This paper documents work sponsored by the FAA, as part of the FAA's Concept Validation Plan. It proposes performance metrics relating improvements in technical capability of air and ground elements to traffic spacing under current and future operational concepts. The metrics proposed and defined are the Required Total System Performance (RTSP), and its component metrics; Required Navigation Performance (RNP), Required Communication Performance (RCP) and Required Surveillance Performance (RSP). The paper discusses the potential need for additional metrics for ATM functions such as conflict probing and resolution. A Short Term Conflict Alert (STCA) controller function was modeled to analyze the effects of radar surveillance performance on conflict detection.