We have described in detail what an FAA PMA part (design AND manufacturing approval) is and two ways (Test and Computations and Identicality) to obtain it. Let’s now understand what an FAA Supplemental Type Certificate is and when it is needed.
An STC is used to approve a major modification of a Type Certified product (airplane, engine, propeller) from its original design. An STC can be for “One only” or “multiple”, most would be for multiple as not to tie the STC to a specific aircraft. The STC approves the modification and how the modification will affect the original design, but it is not a manufacturing approval.
Major Modification:
A major modification is a change that is not minor. For that to make sense, we must understand what a minor change is. Per 14 CFR 21.93, “a minor change is one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the product.”
For part 33 engines, increasing fuel flow, adding additional horsepower, or changing/adding additional hardware would qualify as a change needing an STC. For aircraft, the range of STCs are much broader, upgrading avionics, adding a new engine, increasing power of engine installed (would also require STC on engine), modifying passenger aircraft to cargo, and many more. Based on our experience, aircraft STCs are the most common type. Propeller STCs aren’t as common but they would include lighter materials or increasing the allowable RPM range.
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STC not issued:
Above paragraph gives examples when STCs could be issued, but what are some examples of when an STC is not applicable? The first and most obvious is an approval of a minor change, STCs are only for major modifications to a type certified product. Technical Standard Order (TSO) design changes will also not be approved via STC, we will touch on TSOs and what they fully are in another blog post. In addition, if an applicant cannot meet the applicable FAA regulations, the agency or ODA will not grant an STC.
Summary:
This post gives a brief summary of what an STC is and when it is applicable, further guidance can be found in “FAA Advisory Circular(AC) 21-40 Application guide for obtaining a Supplemental Type Certificate” . The AC lays out the required process to go from concept to FAA Approval. The AC is here to assist but so are we, if you need assistance navigating the process, our DER is here to do just that. Contact us today to learn how to take your idea from thoughts to approved design.
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