This paper aims to test the feasibility of using the 5G mobile network to obtain the position of Unmanned Aerial Vehicles (UAVs) based on multilateration (MLAT) positioning systems. The strategy employed is to test whether the topology of a cellular network deployed in a coverage area meets the positioning accuracy requirements for aircraft. In this case, an Urban Air Mobility (UAM) use case has been considered in Valencia, where it has been assumed that aircraft will follow a particular flight path between two vertiports. In addition, an optimization technique based on genetic algorithms has also been employed to select the optimal spatial distribution of already deployed base stations that provide the best levels of accuracy and thus minimize the resources employed.