You may use previously approved (per STC or field approval) part/material substitutions on like-type aircraft. If the part/material is installed with previously approved parts or material, PMA, technical standard order (TSO), NAS etc., and if it is completed in a similar manner consistent with a previous field approval or STC, you may use those approvals as the basis for approval on your aircraft. However, if you want to use a previous field approval or STC as the basis for approval on your aircraft, you must have all the previous field approval or STC data, including any instructions for continued airworthiness, or develop any missing data through support from an appropriately authorized DER or ACO approval and permission from the STC holder (14 CFR parts 21 and 91, §§ 21.120 and 91.403(d)).

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