In recent years, there has been a vibrating interest in Urban Air Mobility (UAM) with attention on advancements in batteries, distributed electric propulsion, and all technologies that are leading to the development of a new class of aircraft, commonly referred to as electric Vertical TakeOff and Landing (eVTOL) aircraft. These are expected to be safer, quieter, greener, and less expensive to operate and maintain than existing vertical takeoff and landing aircraft. They promise to be much less complex than legacy helicopters (of comparable size and carrying capability), but the reduced complexity of the aeronautical structure does not imply simpler avionics for flight control, navigation, and vehicle management, which will have to address an integration problem. This touches diverse Position Navigation and Time (PNT) technologies and the low-level data fusion between Global Navigation Satellite Systems (GNSS) and Inertial Navigation Systems (INS) is a solution, especially if new features of GNSS signals are exploited. GAUSSIAN addresses the problem of safety and security of UAM applications that rely on PNT modules powered by EGNSS. Specifically, GAUSSIAN wants to demonstrate the value of the authenticated Galileo E1 signals combined to integrated GNSS/INS platforms to have (i) greater robustness against spoofing attempts and (ii) better continuity and availability of PNT data in constrained environments. GAUSSIAN wants to mitigate some security risks and concerns which originate from real needs of flight operators, leveraging advances in existing PNT technologies. The project also includes the application of the Precise Point Positioning (PPP)-RTK corrections provided by the Galileo High Accuracy Service (HAS) to improve the PNT data accuracy. GAUSSIAN starts from existing concepts, prototypes and components developed by the proposing companies, with a strong focus on the creation of new integrated and certified products for the upcoming air mobility market.