The Future of 100LL Avgas


In 1976 under the US Clean Air Act, lead was identified by the Environmental Protection Agency (EPA) as a major pollutant and subsequent action was taken to "get the lead out".

Remarkable progress has been made and according to the EPA average concentrations of lead in the air have dropped 91 percent between 1980 and 2008. Much of the credit for the dramatic drop of lead concentrations is given to the permanent phase-out of lead in motor vehicle gasoline. From 1976-1996 lead was gradually reduced to completely non-existent in highway use vehicles.

In the 1996 ban on leaded gasoline for highway use vehicles, the EPA also identified a few remaining acceptable or necessary uses for lead in fuels: aircraft, racing cars, marine engines, etc.

The natural progression of further eliminating lead concentrations leads to the next largest source, leaded aviation fuels (avgas). The EPA, as required by the Clean Air Act, has formally begun the regulatory process that will ultimately result in the removal of lead from avgas. While a concern it is expected that an alternative fuel will be in place before the current 100LL becomes unavailable.

CIRRUS participation in finding a solution:

Cirrus is actively working with all industry partners to try and find the best possible transition to a future unleaded avgas. Cirrus currently:

  • Chairs the General Aviation Manufactures Association (GAMA) fuels committee which leads the various industry groups working with the EPA and the FAA to find a viable transition plan to an unleaded avgas future.
  • Is a member of the FAA Unleaded Avgas Transition Aviation Rulemaking Committee. The membership consists of the FAA, EPA, General aviation associations, manufacturers, petroleum companies and possible future fuel providers. This is the first time a committee was formed with all stakeholders.
  • Is a member of the ASTM, the appropriate standard organization, aviation fuels committee which is establishing the specifications and methods to validating new aviation fuels.
  • Participates in the Coordination Research Counsel (CRC) – the aviation fuels committee which works with fuel suppliers, engine manufactures and the FAA on researching and testing high octane fuels.
  • Is working directly with fuel suppliers to test promising new fuels.
The Search for Unleaded Avgas

Everyone agrees that every effort should be made to find a transparent to near transparent 100 octane fuel replacement - one that can be mixed with 100LL, distributed the same way and made at about the same price.

The 100 octane rating can be maintained with additives such as MTBE, Ethanol, Manganese, Xylene among others. The challenge is a solution that also addresses issues such as:

  • Operation at temperature extremes.
  • Fuel stability over time.
  • Long-term health and safety aspects of the fuel (the current problem with 100LL!).
  • Compatibility with distribution equipment and aircraft fuel systems.
  • Production in existing refineries.
  • Cost of production and distribution.

Three possible avgas replacement scenarios (in order of highest octane):

  • Identify a transparent replacement fuel. No fuel yet has been identified but there are candidates emerging.
  • Find the closest to 100 octane fuel replacement that address all issues listed above.
  • Adopt 94 octane unleaded fuel (94UL): This is "100LL without the lead". This, of course, addresses all the issues listed above - and is the "backstop" option.

To date many would say no fuel has established itself as a clear front runner for a 100 octane or near 100 octane solution, but there are many hopefuls such as Swift fuel and GAMI's G100UL.

The "backstop" is the 94UL fuel solution. To produce it, the lead in the 100LL refinement process is removed. This solves all the issues listed above, but the drop in octane will mean significant changes (or power reductions) to many higher performance engines.

What will those changes be to higher performance engines?

Until we know the the future fuel this is speculative but the answer will vary: in some cases it will be merely operating limitations at the "corner" of the performance envelope; in others it may involve engine modifications.

There are also some promising new technologies on such as FADEC, anti-knock sensors and GAMI's Prism system that could use electronics to ease any fuel transition.