An aircraft engine is supposed to be used for a specified lifespan, and it is reused through the depot maintenance for a major overhaul when its cumulative service life reaches the lifespan. However, the depot maintenance takes a long time due to the complexity of its process, and thus to continuously operate aircraft, spare engines are required to substitute engines under renovation. Considering the limited capacity of the depot, the uniformity of the quantity and cycle of engines entering the depot maintenance provides an opportunity to the decrease of the spare engines and the improvement of aircraft availability. It is the purpose of engine life management. Furthermore, in establishing flight plans, the time for essential maintenance activities, such as pre/post-flight inspection, servicing, the preparation for next flight, has to guarantee. Especially, fighters additionally require much time for installing weapons for their mission. That is, the rearming procedure can be left out if the adjoining missions are identical. Otherwise, the rearming time is varyingly spent depending on the types of adjacent duties. Therefore, this study proposes the mathematical model for an aircraft-mission assignment considering engine life management and maintenance schedule, and it is formulated based on the time-space network. Moreover, to verify and validate the model, an example was developed by applying realistic aircraft operating environment and simulation to perform air operations for several days was fulfilled. The experimental results presented flight plans corresponding to the purpose of this study, such as engine life management and the assurance of maintenance time.