19 CFR § 122.52 - Aircraft of foreign origin registered in the U.S.
(b) Aircraft entered as an imported article. If an aircraft covered by this section is entered as an imported article, and any applicable duty for the aircraft has been paid on a prior arrival, it may be allowed to proceed as other than an imported article. In this instance, the aircraft commander must file a declaration that states the:
(2) Date duty, if any, was paid; and
(3) Number of the entry.
(c) Aircraft not entered as imported article -
(1) Treatment as other than an imported article. A commercial aircraft covered by this section which has not been entered as an imported article may travel from airport to airport in the U.S. without payment of duty. Each commercial aircraft shall proceed under a permit on Customs Form 7507 or 7509, as provided in § 122.54. Treatment of the aircraft as other than an imported article shall continue for so long as the aircraft:
(i) Is used only for commercial purposes between the U.S. and foreign areas; and
(ii) Will leave the U.S. for a foreign destination in commercial use or carrying neither passengers nor cargo.
(i) Is withdrawn from commercial use between the U.S. and foreign areas; or
(ii) Is used in the U.S. in a way not reasonably related to efficient commercial use of the aircraft between the U.S. and foreign areas.
(3) Aircraft damage and duty payment -
(ii) Less than substantial damage and export. If an accident does not cause substantial damage to a commercial aircraft, salvageable parts of the wrecked aircraft may be exported. In this circumstance, the aircraft, as a whole or in part, is not considered to be withdrawn from commerical use and is not subject to entry or to duty as imported merchandise.
(iii) Less than substantial damage and no export. If an accident does not cause substantial damage to a commercial aircraft and the wrecked aircraft or any salvageable part of it is not exported, then:
(B) A duty payment, if applicable, based on the condition of the aircraft following the accident, is required.