"The continued use of lead in avgas by piston-engine aircraft is a significant source of current lead emissions to the environment," said the Environmental Protection Agency. Last week, the EPA issued an Advanced Notice of Proposed Rulemaking (ANPRM) addressing leaded avgas and how to balance its threat to the environment with the practicality of phasing it out of use — particularly in older aircraft engines. Some possibilities include setting standards for new engines only. An EPA statement read, in part, "Converting in-use aircraft engines to operate on unleaded aviation gasoline would be a significant logistical challenge, and in some cases a technical challenge as well." The EPA further said any phase-out plan for leaded avgas would require careful cooperation with the FAA. The EPA is soliciting comments on how best to consider any phase-out plan — both from technical and logistical grounds (storage and distribution of mixed leaded and unleaded fuels, for example). For example, the agency said it would not consider solutions that increased noise output or compromised safety.