• SJU reference # PJ.11-1 /Release 9
  • Stakeholders
    ANSP
    AU
  • Benefits Safety
  • Status In the pipeline

Airborne collision avoidance systems (ACAS) currently receive information only from Mode C/S interrogations, yet there are other surveillance sources available, such as the more accurate ADS-B, which could enhance this safety layer. In addition, the performance of collision avoidance can be improved by updating the mathematical
processes and modelling used in today’s traffic alert and collision avoidance system (TCAS).

Both these improvements form part of the ACAS Xa being designed for commercial aircraft with the aim of delivering the next generation TCAS beginning in the 2020-2023 timeframe. By introducing additional surveillance data and optimised resolution advisories, ACAS Xa is expected to improve on today’s system without changing the cockpit interface, i.e using the same alerts and presentation. It forms part of ACAS X,
a series of systems being developed for different users, described in the next five solutions.

ACAS Xa implements the surveillance improvement through the surveillance and tracking module (STM) which processes the raw surveillance data coming from the surveillance sensors. Meanwhile the resolution advisory
improvement is dealt with by the threat resolution module (TRM), which uses the estimated intruder parameters provided by the STM to choose an appropriate avoidance manoeuvre, if necessary.

ACAS systems need to be interoperable worldwide which is primarily ensured through the standardisation process. The European requirements identified by SESAR are being fed into the global standardisation process.

Benefits

  • Enhanced safety