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Aircraft Mods

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

Key Takeaways:

  • Aircraft modifications require FAA approval, with the first step being to check for existing Supplemental Type Certificates (STCs) that cover the desired change.
  • Minor modifications might qualify for a Field Approval (Form 337), though this path has become more restricted, with many requests now referred to Aircraft Certification Offices (ACOs).
  • Major or novel modifications necessitate obtaining a new Supplemental Type Certificate (STC), which is a highly complex and costly process involving detailed certification plans, FAA designees, inspections, and extensive testing.
  • Individuals seeking a new STC should be prepared for significant effort, expense, and specialized knowledge, or consider hiring expert companies or Maintenance, Repair and Overhaul (MRO) facilities to manage the process.
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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.

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