Proposed Finding under Section 231 of the Clean Air Act 

that Greenhouse Gas Emissions from Aircraft Cause or 

Contribute to Air Pollution Which May Reasonably Be 

Anticipated to Endanger Public Health and Welfare, and

Advance Notice of Proposed Rulemaking 

Briefing for OMB

March 12, 2015

INTERNAL, DELIBERATIVE
Overview

• Rationale for Action under CAA§231

• Proposed Endangerment Finding under CAA§231

• Proposed Contribution Finding under CAA§231

• Advance Notice of Proposed Rulemaking (ANPR)

• Schedule

2 INTERNAL, DELIBERATIVE
Rationale for Regulatory Action

• Aircraft represent 11% of U.S. transportation GHGs 

– Largest remaining GHG-emitting transportation source not yet subject to any GHG 

regulations 

• The International Civil Aviation Organization (ICAO), at urging of U.S., began 

efforts to develop aircraft CO2 standard in 2010 (cited in President’s Climate 

Action Plan). Expected to finalize the standard in February 2016. 

• The Endangerment and Contribution Findings under§231(a) of the CAA are 

a necessary first step to potentially adopt equivalent aircraft engine CO2 

standards domestically, which is needed to meet our treaty obligations

• ANPR will enable more transparency of ICAO process and allow for public 

comment

• In addition, this proposal is responsive to the D.C. District Court for the 

District of Columbia’s 2011 ruling that §231(a) imposes a nondiscretionary 

duty to issue such findings and a 2007 petition requesting that the EPA 

regulate aircraft GHGs.

INTERNAL, DELIBERATIVE 3
Approach to Proposed Endangerment 

Finding under CAA§231

• Proposal lays out how the legal framework under §231 is essentially 

identical to §202, and that EPA’s interpretation of the CAA under§202, 

and EPA’s approach to utilizing the science, have been upheld in court.

• The Administrator’s proposed finding for purposes of§231 is made in 

light of the evidence, analysis, and conclusions that led to the 2009 

Endangerment Finding, as well as more recent evidence.

– Relying primarily on the extensive scientific and technical evidence in the record 

supporting the 2009 Endangerment Finding under CAA§202, including the major, 

peer-reviewed scientific assessments of the IPCC, USGCRP, and NRC.

– Proposal shows we have also considered new assessments released since 2009. 

These more recent assessments strengthen or provide further support for the science 

underlying the 2009 Endangerment Finding. 

• In proposing this finding for purposes of§231, we are not reopening or 

revising our prior findings under§202.

INTERNAL, DELIBERATIVE 4
Proposed Endangerment 

Finding under CAA§231

• Proposing to define the “air pollution” referred to in CAA§231 to be the 

mix of six well-mixed GHGs: carbon dioxide (CO2), methane, nitrous 

oxide, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur 

hexafluoride (SF6).

– This is the same definition that was used for purposes of§202. 

– More recent science continues to support this definition of the air pollution. 

• Proposing that the total body of scientific evidence compellingly supports a 

finding that elevated concentrations of the six well-mixed GHGs endanger 

both the public health and welfare of current and future generations within 

the meaning of CAA§231.

INTERNAL, DELIBERATIVE 5
Proposed Cause or Contribute 

Finding under CAA§231

INTERNAL, DELIBERATIVE 6

• Proposing to find that GHG emissions from certain classes of 

engines used in “covered aircraft”* contribute to the air pollution that 

endangers public health and welfare.

– * subsonic jet aircraft with a maximum takeoff mass (MTOM) greater 

than 5,7000 kilograms and subsonic propeller drive aircraft (e.g., 

turboprops) with a MTOM greater than 8,618 kilograms.

– Proposal lays out how this categorization ensures equivalent scope of 

applicability as ICAO (see next slide). 

• As was done under§202, our proposal compares U.S. aircraft 

emissions in both the domestic and global context to demonstrate 

“contribution.”
Larger 

Transport 

Jet 

Larger Turboprop 

Helicopters Military

Smaller Turboprop

Examples of Aircraft to be

Included in ICAO CO2 Standard

Examples of Aircraft to be 

Excluded from ICAO CO2 Standard

~90% 

of U.S. GHG 

emissions from 

aviation sector

~ 10% 

of U.S. GHG 

emissions from 

aviation sector

Proposed Cause or Contribute 

Finding under CAA§231
INTERNAL, DELIBERATIVE 8

• Aircraft sector contributes ~11% of 

U.S. transportation GHGs 

– Largest remaining transportation 

category not yet regulated for 

GHGs. 

– 3.2% of total U.S. GHG emissions 

(not pictured). Total transportation 

is about a third.

• The aircraft categories covered by 

ICAO comprise the vast majority of 

aviation sector GHG emissions (U.S. 

~ 90%).

Source: Inventory of U.S. GHG

Emissions and Sinks: 1990-2012

Proposed Cause or Contribute 

Finding under CAA§231
ANPR Discussion 

• ICAO is expected to finalize CO2 standards for aircraft in February 

2016.

– FAA serves as the U.S. representative at ICAO, and is active in the CO2

standards development work.

– EPA is also active in the ICAO working groups that are developing the 

standards.

• ICAO standards are not self-implementing, but rather must be 

implemented through domestic regulation.

• EPA, in consultation with FAA, has responsibility for issuing air 

pollution standards for aircraft engines under CAA§231. 

– We shared drafts of the ANPR with FAA beginning in December, and will 

continue to work with FAA (and other agencies) during the interagency 

process.

• FAA, under CAA§232, has responsibility to prescribe regulations to 

ensure compliance with the emissions standards.

INTERNAL, DELIBERATIVE 9
ANPR Discussion 

• The ANPR sets the stage for a future proposal for aircraft 

CO2 standards.

– It is anticipated that this would be the standards finalized by ICAO next year.

• Provides an overview on ICAO’s Committee on Aviation 

Environmental Protection (CAEP) progress to date on 

establishing aircraft CO2 standard.

– Timeline for finalizing in 2016.

– Decisions agreed to thus far by CAEP, such as the metric system and 

certification procedures for measuring CO2from aircraft.

• Solicits public comment on key aspects of a CO2 standard 

for aircraft.

– Applicability (new type vs. in-production)

– Timing and level of standards

INTERNAL, DELIBERATIVE 10
INTERNAL, DELIBERATIVE 11

Schedule

Milestones Date

Proposal Signature (following 90 day review) End of May, 2015

CAEP/ICAO Final Aircraft Standards February, 2016

Final Endangerment + Cause or

Contribute Rule 

Spring, 2016