• SJU reference # PJ.11-A3 /Release 2019
  • Stakeholders
  • Benefits Safety
  • Status In the pipeline

ACAS provides a valuable layer of safety for all aerial vehicles, manned or unmanned. Research indicates that by adding an additional surveillance source, such as ADS-B, and by improving RAs using advanced mathematical modelling, safety can be enhanced. Among new systems under development, ACAS Xo offers a solution designed
for particular operations not included in other ACAS X solutions – some of which are described previously (see #PJ.11-A1 and #PJ.11-A2). Typical ACAS Xo applications include procedures with reduced separation, such as closely spaced parallel approaches, which might generate an unacceptable number of nuisance alerts unless
the system is able to recognise situations where new separation modes are being applied.

The candidate solution activities include the assessment of how potential cyber-threats could affect ACAS Xo, and the identification of adequate measures to mitigate effectively these threats. SESAR research aims to determine
European needs and requirements related to ACAS Xo usage in the Europe environment including its benefits in the European airspace, when necessary. The work on the SESAR solution also provides input to the European/
US standardisation agencies EUROCAE and RTCA to contribute to ACAS Xo design and standardisation.


  • Enhanced safety