Regulations at airports are similar to those at seaports, particularly in the case of stores. Commanders of aircraft arriving from or leaving for abroad must use, except in emergency, airports Customs and declare cargo carried inwards and outwards. There are facilities for clearing goods from the airports before the entry of the goods is passed and the duty paid. A ‘provisional’ entry is made and the importer leaves a sizeable cash deposit with the Cusleaves a sizeable cash deposit with the Customs authorities. Airports often have a duty-free shop for the convenience of departing passengers. Goods are sold here free of duty and are controlled by Customs officials.
Reference: The Penguin Business Dictionary, 3rd edt.