The unmanned aircraft systems (UAS) are commonly used for aerial photography, express delivery for packets or video monitoring. The UAS technology can help responding to the growing demands of the frequency monitoring by national radiocommunication authorities (NRAs). This article presents a practical usage trial of an unmanned aircraft for monitoring the spectrum usage and finding the interference location. The monitoring of spectrum usage is one part of the NRAs' process for guarantee user compliance with radio license conditions. Finding illegal or malfunctioning transmitters is a challenging task especially in urban environment, due to multi-path propagation conditions. This study focuses on practical assessment of the method for determining accurate location of radio frequency interference sources from the buildings using the UAS technology. The practicability of the UAS technology usage in spectrum monitoring activities was under the evaluation. This study showed promising results that UAS with the measurement equipment setup suits NRAs' as a tool for mobile monitoring on the air.