All direct U.S. and foreign air carriers shall have and maintain in effect and on file in the Department's Docket Operations Office (DOT-OST-1995-236) on OST Form 4523 a signed counterpart to Agreement 18900, an agreement relating to liability limitations of the Warsaw Convention and Hague Protocol, (the Montreal Agreement), dated May 13, 1966, and/or a signed counterpart of any amendment or replacement to such Agreement that may be approved by the Department and to which the air carrier or foreign air carrier becomes a party. U.S. air taxi operators registering under part 298 of this chapter and Canadian charter air taxi operators registering under part 294 of this chapter may comply with this requirement by filing completed OST Forms 4507 and 4523, respectively, in accordance with the provisions of those parts.