1

Office of Transportation EPA420-F-05-015 

and Air Quality November 2005 

Regulatory

Announcement 

New Emission Standards for New 

Commercial Aircraft Engines 

The U.S. Environmental Protection Agency (EPA) is amending the 

existing emission standards for nitrogen oxides (NOx) for new 

commercial aircraft engines. These new standards are equivalent to the 

NOx emission standards (adopted in 1999 for implementation beginning 

in 2004) of the United Nations International Civil Aviation Organization 

(ICAO), and will bring the United States aircraft standards into alignment 

with the international standards. 

These standards will apply to new aircraft engines used on commercial 

aircraft including include small regional jets, single-aisle aircraft, twinaisle aircraft, and 747s and larger aircraft. The standards can also apply 

to general aviation and military aircraft, which sometimes use 

commercial engines. For example, small regional jet engines are also 

used in executive general aviation aircraft, and larger commercial 

aircraft engines may also be used in military transport aircraft. 

Emissions From Aircraft Engines 

Aircraft engines contribute about 1 percent of the total U.S. mobile source 

NOx emissions. However, in some U.S. airport areas, aircraft currently can 

contribute up to 4 percent of mobile source NOx emissions. Commercial 

aircraft emissions are a growing segment of the transportation emissions 

inventory. This growth is occurring at a time when other significant mobile and 

stationary sources are drastically reducing emissions, thereby accentuating the 

growth in aircraft emissions. Recently, the Federal Aviation Administration 
(FAA) reported that flights of commercial air 

carriers will increase by 9 percent from 2002 

to 2010 and 34 percent from 2002 to 2020. 

Health and Environmental 

Concerns 

NOx emissions are a precursor to the formation of ground-level ozone, also called smog. 

Ozone affects human pulmonary and respiratory health. Also, NOx reacts in the atmosphere to form secondary particulate matter 

(PM2.5), which causes detrimental health 

effects. In addition, NOx, ozone, and PM 

adversely affect the environment in various 

ways including visibility impairment, crop 

damage, and acid rain. 

To protect public health and the environment, 

EPA has established National Ambient Air 

Quality Standards (NAAQS) for several air 

pollutants, including ozone and PM. Recent air 

quality data show that about 159 million 

people live in areas that violate air quality 

standards for ground-level ozone. About 88 

million people live in areas that violate air 

quality standards for PM2.5. Because aircraft 

emissions contribute to increases in these air 

pollutants, the aircraft engine standards may 

help states achieve and/or maintain compliance 

with the NAAQS. 

History of EPA’s Regulation of 

Aircraft Engine Emissions 

The aircraft emission standards have been in 

place for about 30 years and essentially apply 

to all commercial aircraft. Over the years, 

emission standards have been set for different 

aspects of aircraft engines: 

• in 1974 for engine smoke (revised 

several times since) and fuel venting 

• in 1984 for hydrocarbon emissions 

• in 1997 for NOx and carbon monoxide 

• in 2005 for additional NOx emission 

standards included in this rulemaking 

EPA’s Participation in ICAO 

EPA has historically worked with the FAA and 

ICAO in the development of international 

aircraft emission standards. The FAA is responsible for enforcing the aircraft emissions standards established by EPA. ICAO was established by the United Nations to ensure safety, 

equality, and consistency among international air 

transport services. One of ICAO’s objectives is 

to lead international bodies in the development 

of standards and procedures for aircraft engines. The United States is one of 188 participating member States. Under the basic ICAO 

treaty established in 1944, a participating nation 

that elects not to adopt the standards must 

provide a written explanation describing why a 

given standard is impractical to comply with or 

not in its national interest. As long as a participating nation adopts aircraft emission standards 

that are equal to or more stringent than ICAO’s 

standards, it satisfies its obligations under 

ICAO. In this rulemaking, EPA adopts standards equivalent to the ICAO standards. 

Main Components of the Rule 

This rulemaking will codify into United States 

law requirements equivalent to ICAO’s February 1999 NOx emission standards and March 

1997 test procedure amendments. The new 

NOx standards generally represent about a 16 

percent reduction (or increase in stringency) 

2
from the existing NOx standards. These 

emission standards will apply to those commercial aircraft engines with rated thrust greater 

than 26.7 kilonewtons (kN) that are newly 

certified (and designed) after the effective date 

of the regulations – 30 days after the date of 

publication of this rulemaking in the Federal

Register. 

Benefits of Adopting ICAO 

Standards 

This rule will establish consistency between 

U.S. and international emission standards and 

test procedures. Because aircraft engines are 

international commodities, there is a commercial benefit to consistency between U.S. and 

international emission standards and control 

program requirements. It will be easier for 

manufacturers to certify products for international markets because the United States can 

certify engines for ICAO compliance. Emission 

certification tests meeting U.S. requirements 

will also be applicable to all ICAO requirements. In addition to the economic benefit, this 

rule will ensure that domestic commercial 

aircraft will meet the current ICAO standards, 

and thus, the public will be assured they are 

receiving the air quality benefits of the international standards. 

Nearly all previously certified or in-production 

engine models currently meet or perform better 

than the standards EPA is adopting in this 

rulemaking. In addition, manufacturers have 

already been developing improved technology 

in response to the ICAO standards. Therefore, 

there are no additional costs that will be 

incurred by the aircraft industry as a result of 

this rule. In addition, the test procedures 

necessary to determine compliance are already 

being adhered to by manufacturers during 

current engine certification tests. Thus, the 

regulations will impose no additional burden on 

manufacturers. 

For More Information 

You can access the final rulemaking 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, please contact EPA at: 

U.S. Environmental Protection Agency 

Assessment and Standards Division 

2000 Traverwood Drive 

Ann Arbor, MI 48105 

Voice-mail: (734) 214-4636 

E-mail: asdinfo@epa.gov 

3