The search for an unleaded replacement to 100LL aviation fuel could finally be over following the US Federal Aviation Administration’s (FAA) signing on 01 September of a supplemental type certificate (STC) that allows General Aviation Modifications Inc.’s (GAMI) 100-octane unleaded aviation fuel (G100UL) to be used in every GA piston engine and every airframe powered by those engines. The move has been hailed by the aviation industry as a major step in the transition to an unleaded GA future.
The requirement for an unleaded alternative to Avgas 100LL, which contains low levels of a toxic compound called Tetraethyl lead (TEL), has been gaining pace over recent years following the announcement that both the US Environmental Protection Agency and the European Chemical Agency were making moves to have TEL banned. It’s fair to state however that the search for such a replacement hasn’t been easy and, according to GAMI co-founder George Braly, has been beleaguered by “malicious interference” from large petroleum companies and even some regulators.
While unleaded piston-engine aviation fuel has been available for a number of years, current versions being sold have a lower octane rating than 100LL and so are only useable in aircraft fitted with low-compression engines. GAMI’s G100UL though is the first and so far, only unleaded fuel to match 100LL in motor octane rating, making it suitable for all piston engine types used in GA aircraft. The fuel is made by blending existing refinery products and yields detonation margins comparable to 100LL. It is slightly more dense than 100LL, but has a 3.5% higher thermodynamic output. A further advantage of the fuel over other unleaded equivalents is that it is compatible with 100LL and can be mixed with it in fuel bowsers and aircraft tanks for use.
In a podcast interview with Hangar Talk, George Braly from GAMI says that their G100UL project started in 2009 and has been market ready for the last six years, but that stalling and interference from large petroleum companies and regulators, who didn’t want to adopt a fuel created by a small private enterprise, has added significant time and cost to project. One of GAMI’s most active supporters has been Mark Baker, president of the Aircraft Owners and Pilots Association (AOPA). Commenting on G100UL’s new approval, Baker said: “I’m proud of GAMI, the industry team, and the FAA for persevering over the long term and getting a fuel that the FAA has recognized as a viable alternative to low lead. It’s vital that we find solutions to what has been plaguing general aviation since the seventies. It’s certainly the biggest issue I have dealt with in my time at AOPA.”
“This is a big deal,” Baker added, “but there is a lot of work yet to be done.”
In 2021 the FAA approved STCs for GAMI’s G100UL covering a smaller number of Cessna 172 engines and airframes, and then expanded the approved model lists (AML) to include essentially all lower-compression engine and airframe combinations. Though that was seen as an encouraging step forward in the path to supply unleaded aviation fuel to the piston aircraft fleet, the STCs did not include aircraft needing the higher-octane fuel that accounts for 60 to 70 percent of Avgas 100LL consumption in the US. This latest announcement by the FAA now addresses the needs of those higher-compression engines.
GAMI’s George Braly said, “This is a big day for the industry. It means that for a lot of our general aviation communities, and especially for a high fraction on the West Coast, relief is on the way. And it means that our industry will be able to go into the future and prosper, and provide the essential infrastructure for this country for everything from Angel Flights to critical training of our future airline pilots.”
Braly thanked AOPA and the GA community for their support through this long process. “Without it we couldn’t have gotten this done,” he said.
Braly has said that Michigan-based fuel supplier Avfuel is standing by to manage the logistics and distribution of G100UL, and said he is open to other partnerships. “Our arrangement is that any qualified refiner or blender of existing aviation fuels will be eligible to produce and sell it subject to the quality assurance requirements that the FAA has approved,” he confirmed.
With the approval now in place, the timing for when G100UL will reach airports remains uncertain at this stage. “It’s going to take a while to manage the infrastructure,” Braly said. “[The supply chain] is still a very wounded infrastructure and that’s not going to make the process any easier, but we have a handle on how to do this, and with the support of the major players I think we can do that. It’s going to be limited to begin with, but it can be ramped up rapidly.”
Baker said it’s important to get any fuels approved for use to the California market as soon as practical, in light of the fact that some municipalities have prematurely banned the sale of leaded avgas. “It is a politically charged issue there, and this will help keep our airports open with fuel that works with all aircraft.”
AOPA says that it will also purchase a quantity of unleaded fuels to use in its fleet of piston aircraft used for GA travel and flight training, showing members it has full confidence in FAA approval pathways and processes.
On the subject of cost, Braly said the smallbatch production process that will initially mark the arrival of G100UL at airports means that the fuel will cost slightly more than leaded avgas. “Small volume batches cost money,” he said. “Until we can get [production] revved up that we’re making millions of gallons at a time, there will be an incremental [additional] cost.”
“It’s not going to be unreasonable,” Braly added. “Pilots in America will not be paying what they’re paying for Avgas in Europe today.”
Talking of Europe, there will of course be a further delay before the fuel starts appearing across the Atlantic and there are some questions over whether the FAA STC will automatically be adopted by the EU Aviation Safety Agency (EASA) and the UK Civil Aviation Authority (CAA). According to the UK CAA, a validation of the STC would be required as per the requirements of current Bilateral Aviation Safety Agreements (BASA) in place between the US and UK. “The level of involvement could potentially be administrative. However, without knowing what’s required by the STC we cannot comment on the appropriate validation pathway for fuels produced under this STC,” the CAA told FTN.
On the cost front, until it starts rolling out in earnest in the US, fuel industry experts are wary of suggesting what price it will likely be at UK and EU airfield pumps, but some have intimated that €1.00 more per litre than current 100LL prices would not be surprising. It could be, however, that European governments will be incentivised to reduce the duty rate on the new fuel in order to phase out 100LL as quickly as possible.
