Report on Lead Emissions Reduction for Piston-Engine Aircraft Released

The ultimate goal? An unleaded drop-in replacement for 100LL, the avgas we use to power a large percentage of the general aviation fleet—and particularly one that serves the roughly one-third of piston airplanes that require at least 100 octane fuel.

However, achieving that goal has been elusive, based in part on three factors. First, a new fuel would require new infrastructure at thousands of airports in the US alone, at a cost that few municipalities or private owners are willing to stomach. Second, new fuel requires new FAA certification in the engines and airframes through which it flows—another time and money problem for a wide-ranging fleet. Third, the use of auto fuel straight from the road transportation system introduces the problem of ethanol content, which wreaks havoc on aircraft fuel systems.

The “Options for Reducing Lead Emissions from Piston-Engine Aircraft” report from the National Academies of Science, Engineering, and Medicine—specifically the Committee on Lead Emissions from Piston-Powered General Aviation Aircraft—has been released, giving several alternatives for near- and mid-term mitigation on lead emissions, but no immediate—or easy—solutions. The committee was comprised of scientists and academic experts—including a number of certificated pilots—and reviewed by industry leaders prior to publication on January 12, 2021.

“Studies indicate that the exhaust from engine run-ups can create geographic areas with higher lead concentrations, such as when situated to combine with exhaust from aircraft taking off at full power,” as noted in the report. “However, the magnitude, frequency, and dispersion of these concentrations and their proximity to people are airport-and context-specific, depending on factors such as the level of traffic activity, meteorological and topographical conditions, and the location and orientation of runways and areas where pilots perform their pre-takeoff checks in relation to buildings and people. Hence, to assess whether changing the location of run-up areas will achieve appreciable benefits in mitigating hot spots for ambient lead concentrations requires detailed information on specific conditions at individual airports, and particularly those that have moderate to high traffic activity, which number in the hundreds or more.”

Because general aviation serves several critical functions in the nation’s transportation system and overall economy, the committee recommends proceeding with any changes with caution. “A multi-pathway approach that pursues lead emission and exposure reductions is needed in which the development of a drop-in fuel proceeds as a part of broader mitigation pathway focused on the development and deployment of lead-free fuels and new propulsion technologies, in combination with mitigation pathways focused on airport operations and practices and on existing fuels and aircraft,” said the report.

Of particular interest to pilots is the recommendation to alter operating procedures—specifically in the location and duration of before-takeoff run-up procedures to reduce the impact of exhaust emissions during high-power ground operations—and careful fuel handling to reduce contact with leaded avgas during refueling. “The outcomes envisioned from these recommendations will result from increasing awareness by the many individuals needed to effect change in everyday operations,” said the report. “Pilots and aircraft owners, airport managers and personnel, and aircraft technicians would understand the hazards created by leaded avgas to themselves and the local community, and would follow best practices for containment during refueling, locating and timing engine run-ups, proper disposal of inspected fuel samples, and exposure protections. Airports would purposefully move pre-takeoff run-up areas to reduce the proximity of lead concentration hotspots to people where airport location, traffic activity levels and exhaust interactions warrant such a response.”

A second near- to mid-term mitigation—an increase in the availability of alternative types of unleaded avgas that already exist—would likely require congressional involvement. For example, incentives would be provided for pilots to use the alternative fuel, and for small airports to add the required storage and delivery equipment. This may result in up to 20 percent lower lead emissions, if the change was made to the existing 100VLL (for “very low lead”) fuel—and up to 40 percent if combined with the use of UL94 fuel in lower-performance aircraft.

But what about the move towards completely unleaded fuel for the whole fleet? “A clear goal should be established that all newly certified gasoline-powered aircraft after a certain point in time (e.g., within 10 years) are approved to operate with at least one ASTM-specified unleaded fuel,” the report suggests. This would continue the work begun in 2013 by the Piston Aviation Fuels Initiative, a collaborative effort between the FAA and the general aviation industry. The full report may be downloaded here.