This paper presents a parametric analysis of the sense and avoid capability for an electro- optical system on unmanned aircraft. Our sensor analysis is based on simulated encounters from a new U.S. airspace encounter model that provides a comprehensive distribution of typical visual flight rule (VFR) aircraft behavior and encounter geometries. We assess the exchange between the sensor field-of-view shape and detection range with the probability of intruder detection prior to near miss. This assessment also includes a trade-off analysis between field-of-view azimuth angle and probability of detection with fixed tracking technology (i.e. pixel array sensor and tracking algorithm). Initial results suggest that current standards are suitable for detecting larger aircraft but may not be ideal for small aircraft such as ultralights.