The plane is idling on the tarmac at Heathrow. You’re looking out the window at the wing, wondering if that slight delay is a mechanical issue or just the usual airport chaos. But there’s something else happening under the fuselage that you can’t see. In the fuel tanks of that Boeing 787, something radical is shifting. It isn't just standard kerosene anymore. It’s Sustainable Aviation Fuel, or SAF. And honestly, it’s basically the only thing standing between the airline industry and a total climate reckoning.
Airlines are in a tight spot. They can’t just "go electric" like Tesla did with cars. Batteries are heavy. Like, ridiculously heavy. If you tried to power a long-haul flight from New York to Singapore with current battery technology, the plane would be so weighed down by the batteries it wouldn't have room for a single passenger. That’s where Sustainable Aviation Fuel comes in. It’s a "drop-in" solution, meaning we don't have to redesign the engines. We just change what we pour into them.
What is Sustainable Aviation Fuel anyway?
Let’s get one thing straight: SAF isn't some magical, carbon-zero juice that smells like roses. It’s a biofuel. When it burns, it still releases carbon dioxide. The trick is where that carbon came from in the first place. Traditional jet fuel is made from crude oil pumped out of the ground. When you burn it, you’re adding "new" carbon to the atmosphere that had been buried for millions of years.
SAF is different. It’s made from renewable resources. We’re talking about used cooking oil from fast-food joints, municipal solid waste (yep, literal trash), and agricultural residues like corn husks or wood chips. Because the plants used to make this fuel absorbed $CO_2$ while they were growing, burning the fuel simply returns that same carbon back to the sky. It’s a cycle. According to the International Air Transport Association (IATA), using Sustainable Aviation Fuel can reduce lifecycle carbon emissions by up to 80% compared to traditional fossil fuels.
That 80% figure is a big deal. It’s not 100%, and we shouldn't pretend it is. There’s still energy used in the refining process and transporting the fuel. But compared to the status quo? It’s a massive leap.
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The "Fatberg" to Fuel Pipeline
You’ve probably heard of "fatbergs" clogging up city sewers. It’s gross. But companies like Neste, a Finnish refiner that has become the world’s leading producer of SAF, see that grease as liquid gold. They take used cooking oil and animal fats—things that would otherwise be thrown away—and put them through a process called Hydroprocessed Esters and Fatty Acids (HEFA).
It’s currently the most common way to make Sustainable Aviation Fuel.
But there’s a limit. There is only so much old french fry oil in the world. To really scale up, the industry is looking at "Power-to-Liquid" (PtL) technology. This is some serious sci-fi stuff. You take renewable electricity (from wind or solar), pull hydrogen from water, grab $CO_2$ directly out of the air, and chemically stitch them together to make synthetic kerosene. It’s expensive. It’s complicated. But it’s the holy grail because the feedstock—air and water—is essentially infinite.
Why haven't we switched over yet?
Money. It’s always money.
Right now, Sustainable Aviation Fuel costs anywhere from two to five times more than regular jet fuel. Airlines operate on razor-thin margins. If Delta or United suddenly switched to 100% SAF tomorrow, your ticket price would skyrocket, and the airline would probably go bust within the month.
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There's also a massive supply issue. In 2023, SAF accounted for less than 0.2% of total global jet fuel use. That is a tiny drop in a very large bucket. We need to build hundreds of new refineries. We need massive government subsidies, like the ones seen in the U.S. Inflation Reduction Act, to make the price competitive.
Then there’s the "food vs. fuel" debate. If we start using prime farmland to grow crops specifically for jet fuel, food prices go up. That's a huge ethical mess. That’s why the industry is pivoting toward "second-generation" feedstocks—waste products that nobody wants, rather than crops like corn or soy that people actually eat.
Real-world proof: It’s already happening
This isn't just a lab experiment. In November 2023, Virgin Atlantic flew "Flight 100"—the first ever 100% Sustainable Aviation Fuel transatlantic flight by a commercial airline. They flew a Boeing 787 from London to New York using a blend of 88% HEFA (mostly fats) and 12% synthetic aromatic kerosene (made from plant sugars).
It worked perfectly. The engines didn't care. The passengers didn't notice a difference.
United Airlines has also been aggressive here. They’ve invested in companies like Alder Renewables and Fulcrum BioEnergy. They’re trying to secure their future supply before the scramble for SAF really kicks off. Because once every airline is mandated to use it, the price is going to get even crazier if the supply hasn't caught up.
The Ethanol Lesson and Avoiding Greenwashing
We have to be careful. Back when ethanol first became a "thing" for cars, people realized that some of the ways we produced it were actually worse for the environment than just using gas. We can't repeat that mistake with Sustainable Aviation Fuel.
If an airline claims they are "flying green" because they used a 1% SAF blend, that’s marketing fluff. It’s greenwashing. We need transparency. Groups like the Air Transport Action Group (ATAG) are pushing for stricter certification. We need to know exactly where the feedstock came from. Did a rainforest get cleared to plant palm oil for that "sustainable" fuel? If so, it’s not sustainable. Period.
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The industry is also looking at "book and claim" systems. This sounds boring but it's vital. It allows an airline to buy SAF and have it injected into the fuel system at an airport where it's available (like Los Angeles or Amsterdam), even if their actual flight is taking off from somewhere else. It's like buying "green energy" for your house; the specific electrons hitting your toaster might not be from a wind farm, but your money ensured that green energy was put into the grid.
The roadmap to 2050
The goal for most of the aviation world is "Net Zero" by 2050. Is that realistic? Kinda. Maybe.
It depends on three things:
- Efficiency: New planes need to use less fuel. The Airbus A321neo is already way better than the old MD-80s.
- Radical Tech: Hydrogen-powered planes for short hops. Airbus is working on the "ZEROe" project, aiming for a commercial hydrogen plane by 2035.
- SAF: This is the big one. It has to do the heavy lifting for long-haul flights.
If we don't scale Sustainable Aviation Fuel, the only other way to hit climate goals is to fly less. And honestly, nobody wants that. People want to see the world. They want to visit family.
What you can actually do
You’ve probably seen the little checkbox when buying a ticket: "Offset your carbon for $15." Most people skip it. Usually, those offsets go toward planting trees, which is fine, but it doesn't actually change the flight itself.
However, some airlines are now letting you specifically buy Sustainable Aviation Fuel credits. Lufthansa and the Air France-KLM group are big on this. When you pay that extra bit, you are directly funding the purchase of SAF for the airline's fleet. It’s a more direct way to lower the impact of your travel than just planting a sapling and hoping it doesn't burn down in a forest fire ten years from now.
Check the airline's sustainability report before you book. Look for their "SAF blend" targets. If they don't have a plan to get to at least 10% SAF by 2030, they aren't taking this seriously.
Actionable Steps for the Conscious Traveler
- Prioritize Direct Flights: Takeoff and landing use the most fuel. One long flight is better than two short ones with a layover.
- Support "Book and Claim": If your airline offers an option to contribute specifically to SAF procurement rather than generic "offsets," choose the SAF.
- Fly Newer Aircraft: When booking, look for planes like the Boeing 787 Dreamliner, Airbus A350, or the A320neo family. They are significantly more fuel-efficient, making the SAF blend go further.
- Pack Light: It sounds silly, but weight matters. Every extra pound requires more fuel to lift. If everyone on a widebody jet removed 5 lbs from their suitcase, the fuel savings would be measurable.
- Watch the Policy: Support legislation that provides tax credits for SAF production. Without government "carrots," the price gap between fossil fuel and sustainable options will never close fast enough to meet our 2050 goals.