Swift Fuels says it will begin commercial distribution of its 100R unleaded avgas sometime in 2025. The company recently earned an STC for the fuel and airframe on R and S-model Cessna 172s with fuel injected Lycoming IO-360 engines. It also had its fuel specification go through the ASTM balloting process on August 29 and there were concerns raised about the testing parameters and formulation of the fuel.
So will we all need an STC to use this new Swift 100 unleaded fuel. If it is a drop in replacement why would it include an STC. I went to Santa Monica Friday and got some Swift 94UL fuel. There was no one there telling me I needed an STC to use it and the pump took my credit card no questions asked and let me fuel my Skyhawk. I have the STC for the Swift 94 fuel by the way, but I wonder why I really even need it. The fuel cost $7.00 per gallon self serve or I could have gone to Adlantic aviation and got 100LL for $8.60 per gallon.
My question is how much additionally will this new product cost me when I am forced to buy it because some people have aircraft that need this more expensive product, which I really don’t need, but probably will be forced to buy it anyway because they say that the 94UL will be removed from sales when the 100 product comes available.
I now hear that the 91UL product currently used in other locations around the world can be used in my airplane without an STC because my airplane’s engine was originally designed to use 91 octane fuel that according to the FAA.
I have heard the same thing, from Swift when one of my intermediate fuel stops dropped mogas in favor of Swift fuel 91UL. The engine was originally certified on 80, has low compression, and runs just fine on 87 mogas, which we cannot find any more so it runs 91 mogas.
Because the current proven route to get approval to use the fuel is by STC - GAMI showed the way, Swift has flipped to copying that.
Note that Swift says the massive pot of molasses called ASTM committee had yahbut questions for Swift.
Read GAMI’s exposition of their G100UL fuel to see some of GAMI’s criticism of the ASTM standard, listing some gaps in the standard and some inappropriate requirements.
There are two rumors which make me suspicious of Swift: First, that they “juiced” a batch of 94UL with ETFE (bad stuff) when a batch didn’t meet octane rating. second, That the 8.5:1 Lycoming engines need greater than100 octane, not 94, to avoid detonation and valve recession. So until detonation tests results are publish for an 8.5:1 Lycoming, i will not use any Swift fuel.
The STC part can be confusing. Go to Swift’s website and look up the particular aircraft. Many aircraft do not need an STC. For example, I looked up a 172M model and it says this:
" Ready To Fly!
Congratulations! This aircraft is FAA-APPROVED TO FLY on UL94 Unleaded Avgas!
This aircraft can use UL94 Unleaded Avgas based upon any of the following criteria:
UL94 Unleaded Avgas meets or exceeds the FAA’s type-certificated fuel requirements of both this engine and airframe. The TCDS fuel requirement for both engine and airframe states one of the following: Grade UL91, Grade 80, Grade 80/87, or a minimum octane requirement of 80 or lower.
UL94 Unleaded Avgas complies with the requirements for Grade 80 unleaded avgas (as originally specified in ASTM D910). Grade 80 was last approved as an unleaded grade of avgas in 1995, per D910-95A.
UL94 Unleaded Avgas also complies with the requirements for Grade UL91 unleaded avgas as specified in ASTM D7547."
John as long as there is a rumor mill out there and conspiracy theories, I don’t think you would ever be able to use anything but 100 low lead. But for the rest of us not dependent on the rumor mill we are ready to move on just as they have done around the world where they now use UL 91 for their Skyhawks with the 8 1/2 to 1 compression ratio without an STC. You probably won’t believe it, but they are not having any problems.
Perhaps we are missing a more subtle point here. GAMI’s G100UL is ready to go and has been demonstrated publically in at least 15 different types of aircraft. But it is not available at our FBO’s. Why? NATA (National Air Transport Association - chaired in Washington DC by Curt Castegna who is also the co-chair of EAGLE) has not allowed its members - the distribution companies like Avfuel in Ann Arbor, MI, to distribute any fuel that does not have an ASTM Specification.
But Swift Fuels also does not have their ASTM Specification either, and yet their CEO says they will commence distribution across the country beginning in 3 months. In fact, there is no ASTM Specification in existence today for “high octane unleaded avgas”. Starting to smell the fish?
The fact is that according to FAA Advisory Circular 20-24D either route - STC or ASTM concensus - to certification is acceptable and neither one is preferred over the other. But there is more.
You may recall that gasoline octane (including avgas) is represented by two (2) numbers, not just one (1). Let’s take 100LL: it is officially known as 100/130 octane. The first number (Motor Octane Number) “100” is the MON. The second number (Performance Number) “130” is the actual resistance of that fuel to detonation at a full rich mixture setting and is often refered to as the “Supercharge Number”. As pilots, we should be concerned about this second number as it descibes the level of protection this fuel provides us at TO under “hot and high” conditions.
GAMI’s G100UL tested (and still does so) off the top of the scale which currently can only go to 160 octane. Swift 100R… while all I can say is they are not advertising it. I wonder if this characteristic of their fuel had anything to do with their failure to procure a favorable vote from the members at ASTM?