Guidebook for Assessing Airport Lead Impacts (2016)

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4C H A P T E R 3 Key design considerations for piston engines used in aircraft include maximizing the work performed per volume of fuel consumed and optimizing the power-to-weight ratio of the engine— both of which are aided by higher compression ratio engines, which in turn necessitate the use of high octane gasoline. As a result, aviation gasolines (AVGAS) have long contained lead in the form of TEL, which is added to boost octane rating, and most piston-engine aircraft have and continue to use AVGAS. However, some piston-engine aircraft can use unleaded MOGAS, provided that the fuel does not contain ethanol or diesel/jet fuel. Despite the continued use of leaded AVGAS, lead emissions related to AVGAS use have declined over time for two reasons: the first is the introduction of 100 octane “low-lead” (100LL) fuel, which halved the maximum allowable lead content from 4.22 to 2.11 grams of lead per gallon; the second is the decline in AVGAS consumption over time. That decline is depicted in Figure 2, which shows the trend in domestic AVGAS consumption product supplied (i.e., consumption) reported by the U.S. Energy Information Administration (EIA) (U.S. Energy Information Administration 2015). While these data show a 61 percent reduction in AVGAS consumption since 1981, EIA forecasts AVGAS consumption will remain at approximately 4.4 million barrels per year for the foreseeable future. Research focused on the development of unleaded AVGAS has been underway for years. Currently, the FAA is continuing with an evaluation program to identify a suitable lead-free replacement for 100LL that addresses both gasoline quality and flight safety needs (Esler 2015, Federal Aviation Administration 2016b). Multiple phases of aircraft testing have been proposed, and a 2018 timeframe for publishing ASTM specifications for the unleaded replacement gasoline is estimated. However, it should be noted that the adoption of unleaded AVGAS specifications does not ensure that the fuel will be available in a timely manner or at a price that is competitive with leaded fuel. Although there are specifications for a 100 octane “very low lead” (VLL) AVGAS that lowers the allowable lead content by about 20% relative to 100LL, it appears that 100LL will be the dominant AVGAS until an unleaded AVGAS becomes commercially available. Use of Lead in Aviation Gasoline

Use of Lead in Aviation Gasoline 5 Figure 2. U.S. aviation gasoline consumption. Source: U.S. Energy Information Administration 2015.