Unmanned Aerial Vehicles (UAVs) use is increasing daily, which results in increasing their security threat landscape. A major security threat to availability for network-based devices is Denial of Service (DoS) and Flooding attacks, which impact the system resources and disturb the network communications. For Mobile Ad hoc Networks (MANETs), there are multiple previous works on DoS attacks implementation and mitigation using different techniques. However, the work is limited for 2D networks with little focus on detecting and mitigating such attacks on 3D networks of Flying AdHoc Networks (FANETs). This study focuses on the RREQ flooding attack on a 3D network of drones and proposes a threshold-based detection and mitigation mechanism that considers the drones limited resources. The simulation experiments demonstrate a 34% throughput improvement and 3% energy saving.