The human factors involved in an unmanned aerial system (UAS) come in a variety of forms that has largely gone poorly represented in literature. In this paper, a holistic approach is taken to identify not only the individual aspects but the interconnection of the human-UAS interaction. First, an examination of human factors involved in a UAS are presented. Next, the metrics of human performance, such as cognitive load, situational awareness and complacency are introduced. Finally, a framework is developed to form the interconnection of human factors with human performance metrics in a UAS. With this framework in place, the intended goal is that an optimal level of cognitive workload for the humans involved in an UAS can be designed and implemented by the utilization of this framework during the development of advanced automation systems and human interface devices.