• SJU reference # PJ.11-A2 /Release 2019
  • Stakeholders
  • Benefits Safety
  • Status In the pipeline

Addressing the same objectives as the previous solution (#PJ.11-A1), this candidate solution aims to enhance ACAS, but is focused on the growing number of RPAS accessing the airspace. ACAS Xu is the therefore variant of the ACAS X concept dedicated to RPAS. Much like the ACAS Xa under development for commercial aircraft, the ACAS Xu includes ADS-B as an additional surveillance source to Mode S. However, it also includes other RPAS sensors such as electro-optical and infrared. It also looks at optimising resolution advisories (RAs) using advanced mathematical models with particular reference to RPAS. This includes adapting the strength and direction of
RAs to the capabilities of the RPAS. For example, horizontal RAs could be introduced for RPAS unable of reaching the vertical acceleration/ speeds required for vertical RAs.

SESAR is focused on determining the needs and requirements related to ACAS Xu usage in Europe, and the benefits, as well as harmonisation with other world regions, including the US. It is also investigating if ACAS Xu helps the integration of RPAS in the European airspace. The solution covers any additional factors affecting collision avoidance with any unmanned platform, such as human factors and system latency.

The coordinated work will provide inputs to EUROCAE and RTCA and contribute to ACAS Xu global design and standardisation.


  • Enhanced safety