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Ah, 100LL.
It’s blue, it’s toxic, and it’s been the lifeblood of general aviation since before most of us learned what a mixture knob does.

Sure, it contains lead — that delightful neurotoxin we banned from cars, paint, and rational human behavior decades ago. But hey, if it keeps the ol’ Lycosaurs from detonating mid-flight, who are we to argue with science from 1945?

Welcome to the slow-motion breakup between general aviation and leaded avgas. It’s not you, it’s the EPA.

100LL Avgas: Low Lead, High Drama

What Is 100LL?

100LL is aviation gasoline with a toxic twist. The "LL" stands for "low lead," which is adorable given it still contains tetraethyllead.

It’s dyed a lovely shade of blue, just to warn you that you’re handling a chemical cocktail from the mid-20th century.

It boasts a 100-octane rating – great for preventing engine knock in high-performance engines. In plain terms: It keeps your vintage aircraft engine from self-destructing, but at the cost of sprinkling lead into the atmosphere with every flight.

Safety and Environmental Concerns (AKA Why Lead in Fuel Is Bad)

Leaded exhaust is no one’s idea of a green perfume. Burning 100LL dumps lead particles into the air around airports, exposing anyone nearby to a known neurotoxin.

In case it wasn’t obvious, lead in the bloodstream is bad news – lowered IQ, developmental problems, cardiovascular issues, you name it.

General aviation is now the dominant source of lead emissions in U.S. air. All the cars gave up leaded gas decades ago, leaving small planes as the last holdouts still emitting this classic poison.

We've even seen children living near airports with elevated blood lead levels, a statistic that doesn’t endear pilots to their neighbors.

As for safety inside the plane: lead isn’t great there either. It gunks up spark plugs and forms deposits in engines. Mechanics get to scrape out chunky lead bromide residue, a fun throwback task about as modern as sock hops and drive-ins.

EPA to 100LL: “We Need to Talk”

After a mere half a century of scientific consensus that lead is bad, the Environmental Protection Agency is acting concerned. In October 2022, the EPA issued a proposed “endangerment finding” – declaring that pumping lead into the air endangers public health (shocking) . By October 2023, this finding became official.

The EPA’s determination triggers a long bureaucratic process to impose actual lead emission standards.

Translation: they acknowledged the problem, but 100LL isn’t yanked off the market just yet. The EPA can’t ban avgas overnight without the FAA on board, so for now it’s a slow dance of inter-agency consultation and rulemaking.

Still, the writing is on the wall (and in the Federal Register). The EPA has made clear, “Leaded avgas days are numbered.” They’re under pressure from environmental groups and lawsuits, not to mention basic common sense.

Even the government realized having the top source of airborne lead come from hobbyist airplanes is a bad look.

FAA: Trying to Have It Both Ways

The Federal Aviation Administration finds itself in a familiar spot: caught between environmental pressure and angry pilots. In public, the FAA agrees lead must go – they’ve even pledged to eliminate 100LL by 2030.

Behind closed doors, they whisper “but please don’t ground any airplanes in the meantime.”

In 2022, the FAA teamed up with industry groups on a grand plan with a heroic name – Eliminate Aviation Gasoline Lead Emissions (EAGLE, because every government effort needs a catchy bird acronym).

EAGLE’s stated goal is a lead-free aviation fuel system by the end of 2030. They promise a “safe transition,” which is FAA-speak for “we’ll ban the nasty stuff once we’re 100% sure your engines won’t fall out of the sky.”

Meanwhile, the FAA has been approving unleaded fuel alternatives at a glacial pace, trying to look busy; they insist on thorough testing (you can’t rush aviation safety). So, the agency line is: “Yes, we’ll dump 100LL, but not until there’s a proven drop-in replacement everywhere and 100LL will stay available during the transition”. In other words, keep calm and keep fueling with lead.

Unleaded Pretenders: G100UL and Friends

Leading the pack is G100UL, a 100-octane brew from a small company (GAMI) that claims to match 100LL’s performance minus the brain-damaging additive. The FAA was impressed enough to approve G100UL for every piston aircraft in 2022 – a fuel that everything from your grandma’s Cessna to a twin-engine workhorse can drink without the lead.

There’s a catch (you knew there’d be one). G100UL is approved on paper, but getting it into your tank is another saga: production and distribution are still ramping up, and it’s not available at your local podunk airfield yet.

A pilot in 2025 can’t taxi up to the pump and ask for “unleaded” unless they’re at one of a handful of test locations, which makes the FAA’s victory lap feel premature.

Next up is UL94, an unleaded 94-octane fuel from Swift Fuels. It’s 100LL without the lead (and without the full octane.

The good news: UL94 is already being sold at select airports for lower-octane needs.

The bad news: about 30% of the GA fleet (the high-compression go-fast types) cannot run on it without risking engine damage. Those 30% of aircraft happen to burn about 70% of all avgas, so UL94 isn’t a silver bullet.

Swift is working on another 100-octane fuel (dubbed 100R – points for creative naming) that got an FAA nod for limited use in late 2024.

There’s also the option of using automotive gasoline in some planes (via STC) if you enjoy logistical challenges and ethanol-induced headaches. For now, G100UL is the leading star to replace 100LL, with UL94 playing the understudy for lower-octane needs.

Timeline: When Will 100LL Kick the Bucket?

The optimistic target for a full transition is 2030. Industry groups and the FAA pinky-swore that by then, leaded avgas will be a relic of history. They’ve got committees, task forces, and a fancy timeline graphic with arrows pointing to 2030.

Will it happen by 2030? Maybe.

The FAA and friends hope so, and the EPA’s patience won’t last that long either. But there’s a lot of fine print. Rulemaking can drag on, fuel infrastructure has to change, and every small airport from Maine to Hawaii needs to offer unleaded fuel.

There’s zero appetite to strand thousands of aircraft that can’t get appropriate fuel. If the rollout of new fuels hits snags, don’t be surprised if that 2030 timeline slips.

In Washington-speak, 2030 is an “aspirational goal.” It’s circled on the calendar, but written in pencil. Pilots have learned to take such deadlines with a grain of salt (and maybe a few grains of lead oxide).

General Aviation Grumbles and Fears

Among aircraft owners and the general aviation community, the mood around 100LL’s demise is mixed. On one hand, nobody likes spewing neurotoxins over school playgrounds – pilots aren’t monsters.

We all understand it’s past time to get the lead out.

On the other hand, there’s a certain anxiety: What if the cure is worse than the disease for our engines and wallets?

A big worry is will the new fuel be available everywhere and affordable? It’s great that G100UL got approved, but until it’s stocked nationwide, many pilots feel stuck. If the local airport has nothing but 100LL, that’s what you’ll keep using.

There’s paranoia about potential price hikes too – if unleaded avgas costs even more than the already extortionate 100LL, cue the groans.

Then there’s the mechanical angle: Avgas with lead has been the status quo for so long that some engines were built around it. Take away the lead and you might get unintended consequences. Case in point: a major flight school tried switching an entire fleet to UL94 and ended up with dozens of valve problems.

Their engines had withdrawal symptoms from losing lead. Stories like that make owners nervous. No one wants to be a guinea pig and find out their trusty engine runs hotter or parts suffer extra wear on the new juice.

Pilots have an allergic reaction to uncertainty. The transition timeline is fuzzy and rumors swirl in every airport café ("Did ya hear the EPA will ban 100LL next year?" "Nah, they’ll just kick the can down the road."). That vague timeline is what bothers aircraft owners – the sense that the rules might change before they’re ready.

The Long Goodbye to Lead

100LL avgas is in a twilight era. Its unique blend of high-octane performance and toxic side effects has outstayed its welcome.

The regulators are sharpening their knives, the industry is scrambling for alternatives, and the pilots are watching the clock – with equal parts hope and cynicism.

American aviation is inching toward a cleaner future, albeit in its typical slow-and-stubborn fashion.

After 80-some years of relying on lead to keep pistons happy, letting go won’t be easy. But change is coming, one way or another.

In the meantime, if you’re an aircraft owner, enjoy that sweet blue 100LL while you can (with a hefty side of sarcasm). It’s the end of an era – sooner or later.

Sources

EPA Realizes Lead is Bad (Breaking News)—EPA chief: "Aircraft that use leaded fuel are the dominant source of lead emissions in our air." No kidding.

GA Industry Promises to Quit Lead… by 2030 – Coalition swears it’ll get the lead out by 2030, just don’t pull 100LL off the shelves until alternatives are ready.

FAA Approves Magic Unleaded Juice for All –FAA issues STC for G100UL, allowing the entire piston fleet to wean off 100LL – in theory.

Local Politicos Try to Ditch 100LL, Chaos Ensues – Santa Clara County bans 100LL, FAA intervenes because, surprise, not everyone can use the shiny new unleaded fuel yet.

Unleaded Fuel Gives Engines the Jitters – Flight school’s grand experiment with UL94 ends with unhappy engines and a hasty return to leaded fuel.

That’s your briefing.

We’ll stay on top of future developments, assuming they’re not buried in a 400-page PDF from 1973. Check back before your airport turns into a Starbucks.

-Tony

P.S.

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