Aircraft Mods

BTeter

Thursday, January 21, 2021 at 12:26 PM ET

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Last year this Twin Cessna visited Yingling Aviation for some extensive modifications.

Key Takeaways:

Aircraft modifications should first check for existing Supplemental Type Certificates (STCs); if a major change is new, it can be pursued through a difficult Field Approval (Form 337) or a complex STC process.
The STC process for major modifications is rigorous, costly, and time-consuming, requiring deep knowledge of FAA regulations, detailed engineering data, conformity inspections, and extensive testing under FAA oversight.
Obtaining an STC involves multiple stages, from initial discussions with FAA Aircraft Certification Offices (ACOs) to developing a certification plan, submitting comprehensive data, and conducting ground and flight tests, often necessitating the expertise of designated engineering representatives (DERs) or specialized companies.

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Some aviators are perfectly happy flying what’s available. Others of us yearn for ever better-equipped aircraft. Somewhere in the middle is taking what you’ve got, and modifying it to better suit your mission, or even just your wishes. There are many avenues by which you can modify your aircraft. Let’s explore the most common. (Note: What follows is not intended to be a checklist or cookbook. Instead, the goal is to give you a good understanding of the complex requirements to approve a proposed modification.)

Has It Been Done?

The first step in your journey should be to check to see if anyone has already made the modification you want. You could Google the mod or go to the FAA’s Regulatory and Guidance Library at https://rgl.faa.gov/. For example, if you have a Cessna 340 and want to improve the turbo intercooler, you can check the database to see if the modification already exists. In this case, STC SA4158NM seems to fit the bill. The Supplemental Type Certificate (STC) owner is American Aviation, Inc. in Hayden Lake, ID.