EUROCONTROL launched the Performance and Safety Aspects of Short-term Conflict Alert - Full Study (PASS) project in October 2007. The aim of this three-year study is to progress towards the establishment of quantified performance requirements for STCAs and to define a consistent overall concept for ground-based and airborne safety nets. The PASS study started with a monitoring phase in order to understand the current operational situation. The aim is to progress towards the establishment of quantified performance requirements for STCAs, as well as the definition of a consistent overall concept for ground-based and airborne safety nets.