Future Fuels


If somehow you’ve not already heard, General Aviation Modifications, Inc. (GAMI) completed its decade-plus-long effort to earn FAA approval of its G100UL unleaded 100 octane aviation gasoline. But it will be a long time before most of us will see G100UL at our favorite FBO. That’s because GAMI says it’s focusing initial distribution efforts on California and Washington state, where leaded fuel is a particularly salient political issue. Regardless, the time will come when you may have to make some unleaded fuel decisions.


The first decision you’ll need to make is whether or when to purchase the G100UL STC. The FAA has approved its use in airplanes, but to exercise that option each owner must acquire rights to use it in the individual aircraft. There are two required STCs, one for compatibility with engines and another showing compatibility with the airframe fuel system. 

Will you buy the STC, and if so, when? Most owners will probably wait until the fuel becomes available in locations they fly. The STC will require placarding the airplane, inserting a flight manual supplement into the POH/AFM, and a mechanic’s endorsement of FAA Forms 337 for the modification as well as in the airframe and engine logbooks. This is probably not something you’d be able to do on the spur of the moment when you find G100UL as the only fuel available. So, be thinking about whether and when you’ll buy the GAMI STC. STCs are serial number specific, so if you buy the GAMI STC for your current engine and then replace it with another engine, you’ll need to check whether the replacement engine comes with the STC. So, include STCs in your engine overhaul/replacement decisions.


Swift Fuels has been quietly pursuing its own unleaded 100R fuel (I think the “R” is for “replacement”) through the STC process. The company already fields an unleaded 94 octane fuel for lower horsepower engines but says once it has 100R approval, it will stop producing 94UL and focus on one fuel that works in all piston engines. Now that there is precedent for fleetwide STC approval, I suspect Swift will earn this approval relatively quickly.

What’s that mean for the airplane owner? You may need to purchase multiple STCs in an unleaded future so you can buy whichever fuel is available at a given airport (it’s highly unlikely FBOs will offer both). Pricing and placarding will probably be about the same as GAMI’s, as the area around your fuel caps takes on a NASCAR sticker look. The alternative will be to pick your destination based on the type of fuel available there. More decisions for the owner and pilot-in-command.


GAMI says G100UL will eventually cost 50 to 90 cents more than 100LL to produce. GAMI’s George Braly says it will cost even more than that in the beginning as it is produced in lower quantity. Mark-up at the pump may be more, also,  as refiners and FBOs recover costs of the transition. Are you willing to pay the price for progress? The more of us who are, the greater volume of G100UL and/or 100R will be produced, and the lower the potential at-the-pump price. As the fleet changes over, the volume of 100LL production will decline, probably raising its price to something closer to the unleaded fuel cost. 

Most pilots will still check the fuel price on their favorite flight planning app to pick where they want to top off. Now you may have to pick an airport based on the STC(s) you’ve purchased.


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