49 U.S.C. § 48104: Operations and maintenance

The balance of the money available in the Airport and Airway Trust Fund established under section 9502 of the Internal Revenue Code of 1986 (26 U.S.C. 9502) may be appropriated to the Secretary of Transportation out of the Fund for—(1) direct costs the Secretary incurs to flight check, operate, and maintain air navigation facilities referred to in section 44502(a)(1)(A) of this title safely and efficiently; and (2) the costs of services provided under international agreements related to the joint financing of air navigation services assessed against the United States Government.