Technical Standard Order

{{Use dmy dates|date=September 2023}}

A Technical Standard Order (TSO) is a minimum performance standard issued by the United States Federal Aviation Administration for specified materials, parts, processes, and appliances used on civil aircraft. Articles with TSO design approval are eligible for use on United States type certified products by following a much lighter process than similar non-TSO approved parts, provided the TSO standard meets the aircraft requirements.{{Cite web |url=https://www.aea.net/events/rotorcraft/files/Aug2013/FAA_InstallofTSOd.pdf |archive-url=https://web.archive.org/web/20140426113951/https://www.aea.net/events/rotorcraft/files/Aug2013/FAA_InstallofTSOd.pdf |archive-date=2014-04-26 |url-status=dead |title=Installation of TSO'd Product Considerations and Guidance |author=FAA}} The TSO authorization (also called TSOA) or a letter of TSO Design Approval does not necessarily convey approval for installation.{{Cite web |url=https://www.gpo.gov/fdsys/pkg/CFR-2011-title14-vol1/pdf/CFR-2011-title14-vol1-part21-subpartO.pdf |title=CFR 2011, Title 14, Volume 1, Part 21, Subpart O}}

Similar standards are maintained by other aviation authorities. For example European Technical Standard Orders (ETSO) by EASA for the European Union,{{cite web | url=https://www.easa.europa.eu/easa-and-you/aircraft-products/etso-authorisations | title=ETSO | date=31 March 2023 |author=EASA}} with limited reciprocal equivalence on a per-country basis.{{Cite web |url=https://www.easa.europa.eu/system/files/dfu/TSOA-ETSOA-Reciprocal-Acceptance-FAQs.pdf |title=FAA Technical Standard Order Authorization (TSOA) and EASA European TSOA (ETSOA) Reciprocal Acceptance Frequently Asked Questions (FAQs) |archive-url=https://web.archive.org/web/20230628202503/https://www.easa.europa.eu/sites/default/files/dfu/TSOA-ETSOA-Reciprocal-Acceptance-FAQs.pdf |archive-date=2023-06-28}} These often have the same numbers as FAA TSOs. For example, the FAA TSO for aviation headsets is C139. In the European Union, it is ETSO-C139.