What are TSO and PMA Parts?

Posted on February 21, 2020 James Williams What are TSO and PMA Parts?

When flying or designing an aircraft, it is always crucial that it is designated as an “airworthy” part. Airworthiness refers to an aircraft’s ability to be considered safe for flight. These standards and certificates are regulated and upheld by various international agencies, including but not limited to the International Civil Aviation Organization, European Aviation Safety Agency, NATO, and European Defense Agency. These requirements for airworthiness are not just for the aircraft, but even for each and every component as well. When sourcing parts, one may recognize some of the common standards, such as TSO and PMA, but what do these designations mean for the parts they encompass?

A technical standard order (TSO) part is a designation provided by the Federal Aviation Administration (FAA) to denote a part that has been deemed airworthy. FAA TSO parts must meet set out minimum performance standards for use on civil aircraft, and often are designed to replace an original part. For parts to be considered “TSO parts” by the FAA, they need to have both their design and production approved. When a part is approved to be a technical standard order part, the manufacturer may produce the part and able it as such. Despite this, it does not mean that the part is permitted to be installed onto an aircraft, as it must then be proven airworthy by the FAA for the specific intended model.

TSO parts can become canceled or withdrawn at the behest of the FAA given certain circumstances. If the FAA determines that a part is inactive, they will cease to issue new authorizations on the part and it will be considered a “canceled TSO”. Nevertheless, the approved part can still be produced but just will not be able to receive any new authorizations. If the FAA decides to revoke authorization on the other hand, it is considered a “withdrawal of a TSO authorization” and the part may no longer be produced legally.
Parts manufacturing approval (PMA) refers to another designation given by the FAA to parts that they have considered airworthy. PMA parts are most often those that are for replacing an Original Equipment Manufacturer (OEM) part. The process of being awarded designation as a PMA part is fairly rigorous, as a PMA part is one that is considered “equal to or better than” the OEM that it is to replace. The process first entails having the FAA determine whether or not the part meets airworthiness standards. If the part passes this stage, it must then undergo inspection and then the part will have to have instructions for repair, inspection, and continued operational safety plans.
While both technical standard order and parts manufacturer parts refer to replacement parts that the FAA has considered airworthy, the two still have some distinct differences that set them apart. For one, PMA parts must have sufficient documentation addressing where the part is to be used on the aircraft and will have a letter and packaging stating the same. With TSO parts, there is no direct indication required for where the part is installed. Further separating them, PMO parts are strictly tested to be the same or better than the part it is intended to replace. A TSO part, on the other hand, simply has to meet basic FAA requirements

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