A TSO, or Technical Standard Order, is a minimum performance standard issued by the FAA for specific aviation materials, parts, and appliances. Each TSO defines the baseline requirements that a particular type of article must meet before a manufacturer is authorized to produce it. There are hundreds of individual TSOs, each covering a different category of equipment, from altimeters and life preservers to fire detection instruments and landing gear brakes.
How a TSO Actually Works
A TSO is not a product. It’s a benchmark. Think of it as a rulebook for one specific type of aviation component. TSO-C10c, for example, covers pressure altimeter systems. TSO-C13g covers life preservers. TSO-C22g covers safety belts. When a manufacturer wants to produce one of these items for use in certified aircraft, it must demonstrate that the product meets every requirement spelled out in the relevant TSO.
Once the FAA is satisfied, the manufacturer receives a TSO Authorization (TSOA). This is a combined design and production approval: it confirms the article meets the standard and gives the manufacturer permission to build it. The manufacturer must maintain a quality system, provide a quality manual in English, designate an accountable manager, and allow FAA inspectors access to its facilities, technical data, and testing at any time.
TSO Authorization Is Not Installation Approval
This is the single most misunderstood aspect of the TSO system. A TSO Authorization does not approve an article for installation in any specific aircraft. It only confirms that the article meets a minimum performance standard on its own, independent of where it might eventually be used. A separate FAA approval is required before the article can actually be installed on a particular aircraft model.
That second step requires showing the article meets the specific airworthiness requirements (the “certification basis”) of the aircraft it’s going into. Wiring, mounting, software integration, electromagnetic interference, weight and balance effects: all of these installation-level concerns fall outside the scope of the TSO itself. The manufacturer’s installation manual must clearly state that TSO approval covers only the article’s standalone performance and that anyone installing it is responsible for verifying compatibility with the specific aircraft.
How TSO Differs From PMA and STC
Aviation uses several different types of design and production approvals, and they serve different purposes.
- TSO Authorization (TSOA) approves a manufacturer to produce an article that meets a standalone performance standard. It’s article-focused and installation-independent.
- Parts Manufacturer Approval (PMA) authorizes a manufacturer to produce replacement or modification parts for a specific type-certificated aircraft. PMA parts are tied to a particular aircraft design, often through test and computation data, an existing Supplemental Type Certificate, or a licensing agreement.
- Supplemental Type Certificate (STC) approves a modification to an existing type-certificated aircraft. If you want to install a new avionics suite or change an engine configuration, an STC covers the design change and its integration into the airframe.
In practice, these approvals often work together. A manufacturer might hold a TSOA for a GPS receiver, while an avionics shop holds an STC authorizing installation of that receiver in a specific aircraft model.
What the Authorization Process Looks Like
To apply for a TSO Authorization, a manufacturer submits an application to the FAA that includes a statement of conformance, certifying the article meets the applicable TSO, along with a copy of all required technical data. The application process is governed by 14 CFR Part 21, Subpart O.
Beyond the paperwork, the manufacturer must establish a quality system that meets FAA standards. This includes a documented organizational structure showing who is responsible for quality, how authority is delegated, and how quality management relates to other parts of the company. The FAA can inspect facilities, witness tests, and examine manufactured articles at any point, including at supplier facilities. The governing policy document for the entire TSO program is FAA Order 8150.1D, last updated in 2017.
Common TSO Categories
The TSO index covers a wide range of aviation equipment. Some of the more recognizable categories include:
- TSO-C2d: Airspeed instruments
- TSO-C10c: Pressure altimeter systems
- TSO-C13g: Life preservers
- TSO-C22g: Safety belts
- TSO-C23f: Personnel parachute assemblies
- TSO-C25a: Aircraft seats and berths
- TSO-C26d: Wheels, brakes, and wheel/brake assemblies
- TSO-C34e: ILS glide slope receiving equipment
The letter suffix on each TSO number indicates the revision. TSO-C13g, for instance, is the seventh revision of the life preserver standard. As technology and safety understanding evolve, the FAA updates individual TSOs to reflect current requirements.
International Recognition
Europe’s equivalent system is the European Technical Standard Order (ETSO), administered by the European Union Aviation Safety Agency (EASA). ETSOs function almost identically to FAA TSOs: they set minimum performance standards for specific article types, and an ETSO Authorization permits manufacture but does not approve installation.
Under a bilateral agreement between the FAA and EASA, the two agencies recognize each other’s TSO and ETSO authorizations. This means an article manufactured under an FAA TSOA can be accepted in Europe without EASA issuing its own separate approval, and vice versa. The agreement covers all current and future authorizations from both agencies, which significantly reduces duplication for manufacturers selling into both markets.
Non-TSO Functions in TSO Articles
Modern avionics and equipment sometimes combine TSO-regulated functions with additional features that fall outside any TSO standard. A navigation unit might include both a TSO-approved GPS function and an integrated non-TSO mapping display, for example. The FAA addresses this through specific policy guidance: the TSO Authorization covers the TSO function, while the non-TSO function receives only “design acceptance on a non-interference basis.” This means the extra feature must not degrade the performance of the TSO-approved function, and installation approval must account for both.