GAMI Gains FAA STC for High-octane Unleaded Avgas

 - July 28, 2021, 12:49 PM

The FAA’s Wichita, Kansas, Aircraft Certification Office issued a supplemental type certificate (STC) to General Aviation Modifications Inc. (GAMI) last week for use of its high-octane unleaded avgas, initially in all models of the Cessna 172. The STC will be expanded using the approved model list process to cover additional aircraft and engine combinations for GAMI’s G100UL avgas.

According to GAMI, “As the approved model list for these STCs expands over the next several quarters, the scope of the aircraft and engines on the AML will provide the functional equivalent of a fleet-wide certification for spark-ignition piston-powered aircraft and engines to operate on G100UL avgas.”

G100UL avgas is a drop-in replacement for the current 100LL avgas, which uses tetraethyl lead to boost octane so engines with high compression ratios can avoid damaging detonation. General aviation remains the only industry that still uses leaded fuel in high quantities, and there is strong pressure from communities near airports, the Environmental Protection Agency (EPA), and others to eliminate lead in avgas. This move is strongly supported by the aviation industry, including such major groups as the Aircraft Owners and Pilots Association, the Experimental Aviation Association, and the General Aviation Manufacturers Association.

GAMI founders George Braly, head of engineering, and Tim Roehl, president, started looking at the 100LL problem in 2010 after the EPA ratcheted up its criticism of the lead used in avgas. “I said to Tim, 'We ought to find a way to replace lead,'” Braly recalled. GAMI built a piston engine test cell for its various engine-related projects, and that proved essential to developing the new fuel. “Nobody else had that capability,” Braly said.

The goal for the 100UL fuel was a drop-in replacement that works on all piston-powered aircraft, meets the same octane requirements with the necessary detonation margin, and is fungible (easily mixed with 100LL), reasonably priced, and manufacturable using normal refining techniques. These goals are all met by 100UL, according to Braly, including the ability to mix 100UL with 100LL in any quantity and in storage tanks, pipes, aircraft fuel tanks, and fuel trucks.

GAMI has run full FAA Part 33 durability tests on Continental and Lycoming engines, including 170 hours of function and reliability testing, and detonation testing. The new fuel is compatible with all materials in fuel tanks and fuel systems. To expand the AML to other aircraft and engine models, GAMI needs to run two remaining tests agreed upon by the FAA. After they're completed in the next three to five months, Braly said, a final report will be prepared and the AML will be “vastly expanded.”

Although Braly won’t reveal the names of the company that will refine and blend the fuel with the octane enhancer nor what the enhancer is made of—other than saying it isn’t lead—he did announce a partnership with fuel distributor Avfuel. GAMI will continue to monitor and be responsible for quality for the manufacture of the 160 to 200 million gallons of avgas needed per year and Avfuel will make the fuel available to airports and FBOs. European company Lanxess, a Bayer subsidiary, is the manufacturer of the octane enhancer.

Aircraft owners will need to purchase an STC for their aircraft to use 100UL, and Braly hasn’t released a price yet, although he did say it would be comparable to existing autogas STCs available to the general aviation industry. He did confirm that the pricing will vary, depending on the horsepower of the engine.

The benefits of 100UL concern not just the elimination of lead combustion byproducts from the environment but also engine condition and durability. Tests showed that engines run on 100UL had much cleaner cylinder combustion chambers, with none of the lead deposits typical of 100LL avgas. Elimination of lead also will allow the use of synthetic oils in aircraft piston engines, something that wasn’t possible with leaded fuel. This will not only extend oil-change intervals but also help extend engine TBO intervals by as much as 25 percent, he said.

GAMI selected the Cessna 172 fleet for the first STC so the fuel will be flown extensively and proven by flight schools that operate that airplane.

As for the price of the fuel, Braly said that 100UL will likely cost more than 100LL, somewhat less than $1 a gallon. However, he added, “There will be substantial meaningful benefits for the owner-operator if we get rid of lead, and this will fully offset the difference in the cost of fuel.”

Braly believes there will be a strong push from environmentalists and the EPA to sunset 100LL quickly. “Based on the progress we’ve made in the last 11 months, we can get this done by the first or second quarter next year,” he concluded.