This bill, titled the Aviation Funding Stability Act of 2025, aims to ensure the continued operation of the Federal Aviation Administration (FAA) during a lapse in federal appropriations. It authorizes the use of unappropriated funds from the Airport and Airway Trust Fund to sustain essential FAA programs, projects, and activities, including operations, facilities, research, and airport grants. This funding mechanism would activate if a regular appropriation measure or continuing resolution is not enacted by the start of a fiscal year. The bill specifies that funding would be available at a rate not exceeding the previous fiscal year's levels and would last for up to 30 days or until a new appropriation law is enacted, whichever comes first. It ensures that expenditures made during this period are charged to the eventual appropriation and amends the Internal Revenue Code to facilitate the use of the Trust Fund. This measure seeks to provide stability and prevent disruptions to critical aviation functions during government shutdowns.