; 125 Stat. 1576), as most recently amended by section 1665 of the National Defense Authorization Act for Fiscal Year 2018 ( Public Law 115–91 ), is further amended in subsection (a)(1) by striking 2019 and inserting 2024 . 1648. Prohibition on use of funds for activities to modify United States aircraft to implement Open Skies Treaty (a) In general None of the funds authorized to be appropriated by this Act or otherwise made available for fiscal year 2019 for research, development, test, and engineering or aircraft procurement, Air Force, for the digital visual imaging system may be obligated or expended to carry out any activities to modify any United States aircraft for purposes of implementing the Open Skies Treaty until— (1) the Secretary of Defense submits to the appropriate congressional committees the certification described in paragraph (2) of section 1235(b) of the National Defense Authorization Act for Fiscal Year 2018 ( Public Law 115–91 ); and (2) the President submits to the appropriate congressional committees the certification described in paragraph (3) of such section. (b) Definitions In this section: (1) Appropriate congressional committees The term appropriate congressional committees means— (A) the congressional defense committees