Why Some Planes Still Run On Leaded Gas And Why That Might Finally Come To An End

In the past couple of months, there have been revolutionary moves in aviation that will make flying a bit healthier for us all. There is finally a drop-in replacement for leaded gasoline that every general aviation plane can run on right now. And the Environmental Protection Agency has published its long-awaited Proposed Endangerment Finding on the health effects of leaded aviation gasoline. Finally, after decades of waiting, aviation gasoline is finally going the way of leaded car gasoline.

Back in August 2021, fuel stations in Algeria finally stopped dispensing leaded gasoline. The nation was the last in the world to fuel cars with leaded gas. Here in the United States, the EPA banned leaded gasoline in 1996, and unleaded fuel was already widely available as early as 1975. With Algeria catching up, it means that no matter where you are in the world, you can rest easy knowing that the car in front of you isn’t spewing out lead.

Since then, there’s been one key place where you could still be exposed to lead emitted from a vehicle, and it’s right above your head. According to the Federal Aviation Administration, there are approximately 167,000 aircraft in the United States that run on leaded avgas. That number bumps up to 230,000 aircraft if you include the rest of the world.

These aircraft include everything from trainer Cessnas to small commercial aircraft and they burn 150 to 175 million gallons of leaded fuel every year. There are different grades of avgas, and the most popular one that you’ll find in the United States is 100LL, or 100 low-lead.

Why Planes Still Burn Leaded Fuel

The EPA says that while airborne lead emissions have dropped 99 percent since 1980, airplanes remain the largest source of remaining airborne lead emissions. Breathing in lead emissions can have detrimental impacts to the human body ranging from nervous system, cardiovascular system, and immune system damage to learning problems and a lower IQ in children. Lead is also absorbed by plants and the ground. There is no known safe level of lead exposure.

These effects have been known for a long time. Yet, when leaded fuel got banned in 1996, the general aviation fleet got an exemption. Why? The FAA says that it comes down to aircraft engines requiring high octane fuel to reduce knocking, and Tetraethyl Lead is an effective way of boosting octane:

Octane is a measure of the performance of a fuel as it burns in an engine combustion chamber. It is a measure of a gasoline’s ability to resist detonation, or “knock”. Octane is important to the safe operation of an aircraft or automobile engine. High compression, high displacement engines, such as those found in many high performance, piston engine aircraft, require high octane fuels so that detonation, which is the uncontrolled ignition of the fuel in the combustion chamber, does not damage pistons and other engine components and result in engine failure. High performance engines allow an aircraft to operate at increased speeds and with more payload, but these engines require higher octane avgas. Operating aircraft or automotive piston engines on fuels with lower octane than they require may result in damage from knock, but it is generally safe to operate piston engines on fuels of a higher octane rating than their minimum requirement. In other words, it is safe to go up in octane, but not down.

[Tetraethyl Lead] is an organic compound that contains lead and, in small quantities, is very effective in boosting octane. The ban of TEL in automobile gas was phased in over a number of years and was largely completed by 1986 and resulted in significant reductions of lead emissions to the environment. TEL was has not yet been banned for use in avgas, because no operationally safe alternative is currently available.

And lead isn’t just bad for the human body, it can be bad for engines. If you don’t use a proper engine operating technique, lead can build up and foul spark plugs.

There has been an effort to replace leaded avgas for decades, and there has been some development. Some aircraft can run Mogas, which is gasoline meant for cars. However, this fuel doesn’t meet the specifications for many aircraft engines.

And as AVWeb’s Paul Bertorelli mentions in his excellent history on leaded avgas, Mogas can have ethanol in it. Ethanol is hydroscopic, which means that it collects water and thus, can result in phase separation. Sucking up watery fuel in your motorcycle is annoying, but ultimately, there aren’t thousands of feet between you and the ground like you’d have in a plane. So running gas meant for a car isn’t the perfect solution.

In Bertorelli’s history, he also notes that some companies have offered hardware modifications to allow aircraft to run unleaded fuel. However, these have often been expensive and haven’t found market penetration. Thus, the search for the universal solution continued.

If you have the time, watch Bertorelli’s video and its sequel, they’re really good:

What Regulators Want To Do About Leaded Avgas

In 2011, the FAA started an unleaded avgas transition aviation rulemaking committee. It resulted in the 2014 Piston Aviation Fuel Initiative, combining the world’s fuel producers and the aviation industry to find a universal solution out of leaded avgas. A major sticking point in the FAA’s effort was to find a single fuel that can replace leaded fuel without modifying the aircraft.

However, as Bertorelli and a Popular Science report point out, the world’s fuel producers seem to have little motivation to spend development money on something like this. Avgas is one-tenth of one percent of what the fuel companies sell for cars. And while avgas has a good profit margin, PAFI asks the fuel producers to invest into a fuel with dwindling sales over decades. Of course, keep in mind that leaded fuel is still legal, so nothing is forcing a company to develop unleaded Avgas. The FAA established a deadline of 2018 for PAFI partners to find a 100LL replacement, yet that never happened.

An Unleaded Fuel For Every Plane

Thankfully, that hasn’t stopped some companies from pushing forward, anyway. Swift Fuels has developed its UL94, an unleaded fuel that could be used in more than half of general aviation aircraft without modification. And on September 1, the FAA approved supplemental type certificates (STCs) for a drop-in fuel that can finally solve this lead problem.

General Aviation Modifications Inc. has certified G100UL, a 100-octane unleaded avgas that can be used in all piston general aviation aircraft without modification. The decades-long dream of eliminating lead is finally getting realized. This fuel has been in development for more than 12 years and GAMI’s first certificate for the fuel were approved in 2021. As AVWeb reports, the certification of this fuel has been a bit controversial, with the FAA delaying approval of the fuel more than once.

Unleaded fuel for every general aviation aircraft is finally here. And getting it is pretty easy. GAMI says that you’ll be able to buy a supplemental type certificate from its website, then you’ll be good to go to fuel up on GAMI’s unleaded fuel wherever you find it. But don’t expect to buy it at your local airport today. GAMI says that it needs to ramp up production and set up distribution. This could take a while and for some time, GAMI admits that its fuel may cost more than 100LL. But the goal is to get the price down to parity.

The EPA Proposes That Lead Emissions Are Bad For You (Obviously)

At the same time, the EPA has published a proposed version its very long-awaited endangerment finding. Environmental groups, physicians, and governments have been asking for an endangerment finding since 2006, and have even accused the regulator of dragging its feet on researching the effects of airborne lead. But finally, a proposed endangerment finding has been published to the Federal Register, and it doesn’t reveal anything surprising:

In this action, the Administrator is proposing to find that lead air pollution may reasonably be anticipated to endanger the public health and welfare within the meaning of section 231(a) of the Clean Air Act. The Administrator is also proposing to find that engine emissions of lead from certain aircraft cause or contribute to the lead air pollution that may reasonably be anticipated to endanger public health and welfare under section 231(a) of the Clean Air Act.

The EPA covers a lot in its 98-page document, and there are a few things worth noting in it. One is the EPA’s estimate that since 1930, America’s general aviation fleet has burned 38.6 billion gallons of fuel, and have emitted 113,000 tons of lead into the air. Those numbers exclude emissions from military aircraft. The most recent data quoted by EPA estimates that 470 tons of lead were emitted by planes in 2017. That data also goes on to note that aircraft emissions for 2017 made up for 70 percent of the total U.S. lead inventory.

The EPA’s proposed endangerment finding quotes a number of studies. These studies have found that airborne lead can contaminate vegetables, and thus offer a pathway of exposure to people. Meanwhile, other studies noted by the EPA have found that levels of airborne lead are higher near airports, and that the blood lead levels of children who live close to airports are higher.

What Happens Next

The important part about this is that when the proposed endangerment finding becomes finalized, it becomes fuel for the EPA to phase out leaded avgas:

The proposed findings in this action, if finalized, would not themselves apply new requirements to entities other than the EPA and the Federal Aviation Administration (FAA). Specifically, if the EPA issues final findings that lead emissions from covered aircraft engines cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare, then the EPA would, under section 231 of the Clean Air Act, promulgate aircraft engine emission standards for that air pollutant.

It’s unclear how long it’ll take to see a ban on leaded avgas, but it is clear that leaded avgas is now living on borrowed time. Two airports in California have already banned leaded fuel. With GAMI’s drop-in replacement for leaded fuel and this proposed endangerment finding, regulators have the tools that they need to force lead out once and for all. Hopefully, soon enough, pilots can still fly their planes and nobody will breathe in lead emissions from those aircraft.