Unmanned aircraft systems are expected to open pathways towards the development of many new services. Owing to their airborne flexible mobility, systems using unmanned aircraft (UA) have a significant potential to change our daily lives. However, several issues with such systems need to be addressed. In particular, wireless transmission of data such as high quality video from a UA to Ground Stations (GSs) is a major challenge affecting how airborne UAs are controlled. In this paper, we attempt to construct a base model of data transmission from UA to GSs in order to most efficiently use communication resources. To do this, we propose a method to allocate resources for individual UA missions that takes differences in requirements and surroundings into account. In this method, time division multiple access (TDMA)-based resource allocation is performed by anticipating the effective throughput according to the surrounding radio wave propagation environment. The effectiveness of this proposed resource allocation method is evaluated through simulation.