Technical Standard Order (TSO)
A TSO is a minimum performance standard for specified materials, parts, and appliances used on civil aircraft. When authorized to manufacture a material, part, or appliances to a TSO standard, this is referred to as TSO authorization. Receiving a TSO authorization is both design and production approval.
Receiving a TSO Authorization is not an approval to install and use the article in the aircraft. It means that the article meets the specific TSO and the applicant is authorized to manufacture it.
Authorization
Receiving a TSO authorization is approval to manufacture an article that may be installed on an aircraft only after showing that the article meets the specific airworthiness requirements (certification basis) of a particular aircraft model. In other words, receiving a TSO authorization means that an article meets a minimum performance requirement independent of the article's intended installation on an aircraft. A separate FAA approval is required to install the article on an aircraft.
Design Approval (Foreign Manufacturers)
What is a letter of design approval?
An FAA design approval for an article manufactured outside the United States that meets a specific TSO.
How do I obtain a letter of TSO design approval?
The FAA will issue a letter of TSO design approval only to manufacturers located in a country with which the U.S. has concluded a bilateral agreement applicable to the article in question. The exporting Civil Aviation Authority (CAA) is responsible for oversight of both the design and production of such articles.
An applicant for an FAA letter of TSO design approval should apply through the exporting CAA with a request that the application and required data be forwarded to the FAA. The exporting CAA should contact the FAA for information concerning the latest FAA technical policy and procedures whenever the CAA receives an application for an FAA letter of TSO design approval to a TSO performance standard for which the CAA has not previously made compliance findings.
The FAA issues a letter of TSO design approval only for articles of a kind for which a minimum performance standard has been published in an FAA Technical Standard Order (TSO).