Our Guide to Getting a Supplemental Type Certification

If you're looking to significantly modify your aircraft, such as upgrading avionics, converting the engine, or completely refurbishing the interior, you'll likely need an FAA-issued Supplemental Type Certification (STC). 

Understanding what an STC is and how the process works is crucial for smooth aircraft maintenance and ensuring that your aircraft meets FAA safety standards.

What is a supplemental type certification?

A supplemental type certification (STC) is an FAA approval required when making major changes to an aircraft's original design. These modifications could involve critical components like engines, avionics systems, or structural adjustments. 

The STC ensures that any alterations are thoroughly vetted, compliant with federal aviation regulations (FARs), and safe for flight operations (FAA.gov).

When do you need a supplemental type certification?

Not every modification requires an STC aircraft certification. Minor adjustments typically don't call for such extensive oversight, but significant changes affecting flight safety or performance do. 

Common scenarios where you’d need supplemental type certification include:

• Upgrading avionics systems
• Converting to a new engine type for enhanced performance
• Interior redesigns that change structural integrity or seating layouts
• ​​Installing advanced communication or navigation systems (e.g., ADS-B or satellite connectivity)
• Modifying fuel systems to accommodate alternative fuels or increased capacity
• Adding winglets or aerodynamic enhancements for improved fuel efficiency or performance
• Changing landing gear systems to a different type or configuration
• Structural modifications such as reinforced fuselage or new cargo doors
• Retrofitting cabins with new emergency evacuation equipment or layouts
• Installing noise reduction modifications to comply with stricter environmental regulations
• Upgrading flight information display systems (FIDS) or electronic flight instrument systems (EFIS)

Without an approved STC aircraft, these alterations could lead to compliance violations or ground your aircraft, triggering Aircraft on Ground (AOG) situations. 

It’s hard to pinpoint what percent of air delays are caused by AOG occurrences, as the FAA tracks and categorizes delays into broader groups such as weather or air carrier delays without isolating AOG-specific incidents. 

We do know, however, that there are around 80,000 AOG events annually in the business and private aviation sector alone (Falcon MGA: A Simple Guide to Mitigate Against AOG Losses), and within commercial aircraft, there are roughly 146 AOG occurrences a year across all Boeing 777 aircraft (ASR Journal). 

Given the crippling nature of any AOG event, staying compliant with proper aircraft certification and documentation is key. 

The step-by-step process for obtaining a supplemental type certification

Understanding the STC process upfront can streamline your experience and help avoid delays.

Step 1: Figure out if you actually need a supplemental type certification

First, you need to see if your planned aircraft modification requires a supplemental type certification (STC). Not every tweak demands FAA approval, but major changes to critical systems or structural elements do. 

Talk to an engineer or maintenance provider who knows the FAA certification rules—they'll quickly tell you whether you're headed down the STC path or can keep it simple.

Step 2: Submit the necessary paperwork 

If you've confirmed you need an STC, it's time to formally apply. This involves submitting FAA Form 8110-12. 

For especially major modifications, you'll likely have an initial meeting with the FAA called a Type Certification Board (TCB) meeting. Don’t stress—this is just a session to get everyone aligned on exactly what's required.

Step 3: Nail down your design details

The FAA requires proof your idea is safe and complies with their standards. You'll provide detailed design documentation, outlining to the FAA exactly how your modification affects the aircraft. This includes detailed drawings, specs, and analysis demonstrating you’re not negatively impacting the original design or safety.

Step 4: Get FAA approval to test your proposed changes  

With your paperwork submitted, the FAA (or an FAA-approved organization known as an ODA or Original Design Authorization) gives you permission—known as a Type Inspection Authorization (TIA)—to test your aircraft modification. It's the green light to install your changes on an aircraft prototype and demonstrate they work exactly as planned.

Step 5: Install, inspect, and test your prototype

At this phase, you can install your modification on a test aircraft. Designated FAA inspectors (DARs and DERs) then closely inspect it, running detailed ground and flight tests to confirm your modification doesn't interfere with other aircraft systems and is safe for operation.

Step 6: Officially receive your STC

If your tests go well and your modification passes inspection, you officially get your STC approval from the FAA. After approval, you'll fill out FAA Form 337—this formally documents the modification, confirms compliance, and returns your aircraft officially back into service.

Step 7: Take it global if needed

If you fly internationally, your FAA-issued STC aircraft may require validation from aviation authorities in other countries, like EASA in Europe. 

Generally, international agreements make this easy, especially if your modification fits into the simpler “Basic” STC category.

How long does it take to get a supplemental type certification?

Obtaining an STC generally takes 3 to 6 months for straightforward modifications. Complex changes, especially those involving intricate avionics or structural overhauls, could extend the timeline to over a year. 

Timelines vary depending on the scope of modifications, FAA workload, and the efficiency of the MRO or engineering team involved.

Common myths about STCs

STC approval guarantees OEM warranty

An STC with FAA certification doesn’t automatically mean that your original equipment manufacturer's (OEM) warranty remains valid. 

OEMs may not recognize certain STC modifications, potentially voiding warranty coverage. It's always wise to check with your OEM before proceeding with modifications.

Only third parties develop STCs

Aircraft manufacturers also frequently use STCs to modernize their existing fleets or to repurpose aircraft, such as converting passenger planes to cargo carriers. 

Boeing, for example, holds more than 160 STCs, reflecting extensive manufacturer involvement in the STC market (FAA STC database).

Avoiding AOG aviation scenarios with proper STC practices

Improper or poorly documented modifications can quickly escalate to aircraft AOG situations, negatively impacting operations and revenue. Reliable AOG support typically depends on meticulous documentation, streamlined compliance checks, and a comprehensive understanding of the STC processes.

Proactive management of your STC applications and approvals helps keep your aircraft operational and minimizes costly downtime.

Best practices when applying for a supplemental type certification

To simplify the STC process, consider the following best practices:

• Choose experienced partners: Collaborate with experienced MROs or certified engineers familiar with FAA regulatory nuances.
• Documentation clarity: Maintain detailed, organized records of all alterations and approvals to streamline future inspections or validations.
• Early OEM consultation: Engage your OEM early to verify the warranty and compliance implications of your intended STC modifications.

Navigating the supplemental type certification process doesn’t have to be overwhelming. With clear planning, knowledgeable partners, and a proactive approach, securing your STC can become a straightforward part of managing your aircraft's lifecycle. 

Proper execution reduces risks associated with AOG aviation incidents and ensures compliance, reliability, and safety.

Through careful adherence to FAA regulations and a thorough understanding of the nuances involved, aircraft owners and operators can confidently undertake significant modifications, enhancing both aircraft value and operational capability.

Simplifying your supplemental type certification journey

Obtaining a supplemental type aircraft certification might seem complex at first glance, but breaking it down into clear steps makes it manageable. With the right preparation, careful documentation, and knowledgeable partners, the STC process ensures your aircraft modifications are safe, compliant, and beneficial for long-term performance and reliability.