This paper proposes an approach to synthesize a high-lift mechanism (HLM) of a transportation aircraft. Such a mechanism is very important for generation of additional lift to an aircraft wing during take-off and landing. The design problem is minimization of error between the motions of a four-bar mechanism for controlling a flap to the target points. The optimum target points are positions and angles of flap at the take-off and landing conditions, which are designed based on maximizing the lift to drag ratio. Design constraints include the conditions of four-bar mechanism to work properly, limiting positions and workplace of the mechanism. A optimizer used in this study, is in a group of metaheuristics (MHs). The results show the optimum mechanism can generate flap motion fulfilling the design targets, thus, the proposed technique can be used to increase the performance of HLM.