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Avfuel: Leading the NO LEAD Initiative

Unleaded Avgas

With a focus on innovation, Avfuel Technology Initiatives Corporation (ATIC) is leading the mission to further industry advancements, including bringing unleaded avgas to market. Toward this effort, ATIC is proud to collaborate with industry organizations by providing its distribution expertise for high-octane unleaded avgas.


Avfuel looks forward to working with all industry partners to help promote the distribution and adoption of unleaded avgas as further progress on the initiative is made.


"We owe it to our industry, our communities and the companies that have worked diligently toward an answer to help make a solution work. Avfuel is honored to provide its expertise to help further the unleaded avgas initiative.”

Craig Sincock, Avfuel President & CEO

History of Unleaded Avgas Initiative

The initiative to develop unleaded avgas was prompted by growing environmental interest in removing the last vestiges of lead from 100LL avgas—the only commercially-available motor fuel to still contain lead. 

Finding a commercially viable unleaded avgas solution is not only important to the industry from an environmental standpoint, but also because spark ignition piston powered aircraft that require avgas are responsible for a number of high-value operations for the aviation industry, as well as local and state communities. These critical infrastructure activities include:

 • Pilot training essential to all aviation segments  • Small businesses requiring flexible connectivity 
 • Medical air transport  • Pipeline inspections that require small aircraft 
 • Search and rescue  • Access to remote communities
 • Firefighting via helicopters and other small aircraft  • Law enforcement
 • Agricultural applications, such as crop spraying  • Border patrol

Prop Plane

Unleaded Avgas FAQs | Revised September 2022

Through its issuance of the new STCs to GAMI, the FAA has approved the use of GAMI’s 100 unleaded avgas (G100UL) in all spark-ignition piston aircraft and engines in the GA fleet. The below is a guide to some frequently asked questions regarding G100UL.


Production and Distribution

Now that G100UL has received functional fleet-wide approval, what are the next steps to bringing it to market?

The are many steps in the commercialization process, including the identification and certification of qualified fuel producers/blenders, the establishment of a fuel distribution network, and the generation of data collection systems for the purpose of fleet experiences relating to the introduction of a new fuel.

How is GAMI going to create the infrastructure to produce and distribute G100UL avgas?

GAMI partnered with Avfuel Corporation through Avfuel Technology Initiatives Corporation (ATIC) to oversee logistics and distribution. Avfuel is a global supplier of aviation fuels and services, and currently sells 100LL to more than 675 FBOs.


Which companies will produce and/or distribute the new fuel?

All qualified producers and distributors will have access to the fuel under license. The fuel will be made available to any licensed distributor on an entirely equitable basis for price and volume. 

GAMI and ATIC believe the contract and licensing terms of G100UL avgas producers, blenders and distributors will result in the elimination of some existing transportation-cost-related market inefficiencies arising out of existing proprietary sourcing and distribution of 100LL.

When does GAMI expect a refiner(s) to join the process and begin making the fuel?

Now that GAMI has received airframe and engine STCs from the FAA, it is in a position to further engage with refiners and other blenders toward commercialization and production of the newly authorized unleaded 100-octane fuel.

Will there be FBOs that can’t carry G100UL avgas due to proprietary licensing to certain suppliers?

No such limitations are expected. ATIC and GAMI have committed that the logistics and licensing of distribution will ensure G100UL is accessible to all and fairly priced.

Will multiple high-octane avgas fuel alternatives exist in the marketplace?

While G100UL is approved to be miscible in any proportion with the currently-certified 100LL aviation gasoline, neither G100UL nor any other candidate unleaded fuel is currently approved to be miscible with one another. 

Because avgas volumes are low relative to jet fuel, and because airport fuel storage tanks have become expensive to construct and maintain, it is unlikely that any given airport or FBO will have multiple unleaded fuels for sale.

What role will the EAGLE initiative play now that the FAA has approved an unleaded avgas?

The EAGLE initiative engages a wide spectrum of general aviation stakeholders (manufacturers, fuel producers and trade organizations) to produce an unleaded, 100-octane aviation fuel by 2030. 

The STC approval for spark-ignition piston engines and airframes to use G100UL is a very important first step to move forward with commercialization and to bring the fuel to market. It is anticipated EAGLE’s responsible stakeholders will support the transition from 100LL in a safe, seamless and efficient manner.


Availability and Price

How long will it take for G100UL avgas to be widely available?

G100UL avgas will expand nationally over a period of a few years at a pace determined by the: 

  1. Eventual depletion of 100LL stocks 
  2. Number and location of new producers and blenders 
  3. Mandates of federal and local governments 

More specifically, experts expect 2023 to be a year of logistics with G100UL avgas appearing more widely in 2024. The first customers for the fuel are likely to be entities like flight schools. 

The fuel will gradually become widely available as production of distribution infrastructure is developed.

Will 100LL be banned before G100UL is widely available?

While that is a concern, it is unlikely that any significant number of municipalities will ban 100LL in the absence of an alternative. Hopefully, municipalities and others will appreciate the progress made to date and understand that the commercialization process takes time to implement. Aviation trade groups are aware of that potential issue and are actively working to mitigate that possibility.


How much more than 100LL is G100UL avgas going to cost?

Current best estimates are that G100UL avgas could cost 60-85 cents/gallon more than 100LL until it becomes more widely available. It is likely the higher fuel price will be offset by lower maintenance costs for the aircraft. 

In addition, because initial production will be limited, the farther an FBO is located from the producer, the higher the price is likely to be. Transportation costs are always a price driver. 


What is an AML STC?

An Approved Model List (AML) STC is a well-established FAA method to gradually approve makes/models of aircraft and engines for any modification to their original certification. When an initial STC is issued, the AML list attached to it will include only a few aircraft and engines. The FAA process simplifies the addition of further makes and models to the AML, because only the STC attachment need be changed as further makes and models are added. 

Which engines and airframes are covered with the STC?

The newly-issued STCs cover all airframes and spark ignition engines listed in the FAA database.

When do the STCs take effect?

The STCs are approved as of now. However, the practical effect will be realized once GAMI’s G100UL avgas is available at the airport. Distribution will phase in over time.


Will I need an STC for my engine or my airframe?

Both. To use GAMI’s G100UL avgas in your airplane, you need to obtain its STCs for both your engine and your airframe. You can contact GAMI for the STCs.


What will the STC cost?

The STC price will be reasonably based on engines and horsepower in a manner similar to the pricing for other fuel STCs that have been available for low-octane gasolines.


What is included in the STC paperwork?

A short Approved Flight Manual Supplement (AFMS), placards to be installed around the fuel filler ports on the aircraft, a placard to be affixed to the engine and any appropriate instructions.

Does this solve the unleaded fuel issue for general aviation?

The general aviation community is now closer to a solution that will enable pilots to fuel their aircraft with unleaded 100-octane avgas. The phase out of lead won’t be complete until 100UL is available everywhere 100LL is sold today; that rollout process will probably take several years. Regulatory restrictions could speed that up, but at present, they are not expected to be a short-term factor. 


Testing and Approval


Have engine manufacturers and other related OEMs endorsed this new fuel?

Engine manufacturers and many OEMs are members of the EAGLE initiative. Their participation will be an important element of the fuel’s market introduction.


Were there any novel discoveries or innovations that led to the successful approval of G100UL avgas?

There were several significant break-through discoveries in the 2012-2014 timeframe. 

In the fall of 2015, after an extensive, year-long internal technical review, the results and applicability of two of those discoveries to the certification of engines for operation on unleaded aviation gasoline were formally approved by the FAA Engine Propeller Directorate in a formal G100UL project issue paper.


What specific tests were conducted?

The list of tests conducted is comprehensive and extensive. Among those: 

  • Material compatibility testing was an early go/no-go requirement that took nearly a year to complete. 
  • Hot day, hot fuel, high-altitude and engine restart tests were completed early in the process. 
  • Thorough detonation testing has been conducted, as noted below.

Were the detonation test plans and testing approved by the FAA?

The means and methods for detonation testing were thoroughly scrutinized, reviewed and approved by the FAA. As far as GAMI is aware, GAMI now has the only modern, internal cylinder pressure sensor based aircraft engine detonation test methodology that is specifically approved by the FAA through its highest-level formal issue paper process.


What was the compression ratio, manifold pressure and the highest horsepower that successfully passed a formal FAA 14 CFR Part 33.47 detonation test?

At the conclusion of the two days of detonation testing, GAMI elected to complete an optional test item from the FAA-approved test matrix. 

That test item was to determine the maximum Brake Horsepower (BHP) at which the 8.7:1 CR IO-550 turbocharged test engine could be operated and continue to pass a standard Part 33.47 FAA detonation test.

With redline cylinder and induction air temperatures, the engine operated at 41.4” MP, 380 actual BHP (414 BHP when corrected to standard day conditions). We were unable to determine how much more additional HP could be obtained because the pressure relief “pop-off” valve on the induction system was limiting further increases in manifold pressure.


Have aircraft and engine OEMs been involved in the development?

Early in the development of G100UL avgas, both Lycoming and Continental sent engineers to GAMI in Ada who evaluated G100UL avgas and flew a turbocharged Cirrus operating on G100UL avgas in one wing tank and 100LL in the other. There were no concerns or objections raised by either OEM engine manufacturer to the observed performance of the G100UL avgas. 

In addition, Cirrus had one of its senior managers come to Ada. He was an experienced pilot who also flew with G100UL avgas in a Cirrus aircraft to evaluate its performance against 100LL. 

Cirrus also conducted extensive material compatibility testing of G100UL avgas with its composite fuel tank materials using its FAA-approved testing protocols.


Have any of the aviation organizations had any direct involvement?

At a critical time in the G100UL avgas project, many organizations have provided technical support.


Does G100UL avgas have an ASTM specification?

GAMI has elected to use the already-approved STC path to an FAA approval of the engines and aircraft in the fleet to operate on a new fuel chemistry; no separate ASTM specification is required.


Are there any new toxicity concerns with G100UL compared to 100LL?

The components in this new high-octane unleaded avgas have been carefully vetted and no new toxicity issues have been found. A draft Material Safety Data Sheet (MSDS) has been developed in consultation with world-class experts in that field. That new MSDS is consistent with existing MSDS documents for other transportation gasolines widely used in the marketplace.


About G100UL Avgas

What is the octane of G100UL avgas?

As its name implies, G100UL is a 100-octane fuel. During FAA-approved detonation testing, the detonation protection from use of G100UL avgas exceeded that of a corresponding ASTM D910 100LL. That detonation testing was personally observed by highly experienced FAA propulsion engineers.


Other than being lead-free, are there other benefits to G100UL avgas?

It is likely spark plug maintenance and replacement intervals will be measurably improved in the absence of metallic lead deposits. It is also likely that, over time, an available synthetic oil may double the interval between required oil changes.


What, if any, are the operating limitations/concerns/exclusions with use of G100UL avgas?

There are no known operating imitations, concerns or exclusions. G100UL avgas performs just as avgas 100LL. The engine, aircraft and pilot will not notice an operating difference when utilizing G100UL. The G100UL fuel is slightly denser than 100LL, at 6.2 to 6.3 lbs/gal, with correspondingly higher energy density.


Will the operation of my engine change with G100UL avgas?

It is likely that no change will be detectable to a pilot operating an aircraft, even with sophisticated engine monitors.


What changes will I have to make to my engine and/or airframe to use G100UL avgas?

No mechanical modifications will be required. STC placards will be placed on the engine, STC appliques will be applied to refueling ports and a simple addition to the POH will be made according to supplied simple instructions.


What is the color of G100UL avgas?

G100UL typically has an orange or amber color. When mixed in a 50% ratio with blue 100LL, the color is green (similar to the color of earlier 100/130 “green” avgas).


My airplane has a MoGas STC. Can I mix G100UL avgas with MoGas?

Comingling of G100UL avgas and other gasolines approved for use in your aircraft is specifically authorized in the limitations section of the STC.


I have heard rumors about problems with other candidate unleaded fuels purported to include cold weather starting problems, paint stripping from spillage at the filler for the gas tank, and metal additives that foul spark plugs. Has GAMI addressed and avoided all of those issues?

All such concerns have been addressed and thoroughly tested. Cold weather operational starting and flight-testing were extensively conducted, including by an FAA test pilot. 

GAMI has completed a highly successful 150-hour engine durability test conducted on an engine that already had 400+ hours of operation on 100LL. The post-test engine teardown demonstrated the engine and combustion chambers were noticeably cleaner at the end of that 150 hours operating on G100UL avgas than before the test started.


Are there any known material compatibility issues?

Following extensive testing, no compatibility issues have been identified in any aircraft, engines, storage tanks or transportation systems. G100UL is a drop-in fuel, ready to be used within the industry’s existing infrastructure.

Avfuel Avgas Refueler Truck

Contact Us to Learn More


Keith Sawyer, manager of alternative fuels | [email protected] | Mobile: 925.989.0479 | Avfuel's Office: 734.663.6466

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