In this article, we consider a scenario of a decode-and-forward (DaF) wireless system supporting the communication of an unmanned aerial vehicle (UAV) with a ground-control-station (GCS) through an intelligent reflecting surface (IRS). Particularly, the UAV moves according to the three-dimensional (3D) random way point model at low altitude in a complex urban environment. However, a stationary relay-station (RS) decodes and forwards the UAV