This rulemaking follows on the EPA's final endangerment and cause or contribute findings for aircraft GHG emissions, which was published on August 15, 2016 (81 FR 54422). As a result of these positive findings, the EPA is obligated under section 231 of the Clean Air Act to set emission standards applicable to GHG emissions from the classes of aircraft engines used in certain types of aircraft covered in the finding. The International Civil Aviation Organization (ICAO) adopted international aircraft CO2 standards in 2017, and the EPA anticipates adopting domestic GHG standards that would be at least as stringent as ICAO's standards.