The Hamburg Flying Club, the Diesel Cessna Running on Used Cooking Oil, and What It Means for the Future of GA Fuel
A Hamburg flying club has received EASA approval to fly three diesel Cessna 172s on HVO100 - renewable fuel made from used cooking oil - marking a milestone for GA fuel alternatives.
A flying club at Hamburg Airport has received regulatory approval from the European Union Aviation Safety Agency (EASA) to operate three diesel-powered Cessna 172s on HVO100, a renewable fuel derived from used cooking oils and agricultural plant waste. The aircraft use Continental CD-135 compression-ignition engines and require no modification to run the alternative fuel. This is one of the first certificated general aviation operations conducting routine training flights on 100% renewable content fuel at a major European commercial airport.
What Is HVO100 and How Is It Made?
HVO stands for hydrotreated vegetable oil. The feedstocks include used cooking oils collected from restaurants and food processors, agricultural plant residue, and animal fats from meat processing. These biological materials are predominantly triglycerides - molecules built around fatty acid chains that carry oxygen atoms, which cause corrosion, instability, and poor cold-flow behavior in aircraft fuel systems.
The hydrotreatment process applies hydrogen gas under pressure and heat to strip those oxygen atoms out, leaving clean hydrocarbon chains that closely resemble conventional Jet-A. The resulting product has high hydrocarbon purity, low sulfur content, low aromatic content, and combustion characteristics within the established Jet-A specification envelope. HVO100 means 100% renewable content - no blending with fossil-derived Jet-A required.
The Continental CD-135 requires no modification to operate on HVO100. It pumps in like Jet-A and burns like Jet-A.
Why European Flying Clubs Already Had Diesel Cessnas
The Cessna 172 Skyhawk is the most recognized training aircraft in the world, and most run Lycoming horizontally-opposed gasoline engines burning 100LL avgas. But a diesel variant has been flying in Europe for years, driven by straightforward economics.
Avgas in Europe is historically expensive - sometimes dramatically more so than in the United States - due to fuel taxes and import infrastructure. Jet-A and automotive diesel are widely available across the European ground transportation network, and that availability extends to airports. A flying club operating a diesel 172 could refuel at more locations, pay lower costs per flight hour, and sidestep ongoing uncertainty around leaded avgas supply.
The engine that made this possible traces back to Thielert, a German company that developed a two-liter aviation diesel adapted from Mercedes automotive technology in the late 1990s and early 2000s. The engine fit directly into the nose of a Cessna 172. After certification challenges and significant company difficulties, Continental absorbed the program and produces the powerplant today as the CD-135. That is the engine in most diesel 172s flying in Europe now, including the three aircraft in Hamburg.
How EASA Approved HVO100 for These Aircraft
EASA did not issue a continent-wide approval for diesel aircraft to burn HVO whenever they can find it. The approval is specific: these aircraft, this engine type, this fuel.
The documentation package required confirmation from Continental of CD-135 compatibility with HVO100, operational testing results, a maintenance review, and verification that the club’s procedures for receiving, storing, and dispensing the new fuel type met established standards. That narrow, incremental approval process is how regulatory agencies build confidence in new technology - each bounded approval contributes to a data set that supports broader approvals over time.
EASA and the FAA share operational safety data through bilateral aviation safety agreements. What EASA accumulates from Hamburg feeds directly into what the FAA evaluates when American operators bring forward similar proposals.
HVO100 Performance and Maintenance Characteristics
HVO has slightly higher energy density per unit volume than conventional Jet-A, which theoretically yields marginally better range on the same fuel load. Its cold-flow properties are superior to fossil Jet-A - an important factor at Hamburg Airport during October, November, and December.
Combustion of HVO produces lower particulate emissions than fossil Jet-A because the hydrotreatment process removes most of the sulfur and aromatic compounds that contribute to exhaust byproducts. Some operators report cleaner fuel system components over time, with reduced deposits in injectors and fuel lines. The long-term maintenance data record is still accumulating, which is precisely why operational programs like this one matter.
The current limitation is infrastructure and cost. Producing HVO requires more energy than refining conventional Jet-A, and supply chains at most airports do not yet exist for it. Hamburg established a dedicated supply arrangement with a fuel provider to support this program - the kind of bespoke agreement that typically initiates alternative fuel adoption at a given location.
Why This Is a Flying Club Story, Not an Airline Story
The Hamburg program was not launched by an airline, a government research initiative, or a major fleet operator. A flying club identified an approved fuel, confirmed compatibility, arranged a supply chain, and started flying.
Flying clubs operate with an institutional flexibility that larger organizations typically lack. When economics and technology align, they can move. The nature of the operation also matters: these three Cessna 172s are conducting training flights with student pilots under instruction, multiple flights per day across the full range of operational conditions. That intensity generates an operational data record faster than a controlled research environment would, and the data reflects real-world training conditions rather than curated test scenarios.
What This Means for GA Pilots in the United States
The direct application for U.S. pilots is currently limited. The diesel GA fleet in America is smaller than in Europe - the avgas-to-diesel economic argument never drove the same level of adoption here. HVO is not available at most American fixed-base operators.
The FAA has engaged with sustainable aviation fuel questions through the CLEEN program (Continuous Lower Energy Emissions and Noise) and through coordination with the Department of Energy and industry on fuel transition pathways. But widespread HVO availability at U.S. airports is not imminent.
For pilots flying diesel-powered aircraft anywhere, the Hamburg approval is worth tracking. The EASA approval documentation is accessible through EASA’s public database. AVweb originally reported the story.
Key Takeaways
- A Hamburg flying club received EASA approval to fly three diesel Cessna 172s on HVO100, a 100% renewable fuel produced from used cooking oil and agricultural waste.
- HVO100 requires no modification to the Continental CD-135 engine - it performs within the existing Jet-A specification envelope, with slightly higher energy density and superior cold-flow properties.
- The EASA approval is specific and narrow - these aircraft, this engine type, this fuel - with each bounded approval feeding a data set that enables broader future approvals.
- Because EASA and the FAA share safety data bilaterally, operational experience from Hamburg directly informs FAA evaluation of similar proposals from American operators.
- The U.S. diesel GA fleet is smaller and HVO is not yet widely available domestically, but Hamburg’s training operations are generating exactly the real-world record regulators need to advance broader approvals.
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