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Technical Standard Order (TSO) and Parts Manufacturer Approval (PMA) | |
 The FAA requires that companies or individuals that produce parts for sale for installation into type certificated aircraft may only sell FAA-approved parts. These "approved" aircraft parts, other than hardware, are parts that are approved by TSO, PMA, a type certificate, or a production certificate. To receive a TSO or PMA approval for a part, the manufacturer of the part must demonstrate to the FAA that the part will operate as intended in an aircraft environment and will be manufactured to FAA standards. The FAA regulations state it is the responsibility of the person installing the parts on an aircraft to insure the parts meet appropriate airworthiness standards. |
The Technical Standard Order (TSO) is one of the procedures the FAA uses to establish standards for aircraft parts. TSOs have been established for many types of aircraft parts such as engines, landing gear parts, environmental system components, and many avionics. TSOs are divided into categories and identify the testing required to cover a wide range of environmental conditions such as heat, temperature, altitude, vibration, etc. If a TSO is available that is suitable for a part, a manufacturer will typically test the part in a FAA-approved laboratory to the requirements of the TSO. If the part successfully passes all the tests, then the manufacturer will receive a letter from the FAA stating the part is approved per the TSO. This TSO approval letter means the part is eligible for installation in any aircraft via an STC or TC as long as the operating environment of the part in the aircraft is within the TSO criteria.
If there are no TSO categories established for the part that the manufacturer wants to sell, the manufacturer can still get FAA approval by testing the part in the actual aircraft type where it is to be used. To accomplish this, the part must first be conformed to the design drawings by a FAA-designated inspector to insure it meets type design. Then it will be installed and tested in accordance with a FAA-approved test plan. Upon successful completion of the tests, submittal of the appropriate documentation, and verification of a FAA-approved manufacturing system for the part, the FAA will issue a letter identifying the part as eligible for installation under PMA for the specific airplane type in which it was tested. The PMA part may then be installed in the aircraft via STC or TC. If the part manufacturer wants to use the part in another aircraft type, additional documentation and testing may be required. In any case, a PMA part can only be installed in an aircraft type(s) where it has specifically been approved.
Aircraft operators, such as an airline, who manufacture parts for their own use, do not require a PMA for the parts since they are not being sold. The parts, however, still must be approved and manufactured to FAA standards and installed using a STC or other FAA-approved installation procedure.
References: AC 21.303.1A, AC 20-62D, FAA Order 8110.42A, FAR Part 21, Subpart K, AC 20-110 (TSO Listing) |
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