Technical Standard Orders and Their Approvals

The authorization encompasses the approval of both the submitted design of a part, as well as the production of said part. This means that an approved submission may be manufactured and labeled as a TSO standard part. This does not however, mean that the approved part may be installed onto an aircraft. After approval, the TSO part still has to be proven “airworthy” by the FAA for the specific model before it can be installed. TSO approval simply refers to the part’s meeting of performance requirements.
 
A TSO authorization can also become a “Canceled TSO” or undergo a “Withdrawal of a TSO authorization,” both having distinct and different meanings. When a TSO has been considered canceled, the Federal Aviation Administration has considered the article inactive and will thus not issue any new authorizations for it. Despite this, any previously approved part is still considered valid and can be manufactured. A withdrawal, on the other hand, denotes that the FAA has revoked the authorization, and the part may no longer be produced by the manufacturer. In short, if a part is canceled, the approved part may still be produced but may not gain any new authorizations, while withdrawal means the approval is completely revoked.
 
Foreign countries may also gain approval and produce TSO parts as well, given that they receive what is referred to as a “letter of design approval” from the FAA. To receive this, the country has to be entered into a bilateral agreement with the US for the particular article, and the country will have to work with the exporting Civil Aviation Authority (CAA). On the FAA’s website, their various regulations and policies, as well as current and past TSO part approvals may be viewed.