Aeronautics Innovation Act This bill reauthorizes through FY2024 the National Aeronautics and Space Administration (NASA) Aeronautics Research Mission Directorate. NASA shall establish a low-boom supersonic aircraft program or project to demonstrate supersonic aircraft designs and technologies to reduce sonic boom noise levels, a subsonic flight program of flight technology demonstrations that use existing aircraft and multiple large-scale X-Plane demonstrator to demonstrate aircraft vehicle and propulsion concepts and technologies, advanced structures, materials, and manufacturing program; and the 21st Century Aeronautics Capabilities Initiative to ensure that it possesses the infrastructure capabilities and tools necessary to conduct flight demonstration projects across the range of NASA aeronautics interests.