Frequently Asked Questions

The following answers are provided strictly as a primer for your basic understanding. We have intentionally omitted as much technical jargon as possible for ease of understanding. Accordingly, we have left out the specific supporting F.A.A. CFR (Code of Federal Regulations) references but if you want these references, we'll be happy to provide them to you. We strongly encourage you NOT to rely only on our interpretations and explanations of the regulations, but direct you to check with your F.A.A. representative or find the F.A.A. on the web at or

F.A.A.- P.M.A. stands for "Federal Aviation Administration - Parts Manufacturing Approval".  It is most easily thought of as a FAA manufacturing license in that it is one method by which the F.A.A. conveys airworthiness to an aircraft part. A PMA part is typically a replacement for an Original Equipment Manufacturer's (OEM) part.  FAA-PMA's are non-exclusive approvals, but there is a high barrier to entry to obtain them. A FAA-PMA holder must demonstrate to the FAA that their replacement part is "Equal to or better than" the part it replaces.

TSO is a Federal Aviation Administration designation which stands for Technical Standard Order. It is another method by which the F.A.A. conveys airworthiness to an aircraft part. Very often (but not always) a TSO part is a replacement for an original part.  A TSO produced part must only meet minimum prescribed F.A.A. mandated standards or requirements.

There are a couple of important differences.  One is that a FAA-PMA part carries a requirement for the PMA holder to document to the FAA where this part can be used on the aircraft, engine or propeller, and to show it on the PMA supplement letter  and parts packaging. This is referred to as the part’s “eligibility.” With a TSO the installer makes the decision on where the part is used. Another thing that is different between PMA’s & TSO’s is the nature of their approval.  In the most basic terms, a PMA holder is providing a part by demonstrating to the FAA that the part he is producing is equal to or better than the original (OEM) part it replaces. In contrast, a TSO produced part must only meet minimum prescribed F.A.A. mandated standards or requirements.

FAA-PMAs are rapidly gaining acceptance around the world as more customers have come to rely upon the quality, performance, availability and cost savings of PMA and TSO parts. If you have any doubts or reservations, please check with your Quality Control Manager and F.A.A.-P.M.I. (Principle Maintenance Inspector) or contact us to arrange a time when we can meet with your Quality Manager or Engineers to your issues discuss in greater depth.

At ACDI our policy is to always make sure we tell you when we quote you the part, before you buy it.  Look on our quotes for “Quoting: (Alternate Part Number)” This is one indication that we will provide an PMA or TSOA part. We also provide a verbal or written statement with the quotation.

A PMA part must be marked with the letters "FAA-PMA" on the part itself and/or the packaging. (an exception exists concerning marking the part if it is too small or otherwise impractical.  In such a case it may be tagged or labeled in such a manner that is acceptable to the administrator (FAA). The installation eligibility must also accompany the part.  In addition, a PMA part must also be supported by a PMA supplement letter which shows what it replaces and it’s installation eligibility.

A TSO part must be marked with the applicable TSOA reference number on the part itself and/or the packaging. For example, certain bearings are covered by TSO-C149, and that will appear on the package label. Another requirement for a TSOA part is a statement on the manufacturer’s packing list which (in part) states that the part meets only minimum performance standards.

According to FAA definition, a standard part is defined as AN, MS or NAS specifications.  It is important to understand that these are Standards, not part numbers. Part numbers made to a Standard meet the Specifications of the applicable standard.  Typically each bearing manufacturer is qualified (QPL) to produce the parts and appears on a QPL Listing. A Manufacturer that produces a part to a Mil Spec will provide their own part number that conforms to the respective AN, MS or NAS number.

It is important to understand that when you order a MS “part number,” you are in fact ordering a Mil Spec (or Military Standard). In every case, you will receive the part number of the QPL manufacturer that corresponds to the respective Mil Spec. Published interchanges are readily available to support the interchanges, and often we can provide that documentation. But to be sure, make sure you request it prior ro placing your order.

Not by FAA definition. Only AN, MS, or NAS parts currently are defined as Standard Parts.

If the supplier to Boeing is selling to anyone other than Boeing then a PMA is required.  Boeing is the PAH, TC Holder or STC holder (Production Approval Holder, Type Certificate Holder, or Supplemental Type Certificate Holder, as defined by the CFR’s). If a part is not PMA or TSOA approved, the part must first go through Boeing’s Quality program to be deemed as airworthy. Unless the parts are covered by PMA, TSO, or other means of FAA approval, the only customer that should buy alternate parts that are represented as meeting the Boeing Specifications are actual suppliers to Boeing.

Not unless the part is covered by a PMA or TSO approval. The interchange information contained in an IPC or Overhaul Manual is not considered by the FAA to be “approved data.” Just because the component manufacturer chooses to include optional information in their manual does not mean that it automatically conveys airworthiness.  The burden of installation of such a part is on the installer. We strongly recommend that any FAA Repair Station purchasing and installing parts that are listed in their manuals as alternates be sure to check with their PMI (FAA Principle Maintenance Inspector) and obtain written authorization. (Your next PMI might not agree and want to know the basis of your actions.)

Yes! We do not use Identicality to obtain PMA on OEM proprietary parts. We use another FAA approved method, call Test & Analysis or Test & Computations; which is sometimes referred to as reverse engineering. First we study and understand the part function, application and criticality. Then we will capture all necessary dimensions, features and characteristics of the OEM part from which we will create our own production drawing and produce the PMA replacement part.