Technical Standard Orders and TSO Authorizations

TSOs apply to particular kinds of articles, which can include equipment, parts, materials or other defined aviation items. The minimum performance standard is specific to that article type. Locate the TSO in FAA's Dynamic Regulatory System and confirm the relevant revision and referenced material. A general description such as aviation grade does not establish that a product has been evaluated against an applicable TSO.

FAA describes a TSO authorization as both design and production approval. The applicant demonstrates compliance with the applicable TSO and the Subpart O requirements, including any approved deviations. The authorization relates to the article and holder identified in it. A component supplier's test report or a statement that a design follows TSO requirements is different from an FAA-issued authorization to manufacture and mark the article.

Subpart O requires a quality system meeting the applicable Part 21 provisions and an approved quality manual. Design data, supplier controls, manufacturing, inspection and nonconformity handling must support continued conformity of production articles. An approved prototype does not justify uncontrolled substitutions. Changes to components, software, facilities or manufacturing arrangements should be assessed through the applicable authorization and quality-system procedures before the revised article is released.

A TSO-authorized article has met minimum performance requirements independent of its proposed installation. FAA states that separate approval is required to install it on an aircraft, with the installation shown to meet the aircraft's applicable airworthiness requirements. Interfaces, power, environmental conditions and system functions can affect that assessment. A purchasing decision should therefore consider both the article authorization and the permitted installation on the specific aircraft configuration.

FAA distinguishes cancellation of a TSO from withdrawal of a particular TSO authorization. A canceled TSO can prevent new authorizations against that revision while existing authorizations may continue; withdrawal of an authorization has a different effect on the holder's manufacturing privileges. Verify the status of the actual authorization instead of assuming that a later TSO revision automatically invalidates every earlier article or that cancellation has no consequences.

Retain the authorization, article model and part number, TSO revision, approved deviations and installation information with the technical purchasing record. If another authority's design approval is involved, verify the applicable acceptance arrangement rather than assuming automatic recognition. A statement that an article is TSO authorized should describe that limited federal approval accurately, without implying approval of the aircraft installation, the supplier's unrelated products or every function claimed in commercial literature.