In April 2010, the Environmental Protection Agency released an announcement that it was proposing to gather data to determine if leaded avgas is an environmental health hazard.
The announcement in the form of an advanced notice of proposed rule making (ANPRM) has created reactions that range from a willingness to move forward in the search for the new lead-free avgas to alarm at the idea of government mandated changes and outrage due to what some see as a misguided plan to replace one boutique fuel with another. Regardless, the ANPRM served as a wake-up call to GA that 100LL is on the way out and the aviation community needs to figure out what to do next.
Responders to the ANPRM questioned whether the tiny amount of lead in the GA fuel supply, which accounts for one-10th of 1 percent of the transportation fuel used in the country each year, presents a credible threat to health. Some bemoaned that scant attention was being paid to the fact that supplies of ethanol-free premium auto gas — a viable and FAA-approved fuel for more than 150 piston-powered airplane types and approximately 70 percent of the airplanes plying the skies — are rapidly shrinking due to congressional mandates to increase ethanol usage, a state of affairs that actually required more pilots to use 100LL instead of a viable unleaded auto-gas alternative.
"This industry is dealing with a massive changeover situation, and people don't seem to realize how big this issue is," said Lycoming senior vice president and CEO Mike Kraft at AirVenture 2010. "When you change the fuel, you change a primary element of this industry."
Tetraethyl lead (TEL) is added in small amounts to aviation gasoline (avgas) to boost the octane number. Avgas must have an octane number of 100 to protect today's high-powered engines from detonation.
TEL was removed from auto gas in 1996, and although there were a few glitches during the transition period, lead-free auto fuel has worked well.
Despite its octane-boosting properties, TEL is not without its share of negative side effects. In addition to toxicity issues, some piston engines are prone to spark plug fouling, valve sticking caused by lead adhering to valve stems and valve guides, piston-ring land contamination and preignition due to lead deposits on piston crowns. Both Teledyne Continental Motors (TCM) and Lycoming have published more than one service directive related to the negative effects of TEL.
The momentum against 100LL has been building for years. In 2006 a petition was filed with the EPA that requested that the agency determine if TEL in avgas constitutes a threat to public health or welfare. And to make matters worse for 100LL, in 2008 the EPA found that adverse health effects occur at much lower blood-lead levels than was formerly understood. As a consequence the National Ambient Air Quality Standard (NAAQS) for lead was reduced by an order of magnitude from 1.5 to 0.15 micrograms per cubic meter.
At a public forum during AOPA Summit late in 2010, the EPA suggested that around 50 percent of the airborne lead in the United States can be linked to 100LL avgas. The EPA is conducting air sampling studies at five busy GA airports around the country to quantify the amount of lead being emitted during flight operations.
Take the lead out of today's avgas and the octane number drops to 94 — still high enough to protect the majority of today's engines but not all engines. Adoption of a new avgas that does not provide the same detonation protection as today's 100LL avgas would instantly render most twin-engine and high-performance airplanes unairworthy.
Toward a New Avgas
Ideally the new lead-free avgas replacement will be affordable, will fit easily into the present production and transportation infrastructure and will be in high enough demand to attract investors and producers.
American Society of Testing and Materials (ASTM) standard D-910 establishes 44 parameters for today's leaded avgas. One of the challenges in creating a lead-free avgas is determining how closely the new avgas formulations comply with these parameters and, if they don't, whether or not the deviations are acceptable. Alignment with the parameters makes it much easier for the airframe and engine manufacturers and the FAA to approve the new avgas for use in both today's legacy airplanes and tomorrow's airplanes.