Why are two STCs necessary or my Aircraft?
Field Information Number 302
Two STC's are needed because there are two main parts to your airplane - the engine and the airframe. The engine must be able to use the fuel with no problems. The airframe must be able to deliver the fuel to the engine with no problems. Modified aircraft and engines must at least duplicate original testing applicable to each to achieve FAA certification. "STC" stands for FAA Supplemental Type Certificate.
EAA chose to do more than required in the Federal Air Regulations and also selected the longer 500-hour flight test for approval rather than the 150-hour engine block testing. The Cessna 150 program extended over 24 months and included periods of hot weather and cold weather testing, with seasonal variation in automobile gasoline volatility. The Cessna 172 program included about 750 hours of FAA supervised pipeline patrol operation.
The FAA defined the change in fuel from aviation gasoline to automotive gasoline as a major change. Therefore, under present Federal Air Regulation, supplemental type certification is required for the engine itself and for the airframe. Part of the responsibility of the IA mechanic completing the FAA "337 Form" is to ensure that the aircraft and engine conform to the original FAA Type Certificate and no changes have been made which would be unsuitable for incorporating the automobile gasoline STC's.
When you sell an airplane with an EAA STC, please be sure to convey all STC documentation to the new owner(s), and ask that individual to notify EAA of the new ownership.
If you have purchased an airplane that already has an EAA STC, check for the log book entry, the FAA 337 Form, the appropriate placards, and a full set of information sheets from EAA. Advise EAA of the new ownership. EAA maintains an N-number record so that you can be kept up-to-date on new developments. Contact EAA if your information package did not come with your airplane. We will be glad to provide another copy at a nominal cost.