Office of Transportation and Air Quality

EPA-420-F-11-019

July 2011

EPA Proposed NOx Emission 

Standards for Aircraft Gas Turbine 

Engines 

The U.S. Environmental Protection Agency (EPA) is publishing 

a proposed rulemaking to adopt the NOx emission standards 

approved by the United Nation’s International Civil Aviation 

Organization (ICAO). 

Overview

EPA is proposing to adopt emission standards and related provisions for aircraft gas 

turbine engines with rated thrusts greater than 26.7 kilonewtons. These engines are 

used primarily on commercial passenger and freight aircraft. The proposal contains 

standards and related provisions that were either previously adopted by ICAO, or 

agreed on at ICAO’s Committee on Aviation Environmental Protection (CAEP) in 

2010. Specifically, EPA is proposing two new tiers of more stringent emission standards for oxides of nitrogen (NOx). These are referred to as the Tier 6 (or CAEP/6) 

standards and the Tier 8 (or CAEP/8) standards. 

The proposed standards would apply differently depending on the date the engine 

model received its original airworthiness certificate as follows. 

•	 Engine models that were originally certificated prior to the effective date of 

the proposed rule may continue production without meeting the proposed 

Tier 6 standards through December 31, 2012. After that date, these engines 

must comply with the proposed Tier 6 standards (this date is generally referred 

to as the Tier 6 production cutoff). This delay in complying with the proposed 

Tier 6 standards for previously certificated engine models is intended to allow 

for an orderly transition to the proposed Tier 6 standards. 

•	 Engine models that were originally certificated between the effective date of 

the proposed rule and December 31, 2013 must comply with the proposed 

Tier 6 standards. 

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•	 Engine models that were originally certificated beginning on or after January 1, 2014 

must comply with the proposed Tier 8 standards. EPA anticipates establishing a future 

production cutoff to require all engine models that were originally certificated before 

the above date to comply with the proposed Tier 8 standards.  We will consider this in a 

future action after first pursuing it within ICAO/CAEP. 

EPA is also proposing several additional changes that would affect all aircraft gas turbine engines 

that are subject to current emission requirements. First, EPA is proposing to clarify when a 

design variation of a previously certified engine model causes the emission characteristics of the 

new version to become different enough from its parent engine that it must conform to the most 

current emissions standards. Second, EPA is proposing amendments to the emission measurement procedures. These revisions are primarily intended to reflect current certification practices. 

Finally, EPA is proposing to require all gas turbine and turboprop engine manufacturers to report 

to EPA, emission data and other information necessary for the purpose of conducting emission 

analyses and developing appropriate public policy for the aviation sector.

These proposed regulatory requirements, except a portion of the proposed engine manufacturer 

reports, have already been adopted or are actively under consideration by the ICAO. The proposed requirements are consistent with the United Nations Convention on International Civil 

Aviation. 

Public Participation Opportunities 

Comments will be accepted for 60 days after the date that the proposal is published in the Federal 

Register. All comments should be identified by Docket ID No. EPA-HQ-OAR-2010-0142 and 

submitted by one of the following methods:

Internet: www.regulations.gov

E-mail: a-and-r-Docket@epa.gov

Mail: 

Environmental Protection Agency

Mail Code 2822T

1200 Pennsylvania Avenue NW

Hand Delivery: 

U.S. Environmental Protection Agency

EPA Headquarters Library

EPA West Building

Room 3334

1301 Constitution Avenue NW

Washington, DC 
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For More Information

You can access the rule and related documents on EPA’s Office of Transportation and Air 

Quality (OTAQ) Web site at: 

www.epa.gov/otaq/aviation.htm

For more information on this proposal, please contact the Assessment and Standards 

Division at: 

Voice-mail: (734) 214-4636 

E-mail: asdinfo@epa.gov 

Mail:

U.S. Environmental Protection Agency

Assessment and Standards Division 

Office of Transportation and Air Quality 

2000 Traverwood Drive 

Ann Arbor, MI 48105