A common example is the end-use relief for products imported for the aviation industry. Almost every item that is imported and ultimately used in the construction of an airplane, either direct or indirect via parts, is exempted from import duties.
As you would expect, the procedure is strictly monitored by the customs authorities and involves various documentary requirements in the way of reports, documents, declarations, etc. The duty exemption will only be definitive once the component has actually been used for its intended purpose, or has reached a point in the production process that would economically exclude it from being used for any other purpose.
Under the terms of UCC Article 254, Customs supervision under the end-use procedure shall end in any of the following cases:
(a) where the goods have been used for the purposes laid down for the application of the duty exemption or reduced rate of duty;
(b) where the goods have been taken out of the customs territory of the Union, destroyed or abandoned to the State;
(c) where the goods have been used for purposes other than those laid down for the application of the duty exemption or reduced duty rate and the applicable import duty has been paid.