The engine that turns the propeller that creates the thrust that moves the air over the wings that creates the lift that keeps a small airplane like a Cessna aloft is not that different from what’s likely in your car.
There are spark plugs and pistons. It burns gas and, thus, produces pollution.
But there is one important difference. While gasoline containing the toxic heavy metal lead was banned for cars in the 1970s because of its harmful environmental and health impacts, leaded gas is still commonly used in piston-engine aircraft. This means that exhaust from those aircraft contains traces of lead that falls to the ground and, potentially, into the bodies of the people those planes fly over.
This has long been a concern for communities close to airports, none more so than those surrounding Rocky Mountain Metropolitan Airport in Broomfield, among the busiest general aviation airports in the country. Studies have shown that children living close to airports have higher-than-average blood lead levels.
“I couldn’t know something like that and then ignore it,” said Bri Lehman, a Lafayette resident who has been fighting against lead pollution from the airport, known as RMMA. “It was sort of an invisible public health crisis.”
Last month, those community efforts notched a win, as RMMA announced it has installed a new tank for unleaded aviation fuel and will begin offering it at prices equal to that of leaded fuel, which is usually cheaper. To bring the cost of unleaded fuel down, RMMA received a $300,000 grant from the Colorado Department of Transportation.
Two of the airport’s flight schools — a major source of the airport’s small-plane traffic — pledged to use unleaded fuel in at least some of their planes.
“This milestone is something that the entire Jefferson County Board of Commissioners are truly proud of because it reflects steady, thoughtful work in response to what our community has asked for for years,” county Commissioner Rachel Zenzinger said at the event.
Meanwhile, in a second victory, the Colorado Court of Appeals last week allowed a portion of a lawsuit filed by Boulder County and the town of Superior against RMMA to continue. While the court upheld the dismissal of part of the lawsuit about airport noise, it returned a second part of the lawsuit over lead pollution to the district court for further consideration. Superior and Boulder County say operations at the airport, which is owned and operated by Jefferson County, harm their residents’ health.
“A small but statistically significant effect”
Lead exposure can cause numerous health problems, especially in children, and there is no level of lead in the body that’s considered safe.
The banning of leaded automotive fuel is regarded as a major public health achievement that significantly reduced the amount of lead found in blood tests of children. Today, lead-based paint and dust found in older homes is believed to be the top source of lead exposure for kids in Colorado.
In 2024, the state Department of Public Health and Environment set out to learn how much leaded aviation fuel, also known as avgas, could be contributing to lead exposure. Using existing data on Colorado kids tested for lead over a 10-year period, the department grouped those results based on how close those kids live to an airport.
What the department found is that children living within 3 miles of an airport had higher-than-average blood lead levels, with kids living within a half-mile having the highest levels.
“Our results suggest that lead emissions from aircraft using leaded avgas have a small but statistically significant effect on the (blood lead levels) of children living near airport point locations in Colorado,” CDPHE researchers wrote in their study, which was published in the journal Discover Environment.
The lead levels found all fell below the Centers for Disease Control and Prevention’s “reference level” for lead — meaning the measure the federal government uses to assess whether a child has an especially concerning blood lead level. And the researchers also wrote that the risk of lead exposure from airports is likely lower than from lead-based paint.
But they wrote that lead exposure from aviation emissions was something worth watching.
“Our findings highlight the value of lead testing in children who may be at risk of exposure from all sources, including those who live near airports,” they wrote.
While CDPHE’s analysis did not look at lead levels near specific airports, people living near RMMA say the problem is particularly acute there.
The airport in 2024 saw more than 294,000 flight operations, many of them involving small planes based at the airport, according to FAA data. Planes used by flight schools, a significant concern of community members, engage in touch-and-go training numerous times a day, flying and polluting at relatively low altitudes over the surrounding neighborhoods.
An analysis by the environmental group Earthjustice found that planes from RMMA emitted more than 580 pounds of lead in 2017. The airport’s traffic has increased by more than 75% since then.
Why it’s hard to get the lead out
But removing the lead from aviation fuel is not so simple.
One main difference between the leaded and unleaded fuels now offered at RMMA is their octane rating. The leaded fuel has a rating of 100, while the unleaded fuel is 94. Higher octane fuels allow planes to go faster and carry more weight, while lower octane fuels could potentially damage their engines.
For this reason, the Federal Aviation Administration requires pilots to obtain a certificate that unleaded fuel can be used safely in their engines. As part of the new unleaded fuel program, RMMA will reimburse pilots for the cost of obtaining the certificate.
Even with these kinds of incentives, pilots may be reluctant to make the leap.
RMMA is the second airport in Colorado to offer unleaded fuel. The first, Centennial Airport, began offering unleaded fuel in 2023, with the same price-matching subsidies and certificate-reimbursement incentives.
Samantha Blymyer, a spokesperson for Centennial Airport, said 26% of the airport’s eligible aircraft have obtained the special FAA certificate allowing them to use unleaded fuel and that unleaded gas accounts for 20% of the airport’s total fuel sales for piston-engine planes. (As is also the case with RMMA, Centennial Airport doesn’t sell the fuel itself but instead works with what is known as a fixed base operator to offer the fuel to pilots.)
“There’s definitely some challenges that we’ve seen with the use of it,” she said. “Naturally, you get a little bit of hesitation from pilots wanting to make the switch.”
As an example, she said, the airport heard from pilots who said they experienced engine overheating while using unleaded fuel during hot summer months. That problem will hopefully be solved when new, higher-octane aviation fuels become more widely available in the coming months, she said.
Erick Dahl, the airport director at RMMA, said his airport cannot require pilots to switch to unleaded fuel, meaning they have to rely on the power of persuasion.
“We can try to encourage that adoption,” he said.
To community members like Lehman, there is frustration that this commitment from the airport didn’t come sooner — and also that its impact is likely to be modest, at least to start. But she said those frustrations shouldn’t block out the progress that RMMA’s new program represents: One of Colorado’s leading sellers of leaded aviation fuel is trying to change.
“Unquestionably, that is a good thing,” she said. “Full stop.”