts are envisaged to further enhance flight safety and prevent such collisions from happening again.

Role of Egis

Egis has extensive knowledge of ACAS safety issues and has internationally recognised and in-depth expertise in ACAS logic. Since the 1990’s, Egis has been involved in all types of ACAS projects for different customers covering:

  • ACAS research on the definition and validation of new systems and functionalities (such as TCAS II version 7.1 or ACAS connection to the auto-pilot function),
  • ACAS compatibility with new concepts (such as Reduced Vertical Separation Minima and Airbus Fello’Fly[1]), new aircraft types (such as helicopters and drones) and new airport local procedures;
  • The contribution to standardisation and certification working groups and studies, leading to two awards for Egis from the RTCA;
  • ACAS events monitoring and operational investigations – including the Überlingen accident; and
  • The training and familiarisation on ACAS for both pilots and air traffic controllers.

These insights and improvements are delivered by a team of experts skilled in airspace modelling based on radar data and simulation tools including all standardised ACAS logics.


Egis has contributed to many achievements for the ACAS community:

  • Development and standardisation of
    • TCAS II version 7.1 – a direct solution to the Überlingen collision;
    • ACAS X (the new family of ACAS systems in the process of being standardised and certified by the American Federal Aviation Administration and EASA – that includes ACAS Xa for commercial aviation and ACAS Xu for Drones); and
    • Two functionalities that permit automated responses to ACAS alerts, reducing by half the risk of collision and by 99% the number of unnecessary alerts to pilots;
  • Assurance of ACAS compatibility with
    • Ground-based safety nets, such as Short-Term Conflict Alert (STCA) and Approach Path Monitoring (APM),
    • Novel aircraft operations, such as Reduced Vertical Separation Minima (RVSM), Airborne Separation Assurance Systems (ASAS) or the first steps of Airbus Fello’Fly concept, and
    • New airport approach procedures at Mexico City and Tianjin,
  • Development of a new European collision avoidance fast-time simulation platform for future validations, 
  • ACAS training and familiarisation campaign for pilots and air traffic controllers,
  • Recommendations at European level for the harmonisation of ACAS events monitoring; that are key elements to anticipate and prevent future collisions to occur.

For further information on this project please contact Charlène Mari, Thierry Arino or Eric Vallauri / /

[1] New concept of commercial Formation Flight operations

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