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Much has been written lately about industry efforts to develop unleaded alternatives for 100LL avgas, and AOPA’s advocacy efforts towards a safe replacement that works for all piston aircraft are ongoing. A couple of unleaded avgas options are already on the market that can work for hundreds of piston aircraft engines (available from GAMI and Swift, as it stands). However, it is important to note that as of this writing, these fuels require a Supplemental Type Certificate (STC) for each airplane in which they are to be used. One cannot simply walk up to the pump and fill up without first ensuring the proper paperwork is in place. The STC will typically require a POH/AFM supplement and placards to be installed by an A&P mechanic with Inspection Authorization in addition to the usual Form 337 and maintenance record entry for major alterations.