In this paper, an emergency fault-tolerant controller is developed for quadrotor unmanned aerial vehicles (UAVs) suffering a total loss of one actuator (rotor/motor). The proposed controller is based on control allocation where the infected actuator is exempted from the control effect, and control efforts are redistributed among healthy actuators. As a result, the emergency controller transforms the infected quadrotor into a trirotor and uses the remaining actuators to ensure that the UAV continues following its path. The main advantage of the newcontroller is that it uses the same simple proportional-integral-derivative (PID) controller applied in fault-free cases by redistributing its controls, rather than designing complex and memory consumable controllers. Experimental results using the augmented reality (AR) Drone 2 platform show that by implementing the quadrotor to trirotor conversion maneuver, the nominal PID controller gains powerful fault-tolerant capabilities and the infected UAV is successful in maintaining its desired path. Performance degradation seen as oscillations did not cause the drone to crash despite the total loss of yaw control, the presence of activation delay, the nonsymmetric structure of the trirotor, and its odd number of rotors that produces imbalance of the rotor moments.