Safe operations in the National Airspace System (NAS) require understanding the individual failure space of avionics technologies, the joint failure space as faults propagate within the distributed environment, and a framework to quantify safety. This paper focuses on the last point, in which the safety assessment framework consists of a set of safety metrics: Loss of Separation (LoS), Traffic Collision Avoidance System (TCAS) II, NASA's Well Clear (WC), and a novel metric called Critical Pair Identification (CPI). The fault space considers the surveillance device Automatic Dependent Surveillance-Broadcast (ADS-B). Using an agent-based model, we demonstrate the framework with a two aircraft example of a perpendicular crossing, in which each aircraft implements self-separation via NASA's Chorus software. We compare three different variations of the crossing: (a) Chorus is absent (open loop), (b) Chorus is operational (closed loop), and (c) Chorus is operational, but one aircraft broadcasts a faulty ADS-B message with a +0.05 deg longitude error (closed loop with a fault). Our results show that the included set of safety metrics cover a variety of dimensions of state information, but may be an overdetermined system for assessing safety. The set or subset appears capable of assessing safety, but requires a detailed case study for understanding faults and their propagating effects within an arbitrary scenario in the NAS.