An aircraft owner or operator may produce articles for installation on their own product without a Parts Manufacturer Approval. The installation of those articles must comply with 14 CFR part 43. If an owner or operator intends to sell these articles for installation in anothers product, then the producing owner or operator requires a Parts Manufacturer Approval.
An air carrier, operating under 14 CFR part 121 or part 135, may produce articles for installation on its own product without a Parts Manufacturer Approval, provided the installation of those articles is approved in accordance with 14 Code of Federal Regulations part 43 and complies with the air carrier's accepted maintenance procedures manual and instructions. If the article is produced with the intent of selling it for installation on a product other than the owner's or operator's, then a Parts Manufacturer Approval would be required.
An article produced by a FAA certificated repair station with the intent of installing it on a type-certificated product that the repair station has in-house for repair. Such articles may not be offered for sale as separate items. See FAA Advisory Circular 43-18, Fabrication of Aircraft Parts by Maintenance Personnel.