A matter of octane
There has yet to be an additive other than lead introduced to aviation fuel which produces the high octane necessary for the safe operation of high-performance piston-driven aircraft.
“At this time, I do not believe it is viable to think that there is some different kind of additive to get to the same level of octane performance as 100LL,” says Desrosier.
FAA agrees, stating in a report to EPA that extensive testing and analysis of a number of additives has not revealed a “drop-in” replacement for the additive tetra ethyl lead (TEL). “Drop-in” refers to an additive which can be blended with a fuel without having to modify the aircraft in any way or add to the existing fuel supply infrastructure.
Additive prospects such as MMT, a magnesium additive which enhances octane, was found to have negative synergistic effects on engine detonation performance, relates FAA.
“So we are faced with a lower octane fuel, which means a very large impact on the transition for the higher horsepowered aircraft,” says Desrosier.
General aviation will continue to fuel its aircraft with leaded avgas until an alternative is formulated and produced, but even the supply of the lead additive for avgas is at risk.
There is currently only one company, Innospec, which produces and supplies TEL. Desrosier believes that as more countries move away from leaded automobile gasoline, the demand for TEL will decline and, even if the company determines that there is still a market to justify continued production, the price for leaded avgas will probably rise.
“We expect that by 2010, the remaining countries in the world that still use leaded auto fuel will likely stop, and that will have an impact on the demand for TEL,” says Desrosier.
FAA indicates that Innospec will be able to supply TEL to the aviation community indefinetly.
As for now, according to comments submitted to EPA by the Aircraft Owners and Pilots Association (AOPA), lead is absolutely needed in aviation fuel. TEL is added to aviation gasoline to increase octane for high-performance aircraft, prevent knock, and prevent valve seat recession and subsequent loss of compression for engines without hardened valves.
According to AOPA, “the use of a leaded fuel in high compression aircraft engines ensures safe flight.”
A matter of proportions
Roughly 70 percent of the general aviation fleet may be able to use unleaded automotive gasoline (mogas) for operation, but this group of aircraft only consumes 30 percent of the amount of fuel supplied to general aviation. The inverse-ratio is also true. While 30 percent of general aviation aircraft have high compression engines and must use leaded avgas, this group of aircraft consume the majority, 70 percent, of the fuel supplied.
According to AOPA, avgas consumption by this portion of the fleet is estimated to be high for two reasons: these aircraft burn more fuel per hour of operation than aircraft with smaller compression engines, and these aircraft are employed in business transport and long haul trips more often than aircraft with smaller engines.
This loose statistic, often referred to as the “70/30 split,” is verified by AOPA, GAMA and Avfuel. What this means is that it is not viable to simply take the lead out of avgas and run the fuel in all general aviation aircraft. The resulting fuel provides an insufficient octane rating for the high-performance aircraft and, thus, safety problems.
It is also been considered not viable to have two types of fuel for general aviation use. Mandating the use of leaded fuel for the high-performance aircraft and unleaded mogas for aircraft with low-compression engines creates a myriad of financial burdens for many segments of the industry.
“We would have to require that all the FBOs and our distribution infrastructure be able to handle two separate fuels,” says Desrosier.
According to Todd Petersen of Petersen Aviation, it’s also getting more difficult to fuel lower performance aircraft with mogas.
Petersen Aviation sells supplemental type certificates (STC) to aircraft owners so they can operate their airplanes with mogas as opposed to avgas. Because mogas is not widely available at airports, most pilots who attain these STCs must purchase fuel at an automobile gas station and then take the fuel to their plane at the airport.
LOS ANGELES, CA — Today Rep. Henry A. Waxman sent a letter to Michael Huerta, Acting Administrator of the Federal Aviation Administration (FAA), to encourage expanded use of unleaded fuels to...
EPA has formally begun the regulatory process required by the Clean Air Act that may ultimately result in standards mandating the industry’s transition to unleaded aviation gasoline (avgas).
... which could spell the end of the use of leaded aviation gasoline in piston aircraft in the U.S. It’s a prospect that has been hanging over the head of general aviation for two...