It is my understanding that fuel composition is a part of engine approval, and it is similar to authorizing a new part if you are using a new fuel. [1] It seems

It is my understanding that fuel composition is a part of engine approval, and it is similar to authorizing a new part if you are using a new fuel. [1] It seems the FAA only recently approved the use of unleaded gasoline for a large number of engines! [2] So while bio-fuel based fuels would be great, there does seem to be some significant, and I think reasonable, bureaucracy in the way of that happening. [1] https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentid/22281/ https://www.faa.gov/regulations_policies/advisory_circulars/... [2] https://www.faa.gov/about/initiatives/avgas https://www.faa.gov/about/initiatives/avgas