14 CFR § 21.621

The FAA may issue a letter of TSO design approval for an article—

Designed and manufactured in a foreign country or jurisdiction subject to the export provisions of an agreement with the United States for the acceptance of these articles for import; and

For import into the United States if—

The State of Design certifies that the article has been examined, tested, and found to meet the applicable TSO or the applicable performance standards of the State of Design and any other performance standards the FAA may prescribe to provide a level of safety equivalent to that provided by the TSO; and

The manufacturer has provided to the FAA one copy of the technical data required in the applicable performance standard through its State of Design.

The FAA issues the letter of TSO design approval that lists any deviation granted under § 21.618.