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Note: Stinson 108-3, Cessna 172B thru 172M, 175, 175A thru 175C and Beechcraft C35 & D35 approved for 250 HP using the turbocharged 6AS-350-A series engine.

The STC’s contains FAA approved instructions and data that will allow you to modify your aircraft. Franklin Aircraft Engines charges a fee to provide you the required permission to utilize an STC.

What does the FAA require when modifying your airplane using an STC?

FAA regulations and Policies regarding STC permission is clear. If you elect to modify your aircraft using an STC, you must obtain written permission from the Holder of the STC and the permission statement must be maintained as part of the permanent aircraft records.

The following are some excerpts from FAA documents:

DEPARTMENT OF TRANSPORTATION - Federal Aviation Administration [Policy Statement Number ACE-00-23.561.01]
An STC cannot be used to modify an aircraft without the permission of the STC holder. Federal Aviation Administration Notice 8110.69 dated June 30, 1997, requires the STC holder to provide the customer (installer or airplane owner) with a signed permission statement that includes the following: (a) Product (aircraft, engine, propeller, or appliance) to be altered, inducing serial number of the product; (b) The STC number; and (c) The person(s) who is being given consent to use the STC. The permission statement needs to be maintained as part of the aircraft records. The requirement for this permission statement originated in the Federal Aviation Authorization Act of 1996 (Public Law 104-264). *This provision was put into law to try to stop the ``pirating'' of STC's.

9 U.S. Code § 44704 - (b) Supplemental Type Certificates. (3) Requirement.— If the holder of a supplemental type certificate agrees to permit another person to use the certificate to modify an aircraft, aircraft engine, propeller, or appliance, the holder shall provide the other person with written evidence, in a form acceptable to the Administrator, of that agreement. A person may change an aircraft, aircraft engine, propeller, or appliance based on a supplemental type certificate only if the person requesting the change is the holder of the supplemental type certificate or has permission from the holder to make the change.

Advisory Circular AC 43-210 - STANDARDIZED PROCEDURES FOR REQUESTING FIELD APPROVAL OF DATA, MAJOR ALTERATIONS, AND REPAIRS. Approved data can be used to substantiate major alterations/repairs and can be derived from: (2) STC data, if it specifically applies to the item being repaired/altered. NOTE: The Federal Aviation Reauthorization Act of 1996 (Public Law 104-264), specifically section 403, STC, contains specific requirements concerning the use of STCs. It requires that the installer obtain permission from the STC holder to use the STC.

Here’s an interesting article regarding permission from an STC Holder: https://www.aviationpros.com/home/article/10388581/intellectual-property

The lack of a simple and structured FAA procedure places a heavy burden on STC Holders to enforce compliance with FAA Regulations and Policies regarding an installer obtaining permission from the STC Holder to use an STC. Outdated FAA procedures provide no checks and balances to enforce their very own Regulations and Policies.

220 HP STC Approved ! Cessna 170, 172 & 175 Series Stinson 108 Series Float STC's Substantial Climb & Cruise Increase 6 cylinder smoothness Unmatched Horsepower and Torque Constant Speed Propeller Increased re-sale value Alternator & Vacuum Pump Upgrade