49 U.S. Code § 47529 - Nonaddition rule
(a)General Limitations.—Except as provided in subsection (b) of this section and section 47530 of this title, a person may operate a civil subsonic turbojet aircraft with a maximum weight of more than 75,000 pounds that is imported into the United States after November 4, 1990, only if the aircraft—
complies with the stage 3 noise levels; or
(c)Aircraft Deemed Not Imported.—In this section, an aircraft is deemed not to have been imported into the United States if the aircraft—
(1) was owned on November 5, 1990, by—
a corporation, trust, or partnership organized under the laws of the United States or a State (including the District of Columbia);
an individual who is a citizen of the United States; or
enters the United States not later than 6 months after the expiration of a lease agreement (including any extension) between an owner described in clause (1) of this subsection and a foreign carrier.