In aviation, a TSO, or Technical Standard Order, is a minimum performance standard the FAA sets for a specific type of component used on civil aircraft. When a manufacturer proves its product meets the standard, the FAA issues a TSO Authorization (TSOA), which approves both the design and the production of that article. It does not, on its own, approve installing the article on any aircraft. That last point is the one most people miss.
What a TSO Covers
Under FAA regulations, an “article” means any material, part, component, process, or appliance used on civil aircraft.1eCFR. 14 CFR 21.1 – Applicability and Definitions A TSO is the minimum performance standard for one of those specified articles.2eCFR. 14 CFR 21.601 – Applicability and Definitions The catalog is broad. Cargo compartment fire detectors, airspeed instruments, terrain awareness systems, emergency locator transmitters, seatbelt hardware, GPS receivers — each has its own TSO number and its own performance requirements.
Each TSO spells out what the article must do and how well it must do it, often by referencing industry consensus standards from bodies like RTCA or SAE International. A manufacturer building an article to that standard must demonstrate compliance before the FAA will grant authorization.
What a TSO Authorization Actually Approves
A TSOA is a design approval and a production approval combined. It confirms that the manufacturer’s article meets the applicable TSO and that the manufacturer has the quality systems in place to keep producing it consistently.3Federal Aviation Administration. Technical Standard Orders – Section: Technical Standard Order Authorization (TSOA) The FAA also recognizes a “letter of TSO design approval,” which covers design only and applies to articles manufactured under a separate arrangement described in the regulations.2eCFR. 14 CFR 21.601 – Applicability and Definitions
The critical limit sits right here: a TSOA does not authorize installing or using the article on any aircraft. It says the article meets a minimum performance requirement in the abstract, independent of any particular installation.3Federal Aviation Administration. Technical Standard Orders – Section: Technical Standard Order Authorization (TSOA) Put plainly, the TSOA confirms that a GPS receiver works as it should. A different approval must confirm it works properly when wired into a specific cockpit.
Installation Requires a Separate Approval
Holding a TSOA for a piece of avionics does not mean the article can be bolted into any airplane. It must still meet the specific airworthiness requirements of the aircraft model where it will be installed.3Federal Aviation Administration. Technical Standard Orders – Section: Technical Standard Order Authorization (TSOA)
In practice, the installation approval usually takes one of two forms. A Supplemental Type Certificate (STC) is the most common path for modifications to type-certificated aircraft, covering wiring, mounting, software integration, and flight manual supplements. For simpler installations, an FAA field approval may be enough. Avionics projects often involve both a component-level approval (the TSOA) and an installation-level approval (the STC). The same company may perform both roles, or the two approvals may sit with entirely different entities.4Federal Aviation Administration. FAA and Industry Guide to Product Certification
Where a TSOA Sits Among FAA Approvals
The FAA’s certification system has several layers, and the TSOA occupies the component level. Placing it next to the others clarifies what each one actually does.
- Type Certificate (TC): covers the aircraft, engine, or propeller as a whole, confirming the complete product’s design meets airworthiness standards.
- TSO Authorization (TSOA): covers individual articles such as avionics boxes, fire detectors, or seatbelt hardware. Combined design and production approval, but not installation.
- Parts Manufacturer Approval (PMA): covers the manufacture of modification or replacement parts, including both a design approval from the Aircraft Certification Office and a production approval from the Manufacturing Inspection District Office.4Federal Aviation Administration. FAA and Industry Guide to Product Certification
- Supplemental Type Certificate (STC): covers a major modification to a type-certificated product, including the installation of TSO-authorized articles.
A manufacturer working across these categories may hold a TC for a product it designs, TSOAs for individual articles within that product, and STCs when installing those articles on other manufacturers’ aircraft. The FAA treats each approval as independent, and companies often work multiple tracks at once on a single project.
Duration, Transferability, and Deviation
A TSOA stays effective until it is surrendered by the holder, withdrawn by the FAA, or otherwise terminated. There is no built-in expiration date.5eCFR. 14 CFR 21.613 – Duration A TSOA cannot be transferred to another company, so if a manufacturer is acquired or sells its product line, the new entity needs its own authorization.6eCFR. 14 CFR 21.614 – Transferability
Manufacturers can request a deviation from a TSO’s performance standards, but only by showing that alternative design features provide an equivalent level of safety. The request and supporting data go to the FAA directly. For articles produced under a foreign authority’s oversight, the request routes through that country’s civil aviation authority first.7eCFR. 14 CFR 21.618 – Approval for Deviation
International Recognition
The European Union Aviation Safety Agency (EASA) operates a parallel system, issuing European Technical Standard Order Authorizations (ETSOAs) under Commission Regulation (EU) No 748/2012.8European Union Aviation Safety Agency. ETSO The EASA structure closely mirrors the FAA’s, with its own Subpart O governing ETSO approvals.
Under bilateral agreements, the FAA and EASA have set up reciprocal acceptance. The FAA accepts an EASA ETSOA for articles from the EU without requiring a separate FAA authorization, and EASA accepts FAA TSOAs for U.S.-origin articles without issuing a duplicate ETSOA. As of the current agreements, the U.S.-EU and U.S.-Canada implementation procedures are the only two that include complete reciprocal acceptance of TSO articles. Articles are marked according to the exporting authority’s requirements, and those markings satisfy the importing authority’s rules as well. No dual marking is required.9Federal Aviation Administration. Reciprocal Acceptance Frequently Asked Questions
For manufacturers selling into markets beyond the U.S., EU, and Canada, whether a local authority accepts a TSOA depends on the terms of any bilateral agreement in place. Many countries model their standards on FAA TSOs, but formal acceptance still varies.