The FAA must validate the foreign STC before it can be installed on a United States-registered aircraft. The FAA will only validate a foreign STC if there is a bilateral agreement in place with the country that issued the STC, and it includes provisions for FAA acceptance of STCs for that specific category of aircraft, engine or propeller. The owner of the foreign STC may then apply for an FAA STC.

If there is no Bilateral Agreement in place, the U.S. will not issue an FAA STC.

Bilateral agreements policies & guidance