The Harmonized System is an international nomenclature developed by the World Customs Organization, which is arranged in six-digit codes allowing all participating countries to classify traded goods on a common basis.

The Agreement on Trade in Civil Aircraft is one of the plurilateral WTO agreements; it entered into force on 1 January 1980. The Agreement eliminates import duties on civil aircraft-related products covered by its product list such as engines, radar, flight recorders, and ground flight simulators. The Agreement also contains disciplines on matters such as government-directed procurement of civil aircraft and inducements to purchase.

There are currently 32 signatories to the Agreement. They are: Albania; Austria; Belgium; Bulgaria; Canada; Denmark; Egypt; Estonia; European Union; France; Georgia; Germany; Greece; Ireland; Italy; Japan; Latvia; Lithuania; Luxembourg; Macao, China; Malta; Montenegro; Netherlands; Norway; Portugal; Romania; Spain; Sweden; Switzerland; Chinese Taipei; United Kingdom; and the United States.

The Civil Aircraft Committee has been working since 2008 to modify the product list of the Agreement to make it compatible with the 2007 version of the Harmonized System.

The protocol and the amended Product Coverage Annex can be downloaded here.