((a)) ** .—** Beginning with fiscal year 1999, any authorization of appropriations for an activity for which amounts are to be appropriated from the Airport and Airway Trust Fund established under section 9502 of the Internal Revenue Code of 1986 shall provide funds for a period of not less than 3 fiscal years unless the activity for which appropriations are authorized is to be concluded before the end of that period.

((b)) ** .—** Beginning with fiscal year 1999, amounts appropriated from the Airport and Airway Trust Fund shall be appropriated for periods of 3 fiscal years rather than annually.