ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 87 and 1068
[EPA-HQ-OAR-2010-0687; FRL-XXXX-X]
RIN 2060-AO70
Control of Air Pollution From Aircraft and Aircraft Engines; Emission Standards and Test Procedures
AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.
SUMMARY:  EPA is adopting several new aircraft engine emission standards for oxides of nitrogen (NOx), compliance flexibilities, and other regulatory requirements for aircraft turbofan or turbojet engines with rated thrusts greater than 26.7 kilonewtons (kN).  We also are adopting certain other requirements for gas turbine engines that are subject to exhaust emission standards as follows.  First, we are clarifying when the emission characteristics of a new turbofan or turbojet engine model have become different enough from its existing parent engine design that it must conform to the most current emission standards.  Second, we are establishing a new reporting requirement for manufacturers of gas turbine engines that are subject to any exhaust emission standard to provide us with timely and consistent emission-related information.  Third, and finally, we are establishing amendments to aircraft engine test and emissions measurement procedures.  EPA actively participated in the United Nation's International Civil Aviation Organization (ICAO) proceedings in which most of these requirements were first developed.  These regulatory requirements have largely been adopted or are actively under consideration by its member states.  By adopting such similar standards, therefore, the United States maintains consistency with these international efforts.
EXECUTIVE SUMMARY:
A.  Purpose of the Regulatory Action
The primary purpose of this rule is to adopt new oxides of nitrogen (NOx) emission standards for aircraft engines with rated thrusts greater than 26.7 kN thrust.  These are mostly commercial passenger and freighter aircraft in common use at airports across the U.S.  It does not include engines used on military aircraft. NOx is strongly correlated with NO2, for which EPA has established National Ambient Air Quality Standards, i.e., a criteria pollutant, and it is an important precursor gas in the formation of tropospheric ozone and secondary particulate matter which are common air pollutants in urban areas where airports are located.  This rule also contains several provisions to facilitate the implementation of EPA's aircraft engine emission regulations and related requirements.  It is also important to note that adoption of the provisions in this rule meets U.S. treaty obligations under the Chicago Convention of 1944 by aligning our regulations with those in the International Civil Aviation Organization Annex 16, Volume II (adopted in 2010) that the U.S. helped to develop and support as part of the international process.  This rule is being implemented under the authority provided in section 231 of the Clean Air Act (42 USC 7571).
B.  Summary of Major Provisions of the Regulatory Action
The rule contains six major provisions. The first two provisions are new NOx emission standards for newly certified engine models. The first standards, Tier 6, take effect when this rule becomes effective.  These represent approximately a 12 percent reduction from current Tier 4 levels. They were actually adopted by ICAO in 2005 with an implementation date in 2008.  The second, Tier 8, takes effect in 2014.  These represent approximately a 15 percent reduction from Tier 6 levels.  Both tiers of emission standards are needed to address local air quality concerns and, as noted above, to meet U.S. treaty obligations under the Chicago Convention.  The third major provision is a production cut-off for newly manufactured engines (as opposed to certified) which basically requires that after December 31, 2012 all newly manufactured engines must meet at least Tier 6 NOx emission standards. This is also consistent with our obligations under the Chicago Convention.  The production cut-off is needed to ensure that the emission reductions envisioned by the emission standards are achieved on new production engines. The fourth major provision is related to potential exemptions or exceptions to the production cut-off requirement.  These include revised provisions allowing manufacturers to request that FAA in consultation with EPA grant exemptions from the production cut-off for a designated number of engines within a prescribed time frame.  These also include a low-volume, time-limited exception provision that will exclude several engines from the production cutoff.   Both of these provisions help to assure an orderly transition to the new standards for engines needing more time to comply or for a few engines at the end of their production life.  Finally, the rule includes a set of provisions which may be considered as minor if viewed separately, but collectively are important in upgrading EPA's regulations by incorporating some related agreements from our ICAO process and clarifying and improving existing provisions.  Examples of this include special provisions for spare engines, provisions related to derivative engine models, test procedure specifications and reporting requirements.  These changes are important for an effective implementation of the new requirements.
C.  Costs and Benefits
This is not an economically significant regulatory action. Aircraft engines are international commodities used on aircraft manufactured and sold around the world. When developing new engine models manufacturers not only consider current emission requirements but also try to anticipate the stringency of future standards and respond appropriately.  Engine manufacturers participated in the deliberations leading up to ICAO decisions on the aircraft engine NOx emission standards and after the ICAO decisions they incorporated engine technology changes as needed to meet the new ICAO requirements.  This helps to ensure the world wide acceptability of their products. Essentially all of these changes are now complete.  Thus, while there is some cost to a manufacturer for responding to the new ICAO provisions, there is no significant further direct cost to the manufacturers created by EPA's adopting the requirements into U.S regulations. In fact, it is likely that our adopting these requirements facilitates the acceptance of U.S. type certificates by aircraft manufacturers and airlines around the world.   Since the majority of engine models slated for future production met the new emission standards when adopted by ICAO the emission gains are modest.  EPA projects that landing and takeoff cycle NOx emissions will be reduced by about 100,000 tons between 2014 and 2030.
DATES: These final rules are effective on [insert date 30 days after publication in the Federal Register.]  The incorporation by reference of certain publications listed in this regulation is approved by the Director of the Federal Register as of [insert date 30 days after publication in the Federal Register.]
ADDRESSES:  EPA has established a docket for this action under Docket ID No. EPA-HQ-OAR-2010-0687.  All documents in the docket are listed on the http://www.regulations.gov Web site.  Although listed in the index, some information is not publicly available, e.g., confidential business information or other information whose disclosure is restricted by statute.  Certain other material, such as copyrighted material, is not placed on the Internet and will be publicly available only in hard copy form.  Publicly available docket materials are available electronically through http://www.regulations.gov or in hard copy at the EPA Docket Center, EPA/DC, EPA West, Room 3334, 1301 Constitution Ave., NW, Washington, DC.  The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays.  The telephone number for the Public Reading Room is<PHONE_NUMBER>, and the telephone number for the Air Docket is<PHONE_NUMBER>.
FOR FURTHER INFORMATION CONTACT:  Richard Wilcox, Office of Transportation and Air Quality, Office of Air and Radiation, Environmental Protection Agency, 2000 Traverwood Drive, Ann Arbor, MI 48105; telephone number:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>; email address<EMAIL_ADDRESS>SUPPLEMENTARY INFORMATION:
     Does This Action Apply to Me?
Entities potentially regulated by this action are those that manufacture and sell aircraft engines and aircraft in the United States.  Regulated categories include:
Category
NAICS[a] Codes
SIC[b] Codes
Examples of potentially affected entities
Industry
336412
3724
Manufacturers of new aircraft engines
Industry
336411
3721
Manufacturers of new aircraft
 [a] North American Industry Classification System (NAICS) [b] Standard Industrial Classification (SIC) system code
This table lists the types of entities that EPA is now aware could potentially be regulated by this action.  Other types of entities not listed in the table could also be regulated.  To determine whether your activities are regulated by this action, you should carefully examine the applicability criteria in 40 CFR 87.1 (part 87).  If you have any questions regarding the applicability of this action to a particular entity, consult the person listed in the preceding FOR FURTHER INFORMATION CONTACT section.
Table of Contents
I.  Overview and Background
	A.  Contents of the Final Rule
	B.  EPA's Responsibilities Under the Clean Air Act
 	C.  Interaction with the International Community
	D.  Brief History of EPA's Regulation of Aircraft Engine Emissions
	E.  Brief History of ICAO Regulation of Aircraft Engine Emissions
II.  Why is EPA Taking this Action?
	A.  Inventory Contribution
	B.  Health, Environmental and Air Quality Impacts
		1.  Background on Ozone, PM and NOx
			a.  What is Ozone?
			b.  What is Particulate Matter?
			c.  What is NOx?
		2.  Health Effects Associated with Exposure to Ozone, PM and 					NOx
			a.  What are the Health Effects of Ozone?
			b.  What are the Health Effects of PM?
			c.  What are the Health Effects of NOx?
		3.  Environmental Effects Associated with Exposure to Ozone, PM 				and NOx
			a.  Deposition of Nitrogen
			b.  Visibility Effects
			c.  Plant and Ecosystem Effects of Ozone
		4.  Impacts on Ambient Air Quality
III.  Details of the Final Rule
	A.  NOx Standards for Newly-Certified Engines
		1.  Tier 6 NOx Standards for Newly-Certified Engines
			a.  Numerical Emission Limits for Higher Thrust Engines
			b.  Numerical Emission Limits for Lower Thrust Engines
	2.  Tier 8 NOx Standards for Newly-Certified Engines
			a.  Numerical Emission Limits for Higher Thrust Engines
			b.  Numerical Emission Limits for Lower Thrust Engines
	B.  Application of NOx Standards for Newly-Manufactured Engines
 		1.  Phase-In of the Tier 6 NOx Standards for Newly-						Manufactured Engines
		2.  Carryover of Previously Generated Emission Data
		3. Exemptions and Exceptions from the Tier 6 Production Cutoff
			a.  New Provisions for Spare Engines
			b.  New Provisions for Engines Installed in New Aircraft
				i.  Time-Frame and Scope
				ii.  Production Limit
				iii.  Exemption Requests
				iv.  Coordination of Exemption Requests
				v.  Low-Volume, Time-Limited Transitional Exception program
			c.  Voluntary Emission Offsets
		4.  Potential Phase-In of New Tier 8 NOx Standards for Newly-					Manufactured Engines
	C.  Application of Standards for Derivative Engines for Emission 					Certification Purposes
	D.  Annual Reporting Requirement
	E.  Standards for Supersonic Aircraft Turbine Engines
	F.  Amendments to Test and Measurement Procedures
	G.  Possible Future Revisions to Emission Standards for New Technology 				Turbine Engines and Supersonic Aircraft Turbine Engines
IV.  Description of Other Revisions to the Regulatory Text
		A.  Applicability Issues
			1.  Military Engines
			2.  Noncommercial Engines
		B.  Non-Substantive Revisions
	C.  Clarifying Language for Regulatory Text
V.  Technical Feasibility, Costs, and Emission Benefits
VI.  Consultation with FAA
VII.  Public Participation
VIII.  Statutory Provisions and Legal Authority
IX.  Statutory and Executive Orders Review
	A.  Executive Order 12866: Regulatory Planning and Review, and Executive 			   Order 13563: Improving Regulation and Regulatory Review
	B.  Paperwork Reduction Act
	C.  Regulatory Flexibility Analysis
	D.  Unfunded Mandates Reform Act
	E.  Executive Order 13132: Federalism
	F.  Executive Order 13175: Consultation and Coordination with Indian 				Tribal Governments
	G.  Executive Order 13045: Protection of Children from Environmental 				Health & Safety Risks
	H.  Executive Order 13211: Actions that Significantly Affect Energy 				Supply, Distribution, or Use
	I.   National Technology Transfer Advancement Act
	J.  Executive Order 12898: Federal Actions to Address Environmental Justice in 	  		Minority Populations and Low Income Populations
	K.  Congressional Review Act
I.  Overview and Background
This section summarizes the major provisions of the final rule for aircraft gas turbine engines.  It also contains background on the EPA's standard setting authority and responsibilities under the Clean Air Act, the connection between our emission standards and those of the international community, and a brief regulatory history for this source of emissions.
Contents of the Final Rule
We are adopting several new emission standards and other regulatory requirements for aircraft turbofan and turbojet engines with rated thrusts greater than 26.7 kilonewtons (kN).  First, we are establishing two new tiers of more stringent emission standards for oxides of nitrogen (NOx).  The standards apply differently to two classes of these engines, i.e., "newly-certified engines" and "newly-manufactured engines."  The newly-certified engine standards apply to aircraft engines that have received a new type certificate and have never been manufactured prior to the effective date of the new emission standards.  Requirements for newly-manufactured engines apply to aircraft engines that were previously certified and manufactured in compliance with preexisting standards, and they require manufacturers to either comply with the newer standards by a specified future date or cease production of the affected engine models.  Newly-manufactured engine standards are also sometimes referred to as "production cutoff" standards.  Second, we are adopting certain time-limited flexibilities, i.e., the potential for exemptions or exceptions as defined in the regulations for newly-manufactured engines that may not be able to comply with the first tier of the NOx standards because of specific technical or economic reasons.
We are also making a number of additional changes that would apply to a wider range of aircraft gas turbine engines than those that would be subject to the new emission standards.  First, we are defining the meaning of a derivative engine for emissions certification purposes.  The intent of this definition is to distinguish when the emission characteristics of a new turbofan engine model vary sufficiently from its existing parent engine design, and must show compliance with the emission standard for a newly-certificated engine.  Second, we are establishing new reporting requirements for manufacturers that produce gas turbine engines subject to any exhaust emission standard.  This will provide us with timely and consistent emission data and other information that is necessary to conduct emission inventory and air quality analyses and develop appropriate public policy for the aviation sector.  Specifically, reports are required for turbofan engines with rated thrusts greater than 26.7 kN, which are subject to gaseous emission and smoke standards, in addition to turbofans less than or equal to 26.7 kN, and all turboprop engines, that are only subject to smoke standards.  Third, we are adopting minor amendments to the test and measurement procedures for aircraft engines.  Finally, as described in section IV, we are making minor amendments to regulator provisions addressing definitions, acronyms and abbreviations, general applicability and requirements, exemptions, and incorporation by reference.
Most of these new regulatory requirements have already been adopted by the United Nation's International Civil Aviation Organization (ICAO).  The requirements contained in this final rule bring the United States into alignment with the international standards and recommended practices.
EPA's Authority and Responsibilities under the Clean Air Act
Section 231(a)(2)(A) of the Clean Air Act (CAA) directs the Administrator of EPA to, from time to time, propose aircraft engine emission standards applicable to the emission of any air pollutant from classes of aircraft engines which in her judgment causes or contributes to air pollution that may reasonably be anticipated to endanger public health or welfare.  (See 42 U.S.C. § 7571(a)(2)(A).)  Section 231(a)(2)(B) directs EPA to consult with the Administrator of the Federal Aviation Administration (FAA) on such standards, and prohibits EPA from changing aircraft emission standards if such a change would significantly increase noise and adversely affect safety.  42 U.S.C. § 7571(a)(2)(B)(i)-(ii).  Section 231(a)(3) provides that after we propose standards, the Administrator shall issue such standards "with such modifications as he deems appropriate."  42 U.S.C. § 7571(a)(3).  The U.S. Court of Appeals for the D.C. Circuit has held that this provision confers an unusually broad degree of discretion on EPA to adopt aircraft engine emission standards as the Agency determines are reasonable.  NACAA v. EPA, 489 F.3d 1221 (D.C. Cir. 2007).
In addition, under CAA section 231(b) EPA is required to ensure, in consultation with the U.S. Department of Transportation (DOT), that the effective date of any standard provides the necessary time to permit the development and application of the requisite technology, giving appropriate consideration to the cost of compliance.  42 U.S.C. § 7571(b).  Section 232 then directs the FAA to prescribe regulations to ensure compliance with EPA's standards.  42 U.S.C. § 7572.  Finally, section 233 of the CAA vests the authority to promulgate emission standards for aircraft or aircraft engines only in EPA.  States are preempted from adopting or enforcing any standard respecting aircraft engine emissions unless such standard is identical to EPA's standards. 42 U.S.C. § 7573.  Section VI of today's final rule further discusses our coordination with DOT through the FAA.   It also describes DOT's responsibility under the CAA to enforce the aircraft emission standards established by EPA.
Interaction with the International Community
We began regulating the air pollution emissions from aircraft engines in 1973.  Since that time, we have worked with the FAA and later with the International Civil Aviation Organization (ICAO) to develop international standards and other recommended practices pertaining to aircraft engine emissions.  ICAO was established in 1944 by the United Nations (by the Convention on International Civil Aviation, the "Chicago Convention") "... in order that international civil aviation may be developed in a safe and orderly manner and that international air transport services may be established on the basis of equality of opportunity and operated soundly and economically."  ICAO's responsibilities include developing aircraft technical and operating standards, recommending practices, and generally fostering the growth of international civil aviation.  The United States is currently one of 191 participating member States of ICAO.[,]
In the interests of global harmonization and international air commerce, the Chicago Convention urges a high degree of uniformity by its member States.  Nonetheless, the Convention also recognizes that member States may adopt their own unique airworthiness standards and that some may adopt standards that are more stringent than those agreed upon by ICAO.
The Convention has a number of other features that govern international commerce.  First, States that wish to use aircraft in international transportation must adopt emission standards and other recommended practices that are at least as stringent as ICAO's standards.  States may ban the use of any aircraft within their airspace that does not meet ICAO standards.   Second, States are required to recognize the airworthiness certificates of any State whose standards are at least as stringent as ICAO's standards, thereby assuring that aircraft of any member State will be permitted to operate in any other member State.  Third, and finally, to ensure that international commerce is not unreasonably constrained, a participating nation which elects to adopt more stringent standards is obligated to notify ICAO of the differences between its standards and ICAO standards.    However, if a nation sets tighter standards than ICAO, air carriers not based in that nation would only be required to comply with ICAO standards or more stringent standards imposed by their own nations, if applicable.
ICAO's Committee on Aviation Environmental Protection (CAEP) undertakes ICAO's technical work in the environmental field.  The Committee is responsible for evaluating, researching, and recommending measures to the ICAO Council that address the environmental impact of international civil aviation.  CAEP is composed of various task groups, work groups, and other committees whose contributing members include atmospheric, economic, aviation, environmental, and other professionals interested in aviation and environmental protection.  At CAEP meetings, the United States is represented by the FAA, which plays an active role at these meetings.  EPA has historically been a principal participant in the development of U.S. policy in various ICAO/CAEP working groups and other international venues, assisting and advising FAA on aviation emissions, technology, and policy matters.  If ICAO adopts a CAEP proposal for a new environmental standard, it then becomes part of ICAO standards and recommended practices (Annex 16 to the Chicago Convention).
Brief History of EPA's Regulation of Aircraft Engine Emissions
As mentioned above, we initially regulated gaseous exhaust emissions, smoke, and fuel venting from aircraft engines in 1973.  Since that time, we have occasionally revised those regulations.  Two of these revisions are most pertinent to today's final rule.  First, in a 1997 rulemaking, we made our emission standards and test procedures more consistent with those of ICAO for turbofan engines used in commercial aviation with rated thrusts greater than 26.7kN.    These ICAO requirements are generally referred to as CAEP/2 standards.  (The numbering nomenclature for CAEP requirements is discussed in the next section.)  That action included new NOx emission standards for newly-manufactured commercial turbofan engines (those engines built after the effective date of the regulations that were already certified to pre-existing standards)  and for newly-certified commercial turbofan engines (those engine models that received their initial type certificate after the effective date of the regulations).  It also included a CO emission standard for newly-manufactured commercial turbofan engines.  Second, in our most recent rulemaking in 2005, we promulgated more stringent NOx emission standards for newly-certified commercial turbofan engines.  That final rule brought the U.S. standards closer to alignment with ICAO CAEP/4 requirements that were effective in 2004.  In ruling on a petition for judicial review of the 2005 rule filed by the National Association of Clean Air Agencies (NACAA), the U.S. Court of Appeals held that EPA's approach of tracking the ICAO standards was reasonable and permissible under the CAA.  NACAA v. EPA, 489 F.3d 1221, 1230-32 (D.C. Cir. 2007).
Brief History of ICAO Regulation of Aircraft Engine Emissions
The first international standards and recommended practices for aircraft engine emissions was recommended by CAEP's predecessor, the Committee on Aircraft Engine Emissions (CAEE), and adopted by ICAO in 1981.  These standards limited aircraft engine emissions of HC, CO, and NOx.  In 1994, ICAO adopted a CAEP/2 proposal to tighten the original NOx standard by 20 percent and amend the test procedures.  At the next CAEP meeting (CAEP/3) in 1995, the Committee recommended a further tightening of 16 percent and additional test procedure amendments, but in 1997 the ICAO Council rejected this stringency proposal and approved only the test procedure amendments.  At the CAEP/4 meeting in 1998, the Committee adopted a similar 16 percent NOx reduction proposal, which ICAO approved on 1998.  The CAEP/4 standards applied only to new engine designs certified after December 31, 2003 (i.e., the requirements did not also apply to previously certified, newly-manufactured engines unlike the CAEP/2 standards).  In 2004, CAEP/6 recommended a 12 percent NOx reduction, which ICAO approved in 2005. [,]  The CAEP/6 standards applied to new engine designs (newly-certified models) certified after December 31, 2007.  At the most recent meeting, CAEP/8 recommended a further tightening of the NOx standards by 15 percent for newly-certified engines.[,]  The Committee also recommended that the CAEP/6 standards be applied to newly-manufactured engines.  ICAO approved these recommendations in 2011.
II. Why Is EPA Taking This Action?
As mentioned above, section 231(a)(2)(A) of the CAA authorizes the EPA Administrator to "from time to time, issue proposed emission standards applicable to the emission of any air pollution from any class or classes of aircraft or aircraft engines which in his judgment causes, or contributes to air pollution which may reasonably be anticipated to endanger public health or welfare."  42 U.S.C. § 7571(a)(2)(A).
One of the principal components of aircraft exhaust emissions is NOx, a precursor to the formation of tropospheric ozone and secondary PM.  Most commercial airports are located in urban areas and many of these areas have ambient pollutant levels above the National Ambient Air Quality Standards (NAAQS) for ozone and fine particulate matter (PM 2.5) (i.e., they are in nonattainment for ozone and PM 2.5).  This section discusses the contribution of aircraft engines used in commercial service with rated thrusts greater than 26.7kN to the national NOx emissions inventory and to NOx emission inventories in selected ozone nonattainment areas, the potential effect of NOx emissions in the upper atmosphere on ground level PM 2.5 in addition to the health and welfare impacts of NOx and PM emissions.
A.  Inventory Contribution
In contrast to all other mobile sources, whose emissions occur completely at ground level, the emissions from aircraft and aircraft engines can be divided into two flight regimes.  The first regime includes the emissions that are released in the lower layer of the atmosphere and directly affect local and regional ambient air quality.  These emissions generally occur at or below 3,000 feet above ground level, i.e., during the landing and takeoff (LTO) cycle.  The aircraft operations that comprise an LTO cycle are: engine idle at the terminal gate (and sometimes during ground delays while holding for the active runway); taxiing between the terminal and the runway; take-off; climb-out; and approach to the airport.  The second regime includes emissions that occur above 3,000 feet above ground level, known as non-LTO emissions.  Collectively, the emissions associated with all ground and flight operations are generally referred to as full flight emissions.
In this section, we will discuss NOX emission inventories for commercial turbine-engine aircraft, both nationally and for selected ozone nonattainment areas (NAAs).  These inventories reflect emissions during the landing and takeoff cycle only.  The most recent comprehensive analysis of historical and current LTO emissions from aircraft engines comes from a study undertaken for us by Eastern Research Group (ERG).   The study analyzed the national emissions of commercial aircraft operations in the United States, and showed that in the most recent year studied (2008), such aircraft LTO operations contributed about 97 thousand tons to the national NOX inventory.  A summary of the national inventory of LTO NOX emissions is shown in Table 1.
When these nationwide LTO emissions are compared to the total U.S. mobile source inventory for 2009, they account for less than one percent of the total.  However, such a comparison may be a bit misleading, as it only includes those aircraft emissions that occur below 3,000 feet altitude, while comparing them to the entirety of other mobile source emissions.  In the U.S., LTO emissions account for only about ten percent of full flight NOX emissions.  When considering full flight aircraft emissions (i.e., including both LTO and non-LTO emissions), the contribution of aircraft to the total mobile source NOX inventory is approximately 7.7 percent.  It is also worth noting that these LTO emissions are more localized in that they occur near airports, which are mostly within urban areas.
Table 1: Current National NOX Emissions from Commercial Aircraft
Aircraft Category
                        2008 Total NOX (thousand tons)
Air Carrier
                                      86
Commuter/Air Taxi
                                      11
Total Commercial
                                      97

In addition, it is important to assess the contribution of commercial aircraft LTO NOX emissions on a local level, especially in areas containing or adjacent to airports.  The historical analysis conducted by ERG also included an assessment of selected ozone nonattainment areas (NAAs).   The NAAs selected for study were chosen as follows.  First, the 25 ozone NAAs with airports which had high commercial traffic volumes were identified.  Second, the 25 ozone NAAs with the largest population were identified.  These lists were combined.  However, there was some overlap, and this led to a total of 40 NAAs being identified for the study.  These NAAs collectively include 200 airports, accounting for about 70 percent of commercial air traffic operations.  Current (2008) and projected (2020) NOX emissions for these 40 NAAs, as well as the percent contribution of aircraft to total mobile source inventories (as compared to 2005 and 2020 mobile source inventories), are shown in Table 2.[,]  The relative contribution of aircraft in any given NAA varies based on activity in other transportation and industrial sectors.   As can be seen from this table, expected growth in aircraft operations in many of these areas combined with anticipated reductions in NOX emissions from other mobile source categories results in the growth of the relative contribution of aircraft LTO emissions to mobile source NOX emissions in NAAs.

     Table 2: Current NOX Emissions in Selected Ozone Nonattainment Areas
Nonattainment Area
                             2008 Total NOX (tons)
                  2008 Aircraft Percent of Mobile Source NOX
                  2020 Aircraft Percent of Mobile Source NOX
Albuquerque, NM
                                      380
                                      1.6
                                      4.3
Anchorage, AK
                                     2,538
                                     23.4
                                     49.3
Aspen
                                      16
                                      2.0
                                      6.6
Atlanta, GA
                                     5,808
                                      2.6
                                      8.2
Baltimore, MD
                                     1,148
                                      1.3
                                      4.4
Boston- including MA and NH NAAs
                                     2,032
                                      1.0
                                      2.7
Charlotte-Gastonia-Rock Hill, NC-SC
                                     1,917
                                      2.6
                                     10.0
Chicago-Gary-Lake County, IL-IN
                                     6,007
                                      1.8
                                      5.0
Cincinnati-Hamilton, OH-KY-IN
                                     1,287
                                      1.5
                                      3.3
Cleveland-Akron-Lorain, OH
                                      680
                                      0.5
                                      1.3
Dallas-Fort Worth, TX
                                     3,880
                                      1.7
                                      6.9
Denver-Boulder-Greeley-Fort Collins-Loveland, CO
                                     2,649
                                      2.5
                                      7.1
Detroit-Ann Arbor, MI
                                     2,312
                                      1.1
                                      3.0
El Paso, TX
                                      223
                                      0.9
                                      1.1
Greater Connecticut, CT
                                      405
                                      0.8
                                      2.4
Houston-Galveston-Brazoria, TX
                                     3,045
                                      1.3
                                      3.4
Indianapolis, IN
                                     1,089
                                      1.4
                                      3.0
Las Vegas, NV
                                     2,308
                                      6.0
                                     15.8
Los Angeles South Coast Air Basin, CA
                                     6,479
                                      1.5
                                      4.5
Louisville, KY-IN
                                     1,211
                                      1.9
                                      6.2
Memphis, TN-AR
                                     2,988
                                      6.3
                                     16.8
Milwaukee-Racine, WI
                                      557
                                      0.9
                                      3.2
Minneapolis-St Paul, MN
                                     2,154
                                      1.0
                                      5.1
New York-N. New Jersey-Long Island, NY-NJ-CT
                                    10,093
                                      2.3
                                      6.3
Philadelphia-Wilmington-Atlantic City, PA-NY-MD-DE
                                     2,308
                                      1.0
                                      2.8
Phoenix-Mesa, AZ
                                     2,298
                                      1.4
                                      3.3
Pittsburgh-Beaver Valley, PA
                                      480
                                      0.5
                                      1.1
Providence (entire State), RI
                                      232
                                      1.0
                                      2.3
Raleigh-Durham-Chapel Hill, NC
                                      565
                                      1.0
                                      3.2
Reno, NV
                                      246
                                      1.9
                                      4.4
Riverside County (Coachella Valley), CA
                                      70
                                      0.2
                                      0.5
Sacramento Metro, CA
                                      603
                                      1.0
                                      2.0
Salt Lake City, UT
                                     1,235
                                      4.4
                                     14.1
San Diego, CA
                                     1,035
                                      1.4
                                      3.4
San Francisco Bay Area, CA
                                     4,405
                                      2.7
                                      6.7
San Joaquin Valley, CA
                                      74
                                      0.0
                                      0.1
Seattle-Tacoma, WA
                                     1,958
                                      1.4
                                      3.9
St. Louis, MO-IL
                                      810
                                      0.6
                                      1.6
Syracuse, NY
                                      139
                                      0.8
                                      1.9
Washington, DC-MD-VA
                                     2,983
                                      2.0
                                      6.2
Table 3 shows how commercial aircraft operations are projected to rise in the future on a nationwide basis.   As operations increase, the inventory impact of these aircraft on national and local NOX inventories will also increase.
Table 3: Current and Projected Commercial Aircraft Operations
Year
                            Air Carrier Operations
                                  (millions)
                                   Commuter/
                              Air Taxi Operations
                                  (millions)
                          Total Commercial Operations
                                  (millions)
         Total increase in commercial  operations over 2008 (percent)
2008
                                     14.1
                                     13.8
                                     27.9
                                      --
2020
                                     16.5
                                     14.1
                                     30.5
                                       9
2030
                                     20.6
                                     16.0
                                     36.6
                                      31
	Source: December 2010 FAA TAF, which is located at http://aspm.faa.gov/main/taf.asp .
B.  Health, Environmental and Air Quality Impacts
NOx emissions from aircraft and other mobile and stationary sources contribute to the formation of ozone.  In addition, NOx emissions at low altitude also react in the atmosphere to form secondary fine particulate matter (PM2.5), particularly ammonium nitrate.  In the following sections we discuss the adverse health and welfare effects associated with NOx emissions, in addition to the current and projected levels of ozone and PM across the country.  The ICAO NOx standards with which we are aligning will help reduce ambient ozone and secondary PM levels and thus will help areas with airports achieve or maintain attainment with the National Ambient Air Quality Standards (NAAQS).
1.  Background on Ozone, PM and NOX
      a. What is Ozone?

Ground-level ozone pollution is typically formed through reactions involving VOC and NOX in the lower atmosphere in the presence of sunlight.  These pollutants, often referred to as ozone precursors, are emitted by many types of pollution sources, such as highway and nonroad motor vehicles and engines, power plants, chemical plants, refineries, makers of consumer and commercial products, industrial facilities, and smaller area sources.
The science of ozone formation, transport, and accumulation is complex.  Ground-level ozone is produced and destroyed in a cyclical set of chemical reactions, many of which are sensitive to temperature and sunlight.  When ambient temperatures and sunlight levels remain high for several days and the air is relatively stagnant, ozone and its precursors can build up and result in more ozone than typically occurs on a single high-temperature day.  Ozone and its precursors can be transported hundreds of miles downwind from precursor emissions, resulting in elevated ozone levels even in areas with low local VOC or NOX emissions.
b.  What is Particulate Matter?
The discussion includes PM2.5 because the NOX emitted by aircraft engines can react in the atmosphere to form nitrate, a component of PM2.5.  Particulate matter is a generic term for a broad class of chemically and physically diverse substances. It can be principally characterized as discrete particles that exist in the condensed (liquid or solid) phase spanning several orders of magnitude in size.  Since 1987, EPA has delineated that subset of inhalable particles small enough to penetrate to the thoracic region (including the tracheobronchial and alveolar regions) of the respiratory tract (referred to as thoracic particles).  The current PM NAAQS uses PM2.5 as the indicator for fine particles (with PM2.5 generally referring to particles with a nominal mean aerodynamic diameter less than or equal to 2.5 micrometers (um)), and use PM10 as the indicator for purposes of regulating the coarse fraction of PM10 (referred to as thoracic coarse particles or coarse-fraction particles; generally including particles with a nominal mean aerodynamic diameter greater than 2.5 um and less than or equal to 10 um, or PM10-2.5).  Ultrafine particles are a subset of fine particles, generally less than 100 nanometers (0.1 μm) in diameter.
Fine particles are produced primarily by combustion processes and by transformations of gaseous emissions (e.g., SOX, NOX and VOC) in the atmosphere.  The chemical and physical properties of PM2.5 may vary greatly with time, region, meteorology, and source category.  Thus, PM2.5 may include a complex mixture of different components including sulfates, nitrates, organic compounds, elemental carbon and metal compounds.  These particles can remain in the atmosphere for days to weeks and travel hundreds to thousands of kilometers.
c.  What is NOX?
Nitrogen dioxide (NO2) is a member of the NOX family of gases.  Most NO2 is formed in the air from the oxidation of nitric oxide (NO) emitted when fuel is burned at a high temperature.    NO2 and its gas phase oxidation products can dissolve in water droplets and further oxidize to form nitric acid which reacts with ammonia to form nitrates, an important component of ambient PM.  NOX and VOC are the two major precursors of ozone.  The health effects of ozone, ambient PM and NOX are covered in section II.B.2.
2.  Health Effects Associated with Exposure to Ozone, PM and NOX
a.  What are the Health Effects of Ozone?
  The health and welfare effects of ozone are well documented and are assessed in EPA's 2006 Air Quality Criteria Document and 2007 Staff Paper.,  People who are more susceptible to effects associated with exposure to ozone can include children, the elderly, and individuals with respiratory disease such as asthma.  Those with greater exposures to ozone, for instance due to time spent outdoors (e.g., children and outdoor workers), are of particular concern.  Ozone can irritate the respiratory system, causing coughing, throat irritation, and breathing discomfort.  Ozone can reduce lung function and cause pulmonary inflammation in healthy individuals.  Ozone can also aggravate asthma, leading to more asthma attacks that require medical attention and/or the use of additional medication.  Thus, ambient ozone may cause both healthy and asthmatic individuals to limit their outdoor activities.  In addition, there is suggestive evidence of a contribution of ozone to cardiovascular-related morbidity and highly suggestive evidence that short-term ozone exposure directly or indirectly contributes to non-accidental and cardiopulmonary-related mortality, but additional research is needed to clarify the underlying mechanisms causing these effects.  In a report on the estimation of ozone-related premature mortality published by the National Research Council (NRC), a panel of experts and reviewers concluded that short-term exposure to ambient ozone is likely to contribute to premature deaths and that ozone-related mortality should be included in estimates of the health benefits of reducing ozone exposure.   Animal toxicological evidence indicates that with repeated exposure, ozone can inflame and damage the lining of the lungs, which may lead to permanent changes in lung tissue and irreversible reductions in lung function.  The respiratory effects observed in controlled human exposure studies and animal studies are coherent with the evidence from epidemiologic studies supporting a causal relationship between acute ambient ozone exposures and increased respiratory-related emergency room visits and hospitalizations in the warm season.  In addition, there is suggestive evidence of a contribution of ozone to cardiovascular-related morbidity and non-accidental and cardiopulmonary mortality.
   	b. What are the Health Effects of PM?
Scientific studies show ambient PM is associated with a series of adverse health effects.  These health effects are discussed in detail in EPA's Integrated Science Assessment for Particulate Matter (ISA).  The ISA summarizes health effects evidence associated with both short-term and long-term exposures to PM2.5, PM10-2.5, and ultrafine particles.
The ISA concludes that health effects associated with short-term exposures (hours to days) to ambient PM2.5 include mortality, cardiovascular effects, such as altered vasomotor function and myocardial ischemia, and hospital admissions and emergency department visits for ischemic heart disease and congestive heart failure, and respiratory effects, such as exacerbation of asthma symptoms in children and hospital admissions and emergency department visits for chronic obstructive pulmonary disease and respiratory infections.  The ISA notes that long-term exposure (months to years) to PM2.5 is associated with the development/progression of cardiovascular disease, premature mortality, and respiratory effects, including reduced lung function growth in children, increased respiratory symptoms, and asthma development.  The ISA concludes that the currently available scientific evidence from epidemiologic, controlled human exposure, and toxicological studies supports a causal association between short- and long-term exposures to PM2.5 and cardiovascular effects and premature mortality.  Furthermore, the ISA concludes that the collective evidence supports likely causal associations between short- and long-term PM2.5 exposures and respiratory effects.  The ISA also concludes that the scientific evidence is suggestive of a causal association for reproductive and developmental effects including respiratory-related infant mortality and cancer, mutagenicity, and genotoxicity and long-term exposure to PM2.5.
For PM10-2.5, the ISA concludes that the current evidence is suggestive of a causal relationship between short-term exposures and premature mortality, cardiovascular effects, and respiratory effects.  Data are inadequate to draw conclusions regarding the health effects associated with long-term exposure to PM10-2.5.
For ultrafine particles, the ISA concludes that there is suggestive evidence of a causal relationship between short-term exposures and cardiovascular effects, such as changes in heart rhythm and blood vessel function.  It also concludes that there is suggestive evidence of association between short-term exposure to ultrafine particles and respiratory effects. Data are inadequate to draw conclusions regarding the health effects associated with long-term exposure to ultrafine particles.
   	c.  What are the Health Effects of NOX?
Information on the health effects of NO2 can be found in the EPA Integrated Science Assessment (ISA) for Nitrogen Oxides.  The EPA has concluded that the findings of epidemiologic, controlled human exposure, and animal toxicological studies provide evidence that is sufficient to infer a likely causal relationship between respiratory effects and short-term NO2 exposure. The ISA concludes that the strongest evidence for such a relationship comes from epidemiologic studies of respiratory effects including symptoms, emergency department visits, and hospital admissions.  The ISA also draws two broad conclusions regarding airway responsiveness following NO2 exposure.  First, the ISA concludes that NO2 exposure may enhance the sensitivity to allergen-induced decrements in lung function and increase the allergen-induced airway inflammatory response following 30-minute exposures of asthmatics to NO2 concentrations as low as 0.26 ppm.  Second, exposure to NO2 has been found to enhance the inherent responsiveness of the airway to subsequent nonspecific challenges in controlled human exposure studies of asthmatic subjects.   Small but significant increases in non-specific airway hyperresponsiveness were reported following 1-hour exposures of asthmatics to 0.1 ppm NO2.  Enhanced airway responsiveness could have important clinical implications for asthmatics since transient increases in airway responsiveness following NO2 exposure have the potential to increase symptoms and worsen asthma control.  Together, the epidemiologic and experimental data sets form a plausible, consistent, and coherent description of a relationship between NO2 exposures and an array of adverse health effects that range from the onset of respiratory symptoms to hospital admission.
Although the weight of evidence supporting a causal relationship is somewhat less certain than that associated with respiratory morbidity, NO2 has also been linked to other health endpoints.  These include all-cause (non-accidental) mortality, hospital admissions or emergency department visits for cardiovascular disease, and decrements in lung function growth associated with chronic exposure.
3. Environmental Effects Associated with Exposure to Ozone, PM and NOX
a. Deposition of Nitrogen
Emissions of NOX from aircraft engines contribute to atmospheric deposition of nitrogen in the U.S.  Atmospheric deposition of nitrogen contributes to acidification, altering biogeochemistry and affecting animal and plant life in terrestrial and aquatic ecosystems across the United States.  The sensitivity of terrestrial and aquatic ecosystems to acidification from nitrogen deposition is predominantly governed by geology.  Prolonged exposure to excess nitrogen deposition in sensitive areas acidifies lakes, rivers and soils.  Increased acidity in surface waters creates inhospitable conditions for biota and affects the abundance and nutritional value of preferred prey species, threatening biodiversity and ecosystem function.  Over time, acidifying deposition also removes essential nutrients from forest soils, depleting the capacity of soils to neutralize future acid loadings and negatively affecting forest sustainability.  Major effects include a decline in sensitive forest tree species, such as red spruce (Picea rubens) and sugar maple (Acer saccharum); and a loss of biodiversity of fishes, zooplankton, and macro invertebrates.
In addition to the role nitrogen deposition plays in acidification, nitrogen deposition also leads to nutrient enrichment and altered biogeochemical cycling.  In aquatic systems increased nitrogen can alter species assemblages and cause eutrophication.  In terrestrial systems nitrogen loading can lead to loss of nitrogen sensitive lichen species, decreased biodiversity of grasslands, meadows and other sensitive habitats, and increased potential for invasive species.
Adverse impacts on soil chemistry and plant life have been observed for areas heavily influenced by atmospheric deposition of nutrients, metals and acid species, resulting in species shifts, loss of biodiversity, forest decline damage to forest productivity and reductions in ecosystem services.  Potential impacts also include adverse effects to human health through ingestion of contaminated vegetation or livestock (as in the case for dioxin deposition), reduction in crop yield, and limited use of land due to contamination.
Atmospheric deposition of pollutants can reduce the aesthetic appeal of buildings and culturally important articles through soiling, and can contribute directly (or in conjunction with other pollutants) to structural damage by means of corrosion or erosion.   Atmospheric deposition may affect materials principally by promoting and accelerating the corrosion of metals, by degrading paints, and by deteriorating building materials such as concrete and limestone.  Particles contribute to these effects because of their electrolytic, hygroscopic, and acidic properties, and their ability to adsorb corrosive gases (principally sulfur dioxide).
b.  Visibility Effects
NOx emissions contribute to visibility impairment in the U.S. through the formation of secondary PM2.5.  Visibility impairment is caused by light scattering and absorption by suspended particles and gases.  Visibility is important because it has direct significance to people's enjoyment of daily activities in all parts of the country.  Individuals value good visibility for the well-being it provides them directly, where they live and work, and in places where they enjoy recreational opportunities.  Visibility is also highly valued in significant natural areas, such as national parks and wilderness areas, and special emphasis is given to protecting visibility in these areas.  For more information on visibility see the final 2009 PM ISA.
c.  Plant and Ecosystem Effects of Ozone
Elevated ozone levels contribute to environmental effects, with impacts to plants and ecosystems being of most concern.  Ozone can produce both acute and chronic injury in sensitive species depending on the concentration level and the duration of the exposure.  Ozone effects also tend to accumulate over the growing season of the plant, so that even low concentrations experienced for a longer duration have the potential to create chronic stress on vegetation.  Ozone damage to plants includes visible injury to leaves and impaired photosynthesis, both of which can lead to reduced plant growth and reproduction, resulting in reduced crop yields, forestry production, and use of sensitive ornamentals in landscaping.  In addition, the impairment of photosynthesis, the process by which the plant makes carbohydrates (its source of energy and food), can lead to a subsequent reduction in root growth and carbohydrate storage below ground, resulting in other, more subtle plant and ecosystems impacts.  These latter impacts include increased susceptibility of plants to insect attack, disease, harsh weather, interspecies competition and overall decreased plant vigor.  The adverse effects of ozone on forest and other natural vegetation can potentially lead to species shifts and loss from the affected ecosystems, resulting in a loss or reduction in associated ecosystem goods and services.  Lastly, visible ozone injury to leaves can result in a loss of aesthetic value in areas of special scenic significance like national parks and wilderness areas.  The final 2006 Ozone Air Quality Criteria Document presents more detailed information on ozone effects on vegetation and ecosystems.
 4. Impacts on Ambient Air Quality
The aircraft NOx emission standards we are promulgating would affect ambient concentrations of air pollutants.  Nationally, levels of PM2.5, ozone, and NOX are declining.  However approximately 144 million people currently live in areas designated nonattainment for one or more of the current NAAQS.  These numbers do not include the people living in areas where there is a future risk of failing to maintain or attain the NAAQS.
States with ozone nonattainment areas are required to take action to bring those areas into attainment.  The attainment date assigned to an ozone nonattainment area is based on the area's classification.  Most ozone nonattainment areas are required to attain the 1997 8-hour ozone NAAQS in the 2007 to 2013 time frame and then to maintain it thereafter.  We anticipate designating areas for the 2008 ozone standards in late spring 2012; thus, the attainment dates for areas designated nonattainment for the 2008 8-hour ozone NAAQS would likely be in the 2015 to 2032 timeframe, depending on the severity of the problem in each area.  In addition, EPA is working to complete the current review of the ozone NAAQS by mid-2014.  If EPA revises the ozone standards in 2014 pursuant to that review, the attainment dates associated with areas designated nonattainment for that NAAQS would likely be in the 2019 to 2036 timeframe, depending on the severity of the problem in each area.
Areas designated as not attaining the 1997 PM2.5 NAAQS will need to attain the 1997 standards in the 2010 to 2015 time frame, and then maintain compliance with them thereafter.  The 2006 24-hour PM2.5 nonattainment areas will be required to attain the 2006 24-hour PM2.5 NAAQS in the 2014 to 2019 time frame and then be required to maintain the 2006 24-hour PM2.5 NAAQS thereafter.
EPA has already adopted many emission control programs that are expected to reduce ambient ozone and PM2.5 levels and which will assist in reducing the number of areas that fail to achieve the NAAQS.  Even so, our air quality modeling projects that in 2030 as many as 10 counties with a population of over 30 million may not attain the 2008 ozone standard of 0.075 ppm (75 ppb) without additional controls.  In addition, our air quality modeling projects that in 2030 at least four counties with a population of nearly 7 million may not attain the 1997 annual PM2.5 standard of 15 ug/m[3] and 22 counties with a population of over 33 million may not attain the 2006 24-hour PM2.5 standard of 35 ug/m[3] without additional controls.  These numbers do not account for those areas that are close to (e.g., within 10 percent of) the standards.  These areas, although not violating the standards, would also benefit from any reductions in NOX ensuring long-term maintenance of the NAAQS.
The primary NAAQS for NO2 was revised in January 2010.  EPA completed area designations in January 2012 and there are currently no nonattainment areas.  The designations were based on the existing community-wide monitoring network.  Once the expanded network of NO2 monitors is fully deployed and three years of air quality data have been collected, EPA intends to redesignate areas after 2015, as appropriate, based on the air quality data from the new monitoring network.
In summary, the aircraft NOx reductions resulting from these new aircraft engine emission standards will be useful to states in attaining or maintaining the ozone, PM2.5 , and NO2 NAAQS standards.
III.  Details of the Final Rule
The following is a description of the regulations being adopted in this final rule, with any changes from the proposal also noted.  The descriptions also include our response to the most significant comments received on the proposal.  A full summary of the comments and our responses are contained in the response to comments document for the rule that is available in the public docket for this action.
We are establishing two different levels or "tiers" of increasingly more stringent  NOx emission standards for gas turbofan engines with maximum rated thrusts greater than 26.7 kilonewtons (kN).  Each of the tiers apply to newly-certified engines.  Newly-certified aircraft engines are those that would receive a new type certificate after the effective date of the applicable standards.  Such engine types or models would not have begun production prior to the effective date of the new requirement.
We are also requiring newly-manufactured engines to comply with the first tier of the two tiers of standards.  Newly-manufactured aircraft engines are those that have been previously certified and manufactured in compliance with preexisting standards, and will continue to be produced after the effective date of a new applicable standard.  Normally, these newly-manufactured engines must comply with the same NOx limits as newly-certified engines, but at a later date or cease production.  The end of this "phase-in" period for the newly-manufactured engine standards is sometimes referred to as a "production cutoff.".   Again, we are adopting only the first of the two new tiers of NOx standards for newly-manufactured engines.  These provisions are described in detail below.
Five other regulatory features are being established in this final rule.  First, we are revising provisions for certain time-limited flexibilities, i.e., potential exemptions, for newly-manufactured engines that may not be able to comply with the first tier of the new NOx standards because of specific technical or economic reasons.  Second, we are defining "derivative engine" for emissions certification purposes.  The intent of this definition is to distinguish when the emission characteristics of a new turbofan engine model vary substantially from its existing parent engine design, and must show compliance with the emission standards for a newly-certificated engine.  Third, we are establishing new CO and NOx standards for turbofan engines that are used to propel supersonic aircraft.  These standards were adopted by ICAO in the 1980s, but were not previously added to our HC emission standard for these engines.  Promulgating these standards meets our treaty obligation under the Convention on International Civil Aviation as previously described in section I.C.   Fourth, we are making several changes to the emission testing and measurement procedures in our regulations that are intended to implement ICAO's Annex 16 and to incorporate the entire annex in our regulations by reference.  Finally, as described in section IV, we are amending the current regulatory provisions that address definitions, acronyms and abbreviations, general applicability and requirements, exemptions, and incorporation by reference.  These amendments are intended to clarify requirements, make them more consistent with other parts of the program, update the text to be consistent with current standard language conventions, or remove obsolete provisions.
As discussed further below, with the exception of the annual reporting requirement described in section III.D, the amendments reflect those changes that were previously adopted by ICAO.
This final rule also is consistent with our authority and obligations under the CAA as described in section I.B.  More specifically, the technical feasibility and cost of the emission standards were well documented by our own analyses and CAEP as described later in this section and in section V, Technical Feasibility, Costs, and Emission Benefits.   We think that the final rule provides adequate lead time for the development and application of the requisite technology with appropriate consideration to the cost of compliance.  We have consulted with the Department of Transportation through the FAA regarding lead time, noise, safety, and the technical feasibility of the new standards.  Today's final rule is also consistent with U.S. treaty obligations under the Chicago Convention as described in section I.C., because the requirements are consistent with current ICAO standards.
Except to the extent needed to make our standards conform to ICAO's standards by making them applicable to both commercial and non-commercial engines, we are not revising exhaust emission standards for HC, CO, or smoke. Those standards remain in effect as currently promulgated.  All engines subject to the new NOx standards would also continue to be subject to the existing HC, CO, and smoke standards.   It is worth emphasizing that although we are including these existing HC, CO, and smoke standards in a new section 87.23, which would also contain the new Tier 6 and Tier 8 NOx standards, we are not actually adopting new standards for these three pollutants, since under the current form of part 87 these HC, CO and smoke standards would already continue to apply to new engine types subject to future revised NOx standards.
As discussed above, we are adopting a new naming convention in this preamble and the regulatory text to more easily distinguish between the tiers of increasingly more stringent NOx emission standards.  This convention is also consistent with the numeric identifier that CAEP uses to differentiate the CAEP work cycle that produces new NOx standards.  (The CAEP naming convention is described in section I.E.)  As a result, the first tier of NOx standards, which correspond to CAEP/6, are referred to as Tier 6 in the remainder of today's notice.  The second tier of standards is referred to as Tier 8, which correspond to CAEP/8.  We are also incorporating the new naming convention in the regulations for the existing NOx emission standards, i.e., Tier 0, Tier 2, and Tier 4.  There is no material change to the existing NOx standards themselves, except to the extent that when today's final rule becomes effective, the existing NOx standards would be superseded by Tier 6 standards.
We acknowledge that this new naming convention is a change from the past practice of not describing aircraft engine emission standards as tiers.  However, we believe the new naming scheme is a valuable tool that makes referring to individual NOx standards much easier.  It is also similar to the terminology we use for other mobile source sectors that are subject to environmental regulation and for which standards have become more stringent or have otherwise been amended over time.
A.  NOx Standards for Newly-Certified Engines
We are adopting two different tiers of increasingly stringent NOx standards.  These standards would apply for all for newly-certified turbofan aircraft engines with maximum rated thrusts greater than 26.7 kN.  (See section III.B for a discussion of how these standards apply for newly-manufactured engines that are not considered to be newly certified.)  The numerical value of the applicable standard for an individual engine model is defined by the engine's thrust level and pressure ratio.  Simply stated, the pressure ratio is the numerical ratio of the air pressure entering the engine to the air pressure at the entrance to the combustor, i.e., after the air has passed through the compressor section of the engine.    The new tiers are described separately below.
1.  Tier 6 NOx Standards for Newly-Certified Engines
This first tier of new standards is equivalent to the CAEP/6 NOx limits that were adopted by ICAO and became internationally applicable after December 31, 2007.  Given that aircraft turbofan engines are international commodities, engine manufacturers introduced engine models after that date that demonstrate compliance with these international standards, or are already planning to do so for upcoming engine designs.  Based on this, our evaluation of the necessary lead time, and the lack of any comments on this aspect of the proposal, this tier of standards takes effect immediately upon the effective date of this final rule.
The basic form of the NOx standards for turbofan engines is different for higher- and lower-rated thrust engines.  Higher output engines are defined as having rated thrusts equal to or greater than 89 kN, while lower output engines are defined as having rated thrusts less than 89 kN but greater than 26.7 kN.  The new Tier 6 NOx standards for each of these power grouping are described separately below.
a.  Numerical Emission Limits for Higher Thrust Engines
The Tier 6 NOx standards for newly-certified gas turbine engines with rated thrusts of 89 kN or more are differentiated by pressure ratio as shown below.
::  For engines with a pressure ratio of 30 or less:						g/kN rated output  = 16.72 + (1.4080 * engine pressure ratio)
::  For engines with a pressure ratio of more than 30 but less than 82.6:
g/kN rated output  =  -1.04 + (2.0 * engine pressure ratio)
::  For engines with a pressure ratio of 82.6 or more:
g/kN rated output  = 32 + (1.6 * engine pressure ratio)
The new Tier 6 NOx standards for these higher thrust engines are presented in Figure 1 along with the previous EPA NOx standards, which were based on CAEP/4, for comparison.

As a matter of convention, the relative stringency from one CAEP standard to another is expressed relative to a pressure ratio of 30, because the percentage reduction is usually inconsistent across all of the possible pressure ratios, which otherwise makes a simple comparison difficult.  Using that convention, the Tier 6 standards (CAEP/6) are referred to as being 12 percent more stringent than the existing EPA NOx Tier 4 standards (CAEP/4).  The relative stringency can also be illustrated at other pressure ratios.  At pressure ratios less than 30 the reductions are also 12 percent.  At pressure ratios above 30, however, the percent reduction decreases as the pressure ratio is increased.  Based on the figure, the percent reduction for current technology engines ranges from about 8 to 12 percent.
b.  Numerical Emission Limits for Lower Thrust Engines
The new Tier 6 NOx standards for newly-certified gas turbine engines with rated thrusts between 26.7 and less than 89.0 kN are differentiated by both pressure ratio and rated thrust as shown below.
::  For engines with a pressure ratio of 30 or less:
g/kN rated output  =  38.5486 + (1.6823 *  engine pressure ratio) - (0.2453 *  kN rated 	thrust) - (0.00308 *  engine pressure ratio *  kN rated thrust)
::  For engines with a pressure ratio of more than 30 but less than 82.6:
g/kN rated output  = 46.1504 + (1.4285 * engine pressure ratio) - (0.5298 *  kN rated 	thrust) + (0.00642 *  engine pressure ratio *  kN rated thrust)
In developing the corresponding NOx standards for lower thrust engines, CAEP recognized the technical challenges that physically smaller-sized engines sometimes present relative to incorporating some of the lowest NOx technology approaches, which are otherwise available to their larger counterparts.  These technical difficulties are well documented and increase progressively as size is reduced (from around 89 kN).  For example, the relatively small combustor space and section height of these engines creates constraints on the use of low NOx fuel-staged combustor concepts which inherently require the availability of greater flow path cross-sectional area than conventional combustors.  Also, fuel-staged combustors need more fuel injectors, and this need is not compatible with the relatively smaller total fuel flows of lower thrust engines.  (Reductions in fuel flow per nozzle are difficult to attain without having clogging problems due to the small sizes of the fuel metering ports.)  In addition, lower thrust engine combustors have an inherently greater liner surface-to-combustion volume ratio, and this requires increased wall cooling air flow.  Thus, less air will be available to obtain acceptable turbine inlet temperature distribution and for emissions control.  With these technological constraints in mind, CAEP fashioned the CAEP/6 NOx standards across the range of thrusts represented by low-thrust engines to become comparatively less stringent, i.e., CAEP/6 relative to CAEP/4, as the rated output and physical size of the engines decrease.  We agree with this approach.
As mentioned, the new Tier 6 standards depend on an individual engine's rated thrust and pressure ratio.  With two variables in the calculation, the standards cannot be represented in a simple figure, i.e., no single line graph showing the standards for all engines within the thrust range is possible as it was for higher thrust engines.  Regardless of this complexity, however, some general observations are useful to characterize the Tier 6 NOx standards for lower thrust engines based on the engine size versus technological challenge described in the previous paragraph.
Comparing the new lower and higher thrust standards at 89 kN, which is the demarcation point between the two sets of standards, shows that the standards for lower thrust engines are numerically equivalent to the limit for higher thrust engines at each pressure ratio.  This is as expected because the engine sizes and ability to incorporate low-NOx technologies are the same at 89.0 kN delineation point.
Again focusing only on 89 kN engines, the new Tier 6 standards represent a 12 percent reduction from the existing EPA Tier 4 (CAEP/4 based standards) for pressure ratios of 30 or less as shown below in Figure 2.  This includes the region represented by almost all current engine designs.  At higher pressure ratios, the relative numerical reduction is progressively less because the slope of the two standards is essentially the same.

At other thrust ratings the percent reduction between the new Tier 6 and existing EPA NOx standards at any pressure ratio becomes progressively smaller as thrust decreases.  This is illustrated in Figure 3 for a pressure ratio of 30.   This pressure ratio was chosen for the example because, as before, the relative stringency of CAEP NOx standards is generally compared at this point as a matter of convention.  As shown in the figure for current engines, the reduction ranges from 12 percent at the upper end of the thrust range to 0 percent at the lower end of the range.  The pattern is similar for the other pressure ratios.  Only the actual numerical value for percentage reduction at 89 kN, as shown on the far right of the figure, may vary by pressure ratio, as described at the beginning of this paragraph.   However, in the region of pressure ratios represented by today's engines, the results are identical to those shown in the figure, i.e., a 12 percent reduction at 89 kN decreasing to 0 percent at 26.7 kN.

2.  Tier 8 NOx Standards for Newly-Certified Engines
The second tier of new standards, i.e., Tier 8, are equivalent to the NOx limits that were most recently recommended at CAEP/8 in February 2010 for adoption by ICAO.  The CAEP/8 recommended standards have a recommended applicable date after December 31, 2013.  As discussed further in section V of today's notice, we agree with CAEP that this provides engine manufacturers with adequate lead time to respond to these more stringent NOx standards considering the technical feasibility and cost associated with the requirements.  Therefore, this tier of standards takes effect on January 1, 2014.  As with the new Tier 6 NOx standards, the basic form of the new Tier 8 standards for turbofan engines is different for higher- and lower-rated thrust engines.  Higher output engines are defined as having rated thrusts equal to or greater than 89 kN, while lower output engines are defined as having rated thrusts less than 89 kN but greater than 26.7 kN.  The longer-term standards for each of these power grouping are described separately below.
a.  Numerical Emission Limits for Higher Thrust Engines
The new Tier 8 NOx standards for newly-certified turbofan engines with rated thrusts of 89 N or more are differentiated by pressure ratio as shown below.
::  For engines with a pressure ratio of 30 or less:						g/kN rated output  =  7.88 + (1.4080* engine pressure ratio)
::  For engines with a pressure ratio of more than 30 but less than 104.7:
g/kN rated output  =  -9.88+ (2.0 * engine pressure ratio)
::  For engines with a pressure ratio of 104.7 or more:
g/kN rated output  =  32 + (1.6 * engine pressure ratio)
The new Tier 8 NOx standards for these higher thrust engines are presented in Figure 4 along with the new Tier 6 standards for comparison.

As noted previously, as a matter of convention the relative stringency from one CAEP standard to another is generally expressed relative to a pressure ratio of 30.  Using that convention, the new Tier 8 standards (CAEP/8) are referred to as being 15 percent more stringent than the new Tier 6 NOx standards (CAEP/6).  The relative stringency can also be illustrated at other pressure ratios.  At pressure ratios less than 30 the reductions increase.  At pressure ratios above 30, however, the percent reduction decreases.  Based on the figure, the percent reduction for current engine designs range from about 11 to 19 percent.
b.  Numerical Emission Limits for Lower Thrust Engines
The new Tier 8 NOx standards for newly-certified gas turbine engines with rated thrusts between 26.7 but less than 89.0 kN are differentiated by both pressure ratio and rated thrust as shown below.
::  For engines with a pressure ratio of 30 or less:
g/kN rated output  =  40.052 + (1.5681 *  engine pressure ratio) - (0.3615 *  kN 	rated 	thrust) - (0.0018 *  engine pressure ratio *  kN rated thrust)
::  For engines with a pressure ratio of more than 30 but less than 104.7:
g/kN rated output  = 41.9435 + (1.505 * engine pressure ratio) - (0.55823 *  kN 	rated 	thrust) + (0.005562 *  engine pressure ratio *  kN rated thrust)
In developing the corresponding CAEP/8 NOx standards for low thrust engines, CAEP recognized the technical challenges that physically smaller-sized engines represent relative to incorporating some of the lowest NOx technology, which is otherwise available to their larger counterparts.  These technical difficulties were described in the previous section for the Tier 6 low-thrust engine standards.
Also as previously described, no single line graph showing the standards for all engines within the thrust range is possible as it was for higher thrust engines, because the equations have two variables.  However, some general observations are useful to characterize the new Tier 8 NOx standards for lower thrust engines based on the engine size versus technological challenge described in the previous paragraph.  First, the new Tier 8 NOx standards for lower thrust engines are numerically equivalent to the limit for higher thrust engines across all pressure ratios at the highest rating of 89 kN, where the engine sizes and ability to incorporated low-NOx technologies are comparable.  This same characteristic was observed for the Tier 6 standards.  Second, as shown below in Figure 5 for 89 kN engines, at this thrust rating the new Tier 8 standards represents a 15 percent reduction from the Tier 6 standards for a pressure ratio of 30.  However, within the region of pressure ratios for all current engine designs, the reductions range from 19 to 23 percent.

  Third, at other thrust ratings the percent reduction between the new Tier 6 and Tier 8 standards at any pressure ratio becomes progressively smaller as thrust decreases.  This is illustrated in Figure 6 for a pressure ratio of 30, following the convention described above.   Also as shown in the figure for current engines, the reduction ranges from 15 percent at the upper end of the thrust range to 5 percent at the lower end of the range.  While not depicted in a figure, the pattern is similar for the other pressure ratios.  However, the actual numerical values for percentage reductions at both ends of the thrust range, i.e., 26.7 to 89 kN, may vary by pressure ratio.   In the region of pressure ratios represented by today's engines, the results are identical to those shown in Figure 6 at 26.7 kN, i.e., a 5 percent reduction at all pressure ratios for that thrust rating.  However, percent reductions increase linearly up to a maximum 23 percent reduction for 89 kN engines with pressure ratios of about 15.

B.  Application of the Tier 6 NOx Standards to Newly-Manufactured Engines
This section describes the application of the new Tier 6 NOx standards to newly-manufactured engines, and our amended temporary flexibilities for newly-manufactured engines that show significant problems complying with these requirements.  Also, consistent with CAEP/8, we are not applying the new Tier 8 NOx standards to newly-manufactured engines at this time.  This section concludes with a description of future efforts to examine such a possibility.
1.  Phase-In of the Tier 6 NOx Standards for Newly-Manufactured Engines
As described above, the new Tier 6 NOx standards apply to all engine types or models that receive a new type certificate after the effective date of the final rule.  We are also phasing in these same NOx limits for newly-manufactured engines for engine models (and their derivatives for emissions certification purposes) that were originally certified to less stringent requirements (i.e., Tier 2 or Tier 4) and were already being produced for installation on new aircraft prior to the effective date of the final rule.  As a result, manufacturers need to bring newly-manufactured engines of these previously certified models into compliance with the applicable Tier 6 standards by a future date or cease production of those engine models. As we discussed and described in our analysis of the need for a CAEP/6 production cutoff during the CAEP process, establishing a date certain for compliance with any emission standard is necessary to ensure that the full benefits of newer, more stringent requirements will be achieved in a reasonable time.  We are, however, adopting certain limited flexibilities for engines that cannot be made compliant because of specific technical or economic reasons, as discussed later in this section.
As described in the proposal, the effective date of January 1, 2013 for the newly-manufactured engine standards is consistent with the expected market demand for these previously certified engine types.  Historically, engine manufacturers have often responded to the adoption of more stringent NOx standards by bringing older engine types into compliance with the newer requirements well before the required date in anticipation of the likely market demand, or planning for the orderly withdrawal of these engines from the marketplace.  Information developed during the ICAO process in 2008 and 2009[,][,] and our more recent discussions with manufacturers indicate that:  1) all but a few models are already compliant with CAEP/6 standards, 2) nearly without exception, all current production models will meet the CAEP/6 requirements by the 2012 time frame, and 3) any noncompliant models will be phased out of production because of low market demand.
We think that the five-year phase-in period from ICAO's effective date of the CAEP/6 standards (corresponding to our new Tier 6 NOx standards) for newly-manufactured engines is adequate for manufacturers and their customers to respond to the new requirements without disrupting their future planning and purchasing decisions.[,]  This phase-in period for applying the Tier 6 NOx standards to newly-manufactured engines is also identical to the date for this same requirement that was adopted by ICAO.  No comments were received expressing concern with this phase-in period for newly-manufactured engines.
We did, however, receive two comments expressing the view that the time between the date of our final rule and the January 1, 2013 effective date of the production cutoff would be too short if it is less than one year.  General Electric Aviation (GE) was the most detailed and began by noting that most of the engine models currently in production were certified to the Tier 4 standards and had demonstrated NOx emissions below the Tier 6 at that time.  They continued that if the original certification reports are sufficient for the FAA to formally certify these engines to the Tier 6 standards, then none of these engines would be adversely affected by the production cutoff.  However, GE expressed the concern that if additional interactions or formal action by the FAA were needed, or revisions to the FAA's FAR Part 34 were required, then having less than one year between EPA's final rule and the production cutoff could disrupt current engine production.  As a result, GE asked that the date of the production cutoff be delayed to take effect 12 months after the final rule.  The other joint comment from the Aerospace Industries Association (AIA) and the General Aviation Manufacturers Association (GAMA) was similar in nature, but without supporting details.
The commenters' concerns do not relate to the technical or economic feasibility of newly-manufactured engines achieving emission levels in compliance with the new Tier 6 standards by the date of the production cutoff as proposed.  The concerns expressed do not argue that additional time is necessary "to permit the development and application of the requisite technology" to comply with the standards under CAA section 231(b).  Therefore, the date of the Tier 6 production cutoff is appropriate and consistent with the Clean Air Act.
Section 232(b) of the Act directly addresses our obligation relative to the effective date of the regulation.  Specifically, it says: "Any regulation prescribed under this section (and any revision thereof) shall take effect after such period as the Administrator finds necessary (after consultation with the Secretary of Transportation) to permit the development and application of the requisite technology, giving appropriate consideration to the cost of compliance within such period."  Based on the information provided above, the aircraft engine models described by GE are already capable of complying with the EPA Tier 6 NOx standards using already applied requisite technology, i.e., the cost of applying with has already been borne, as the effective date of the corresponding ICAO CAEP/6 NOx standard has already passed.  We do not believe there are any technical feasibility or economic implications arising from the continued application of the requisite technology for those engines to meet the Tier 6 NOx standards. Also, consistent with our most recent previous amendment to the NOx standards, which similarly promulgated the standard at a level that was already being met by aircraft engine manufacturers who were already applying the requisite technology, the effective date does not need to include additional lead time for the development and application of additional technology that would be needed to comply with the standards. See, e.g., 70 FR 69604, 69674-76 (Nov. 17, 2005).  As a result, the implementation dates provide more than adequate lead time under the statute.  Therefore, because aircraft engine manufacturers are already able to comply with the Tier 6 NOx standard through the continued use of already applied requisite technology, and because the effective date of the corresponding ICAO CAEP/6 NOx standard has already passed (and also based on the assessment described in section V. Technical Feasibility, Cost, and Emission Benefits), we find that the dates provide more than adequate lead time under the statute for application of requisite technology.
We also want to stress that the production cutoff is actually an ICAO standard and we think it is important to stay aligned with the CAEP production cutoff date. We note that this is also being adopted by the European Aviation Safety Agency (EASA) and perhaps other aviation certification authorities. Our adoption of the proposed date insures international consistency regarding the production cutoff date and avoids contradicting our international bilateral agreements with other governments, e.g., the European Union.
	Regarding the need for engine models to be formally recognized by the FAA as complying with the new Tier 6 standard, this is completely within the purview of the FAA. In our previous most recent amendment to the NOx standard, we provided just a one-month lead time period before the revised standard became effective, and FAA did not adopt corresponding implementing regulations until one year later, with no apparent disruption to the industry.  (See 70 FR 69664, Nov. 17, 2005.)  The new Tier 6 standards are the same as the CAEP/6 standards that were approved by ICAO in 2005 with an effective date of beginning after December 31, 2007.  Therefore, just as for the 2005 revised NOx standard that we similarly promulgated significantly later than the effective date of the corresponding ICAO CAEP standard, we do not believe that it is necessary to delay the effective date based on a need for the FAA to revise its own implementation and enforcement regulations.

	Finally, section 232(a) of the Act directs the FAA to ensure compliance with our standards.   In this regard, the FAA has developed a streamlined process to recognize compliance with Tier 6 and or Tier 8 as appropriate for currently type certified engine models which meet the emission standards and they have assured the regulated industry that they will dedicate the necessary resources to formally recognize conformance with the standards before the production cutoff date.  This process will rely on part 87 rather than the FAA's FAR part 34, due to the time needed to amend its current regulations through formal rulemaking.  Further, the FAA has informed us that they are pursuing the use of an expedited regulatory process, called a direct final rule to promulgate the necessary amendments to FAR part 34 in a timely manner.  Based on the FAA's assurances and description of the streamlined process to formally recognize conformance with the new standards, engine manufacturers now support promulgating the production cutoff date as proposed.
For the reasons stated above, EPA is promulgating the Tier 6 production cutoff with the originally proposed effective date of January 1, 2013.
2. 2.  Carryover of Previously Generated Emission Test Data
Aircraft engine models normally receive type certificates, which include a determination that the model meets the emission standards in force at the time the type certificate is granted. EPA has not updated its aircraft emission standards or test procedure regulations since 2005.  In this action we are adopting Tier 6 and Tier 8 NOx emission standards and are adopting either in 40 CFR part 87 directly or through incorporation by reference of Annex 16, Volume II a number of minor changes to test procedures and related requirements. These changes will become effective on the date when the rule becomes effective.
 This leaves open a question regarding the future validity and acceptability for amended type certificates of emission tests and emission test data generated under previously specified test procedures and related requirements.  For example, there may be an engine model tested in 2004 that demonstrated HC, CO, and NOx emission levels below the exhaust emission standards in effect at that time and also below the Tier 6 or perhaps even the Tier 8 standards that are being promulgated in this final rule.  We want to be clear that we do not intend minor changes to test procedures or related provisions and requirements to trigger the need for additional testing.  Thus, in cases where a manufacturer has a valid current type certificate based on emissions information generated under the test procedures in force at the time the type certificate was granted, we consider that data to be valid for any formal FAA recognition of compliance, e.g., an amended type certificate, with the Tier 6 or Tier 8 NOx emission requirements if the original test data demonstrate such compliance. The same is true for the HC and CO emission standards.  This clarification should greatly facilitate compliance determinations by the FAA and eliminate any uncertainty regarding the potential for otherwise minor test procedure changes to trigger new emissions testing for previously certificated engines with emission levels below the new NOx standards.
3.  Exemptions and Exceptions from the Tier 6 Production Cutoff
In conjunction with the implementation of the new Tier 6 NOx standards, we are establishing provisions which allow engine manufacturers to request an exemption or exception from meeting the Tier 6 NOx standards for newly-manufactured engines.  These provisions replace existing provisions addressing exemptions that are currently promulgated in section 87.7 of our aircraft engine regulations.  (Any exemptions previously issued under section 87.7 would not be affected by the revisions.)   This section of the preamble describes these exemption and exception provisions, i.e., exemptions for engines installed in new aircraft and exceptions for spare engines used in existing aircraft for maintenance purposes.  It also includes a description of a short-term exception program (termed the low-volume, time-limited transitional exemption program).  These provisions have largely been crafted to be consistent with exemption provisions in the ICAO Environmental Technical Manual (ETM).[,]  The provisions of the ETM guidance were developed in the context of the CAEP/6 NOx production cutoff deliberations leading up to the CAEP/8 meeting in February 2010.
While we are revising our regulations, the process for evaluating any request for an exemption, i.e., petition, and any final decision on its disposition would be unchanged.  In this regard, the FAA is the process owner under its enforcement authority contained in section 232 of the Clean Air Act.  The FAA must consult with EPA in evaluating the merits of the request, and the EPA must formally concur with any decision regarding the granting or denial of the request.  We are deleting from our regulations the requirement in §87.7(e) that the FAA publish a notice of the exemption in the Federal Register.  This provision was originally adopted in 1982 when publication in the Federal Register was the most reliable method to ensure the public was notified.  We now believe it is more appropriate to allow the FAA to determine how best to notify the public of exemption actions.  We note that removing this provision from our regulations does not preclude the FAA from keeping such a requirement in its regulations, which we strongly support.
Under the existing regulations, the FAA, with EPA concurrence, may also exempt low-production volume engines from being fully compliant with the emission standards.  Several such short-term exemptions were granted in the 1980s when emission standards were first applied.  These exemptions have since expired, and requests for new exemptions under those provisions have not been submitted.  We have determined that these provisions, which were adopted in conjunction with revised emission standards in 1982, are no longer of any utility.   Therefore, we are deleting these provisions to avoid confusion.
We are also deleting the time-limited exemption provisions for in-use engines that are contained in section 87.7(d).  These provisions, which were intended for when the standards of sections 87.11(a), 87.31(a), and 87.31(c) first took effect, are now obsolete.
We proposed to delete the existing provisions for temporary exemptions based on flights for short durations and infrequent intervals.  This proposal was based on the EPA's and FAA's belief that the provisions were unnecessary because our standards apply to aircraft certificated by the FAA, and the FAA does not address in the certification process whether an aircraft will be used for short durations or infrequent intervals.  Hence, the provisions appeared to have no utility.
We received two comments from the Aerospace Industries Association (AIA) and the General Aviation Manufacturers Association (GAMA) requesting that the provision be retained. First, they argued that as in the past, a new aircraft may be produced at a commercial facility that is destined for immediate conversion to a military only application at a separate facility.  These aircraft may require a small number of airworthiness flight tests before being delivered to the conversion facility and conceivably would be subject to EPA standards during flight testing.  While these aircraft would generally utilize compliant engines, it may be possible that non-compliant engines could be used (our standards do not apply to engines used on military aircraft as discussed later) and temporary exemptions would be necessary.  Second, AIA and GAMA commented that it would be helpful if the provision also allowed for granting a discrete number of exemptions over a specified time period, rather than having to request the exemption prior to each flight as currently required.
In considering the commenters' suggestion to retain the exemption provision, we note that allowing such operations will not have any significant adverse affect on the environment because of the infrequent nature and short duration of such flights.  Retaining the exemption is also consistent with exempting military aircraft from emission control requirements as discussed later.  Therefore, we have retained the provision with one change, made in response to the comments, as described below.
The current provision calls for the Secretary of Transportation to consult with the EPA Administrator when considering any exemption request for infrequent interval and short duration flights not explicitly allowed by the regulations.  Given the inconsequential nature of such flights on the environment, we believe that the Secretary should be able to consider and act on these petitions unilaterally to streamline the process.  Therefore, we are deleting that portion of the previous exemption provision. Of course, we will consult with the Secretary if asked to do so.  As for requesting a discrete number of temporary exemptions, we believe this is an issue that the Secretary of Transportation may address under its enforcement role as described in section 232 of the CAA.
The current regulations also provide for permanent exemptions for newly-manufactured engines based on consideration of the certain factors specified in section 87.7(c).  We are replacing these provisions with new regulatory text generally consistent with the ETM that would provide for permanent exemptions or exceptions for newly manufactured engines used on new aircraft and spare engines used for maintenance or replacement purposes.  These are summarized below.  (See §87.50 of the regulations for additional details on these exemptions/exceptions.)
   a.  New Provisions for Spare Engines
We are revising the regulations to allow the sale of a newly-manufactured engine for installation on an in-service aircraft, i.e., a spare engine that does not conform to the applicable emissions standards at the time it was produced.  It does not allow for installing such an engine on a new aircraft.  Spare engines are produced from time to time in order to keep an aircraft in revenue service when the existing in-service engine must be removed for maintenance or replacement purposes as needed.  Otherwise removing these aircraft from active service would be very expensive and logistically difficult.
As we explained in the proposal, explicitly allowing for the production of spare engines is not addressed in the existing regulations because there is no production cutoff for the current Tier 4 NOx standards.  Thus manufacturers have been allowed to continue production of older engine designs under type certificates first issued before the Tier 4 standards took effect (e.g., Tier 2).  However, final regulations now apply a Tier 6 NOx production cutoff to all newly- manufactured engines.  This means that if we did not also adopt a provision for the continued production of spare engines, manufacturers would be prohibited from producing Tier 4 engines under the existing type certificates for this purpose.  We see no reason to change our policy of allowing manufacturers to produce new engines for use as spares.  Therefore, the final regulatory provisions allow this practice to continue.
To ensure there would be no adverse environmental effect from allowing the use of a spare engine as a direct replacement for an existing engine, we proposed that the spare could be used only when the emissions for all pollutants of that engine were equal to or lower than those of the engine it replaced.  This proposed requirement was consistent with the ETM, which also contains this allowance.  We received a joint comment from AIA and GAMA stating that this is impractical because, while unlikely, a spare engine might have a different emissions profile for some pollutants than the engine it would replace.  As an example, they stated that the two engines could have somewhat different combustion systems that might make one engine lower in NOx but higher in CO.  They also suggested that EPA should consider the totality of the emissions in the decision, or delete the requirement in the final rule.
These comments are surprising because this ETM provision, as well as the exemption provisions, was subject to significant discussions within CAEP that included the engine manufacturers as well as a representative from AIA.  Nonetheless, in this instance we believe the proposed provision should be modified to accommodate the potential for unusual circumstances as explained by the commenter.
As noted above, AIA and GAMA suggested that EPA consider of the totality of emissions relative to their environmental effects as the basis for evaluating spare engine exemptions.  This would entail understanding and comparing the environmental consequences of the different pollutants.  We find that could be very complicated because different pollutants have different health and welfare end points and consequences. For example, in the illustration offered by the commenters, the effects of LTO NOx and CO are largely unrelated to one another.
We think a preferred option to evaluating total environmental effects, or even dropping the provision entirely, is to incorporate an anti-backsliding requirement which ensures that at a minimum the excepted spare engine at least meets the same emission standards that are applicable to the engine it is replacing. For this reason, in response to the AIA and GAMA comment, we are modifying this provision in the final rule to allow an excepted spare engine to have different emission levels compared to the engine it replaces as long as it remains compliant with each of the applicable emission standards and any other requirements of its type certificate.  Given the limited number of spare engines in the fleet, we expect allowing these engines to have somewhat different emissions profile from engines they are replacing will have no significant adverse environmental effect.  This is especially true given that we expect the emissions of an excepted spare engine will be equal or better than the engine it is replacing in most cases in accordance with the basic tenant of the ETM.
We are not requiring engine manufacturers to obtain FAA or EPA approval before producing spare engines.  However, they must submit information about the production of spare engines in an annual report to EPA (see section III. D for more on the annual report).  We proposed that because manufacturers are not required to seek or obtain formal approval to produce spare engines, this allowance was referred to as an "exception" rather than an "exemption".  This terminology would be consistent with current FAA regulations.  Furthermore, we proposed that the permanent record for each engine excepted under this provision would need to indicate that the engine is an excepted spare engine and the engine itself would need to be labeled as "EXCEPTED SPARE." in accordance with FAA marking requirements of 14 CFR.
We received comments relating to allowing spare engines to be produced without requiring prior approval and the use of the terms "exceptions" or "excepted."   The Air Transport Association (ATA) appreciated that there would be no case-by-case approval, noting that it simplifies administering the provision for FAA without compromising the structure of the exemptions program set forth in the ETM.  Regarding the terminology, AIA and GAMA noted that the terminology was inconsistent with current engine name plate labeling practices.  They stated that engines are currently either marked "COMPLY" or "EXEMPT" for emissions. Both organizations generally felt the change in terminology for spare engines might be concerning to the operators holding an engine with a plate reading "EXCEPTED."  They concluded that the name plate for spare engines should continue to use "exempt."  The ATA appeared to give at least tacit approval to the new terminology by acknowledging without objection that spare engines would be labeled accordingly.
First, we are puzzled that operators with a spare engine labeled as "excepted spare" rather than "exempt" may have a concern, because AIA and GAMA did not elaborate on just what the concern might be.  Without at least an example, we are unable to discern the nature of the concern and respond directly to it.  We also find it puzzling that the two organizations that represent aerospace manufacturers expressed a concern regarding operators of aircraft and aircraft engines when the actual organization representing those companies, ATA, did not express such a concern.
Second, regarding the terminology, the Tier 6 production cutoff does not apply to the continued production of engines that are designated spares. Spare engines are produced to replace a similar engine already in service that was removed from service for maintenance purposes. Accordingly, the production of a spare engine is not restricted by the production cutoff, and the regulation does not apply to these engines.  The non-applicability of the cutoff eliminates the need to process an exemption for continued production of these engines beyond December 31, 2012.
Conversely, engines that are intended to be produced for new installations (i.e. not replacing an engine already in service) are subject to the production cutoff regulation and the continued production of such engines beyond the cutoff date would require a grant of exemption. Since the production of spare engines is not subject to the new cutoff regulations, the FAA proposed and the EPA accepted the idea that referring to these engines as exceptions to the regulation was more appropriate than requiring case-by-case consideration of exemptions when the regulation did not apply.
Moreover, the word "exemption" is a meaningful regulatory term.  It is used by the FAA in 14 CFR Part 11 to mean that an applicant is subject to a particular regulation and is requesting time-limited relief under a specific set of criteria.  It is a specialized form of rulemaking.  When an entity or its product is specifically left out of a regulatory provision, it is considered "excepted".  Any regulation adopted by the FAA would use these terms consistently.
As already mentioned, assuming incorporation of these provisions by the FAA, engines meeting the requirements for spare engines could be produced and entered into commerce without prior approval from EPA or FAA.  It is important to note that while spare engines would be excepted from the Tier 6 NOx standards being promulgated today, they still need to be produced under an FAA type certificate.  (This FAA oversight would serve the same role as the exemption approval step envisioned by ICAO in its ETM language for spare engines.)  We also expect little or no additional burden for manufacturers, since we are not establishing new restrictions, monitoring, recordkeeping, or reporting requirements other than the end of year report.
b.  New Provisions for Engines Installed in New Aircraft
The primary purpose of allowing limited continued production of Tier 4 engines is to provide for an orderly implementation of the Tier 6 NOx production cutoff.  It addresses engines reaching the end of their production cycles in the time frame when new emission standards take effect.  The typical production cycle would have annual production volumes ramp up quickly, remain at relatively large volumes for several or many years, and then fall off over a few more years.  When new emission standards are adopted in the middle of a production cycle to take effect a few years later, manufacturers generally devote technical resources to bring into compliance those engine models expected to be produced in large numbers in the time frame when the new standards are in effect.  In contrast, they may plan not to invest in upgrading the emissions of engine models that would be very near the end of their normal production cycles when compliance with the new standards becomes required.  The actual length and shape of this tail of production volumes can be affected by factors not fully within the engine manufacturers' control, e.g., unexpected market demand.  Thus, exemptions may be justified if a manufacturer does not complete the production cycle before the production cutoff date and projected production volumes are not adequate to justify investing the necessary resources to reduce emissions or there are other technological issues.
Furthermore, in certain exceptional circumstances exemptions may also be appropriate.  These are "hardship" situations that may arise as a result of unforeseen technical or economic circumstances or events beyond control of the manufacturer.  For example, this could vary from unexpected problems with technology upgrade programs to labor disruptions or natural events disrupting production or parts availability.
Our regulations currently address these kinds of situations in section 87.7(c), entitled, "Exemptions for New Engines in Other Categories."  We are replacing this provision with a new set of provisions addressing exemptions for new engines.
i.  Time Frame and Scope
The final regulations allow engine manufacturers to request an exemption for newly-manufactured engines not meeting the Tier 6 NOx standards so they may be installed in new aircraft.  If granted, manufacturers may produce a limited number of these newly-manufactured engines in a four year time period beginning after December 31, 2012 and going through December 31, 2016.  This four-year time period is consistent with the ETM.  The period for any given approved exemption could be shorter depending on the specifics of the application, but it could not be longer.  This exemption limits NOx emissions from engines that are covered by a valid type certificate issued by FAA.  The engines must meet all other applicable requirements.  More specifically, an engine exempted from the Tier 6 NOx standards must be covered by a previously issued type certificate showing compliance with the Tier 4 NOx standards, as well as the current HC, CO, fuel venting, and smoke standards.
As explained above, the scope of the exemption provisions are limited to newly-manufactured engines that do not comply with the Tier 6 NOx standards.  No need has been identified to apply such exemption language to the other regulated exhaust pollutants, i.e., smoke, hydrocarbons and carbon monoxide.  The emission standards for those pollutant species have remained unchanged for nearly three decades and present no technical issues for modern turbofan engines.  If new emission standards for these pollutants are considered in the future, the potential need for exemption provisions will also be assessed at that time.
We received comments requesting that exemptions be available for newly-certified engines in addition to newly-manufactured engines.  General Electric Aviation (GE) stated that unforeseen circumstances may arise during the lengthy aircraft engine development process that necessitates a change in design, and that may affect the ability of that engine model to meet the prevailing Tier emission standard at certification.  For that reason, GE concluded that exemptions for newly-certified engine would be beneficial.  The AIA and GAMA jointly stated that the existing 40 CFR section 87.7(c) not only provides the flexibility to exempt newly-manufactured engines from a production cutoff, but also for newly-certificated engine models subject to any emission standards, e.g., the Tier 8 NOx standards.  They requested that this flexibility should be retained.
Regarding the availability of exemptions for newly-certified engine models, the proposed regulatory text made clear that the exemption provisions would only apply to newly-manufactured engines.  Specifically, the intent was to establish provisions for newly-manufactured engines to address the potential technology and economic adversities that may arise as part of adopting the Tier 6 production cutoff. The ICAO ETM provisions are clearly intended for that same purpose.  Also, the original intent of EPA's current exemption provisions in section 87.7(c), which we are modifying in this rulemaking, is clear from the proposed rulemaking and final rulemaking that resulted in those provisions. The March 24, 1978 proposal described the concern as "...engines which are nearly [at] the end of their production life would be terminated prematurely because there would be insufficient future sales to justify incorporating emission controls." (See 43 FR 12619, March 24, 1978.)  The December 30, 1982 final rule referenced "...the removal of an engine model from the market because of its failure to comply." (See 47 FR 58468, December 30, 1982.)  Obviously, the intent of the existing exemption provision cited by AIA and GAMA was to make it apply only to newly-manufactured engines.
As a general matter, we believe an exemption from the Tier 6 standard, or any other standard, for newly-certified engine models is speculative at this time and would undermine the goal of regulatory compliance by new engine designs.  In any event, neither the current ICAO Annex 16, Volume II provisions nor the ETM provide for newly-certified engine exemptions.  We believe that such would be a fundamental shift from Annex 16 and the ETM should be explored within the framework of ICAO/CAEP.  Furthermore, engine manufacturers already have significant leadtime between the date CAEP adopts a new emission standard and the standard's effective date, e.g., usually 3-5 years.  Finally, engine manufacturers historically design new engine models to comply with the most stringent future standard that also provides for a longer development time horizon. Therefore, we are promulgating the exemption provisions for newly-manufactured engines as proposed.
	ii.  Production Limit
The final regulations reflect the essence of the general exemption language for exhaust emission standards regarding how to determine the number of allowable exemptions that is embodied in current section 87.7(c) of the regulations.  That provision generally states that the FAA, with EPA's concurrence, may grant exemptions to exhaust emission standards based on factors such as adverse economic impact on the engine manufacturer, aircraft manufacturer, or airline industry; in addition to the effects on public health and welfare.
As a result, section 87.7(c) does not specify a nominal number of exemptions.  Rather, each request for exemption would be evaluated on a case-by-case basis, using the information provided by the applicant and any other relevant information that is available to FAA and EPA at the time.  Any approved exemption would include a specific limit on the number of such engines based on that information and is not defined on a basis such as type certificate.  (See section III.B.b.iii for a description of what the request must contain.)  The intent, of course, would be to exempt the minimum number of engines that can be clearly justified, including a consideration of the public health and welfare effect associated with the exemptions.
In the proposal, we acknowledged that our approach to determining limits on the number of exempt engines differs from the language contained in the current ICAO ETM guidance.  The ETM states that "[t]he number of engines exempted would normally not exceed 75 per engine type...."   We chose not to propose adopting this language on the nominal number of engines based on a single type certificate.  Our reasons for this deviation were detailed in the proposal and are summarized below.
At the time of the CAEP deliberations, the ICAO Emissions Data Bank identified 20 unique engine models/sub models that could have been affected by the production cutoff.  Those models had valid type certificates and, therefore, were considered to be "in production."  During further discussions the engine manufacturers clarified that most of these 20 were not in active production because the airlines normally purchase new aircraft with engines meeting the latest emission standards.  Nonetheless, it was stated that if the demand arose, 14 of these 20 models could potentially be produced under the exemption provisions since they had valid type certificates and met the previously mentioned exemption emission requirements.[,][,][,]   After much deliberation, the CAEP technical working group settled on a value of 75 engines per type certificate over the four years for the ICAO ETM guidance based on the information available at the time.
This value and the maximum number of engines it could represent were of immediate concern to EPA.  First, in a hypothetical worst case, the number of potentially exempted engines was very large relative to average annual engine sales  Second, it was unclear to us if that number of potential exemptions, i.e., 75 per type certificate, was necessary.  Both of these gave the appearance that the ETM nominal limit was potentially very excessive.  We also noted that, from a broader perspective, while EPA regulations normally include hardship type provisions, it is abnormal for EPA to include specific transitional exemptions of this magnitude in our regulations.
As we continued efforts to identify how many exemptions might potentially be needed for the CAEP/6 production cutoff, three new pieces of information became available during the development of the proposed rule that were not considered during the deliberations leading up to the ICAO decision for the ETM guidance.  First, a review of previously unavailable information on past exemption requests to FAA under the previous less specific ICAO language indicated that of the eight requests granted since 1983, only three involved exemptions during standards transition (two related to smoke for turboprop engines and one related to NOx for a turbofan engine).  These three exemption petitions in combination ultimately affected less than 50 engines.  Second, engine manufacturers indicated individually that the potential need for exemptions was not as large as EPA understood during the technical working group deliberations, and that absent unforeseen events, a much smaller value was workable on a per manufacturer basis as opposed to a per type certificate basis.[,][,]  Third, our most recent discussions with the engine manufacturers that are directly affected by the proposed Tier 6 NOx standards, i.e., CAEP/6 standards,  concluded that only one or two engine models may be candidates for exemptions.  Those discussions also concluded that the likely potential number of justifiable exemptions would be less than 75 in total.
Considering all of these factors and the basic intent of the CAEP ETM exemption provisions, we proposed to adopt language in our new regulatory text addressing exemptions that reflects the essence of the general exemption language for exhaust emission standards embodied in current section 87.7(c) of the regulations.  As stated above, that provision generally states that the FAA, with EPA's concurrence, may grant exemptions to exhaust emission standards based on factors such as adverse economic impact on the engine manufacturer, aircraft manufacturer, or airline industry; in addition to the effects on public health and welfare.    We also noted that the proposed exemption provision had no cost associated with it for the government or industry, and there is no difference in potential cost savings under either approach.  Both were designed to provide manufacturers with an opportunity to reduce costs or other adverse effects should the need for exemptions arise.
Finally, we concluded that the proposed approach addressed the intent of the ICAO guidance in addition to the potential needs of the engine manufacturers, while minimizing the potential for adverse environmental impacts from exemptions and aligning with EPA's general approach with regard to exemptions and hardship provisions.
We received several comments focusing primarily on the number of exemptions and the underlying process that is embodied in the ETM and our proposal.  General Electric Aviation  (GE) maintained that harmonization with the international community is not only required by the Chicago Convention, but also provides streamlined processes and procedures within the regulated industry.  They argued that any purported benefits to EPA's unique exemption scheme were outweighed by setting up a conflict with the remainder of the world.  They also suggested that if EPA wants a different approach for evaluating exemptions, it would be more appropriate to work inside the ICAO/CAEP process toward that end.
The ATA commented that EPA's case-by-case approach to determining the number of engines is a rejection of the ICAO/ETM provisions that limit "...the number of exemptions ... to 75 engines per type certificate...".  They argued that this would create a serious discontinuity between the U.S. and the rest of the world, undermining ICAO's objective of international uniformity.  The ATA also argued that the ICAO exemption limits are intended to be coordinated among international aviation authorities, and that differing rules would make this impracticable.  As evidence of this problem, ATA cited the European Aviation Safety Agency's (EASA) proposed rulemaking, which they noted was based on the assumption that the ICAO proposals will be adopted unaltered by other aviation authorities of the world.  The ATA also stated that the ICAO ETM guidance document supplements the official standards of Annex 16, Vol. II and, therefore, the ETM provides technical elaboration on the implementation of Annex 16.  From this ATA concluded that differing practices in this regard are counter to the Chicago Convention.
Regarding consistency with the Chicago Convention, our proposal thoroughly explained that the ETM is guidance material; not an ICAO standard or regulation of any type.  Moreover, even if the ETM were wrongly considered a standard, consistency is not compelled when a deviation is justified, and we were comfortable with our proposed exemption provision for those reasons.  Therefore, we disagree with the commenters on this point, and specifically with ATA's comment that the ICAO guidance is effectively the equivalent of an ICAO Annex 16 standard.
Turning to ATA's comment regarding the ETM cap of 75 engines per type certificate, we first want to point out that this is not a maximum limit on the number of potential exemptions per type certificate.  Rather the ETM provision is an expectation that "[T]he number of engines exempted would normally not exceed 75 per engine type certificate ...." as stated in the document.  With this perspective both the ETM and our approach are similar in that the maximum number of exempted engines is based on a consideration of the petitioner's justification for such exemptions.
Finally, we disagree with the comment that the differences with the ETM make international coordination unworkable.  In fact, one of the proposed justification elements, i.e., how many affected aircraft will be registered in the U.S. and other countries (estimate allowed), was described in the preamble for the proposal as being aimed at helping to facilitate consultation and coordination.  Also, as noted above, the ETM's expectation that exemptions would normally not exceed 75 per type certificate and our proposal are similar in that the maximum number of exempted engines under both approaches is based on a consideration of the petitioner's justification for such exemptions.  As we described in the proposal, it now appears that only one or two engine models may be candidates for exemptions, and that the potential number of justifiable exemptions would be less than 75 in total.  We do not think coordination with foreign aviation authorities, most likely EASA, with these few exemptions should pose any problems.  Therefore, we find nothing in the justification elements that should impinge upon the ability to internationally collaborate and consult on exemptions.
After considering the above comments on the number of exemptions and the underlying process embodied in the ETM and our approach, we are promulgating the provisions relating to the comments as originally proposed.
iii.  Exemption Requests
We are establishing a process for requesting exemptions (for engines used on new aircraft) that would be more formal and structured than the current process.  We are requiring manufacturers submit their request to the FAA, as currently required.  The FAA will then share the submittal with EPA and execute the consultation process.
To ensure that we have the information necessary to evaluate exemption requests in this specific manner, the requests need to include the following details to describe the specific engine model for which the manufacturer is requesting the exemption.  The final provisions contained in §87.50, which are summarized below, are consistent with and in some areas expand on the provisions in the ETM:
General Information
::  Corporate name and an authorized representative's contact information (including a 	signed statement verifying the information);
::  Description of the engines for which you are requesting the exemption, including the 	engine model and sub-model names;
::  The number of engines that you would produce under the exemption and the period 	during which you would produce them;
::  Identify the authorizing type certificate (type certificate number and date);
::  Information about the aircraft in which the engines will be installed, including the 	airframe models and expected first purchasers/users of the aircraft, and the countries in 	which you expect the aircraft to be registered (including an estimate of how many will be 	registered in the U.S.); and
::  List of other certificating authorities from which you have requested (or expect to 	request) exemptions, and a summary of each request.
Justification and Impacts Assessment
::  A detailed description and assessment of the environmental impact of granting the 	exemption;
::  Technical issues, from an environmental and airworthiness perspective, which may 	have caused a delay in compliance with a production cutoff, if any;
::  Any economic impacts on the manufacturer, operator(s), and aviation industry at large; 	and
::  Projected future production volumes and plans for producing a compliant version of the 	engine model in question.
 Other Factors
::  Hardship: Impact of unforeseen technical circumstances, business events, or other 	natural or manmade calamities beyond your control, and
::  Equity issues in administering the production cutoff among economically competing 	parties.