Exploring Avgas Alternatives For General Aviation

Amber Berlin

For Part 1 of this discussion, click here.

The health hazards, loss of IQ points, and associated costs of lead (Pb) fuel emissions leaves only one option for the General Aviation (GA) fleet: stop using leaded fuel. In order to accomplish this task, GA has several options to consider, including Avgas alternatives such as renewable biofuel, fleet-wide modification or to continue searching for a “drop-in” replacement that will meet or exceed the current engine specifications. Considering the severe cost of fleet-wide modification, it has become a last-resort option as all other avenues are explored.

Biofuel Avgas Alternatives

Because petroleum is a finite natural resource, a long-term solution is to replace Avgas and other petroleum-based fuel with renewable energy. One type of renewable energy is biomass, which is converted into bio-oil and then biofuel. Biomass has been considered from many different crops and each are classified by generation. First generation biofuel was made from sugarcane, sugar, beet, maize and rapeseed, but the use of these crops proved to be unsustainable because biofuel production drew on resources needed for food, and subsequently raised food prices. Second generation biofuel was made from wood, organic waste and food crop waste, which did not impact food production, but these crops had the limitation of year-round availability and high conversion costs. Third generation biofuel shows promise by using microalgae as biomass, which does not share resources with our food supply and can be produced year-round.

Microalgae produce more oil than oilseed crops and can be processed in various ways to produce several different types of fuel. With thermo-chemical production, microalgae can produce oil and gas, while biochemical production results in ethanol, biodiesel, and biohydrogen (Demirbas, 2010). According to Brennan and Owende (2009) bio-oil is created through the thermo-chemical process of pyrolysis, which supports large-scale production of biofuel and has the potential to eventually replace petroleum. Biomass already supplies approximately 13% of the world primary energy supply, and as production methods become more efficient bioenergy is expected to replace a greater amount of petroleum each year, providing 25-33% of global energy by 2050 (Hossain and Davies, 2013).

According to Demirbas (2010) there is potential for large-scale production of microalgae through the use of raceway ponds and tubular photobioreactors, however, microalgae production has not matched theoretical claims of oil yields. Limitations on the ability to supply nutrients and CO2 may inhibit large-scale production, and may become more restrictive as production capacity nears 10 billion gallons per year (Pate, Klise and Wu, 2011). Improvements are needed in the growing and harvesting of microalgae to reduce costs and enhance the production of algal biomass. With such a large infrastructure and dependence on petroleum, it is unknown if these improvements will allow microalgae production to compete and replace petroleum-based fuel completely.

While bioethanol is not a prime candidate for use in the aviation industry, and biodiesel can be used in limited quantities with kerosene as a fuel extender, the efficiency of hydrogen biofuel is worth a second look. Hydrogen can be produced by algae under specific conditions, such as direct and indirect photolysis, and ATP-driven hydrogen-production (Demirbas, 2010). Liquid hydrogen (LH2) powered aircraft boast a much lower fuel weight, which decreases operating costs and improves efficiency. The trade-off is higher pricing for LH2 and the increased frequency of contrail formation, with these aircraft expected to enter into commercial service around 2040 (Yilmaz, Ilbas, Tastan and Tahran, 2012).

Because of the prohibitive cost of modifying the entire fleet of piston-engine aircraft, the general aviation sector has been searching for a “drop-in” solution. A true “drop-in” solution would allow the aircraft to operate on the avgas alternative without any modifications. To support the reduction in Pb emissions, the Federal Aviation Administration (FAA) has set a goal of 2018 for the procurement of an avgas alternative that is usable in most piston-engine aircraft (FAA, 2013).

Currently, the FAA has entered Phase 2 of the Piston Aviation Fuel Initiative (PAFI), a program designed to evaluate potential avgas alternatives for suitability as a drop-in replacement for 100LL. Phase 1 included assessments in emissions and toxicology, production and distribution, and performance in worst-case conditions. The FAA has selected two fuel prospects, Swift Fuels and Shell, to continue Phase 2 testing at the engine and aircraft level with the purpose of being adopted across as much of the existing fleet as possible. According to the FAA,”…the PAFI process is not intended to be a barrier to entry for proposed fuels but rather is designed to enable the most promising fuels to undergo the necessary independent peer review and data collection necessary to gain broad based industry, regulatory, and consumer acceptance leading to production and sale across the entire aviation marketplace.” (FAA, n.d.).

While the well-known industry giant Shell submitted a promising fuel formulation, Swift Fuels, established in 2005, also advanced with their UL102, an “all-hydrocarbon” unleaded 102 Motor octane aviation gasoline that meets ASTM D7719. With Phase 2 testing of the PAFI set to continue for the next couple of years, GA’s era of leaded fuel is finally coming to an end. The environmentally-friendly, high-performance unleaded avgas alternatives of the future will prove a wise choice for generations to come. Generations who will be, quite literally, smarter than the last.

Get Started With Your Flight Training Today

You can get started today by filling out our online application. If you would like more information, you can call us at (844) 435-9338, or click here to start a live chat with us.


Brennan, L. & Owende, P. (2009). Biofuels from microalgae- A review of technologies for production, processing, and extractions of biofuels and co-products. Renewable and Sustainable Energy Reviews, 14, 557-577.

Demirbas, A. (2010). Use of algae as biofuel sources. Energy Conversion and Management, 51, 2738-2749.

Federal Aviation Administration. (n.d.). White Paper. Piston Aviation Fuel Initiative.

Federal Aviation Administration. (2013). FAA Issues Request for Unleaded Replacements for General Aviation Gasoline (Avgas).

Hossain, A. K. & Davies, P. A. (2013). Pyrolysis liquids and gasses as alternative fuels in internal combustion engines- A review. Renewable and Sustainable Energy Reviews, 21, 165-189.

Pate, R., Klise, G., & Wu, B. (2011). Resource demand implications for US algae biofuels production scale-up. Applied Energy, 88, 3377-3388.

Yilmaz, I., Ilbas, M., Tastan, M., Tarhan, C. (2012). Investigation of hydrogen usage in aviation industry. Energy Conversion and Management, 63, 63-69.

Why General Aviation Needs To Stop Using Leaded Avgas

Amber Berlin

The Clean Air Act, last amended in 1990, established a higher standard of environmental responsibility in the United States. In order to meet this standard, several initiatives were undertaken to reduce air emissions deemed harmful to human health. One such initiative was a close examination of the hazards presented by lead (Pb) fuel emissions. Pb fuel emissions are a by-product of the combustion of leaded gasoline in piston-engines, which are released into the air through the exhaust system. When airborne Pb is inhaled, it enters the bloodstream and raises the blood lead level (BLL) in the body. Because blood carries Pb through the entire body, it can result in widespread biological damage to cells and interruption of the cellular processes essential for cell survival.

Pb exposure is particularly dangerous to the brain because Pb has the ability to substitute for calcium ions and pass through the blood-brain-barrier (Sanders, Liu, Buchner & Tchounwou, 2009). Once in the brain, the toxic effects of Pb destroy healthy brain tissue and cause permanent damage in the central nervous system. According to Wu, Edwards, He, Zhen and Kleinman, (2010) substitution of Pb for calcium ions also affects the process of bone formation and remodeling, with Pb deposited in the bones in lieu of calcium and later released from bone tissue to recirculate in the body.

While it is known that large amounts of lead can be toxic, new research has shown that low-level lead exposure will also inhibit the brain’s ability to function. In a study on children, Miranda et al. (2007) show blood lead levels as low as 2 µg/dL (micrograms of lead in 100 ml of blood) have a significant impact on academic performance. This reduction in cognitive ability is identified as by The World Health Organization (2004) as “mild mental retardation resulting from loss of IQ points,” which has many negative effects on individuals and society as a whole (p.1495).

A loss of 2 IQ points has many social implications, such as moving an individual with a 71 IQ to below 70, an area considered mild mental retardation. While a drop in intelligence may affect the individual’s ability to perform academically, it also affects the way he or she is able to respond to the world. Individuals with limited intelligence tend to make less educated decisions than intelligent individuals, which may lead to fewer employment opportunities and various mistakes, even resulting in death. Furthermore, a self-awareness of having a below 70 IQ may create additional social problems because of a lack of confidence or self-esteem.

The monetary impact from a loss of 2 IQ points is substantial, with studies estimating the lifetime loss of income from the loss of IQ points ranges from $8,300 to $50,000/IQ point (Dockens, 2002; Pizzol, Thomsen, Frohn & Andersen, 2010). These losses extend beyond individual income and affect each member of society through our taxpayer dollars. An IQ below 70 qualifies children for special education classes and is also a qualifier for Social Security Disability benefits for intellectual disability (formerly known as mental retardation), which together cost nearly $8 billion a year.

While issues such as intellectual disability are apparent, the amount of toxic dust produced by Pb emissions often goes unnoticed. Pb dust is an invisible danger, settling on the surface of objects, vegetation, and into the top layers of soil. This dust is not easily removed from the environment, and according to Wu et al. (2010) Pb “does not appreciably dissolve, biodegrade, or decay and is not rapidly absorbed by plants” (p.309). The Pb in soil is a continuous hazard to small children because they absorb Pb more easily than adults and are more likely to ingest dirt. According to the World Health Organization (2010), an economic analysis revealed the cost of childhood lead poisoning to be $43 billion annually.

The Environmental Protection Agency (EPA) is the regulatory body charged with monitoring the national ambient air quality for Pb. After the identification of Pb fuel emissions as a health hazard, the EPA sought to reduce the amount of Pb in gasoline with the Clean Fuel Program in 1973. Highway use of leaded gasoline was finally prohibited in 1995.

In 2008, the EPA issued a final rule, lowering the National Ambient Air Quality Standard (NAAQS) from 1.5 µg/m3 (micrograms per cubic meter) to 0.15 µg/m3. The EPA acknowledged the acceptable risk of a loss of 2 IQ points, and used this as the measure to set the NAAQS for Pb (Chari, Burke, White & Fox, 2012). By 2012, the EPA had still not met the new standard and reported approximately 8.1 million people living in counties where Pb exceeds the NAAQS. The EPA also reported General Aviation (GA) is the leading contributor to Pb emissions through fossil fuel combustion in piston-engine aircraft, contributing an estimated 653 tons of airborne Pb annually (EPA, 2010).

Historically, General Aviation and GA aircraft have been exempt from a ban on leaded fuel because of its social and economic contribution. In 2005, General Aviation contributed $150.3 billion and over 1.2 million jobs to the U.S. economy (GAMA, 2006). Of the 3,300 airports open to the public and included in the FAA’s National Plan of Integrated Airport Systems (NPIAS), there are 2,952 landing facilities which depend on general aviation for community services such as aerial fire fighting support, aeromedical flights, agricultural support, aerial surveying, air cargo, disaster relief, remote population/island access, and U.S. Customs and border protection. GA links communities that would otherwise have no air support, providing vital services necessary for successful community development.

In 2010, piston-engine aircraft made up approximately 70% of the GA fleet, flying over 14.7 million hours. The majority of piston-engine aircraft use 100LL (Avgas), which may contain as much as 2.12 grams of Pb based fuel additive tetraethyllead (TEL) per gallon (EPA, 2008). The TEL additive boosts the octane rating and prevents early detonation of the fuel which may cause engine failure, but it is also the ignition of TEL that produces the Pb emission hazard.

While the entire population is affected by airborne Pb emissions, none is more affected than the population near airports. It is airports where Avgas is sold and used, where GA aircraft taxi and depart, and where the majority of Pb emissions are concentrated. A study on the impact of Avgas confirmed those living closest to the airport incur the greatest risks, including an estimated 16 million people living within 1km of an airport using Avgas, and 3 million children attend school within the same area (Miranda, Anthopolos & Hastings, 2011). The EPA also recognized their existing lead monitoring network is not sufficient to determine if all areas meet the new Pb NAAQS of 0.15 µg/m3.

The external costs of Pb emissions have been calculated at 41-83€/kg of emitted Pb (Pizzol et al., 2010), and for piston-engine aircraft, these external costs run approximately $37.5-$75.8 million per year.The health hazards and associated costs of Pb fuel emissions leave only one option for the GA fleet: stop using leaded fuel. In order to accomplish this task, GA has several options to consider, including renewable biofuel, fleet-wide modification, or to continue the search for a “drop-in” replacement that will meet or exceed the current engine specifications. Join us for the upcoming second part of this discussion as we discuss the future of GA fuel, including alternatives, and the FAA’s plan to phase out leaded avgas in Exploring Avgas Alternatives For General Aviation.

Get Started With Your Flight Training Today

You can get started today by filling out our online application. If you would like more information, you can call us at (844) 435-9338, or click here to start a live chat with us.


Chari, R., Burke, T. A., White, R. H. & Fox, M. A. (2012). Integrating Susceptibility into Environmental Policy: An Analysis of the National Ambient Air Quality Standard for Lead. Int J Environ Res Public Health., 9(4), 1077–1096. doi: 10.3390/ijerph9041077

Dockins C. (2002). Valuation of childhood risk reduction: the importance of age, risk preferences and perspective. In: Jenkins R, Owens N, Simon N, Wiggins L, editors. Risk Anal: Int J, 22(2), 335–46.

Environmental Protection Agency. (2008). EPA-420-R-08-020.

Environmental Protection Agency. (2010). Development and Evaluation of an Air Quality Modeling Approach from Piston Engine Aircraft Operating on Leaded Aviation Gasoline. EPA-420-R-10-007. http://www.epa.gov/nonroad/aviation/420r10007.pdf

General Aviation Manufactures Association. (2006). GA Contribution. Retrieved from https://www.gama.aero/files/ga_contribution_to_us_economy_pdf_498cd04885.pdf

Miranda, M. L., Kim, D., Galeano, M. A., Paul, C. J., Hull, A. P. & Morgan, S. P. (2007). The relationship between early childhood blood lead levels and performance on end-of-grade tests. Environ Health Perspect, 115(8), 1242-7.

Miranda, M. L., Anthopolos, R., & Hastings, D. (2011). A Geospatial Analysis of the Effects of Aviation Gasoline on Childhood Blood Lead Levels. Environ Health Perspect, 119(10), 1513–1516. doi: 10.1289/ehp.1003231.

Pizzol, M., Thomsen, M., Frohn, L. M. & Andersen, M. S. (2010). External costs of atmospheric Pb emissions: Valuation of neurotoxic impacts due to inhalation. Environmental Health, 9(9). doi: 10.1186/1476-069x-9-9.

Sanders, T., Liu, Y., Buchner, V., & Tchounwou, P. B. (2009). Neurotoxic Effects and Biomarkers of Lead Exposure: A Review. Review of Environmental Health, 24(1), 15-45.

World Health Organization. (2004). Comparative Quantification of Health Risks. Global and Regional Burden of Disease Attributable to Selected Major Risk Factors. Chapter 19, p. 1495. Retrieved from http://www.who.int/publications/cra/chapters/volume2/1495-1542.pdf

World Health Organization. (2010). Childhood Lead Poisoning. Retrieved from http://www.who.int/ceh/publications/leadguidance.pdf

Wu, J., Edwards, R., He, X. (E.), Zhen, L., & Kleinman, M. (2010). Spatial analysis of bioavailable soil lead concentrations in Los Angeles, California. Environmental Research, 110, 309–317.

Featured Image: Erik Brouwer