: Nowadays, with the development of technology and automation of devices, multi agent systems are in the center of attention. One of the interesting and high-tech fields in these systems is assigning cooperative tasks to each agent in a group to accomplish a certain task. The problem of load traortation using multiple UAVs is one of the applications of cooperative task assignment in aerial multi agent systems. The goal of this task is traorting load with safest possible way and minimal vibration. With improvements in UAV technologies, load traortation is a developing technical research field. In this thesis, we consider modeling of a system consisting of a load suspended from multiple UAVs. The proper controller is then designed. A formation flight is achived while UAVs have symmetric positioning with respect to a load. Otherwise, because agents are moving with respect to each other and collision and collapse of the wire, there is a possibility of vibration and damage to the load. The designed controller must be able to keep the formation in 3D space in addition to removing the influence of the load that created by gravity force and traorting the load successfully. In the next step and during the flight, we add a fault to the system, which disconnects one of the connecting wires between the agents and the load. By immediate detecting of the fault, the formation of the group is changed in a way that the connected agents realign with respect to the load and rapidly eliminate the introduced vibrations. The disconnected agent retains the structure of the group without bearing the load and wouldn’t interfere in information exchange in the group. Finally, the operation of the designed system is evaluated through simulation. Keywords: Multi Agent Systems, Task Assignment, Unmanned Aerial Vehicle, Formation Flight, Switching Formation, Optimal Control, Load Traortation, Udwadia-Kalaba, Fault Detection, Fault Tolerant Control