Question: If a modification to an aircraft has been made by a supplemental type certificate (STC), what required paperwork must be carried aboard the aircraft to document airworthiness? For example, you’re renting a Cessna 172 that has been modified with a 180-hp engine, or perhaps to use automotive fuel. What, if any, additional documentation is needed to document that the aircraft is airworthy?
Answer: The STC itself is not required to be physically carried aboard the aircraft. However, the documentation that proves the STC has been properly incorporated is required to be part of the aircraft’s permanent records, and some documentation must also be carried aboard the aircraft. If an aircraft has been modified under an STC, the following documentation must be carried onboard the aircraft to substantiate the aircraft’s airworthiness:
- Form 337: This FAA form documents major repairs or alterations, including STC installations
- Logbook Entry: Maintenance records must reflect the STC installation
- POH/AFM Supplement: If the STC affects aircraft operation, a supplement to the Pilot’s Operating Handbook or Aircraft Flight Manual must be onboard
- Instructions for Continued Airworthiness (ICA): These must be retained and followed for ongoing maintenance
- Written Permission from STC Holder: If you’re not the original STC holder, you must have written authorization to use it
While the STC certificate itself can stay in your maintenance records, the POH/AFM supplement and ICA are critical for airworthiness and legal operation. If the FAA inspects your aircraft and finds a modification without proper documentation, it could be deemed unairworthy.