Before Reduced Vertical Separation Minima (RVSM) operations commenced in European airspace, work was carried out to ensure that Airborne Collision Avoidance System (ACAS) II would be compatible with RVSM and would deliver the expected safety benefit.

TCAS II Version 7 successfully addressed compatibility issues related to the reduced vertical separation. As importantly, EUROCONTROL conducted an extensive safety study which used modelling of TCAS II encounters in RVSM. It concluded that, although there were instances when RAs could occur due to high vertical rates in level-off manoeuvres with 1000ft separation or due to poor altitude station keeping, TCAS II would provide the expected additional safety benefit.