EPA has issued a proposed rule that would establish nitrogen oxides emission standards for aircraft gas turbine engines. Released on July 6, 2011, and endorsed by the United Nations Civil Aviation Association, the proposed standards would apply to gas turbine engines with rated thrusts greater than 26.7 kilonewtons and used in commercial passenger and freight aircraft, including 737s, 747s and 767s.

The proposal would set two tiers of emission standards, known as Tier 6 and Tier 8. Engine models certified before the rule’s effective date could continue to be produced through December 2012, after which they would have to comply with the Tier 6 standards. Engine models certified after the rule’s effective date but before December 2013 would also be required to comply with the Tier 6 standards. Engine models certified after January 2014 would have to comply with Tier 8 standards. EPA will accept comments for 60 days after publication in the Federal Register.