EO12866_Aircraft Engine Emission Standards 2060-AO70 NPRM Rulemaking Document_2011/03/25

                        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; Proposed Emission Standards and Test Procedures

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.
SUMMARY:  This action proposesseveral new NOxemission standards, compliance flexibilities, and other regulatory requirements for aircraft turbofan or turbojet engines with rated thrusts greater than 26.7 kilonewtons (kN).  We also are proposing certain other requirements for gas turbine engines that are subject to exhaust emission standards.   First, we are proposing to clarify 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 proposing a new reporting requirement for manufacturers of gas turbine engines that are subject to any exhaust emission standard toprovide us with timely and consistent emission-related information.  Third, and finally, we are proposing 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 proposed requirements were first developed.  These proposed regulatory requirements have largely been adopted or are actively under consideration by its member states.  By adopting such similar standards, the United States will (1) further reduce emissions from mobile sources, (2) embrace the science and technology that have considered these issues on an international level, and (3) maintain consistency with these international efforts in accordance with the agreements of the ICAO.
DATES: Comments must be received on or before [insert date 60 days after publication in the Federal Register.]
Hearing: The public hearing will be held [insert dateno fewer than 15 days after publication andat least 30 days before end of comment period]at the Environmental Protection Agency, XXXBuilding, Room Number XXX,1201 Constitution Avenue, NW, Washington, DC20004, Telephone:<PHONE_NUMBER>.  See section VIII for more information about public hearings.
ADDRESSES:  Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2010-0687, by one of the following methods:
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Docket: All documents in the docket are listed in the www.regulations.gov index.  Although listed in the index, some information is not publicly available, e.g., CBI or other information whose disclosure is restricted by statute.  Certain other material, such as copyrighted material, will be publicly available only in hard copy.  Publicly available docket materials are available either electronically in www.regulations.gov or in hard copy at EPADocketCenter, 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 EPADocketCenter is<PHONE_NUMBER>
FOR FURTHER INFORMATION CONTACT:Bryan Manning, Office of Transportation and Air Quality, Office of Air and Radiation, Environmental Protection Agency, 2000 Traverwood Drive, Ann Arbor, MI 48130; telephone number:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>; email<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 Codes[b]
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.  Summary of the Proposal
	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.  NOxInventory Contribution
		1.  Landing and Takeoff (LTO) Emissions
		2.  Non-LTO Emissions
	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 Proposed Rule
	A.  NOxStandards 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 NOxStandards for Newly-Manufactured Engines
	1.  Phase-In of the Tier 6 NOx Standards for Newly-					Manufactured Engines
		2.  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.  Foreign Aircraft
			c.  Voluntary Emission Offsets
		3.  Potential Phase-In of New Tier 8 NOx Standards for Newly-				Manufactured Engines
	C.  Application of Standards for Derivative Engines for Emissions Certification Purposes
	D.  Annual Reporting Requirement
	E.  Proposed 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
	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

I.  Overview and Background
This section summarizes the major provisions of the proposed 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.
Summary of the Proposal

	We are proposing 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 proposing two new tiers of more stringent emission standards for oxides of nitrogen (NOx).  The proposed standards would apply differently to two classes of these engines, i.e., "newly-certified engines" and "newly-manufactured engines."  The newly-certified engine standards would 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 would apply to aircraft engines that were previously certified and manufactured in compliance with preexisting standards, and would require manufacturers to either comply with the newer standards by a specified future date or cease production.  Newly-manufactured engine standards are also sometimes referred to as "production cutoff" standards.Second, we are proposing certain time-limited flexibilities, i.e., the potential for exemptions as defined in the regulations for newly-manufactured engines that may not be able to comply with the first tier of the proposed NOx standards because of specific technical or economic reasons.
	We are also proposing a number of additional changes that would apply toa wider range of aircraft gas turbine engines thanthose thatwould be subject to the proposed new emission standards.  First, we are proposing to define 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 emissions standard for a newly certificated engine.  Second, we are proposing new reporting requirements for manufacturers that produce gas turbine engines subject to any exhaust emission standard.  This wouldprovide us with timely and consistent emission data and other information that is necessary to conduct emission analyses and develop appropriate public policy for the aviation sector.  Specifically, reports wouldbe 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 areonly subject to smoke standards.  Third, we are proposing amendments to the test and measurement procedures for aircraft engines.  Finally, as described in section IV, we are proposing minor amendments to provisions addressing definitions, acronyms and abbreviations, general applicability and requirements, exemptions, and incorporation by reference.
	Most of these proposed regulatory requirements have already been adoptedor are actively under consideration by the United Nation's International Civil Aviation Organization (ICAO).  The proposed requirements would bring the United States into alignment with the internationalstandards 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 herjudgment causes or contributes to air pollution thatmay 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. Departmentof 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 insure 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 proposal 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 emissions from aircraft engines in 1973.  Since that time, we have worked with the FAA and 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 190 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 practicesthat 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 assuringthat aircraft of any member State will be permitted to operate in any other member State.  Third, and finally, to ensure that international commerceis 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 (foreign-flagged carriers) would only be required to comply with ICAO standards or more stringent standards imposed by their own nations, if applicable.
ICAO Council'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 study groups, work groups, committees and other contributing memberships that include atmospheric, economic, aviation, environmental, and other professionals.  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 proposal.  First, in a 1997 rulemaking, we made our emission standards and test procedures moreconsistent 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.)  This included new NOx emission standards for newly-manufacturedcommercial turbofan engines (those engines built after the effective date of the regulations that were already certified to pre-existing standards) and for newly-certified commercialturbofan 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 commercialturbofan engines.  Second, in our most recent rulemaking in 2005, we promulgated more stringent NOx emission standards for newly-certified commercialturbofan 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 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 newly-certified engine models beginning 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 is currently considering the CAEP/8 recommendations.  We expect final ICAO action regarding the CAEP/8 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 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.  NOx is a precursor to the formation of ozone.Many 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 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, theemissions associated with all ground and flight operations are generally referred to as full flight emissions.
The aircraft engine NOx emission inventories for the LTO and non-LTO flight regimes described above are discussed separately in the following sections.
 1.  Landing and Takeoff 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 land 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 operations contributed about 97 thousand tons to the national NOX inventory, and according to the EPA National Emissions Inventory for 2008, the contribution of commercial aviation NOx emissions is less than 1% of the total inventory for the United States.  A summary of the national inventory is shown in Table 1.
       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
This historical analysis also included an assessment of selected ozone nonattainment areas (NAAs).  The top 25 ozone NAAs were identified based first in terms of NAAs with airports which had high commercial traffic volumes and then those with the largest population. There was some overlap, and this led to a total of 41 NAAs for the study.  These 41 NAAs collectively include 200 airports, accounting for about 70 percent of commercial air traffic operations.  Current (2008) NOX emissions for these 41 NAAs are shown in Table 2.  The relative contribution of aircraft in any given NAA would vary based on activity in other transportation and industrial sectors.

     Table 2: Current NOX Emissions in Selected Ozone Nonattainment Areas
Nonattainment Area
                             2008 Total NOX (tons)

Albuquerque, NM
                                      382
Anchorage, AK
                                     2562
Aspen
                                      19
Atlanta, GA
                                     5834
Baltimore, MD
                                     1159
Boston-Lawrence-Worcester (eastern MA), MA
                                     1907
Boston-Manchester-Portsmouth (southeast NH), NH
                                      224
Charlotte-Gastonia-Rock Hill, NC-SC
                                     2039
Chicago-Gary-Lake County, IL-IN
                                     6024
Cincinnati-Hamilton, OH-KY-IN
                                     1289
Cleveland-Akron-Lorain, OH
                                      712
Dallas-Fort Worth, TX
                                     3900
Denver-Boulder-Greeley-Fort Collins-Loveland, CO
                                     2685
Detroit-Ann Arbor, MI
                                     2328
El Paso, TX
                                      224
Greater Connecticut, CT
                                      413
Houston-Galveston-Brazoria, TX
                                     3062
Indianapolis, IN
                                     1093
Las Vegas, NV
                                     2314
Los Angeles South Coast Air Basin, CA
                                     6532
Louisville, KY-IN
                                     1211
Memphis, TN-AR
                                     2996
Milwaukee-Racine, WI
                                      558
Minneapolis-St Paul, MN
                                     2170
New York-N. New Jersey-Long Island, NY-NJ-CT
                                     10319
Philadelphia-Wilmington-Atlantic City, PA-NY-MD-DE
                                     2432
Phoenix-Mesa, AZ
                                     2307
Pittsburgh-Beaver Valley, PA
                                      508
Providence (entire State), RI
                                      240
Raleigh-Durham-Chapel Hill, NC
                                      593
Reno, NV
                                      249
Riverside County (Coachella Valley), CA
                                      75
Sacramento Metro, CA
                                      608
Salt Lake City, UT
                                     1250
San Diego, CA
                                     1046
San Francisco Bay Area, CA
                                     4447
San Joaquin Valley, CA
                                      86
Seattle-Tacoma, WA
                                     2242
St. Louis, MO-IL
                                      813
Syracuse, NY
                                      152
Washington, DC-MD-VA
                                     3028
Table 3 shows how commercial aircraft operations are projected to rise in the future.   As operations increase, the inventory impact of these aircraft on national and local NOX inventories and on ozone and PM levels 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

2.  Non-LTO Emissions
Historically, emphasis has been placed on evaluating emissions during LTO operations given their obvious impact on local air quality.  Less emphasis has been placed on evaluating emissions from non-LTO operations (emissions at altitudes greater than 3,000 feet above ground level) based on the assumption that such emissions have a lesser impact on local air quality.  However, modeling by Barrett et al. (2010) finds that these upper atmosphere emissions may adversely affect public health more than was previously thought.  Based on the data and methodology of the authors, this effect is caused primarily by two pathways:
   1. The formation of fine particulate matter, i.e., PM2.5, from emission of gaseous precursors of PM (NOx and SO2) in the upper atmosphere that are then transported to the lower atmosphere.  (The formation of secondary PM2.5 from NOx is discussed further in section II.B.1.b).
   2. Aviation NOx emissions promote ozone formation throughout the troposphere and hence increase OH concentrations. This increases the oxidation of non-aviation SO2 (such as that emitted from power stations) in the gas phase relative to aqueous oxidation and dry deposition thereby increasing atmospheric sulfate (a type of PM2.5) concentrations.
The authors of this work estimated that full flight emissions cause almost 10,000 premature mortalities (their central estimate) per year worldwide, with over 450 per year in the U.S.  The pollutants emitted during cruise operations were estimated to be about 80 percent of the population-weighed PM2.5 from aviation, with the remainder being associated with LTO operations (although they note the LTO portion may be under-estimated). The study asserts that over 380 premature mortalities per year in the U.S. can be attributed to secondary PM2.5 associated with non-LTO operations.  We request comments on the results of these studies, the existence of other research into this area, and the implications of these analyses on assessing the need for additional controls on aircraft engine emissions in the future.

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 proposing to align will help reduce ambient ozone and secondary PM levels and thus will help areas with airports achieve and/or maintain compliance 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 by the reaction of 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 can be transported hundreds of miles downwind from the sources of precursor emissions, resulting in elevated ozone levels even in areas with low local VOC or NOX emissions.

	b.  What is Particulate Matter?

      The discussion focuses on 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). Current NAAQS use PM2.5 as the indicator for fine particles (with PM2.5 referring to particles with a nominal mean aerodynamic diameter less than or equal to 2.5 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 aerodynamic 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 pollutants 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 through the oxidation of nitric oxide (NO) emitted when fuel is burned at a high temperature.  NO2 can dissolve in water vapor and further oxidize to form nitric acid which reacts with ammonia to form nitrates, an important component of ambient PM.  NOX along with non-methane hydrocarbon (NMHC) 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 (ozone AQCD) 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 recent 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 evidence associated with PM2.5, PM10-2.5, and ultrafine particles (UFPs), and concludes the following.
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 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 (COPD) and respiratory infections.The ISA notes that long-term exposure to PM2.5(months to years) is associated with the development/progression of cardiovascular disease, premature mortality, and respiratory effects, including reduced lung functiongrowth, 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 PM2.5and cardiovascular effects and 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 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 cardiovascular effects, such as hospitalization for ischemic heart disease.  There is also suggestive evidence of a causal relationship between short-term PM10-2.5 exposure and mortality and respiratory effects.  Data are inadequate to draw conclusions regarding the health effects associated with long-term exposure to PM10-2.5.
For UFPs, the ISA further 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 UFPs and respiratory effects. Data are inadequate to draw conclusions regarding the health effects associated with long-term exposure to UFP's.
   	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 following30-minute exposures of asthmatics to NO2 concentrations as low as 0.26 ppm.  In addition, small but significant increases in non-specific airway hyper-responsiveness were reported following 1-hour exposuresof asthmatics to 0.1 ppm NO2.  Second, exposure to NO2 has been found to enhance the inherentresponsiveness of the airway to subsequent nonspecific challenges in controlled human exposure studies of asthmatic subjects.   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 U.S.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 (Picearubens) 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 and damage to forest productivity.  Across the U.S. there are many terrestrial and aquatic ecosystems that have been identified as particularly sensitive to nitrogen deposition.  The most extreme effects resulting from nitrogen deposition on aquatic ecosystems are due to nitrogen enrichment which contributes to "hypoxic" zones devoid of life.  Three hypoxia zones of special concern in the U.S. are the zones located in the Gulf of Mexico, the Chesapeake Bay in the mid-Atlantic region, and Long Island Sound, in the northeast U.S.
The deposition of airborne particles 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.   Particles 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 2009PM 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 proposing would impact ambient concentrations of air pollutants.  Nationally, levels of PM2.5, ozone, and NOX are declining.  However as of 2008, approximately 127 million people lived in counties that exceeded any 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 nonattainment areas are required to take action to bring those areas into compliance in the future.  Based on the final rule designating and classifying 8-hour ozone nonattainment areas for the 1997 standard (69 FR 23951, April 30, 2004), most 8-hour ozone nonattainment areas will be required to attain the ozone NAAQS in the 2007 to 2013 time frame and then maintain the NAAQS thereafter.EPA is reconsidering the 2008 ozone NAAQS.  If EPA promulgates different ozone NAAQS as a result of the reconsideration, these standards would replace the 2008 ozone NAAQS and EPA would subsequently designate nonattainment areas for the revised primary ozone NAAQS.  The attainment dates for areas designated nonattainment for a revised primary ozone NAAQS could range from 2015 to 2032, depending on the severity of the problem.
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 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.   The aircraft engine emission standards being proposed today were approved by ICAO/CAEP and wouldhave an implementation date of 2013.  Therefore, the aircraft engine emission reductions that are being proposed today should be useful to states in attaining or maintaining the PM2.5 NAAQS.
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 16 counties with a population of almost 35 million may not attain the 2008 ozone standard of 0.075 ppm (75 ppb).  In addition, our air quality modeling projects that in 2030 at least 9 counties with a population of almost 28 million may not attain the 1997 annual PM2.5 standard of 15 ug/m[3] and 26 counties with a population of over 41 million may not attain the 2006 24-hour PM2.5 standard of 35 ug/m[3].  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, wouldalso benefit from any reductions in NOX ensuring long-term maintenance of the NAAQS.
There are currently no NO2 nonattainment areas.  However, the NO2 standards were recently revised and a new 1-hour NO2 standard was promulgated.  Nonattainment area designations for the 1-hour NO2 standard are expectedto be finalized in 2012.  These proposed aircraft NOx reductions would be useful to states in attaining or maintaining the NO2 standards.
III.  Details of the Proposed Rule
We are proposing 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 would potentially apply to newly-certified engines.  Newly-certified aircraft engines are those thatwould 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 proposing to apply the first tier of the two tiers of standards to newly-manufactured engines.  Newly-manufactured aircraft enginesare 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 would need to 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 sometimesreferred to a "production cutoff," for obvious reasons.   Again, we are proposing 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 proposed in today's action.  First, we are proposing to revise provisions addressingcertain time-limited flexibilities, i.e., potential exemptions, for newly-manufactured engines that may not be able to comply with the first tier of the proposed new NOx standards because of specific technical or economic reasons.  Second, we are proposing to define 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 emissions standard for a newly certificated engine.  Third, we are proposing 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.The proposed standards would meet our treaty obligation under the Convention on International Civil Aviation as previously described in section I.B.   Fourth, we are proposing several amendments 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 proposing amendments to current regulatory provisions addressing 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 discussed in section III.D.,the proposed amendments reflect those changes that were previously adopted by ICAO or that CAEP has recommended for adoption by ICAO in the near future.  In this latter case, we are proposing these standards and recommended practices at this time rather than wait until ICAO takes final action to help ensure that our standards, and the FAA's implementing regulations, are adopted in a timely manneronce ICAO completes its process.  We anticipate that our final standards would generally conform to ICAO's final standards, once adopted.  This wouldbetter enablethe regulated industry to respond to new, globally harmonized requirements in an orderly manner, which is important given the international nature of the market for the aircraft engines that would be affected by today's proposed rule.  It would also avoid continuing the significant lag time that has sometimes occurred between ICAO's adoption of international standards and our adoption of corresponding standards under U.S. law.  To the extent ICAO adopts standards that differ from those recommended by CAEP before we issue our final rule, we would then consider whether to make conforming amendments in our final standards, or to issue a supplemental proposal reflecting the amended ICAO standards, if appropriate.
This proposal 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 proposed emission standardswerewell documented by our own analyses and CAEP as described later in this section and in section V., Regulatory Impacts.   We think that the proposal would provide 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 regardingleadtime, noise, safety, and the technical feasibility of the proposed standards.  Today's proposal is also consistent with U.S. treaty obligations under the Chicago Convention as described in section I.C., because the proposed requirements are consistent with current ICAO standards or those that we expect ICAO to adopt prior to the promulgation of any final rule.
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 proposing revised exhaust emission standards for HC, CO, or smoke, which would remain in effect as currently promulgated.  All engines subject to the proposed 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 proposing to include these existing HC, CO, and smoke standards in a new section 87.23, which would also contain the proposed Tier 6 and Tier 8 NOx standards, we are not actually proposing new standards, 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.
We are proposing to adopt a new naming convention in this preamble and the regulatory text to more easily distinguish between the proposed 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 proposed NOx standards, which are consistent with CAEP/6, will be referred to as Tier 6 in the remainder of today's notice.  The second tier of proposed standards will be referred to as Tier 8, which is consistent with 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 NOxstandards themselves, except to the extent that upon the effectiveness of a final rule reflecting today's proposal 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 proposing 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 26.7kN.  (See section III.B for a discussion of how these standards would 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 a 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.  Each of the proposed tiers is described separately below.
1.  Tier 6 NOx Standards for Newly-Certified Engines
This first tier of proposed standards is equivalent to the CAEP/6 NOx limits that were already adopted by ICAO and became internationally effective after December 31, 2007.  Given that aircraft turbofan engines are international commodities, engine manufacturers have already introduced engine models after that date that demonstratecompliance with these internationalstandards, or are already planning to do so for upcoming engine designs.  Based on this, and on our evaluation of the necessary leadtime, we are proposing that this tier of standards take effect immediately upon the effective date of our final regulations.
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 89kN, while lower output engines are defined as having rated thrusts less than 89kN but greater than 26.7kN.  The proposed Tier 6 NOxstandards for each of these power grouping are described separately below.
a.  Numerical Emission Limits for Higher Thrust Engines
The proposed 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 corresponding CAEP/6 standards were derived by CAEP using the following methodology:
::  Make the CAEP/6 standard 12 percent more stringent than the CAEP/4 requirement at a pressure ratio of 30;
::  Retain the same percent reduction, i.e., 12 percent, for pressure ratios below 30;
::  Retain the slope of the CAEP/4 standard for pressure ratios of 30 to 62.5 for the CAEP/6 pressure ratios of 30 to 82.6;
::  Retain the slope of the CAEP/4 standard for pressure ratios equal toor greater than62.5 for the CAEP/6 pressure ratios at or above 82.6.
The resulting proposed Tier 6 NOx standards for these higher thrust engines are presented in Figure 1 along with the most recently adopted existing EPA NOxstandards, 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 proposed Tier 6 standards (CAEP/6) are referred to as being 12 percent more stringent than the existing EPA NOxTier 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 proposed Tier 6 NOx standards for newly-certified gas turbine engines with rated thrusts between 26.7 and less than 89.0kN 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 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 are well documented and increase progressively as size is reduced (from around 89kN).  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 proposed 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 proposed Tier 6 NOx standards for lower thrust engines based on the engine size versus technological challenge described in the previous paragraph.
Comparing the proposed lower and higher thrust standards at 89kN, which is the demarcation point between the two sets of standards, shows that the standards for lower thrust engines arenumerically 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 89.0kN delineation point.
Again focusing only on 89kN engines, the proposed Tier 6 standards represent a 12 percent reduction from the existing EPA CAEP/4-based standards (Tier 4) 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 proposed 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 89kN, 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 89kN decreasing to 0 percent at 26.7kN.

2.  Tier 8 NOx Standards for Newly-Certified Engines
The second tier of proposed standards, i.e., Tier 8, are equivalent to the NOx limits that were most recently recommended at CAEP/8 in February 2010for adoption by ICAO.  The CAEP/8 recommended standards have a recommended effective date afterDecember 31, 2013.  As discussed further in section V. of today's notice, we agree with CAEP that this provides engine manufacturers with adequate leadtime to respond to these more stringent NOx standards considering the technical feasibility and cost associated with the requirements.  Therefore, we are proposing that this tier of proposed standards would take effect on January 1, 2014, provided ICAO adopts CAEP/8's recommended standards and effective date.  If ICAO adopts different standards or a different effective date, we would evaluate whether to similarly adopt correspondingly different standardsand effective dates,or seek further public comment before doing so.
As with the Tier 6 NOx standards, the basic form of the Tier 8 standards for turbofanengines is different for higher- and lower-rated thrust engines.  Higher output engines are defined as having rated thrusts equal to or greater than 89kN, while lower output engines are defined as having rated thrusts less than 89kN but greater than 26.7kN.  The longer-term standards for each of these power grouping are described separately below.
a.  Numerical Emission Limits for Higher Thrust Engines
The proposed Tier 8 NOx standards for newly-certified turbofanengines 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 corresponding CAEP/8 standards were derived by CAEP using the following methodology:
::  Make the CAEP/8 standard 15 percent more stringent than the CAEP/6 requirement at a pressure ratio of 30;
::  Retain the slope of the CAEP/6 standard for pressure ratios below 30;
::  Retain the slope of the CAEP/6 standard for pressure ratios of 30 to 82.6 for the CAEP/8 pressure ratios of 30 to 104.7;
::  Retain the slope of the CAEP/6 standard for pressure ratios above 82.6 for the CAEP/8 pressure ratios equal to or greater than 104.7.
The resulting proposed Tier 8 NOx standards for these higher thrust engines are presented in Figure 4 along with the proposed 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 proposed Tier 8 standards (CAEP/8 ) are referred to as being 15 percent more stringent than the proposed 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 technology engines ranges from about 11 to 19 percent.
b.  Numerical Emission Limits for Lower Thrust Engines
The proposed Tier 8 NOx standards for newly-certified gas turbine engines with rated thrusts between 26.7 but less than 89.0kN 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 proposed 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 proposed Tier 8 NOx standards for lower thrust engines based on the engine size versus technological challenge described in the previous paragraph.  First, the proposed 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 89kN, where the engine sizes and ability to incorporated low-NOx technologies are comparable.  This same characteristic was observed for the proposed Tier 6 standards.  Second, as shown below in Figure 5 for 89kN engines, at this thrust rating the proposed Tier 8 standards represents a 15 percent reduction from the proposed 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 proposed 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 89kN, may varyby pressure ratio.   In the region of pressure ratios represented by today's engines, the results are identical to those shown in Figure 6 at 26.7kN, 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 89kN engines with pressure ratios of about 15.

B.  Application of the Tier 6 NOxStandards to Newly-Manufactured Engines
This section describes our proposal toapply the proposed Tier 6 NOx standards to newly-manufactured engines, and our proposed amendedtemporary flexibilities for newly-manufactured engines that may have significant problems complying with these requirements.  Also, consistent with CAEP/8, we are not proposing to apply the 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 proposed Tier 6 NOx standards would apply to all engine types or models that receive a new type certificate after the effective date of the final rule.  We are also proposing to phase-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 orTier 4)and were already being produced for installation on new aircraft prior to the effective date of the final rule.  As a result, manufacturers would 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 foundational to its basic design and purpose and helps to ensure that the full benefits of newer, more stringent requirements will be achieved in a reasonable time.We are, however, proposing certain limited flexibilities for engines that cannot be made compliant because of specific technical or economic reasons, as discussed later in this section.
The proposed effective date of January 1, 2013for 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 2011 time frame, and3) any noncompliant models will be phased out of production because of low market demand.
We think thatthe proposed five-year phase-in period from ICAO'seffective date of the CAEP/6 standards (corresponding to ourproposed Tier 6 NOx standards) for newly-certified engines is adequate for manufacturers and their customers to respond to the new requirements without significantly disrupting their future planning and purchasing decisions.[,]  This phase-in period for applying the Tier 6 NOx standards to newly-manufactured engines is identical to the date for this same requirement that CAEP/8 has recommended to ICAO for adoption.  Therefore, we are proposing that all engines newly-manufactured after December 31, 2012 must comply with the Tier 6 NOx standards.  Again, if ICAO ultimately adopts a production cutoff date that differs from this proposed date, we would evaluate whether to adopt a correspondingly different date in the final rule or to seek further public comment on the change.
      2. Exemption from the Tier 6 Production Cutoff
In conjunction with the implementation of the proposed Tier 6 NOx standards, we are proposing provisions which would allow engine manufacturers to request exemption from meeting the Tier 6 NOxstandards.  These proposed provisions would replace existing provisions addressing exemptions, 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 proposed revisions.)   This section of the preambledescribes these proposed exemption provisions that will be implemented consistent with international guidance as provided in the ICAO Environmental Technical Manual (ETM).[,]The provisions of the ETM guidance were crafted in the context of the CAEP/6 NOx production cutoff deliberations leading up to the CAEP/8 meeting in February 2010.
While we are proposing to revise our regulations, the process for evaluating any request for an exemption and any final decision on its disposition would be unchanged.  In this regard, the FAA is the process owner under its authority contained in section 232 ofthe Clean Air Act. The FAA must consult with EPA in evaluating the merits of any request, and the EPA must formally concur with any decision regarding the granting or denial of the request.
Under the existing regulations, theFAA, with EPA concurrence, may 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 this provision, which was adopted in conjunction with the original emissions requirements, is no longer of any utility, and needs to be deleted to avoid confusion with current standards.  We are also proposing to delete the existing provisions for temporary exemptions based on flights for short durations and infrequent intervals.  These provisionsare not necessary 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, which are operational rather than certification limitations.
The current regulations also provide for permanent exemptions based on consideration of the certain factors specified in §87.7(c).  We are proposing to replace these provisionswith new regulatory text consistent with the ETM that would provide for two separate types of permanent exemptions: exceptions for spare engines and exemptions for engines on new aircraft.  These are summarized below.  (See §87.50 of the proposed regulations for additional details on these exemptions.)
Finally, we are deleting the exemption provisions in §87.7(d).  These provisions, which were intended for when the standards of §§87.11(a), 87.31(a), and 87.31(c) took effect, are now obsolete.
a.  New Provisions for Spare Engines
This proposed exception to the production limits is intended to allow production and sale of a newly-manufactured engine for installation on an in-service aircraft (i.e., a "spare engine").  It would 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. Also, under our proposed regulations, there would be no adverse environmental effect from allowing the use of a spare engine as a direct replacement for an existing engine, because a spare could be used only when the emissions of the spare engine are equal to or lower than those of the engine it is replacing, for all pollutants.  Manufacturers would not be required to obtain FAA or EPA approval before producing spare engines, thus they are considered "excepted" rather than exempted.  Manufacturers would have to submit information about the spare eingines produced in an annual report to the EPA.  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.
Exceptions for spare engines are not addressed in the existing regulations because there is no production cutoff for the currentTier 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, our proposal to apply a Tier 6 NOx production cutoff to all newly- manufactured engines means that if we did not also propose this exemption process, manufacturers would be prohibited from producing Tier 4 spare engines under the existing type certificates. We see no reason to change our policy of allowing manufacturers to produce new engines for use as spares.  The proposed regulatory provisions would allow this practice to continue.
Under the proposed regulations, engines meeting the requirements for spare engines could be produced and enter into commerce without prior approval from EPA or FAA.  (This marking requirement would need to be promulgated by the FAA for 14 CFR Part 45.)  It is important to note that while spare engines would be excepted from the Tier 6 NOx standards being proposed today, they would 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 would expect little or no additional burden for manufacturers, since we are not proposing new restrictions, monitoring, recordkeeping, or reporting requirements other than the end of year report.  When combined with the proposed prohibition against using spare engines to replace lower emitting engines, this program will ensure that using a spare engine would not increase emissions, but would at the same time allow the availability of spares for maintenance or replacement as needed.
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 bringing 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 needed if a manufacturer does not complete the production cycle before the production cutoff date and projected production volumes are not adequate to justify resource investment to reduce emissions or there are other technological issues.
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 sections 87.7(c) and (d), entitled, respectively, "Exemptions for New Engines in Other Categories," and "Time Limited Exemptions for In Use Engines."  Today's proposed amendments would replace these provisions with a new set of provisions addressing exemptions for new engines.We invite public comment on any other ways to address the need for flexibilities in the above circumstances.
i.  Time Frame and Scope
The proposed regulations would allow manufacturers to request an exemption for engines  not meeting the Tier 6 NOx standards to be installed in new aircraft.  If granted, the exemption would allow manufacturers to produce a limited number of newly-manufactured engines, in a time period beginning after December 31, 2012 and ending December 31, 2016.  The time period for any given approved exemption could be shorter depending on the specifics of the application but could not be longer. This exemption would be limited to NOx emissions from engines that are covered by a valid type certificate issued by FAA.  The engines would be required to meet all other applicable requirements.  More specifically, an engine exempted from the Tier 6 NOx standards would need to be covered by a previously issuedtype certificate showing compliance with the Tier 4 NOx standards, as well as the current HC, CO, fuel venting, and smoke standards.
ii.  Production Limit
	We are proposing that the number of engines eligible for exemptions would be limited to what is justified by the circumstances at the time of application, and limited by the guidance provided in the ICAO ETM, currently 75 engines per type certificate.  Approved exemptions would be tailored to include specific limits based in part on the information presented in the manufacturer's exemption request.
	Prior to the CAEP/8 meeting in February 2010, ICAO had no specific provisions regarding exemptions.  The only language regarding exemptions was contained in Annex 16 Volume II section 2.1.1 which rather generically stated that:
       In considering exemptions, certificating authorities should take into account the probable number of such engines that will be produced and their impact on the environment.  When such an exemption is granted, the certificating authority should consider imposing a time limit on the production of such engines for installation on new aircraft or on existing aircraft as spares.
	When ICAO/CAEP began considering a production cut-off for the CAEP/6 NOx standard, there was a consensus among the participants in the technical working group that more specific provisions were needed with respect to potential exemptions from that requirement.   The provisions would help support an orderly transition in the implementation of the production cut-off.   Toward that end, the group consulted periodically over several months to craft provisions addressing number, time limit, and emission levels (impact on the environment).  The deliberations were complicated by the fact that the language in Annex 16 simultaneously addressed both engines for new production aircraft and spare engines for existing aircraft.
	For both new production and spare engines, agreement was reached relatively quickly that exemptions to be available should be four years after the production cut-off becomes effective, and that any engine model for which an exemption was requested must at a minimum comply with the emission standards being affected by the cut-off.   In this case engines would have to meet at least CAEP/4 NOx requirements.   Similarly, it was readily agreed in the technical working group that there would be no limit on the number of spare engines during the four-year period since these would essentially be installed for in use engines removed for maintenance or replacement, as needed.
	However, discussions and deliberations were more difficult with regard to the number of potential exemptions for engines for new production aircraft.  This difficulty stemmed from the fact that 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.  However, it was stated that if the demand existed, 14 of these 20 models could be produced under the exemption provisions since they had valid type certificates and met the previously mentioned exemption emission requirements.[,][,][,]   After much deliberation, the technical working group settled on a value of 75 engines per type certificate over the four years for the ICAO ETM guidance.
	This value was of concern to EPA and the maximum number of engines it could represent.
Our assessment of a reasonable limit for potential exemptions from the CAEP/6 standards began with the underlying conditions that may support the need for such provisions.  In this regard, it is often the case that the engine modifications needed to meet more stringent standards and subsequent recertification are often an expensive undertaking.  When future sales are projected to be larger in number, manufacturers have argued that economics favor a return on investment and that market forces dictate that they make the investment to so that they have fully compliant engines to meet customer demands.[,]  In these cases exemptions would probably not be necessary.  However, when an engine model has low expected future sales, i.e., near the end of its production life, then the economics involved in transitioning to a new emission standard are less attractive and the market forces argument is less compelling.  In such cases, limited exemptions may be appropriate.
	To help inform us regarding situations such as those described above, we looked at past production histories and projected future orders of engine models, focusing on the years associated with the production cutoff wherever possible.  We utilized the ASCEND Database to conduct this analysis.  ASCEND contains information on past production volumes and projected production volumes for future years based on either actual orders for aircraft or potential new orders.  The results of this analysis supported  a limit for potential exemptions from the CAEP/6 standards that was much less than the ETM guidance of 75 engines per type certificate, and that a number closer to 100 engines per type certificate holder was likely to be adequate.
	In addition, two new pieces of information became available during the development of this proposed rule that were unavailable during the deliberations leading up to the ICAO decision for the ETM guidance.  First, a review of information on past exemption requests to FAA 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.[,][,]
	Our subsequent discussions with engine manufacturers also resulted in the conclusion that the expectation was that fewer engines than the ICAO guidance suggested would be the subject of exemption requests.  For the proposed Tier 8 NOx standards, while we are not proposing requirements on manufactured engines at this time, any numerical limit associated with those standards would need to be evaluated based on information available at the time.
	As a result of these varying predictions by ICAO members and subsequent conversations with manufacturers, we are proposing an exemption limit that is consistent with ETM guidance but allows U.S. authorities the flexibility to consider all factors that affect the application for exemption.  The goal will to be to exempt as few engines as possible under the circumstances presented at the time of petition for exemption.  We believe this approach addresses the intent of the ICAO guidance and the potential need of the 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.

iii.  Exemption Requests
We are proposing a process for requesting exemptions (for engines used on new aircraft) that would include more information than the current process.  We are proposing that manufacturers be required to submit their request to the FAA, as currently required.  The FAA will then share the submittal with EPA and execute the consultation provisions required under the Clean Air Act.
To ensure that we have the information necessary to evaluate exemption requests in this specific manner, the requests would need to include the following details to describe the specific engine model for which the manufacturer is requesting the exemption.  The proposed 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.

::Hardship: Impact of unforeseen technical circumstances, business events. Or other natural or manmade calamities beyond your control, and

It is important that any action on a potential exemption request be in the public interest; the fairly comprehensive list of application information in the proposed regulations is intended to gather the information needed for this assessment.  We would expect to take a broad perspective in evaluating what is or is not in the public interest.  This is why the manufacturer justifications would need to include a quantified description of the environmental effects of granting the exemption, as well as discussion of economic and technical issues related to bringing the engine into compliance.  The analysis of environmental impacts would need to specify by how much the exempted engines would exceed the standards, the in-use effects in terms of lifetime tons of NOx, and estimate the emissions rates of engines/aircraft that could potentially be used if the exemption was not granted.  While exemptions granted under the proposed regulations would apply only for NOx emissions, the analysis could also include possible benefits regarding noise levels or reduced emissions of pollutants other than NOx.  Relevant economic impacts could include effectson the engine manufacturer, airframe manufacturer, airline(s), and the general public.
In the past, some manufacturers have requested exemptions based on the largest number of engines they hoped to continue producing without knowing how many they would actually be able to produce or who would purchase them.  The new exemption language calls for manufacturers to target their requests more specifically based on likely production needs and time periods.  At any time before approval, manufacturers could revise their requests to justify covering additional engines.  We would then review the revised request. For exemptions that have already been approved, manufacturers could also request that additional engines be added after providing the justification for the increase.
While we expect a manufacturer to have this specific information when they submit a request, the regulations would allow us to process exemption requests with somewhat less specific information.  However, we would expect this to apply only for unusual circumstances.
If, after consulting with FAA, we determine that the exemption request is fully documented and approval would be in the public interest, we would concur with approving the request if the FAA also concluded that the request should be granted.  Note that we could approve the exemption for a smaller number of engines than the manufacturer requested, or we could include certain other conditions.
In order to allow us to oversee these exempted engines, manufacturers would be required to provide an annual report to EPA on exempt engines similar to the information about excepted spare engines.  The permanent record for each engine exempted under this provision would need to indicate that the engine is an exempted engine and the engine itself would need to be labeled as "EXEMPT NEW" in accordance with FAA marking requirements of 14 CFR.
iv.  Foreign Aircraft
We are proposing that manufacturers also include in their requests a list of countries in which the aircraft are expected to be registered (i.e., "flagged"), as previously noted.  While not specifically listed in the ETM, we believe that this information is consistent with the ETM as it would be necessary to ensure proper coordination with other countries in which these aircraft are expected to be registered.  This coordination is necessary because many countries require FAA certification even for aircraft that will never operate in the U.S.  Normally, we would not expect that we would approve an exemption for engines used on aircraft that would be registered in countries opposing the exemption.

c.  Voluntary Emission Offsets
We are requesting comment on establishing a voluntary EPA program by which manufacturers could receive emission credits for producing cleaner engines, which they could use to offset higher emissions from exempted engines.  An example of such a program is summarized in a memorandum to the docket, and a basic overview of how credits might be generated is presented in the following paragraph.The types of programs being considered would be developed, promulgated, and administered solely by EPA.We would expect manufacturers to be interested in generating offsets for one of three purposes.  First, manufacturers might choose to generate offsets as part of their justifications for exemptions.  For example, where we determine that an exemption would not be in the public interest because it would have anundue adverse effect on air quality, a manufacturer might use offsets so that the combination of the exemption and offsets would be more emission neutral.  Second, manufacturers might choose to generate offsets as part of a justification for being allowed to exceed the limitof 75 exempted engines per manufacturer.  Note that since this is not specifically allowed in the proposed regulations, we would need to amend the proposedregulations as part of the final rule to allow this option.  We are asking for comment on this option, and could include it in the final rule based on the comments and our assessment of the inputs and issues.  Third, a manufacturer might also be interested in generating offsets to bank for use for exemptions of engines to be produced after the credit generating engines are produced, or possibly against a future production cutoff.  This would also require a change to the proposed regulations.
Under this approach, generation of offsets would be voluntary and would be open to all certifying engine manufacturers.  One concept would be to allow credits to be generated only from engine models that are introduced after this rule and that had characteristic levels significantly below the otherwise applicable standard (e.g., at least 10 percent below).It is a separate question, however, how to calculate the credit.  If we adopted a 10 percent threshold for eligibility, we would probably also allow credits only to the degree which the NOx characteristic level was more than 10 percent below the standard.  For example, an engine that was 15 percent below the standard would generate credits equivalent to 5 percent of the standard. This would ensure a net improvement in emissions.  If we were to finalize such a program, we could reserve the right to restrict the use of credits so that they were used in a manner that ensured there was no net adverse impact on air quality.  Such a program would need to ensure that emission benefits from one aircraft model truly offset the higher emissions from another model.  For example, emissions from regional aircraft may not be directly equivalent to emissions from aircraft designed for longer cross-country or international flights.  Equivalency factors could be developed to account for differences in the number of LTOs per years, the lifetime of the aircraft, and the number of LTOs per mile,These factors could be developed based on the operation characteristics from existing sources of information and would not require the collection new operational data.  Commenters are encouraged to review additional information contained in the memorandum to the public docket and provide input on the ideas, concepts, and options presented therein.
3.  Potential Phase-In of New Tier 8 NOx Standards for Newly-Manufactured Engines
We are not proposing to phase-in the proposed Tier 8 NOx standards for newly-manufactured engines at this time, since such a feature is not included in the CAEP/8 recommendation to ICAO.  This means that engine manufacturers may continue to produce Tier 6 compliant engines within already certified models after the proposed Tier 8 standards become effective for newly-certified engine models.  As noted elsewhere, EPA is working within the ICAO/CAEP framework to develop harmonized international standards for aircraft turbine engines.  At the February 2010 meeting of CAEP, where the CAEP/8 NOx standards were approved for recommendation to ICAO, the committee decided to continue considering a related newly-manufactured engine standard as a future work item at CAEP, pending new information on technology and market responses.
We will continue our efforts to evaluate a newly-manufactured engine standard as a complement to the Tier 8NOx standards as part of the future CAEP work programs.  We believe that such a requirement is a necessary component of any effective NOx control strategy for aircraft turbine engines.  It provides an orderly, stable transition between emission requirements that is helpful for product planning by engine and airframe manufacturers, and in making purchasing decisions by their customers.  It also ensures compliance with any new emission standard in a reasonable period of time, thereby providing the public with all the environmental benefits that a new emissionstandard can provide.  However, in order to maximize consistency with the CAEP/8 NOxstandard as currently recommended to ICAO, our proposed Tier 8 standard does not contain a production cutoff.
Assuming a CAEP/8 production cutoff is adopted at some time in the future, we will re-examine the permanent exemption provisions to ensure a timely and orderly phase-out of engine models that do not meet the CAEP/8 NOx standards.  We would expect this to be done as part of future CAEP deliberations and through a notice and comment rulemaking process to amend our own regulations.
      C. Application of Standards for Derivative Engines
It is very common for a manufacturer to make changes to an originally type certificated engine model that is in production while keeping the same basic engine core and combustor design. In some cases these modifications may affect emissions.  As a result, the certificating authority must decide whether the emission characteristics of the modified design were significant enough from the parent engine's certification basis that a demonstration of compliance with newer emission standards is necessary, or if the changes were minor relative to the parent engine's emission certification basis so that it is considered a derivative version of the original model with no emissions changes.  This may be further complicated because of the common practice of making iterative changes over time, that leaves open the question as to when the cumulative changes reach a point where a new demonstration of compliance is warranted.
In the past, these determinations were made for turbofan engines by an engineering evaluation that was performed by the engine manufacturer and then approved by the FAA.   As part of the ICAO/CAEP deliberations leading up to the February 2010 CAEP/8 meeting, a new standardized guidance was agreed upon as described in the ETM.  The guidance, which the U.S. fully supported,  includes specific criteria that can be used to determine when a design modification requires a new demonstration of compliance with newer emission standards, or when a modification was simple enough to be considered a no emissions change.
We are proposing to include the ETM language in our regulations.  This addresses a longstanding need to provide consistent standards for the decision process regarding derivative engines and applicable emission standards.  The definition of "derivative engines for emissions certification purposes," along with the criteria for making this determination,  will provide engine manufacturers and regulators with more certainty regarding emission standard requirements for future modifications made to certificated models.  Finally, it will make the decision criteria enforceable. To ensure that the numerical decision criteria can be administered in to allow for the consideration of unusual circumstances or special information, we are also proposing that the FAA have some flexibility to make adjustments to the specific criteria based on good engineering judgment.  In summary, if the FAA determines that an engine model is sufficiently similar to its parent engines so as to meet the criteria established in proposed §87.48, the manufacturer may demonstrate certification compliance and continue production of the engine model to the same extent as allowed for the original engine model. However, if the FAA determines that an engine model is not an derivative for emissions certification purposes, the manufacturer would be required to demonstrate compliance with the most recent emissions standards.  This determination will be made using numerical criteria consistent with ICAO provisions, and will apply to modified engine models if it is 1) derived from an original engine that had received U.S. certification, (2) the original engine was certificated to the requirements of 14 CFR, and (3) the

emissions from the derivative engines are equivalent to or lower than the original engine.
The proposed regulations specify that to show emissions equivalency, the engine manufacturer must demonstrate that the difference between emission rates of a derivative engine and the original engine are within the following allowable ranges, unless otherwise adjusted using good engineering judgment, as determined by the FAA:
	+- 3.0g/kNfor NOx.
	+- 1.0g/kN for HC.
	+- 5.0g/kN for CO.
	+- 2.0 SN for smoke.
Engine models represented by characteristic levels at least five percent below all applicable standards would be allowed to demonstrate equivalency by engineering analysis.  In all other cases, the manufacturer would be required to test the new engine model to show that its emissions met the equivalency criteria.
      D.  Annual Reporting Requirements
In May of 1980, ICAO's Committee on Aircraft Engine Emissions (CAEE) recognized that certain information relating to environmental aspects of aviation should be organized into one document.  This document became ICAO's "Annex 16 to the Convention on International Civil Aviation, International Standards and Recommended Practices, Environmental Protection" and was split into two volumes  -  Volume I addressing Aircraft Noise topics and Volume II addressing Aircraft Engine Emissions. Annex 16 has continued to grow and today Annex 16 Volume II includes a list of mandatory requirements to be satisfied in order for an aircraft engine to meet the ICAO emission standards.These requirements include information relating to engine identification and characteristics, fuel usage, data from engine testing, data analysis, and the results derived from the test data.  Additionally, this list of aircraft engine requirements is supplemented with voluntarily reported information which has been assembled into an electronic spreadsheet entitled "Emissions Databank" (EDB)for turbofan engines with maximum thrust ratings greater than 26.7 kNin order to aid with emission calculations and analysis as well as help inform the general public.
In order to understand how current gaseous emission standards are affecting the current fleet, we need to have access to timely, representative emissions data of the engine fleet at the requisite model level.The EDB is a useful tool for providing a general overview of the aircraft fleet, as it contains information on engine exhaust emissions and performance tests.  However, it is not updated on a consistent basis, it contains a varying amount of voluntarily reported data from each manufacturer, and it does not specifically list every engine sub-model.  It also does not contain information on smaller thrust category turbofans or turboprops, and contains no information on past or recent engine production volumes.  We need this data to conduct accurateemission inventories and develop appropriate policy. Accordingly, we do not consider the EBD to be a sufficient tool upon which to base policy decisions or adopt future standards.Furthermore, in the context of EPA's standards-setting role under the Clean Air Actwith regard to aircraft engine emissions, it is consistent with ourpolicy and practice to ask for timely and reasonable reporting of emission certification testing and other informationthat is relevant to ourmission.  Under the Clean Air Act, we are authorized to require manufacturers to establish and maintain necessary records, make reports, and provide such other information as we may reasonably require discharge our functions under the Act.  (See 42 U.S.C. § 7414(a)(1).)
Therefore, we are proposing to require that any engine manufacturer submit a production report directly to EPAwith specific informationfor each individual engine sub-model that:  1) is designed topropel subsonic aircraft, 2) is subject to our exhaust emission standards, and 3) has received a U.S. type certificate.  More specifically, the scope of the proposed production report would include turbofan engines as described above with maximum rated thrusts greater than 26.7 kN, i.e., those subject to gaseous emission and smoke standards.  In addition, it would include turbofans with maximum rated thrusts less than or equal to 26.7 kN and all turboprop engines, i.e., those only subject to smoke standards.  We are also proposing that this specific exhaust emission related information be reported to us in a timely manner, which will allow us to conduct proper emissions inventory analyses of the existing fleet and to ensure that any public policy we create based on this information will be well informed.
We are proposing to have each affected enginemanufacturer report a reduced number of specific data elements to us as compared to those already reported voluntarily and periodicallyby most engine manufacturers to the EDB. We feel that this minimizes the reporting burden for each manufacturer while still providing us with sufficient information to perform our job. All of the specific reporting items we are proposing are same as requested for the EDB, with the exception of total annual engine production volumes, information on type certificates, and the emission standards to which the engine sub-model was certified.
This information will be used in conjunction with the NOx and CO2emission data already required to be submitted to us under part 87.64 for purposes of greenhouse gas (GHG) reporting to establish our own independent engine exhaust emissions database. We would expect most manufacturers generally to add the proposed information items to the annual GHG report.  We want to clarify, however, that comments are invited only on the proposed incremental data reporting elements that comprise the production report.  No changes are being proposed to the contents of the GHG report.
  The proposed incremental reporting elements for each affected gas turbine engine sub-modelare listed below.  The reporting elements of the existing GHG report are also identified for completeness.
::Company corporate name as listed on the engine type certificate (GHG);
::Calendar year for which reporting (GHG);
::Complete sub-model name (This will generally include the model name and the sub-model identifier, but may also include an engine type certificate family identifier) (GHG);
::The type certificate number, as issued by theFAA(Specify if the sub-model also has a type certificate issued by a certificating authority other than theFAA) (GHG);
::Date of issue of type certificate and / or exemption, i.e. month and year (GHG);
::Emission standards to which the engine is certified, i.e., the specific Annex 16, Volume II, edition number and publication date in which the numerical standards first appeared.
::If this is a derivative engine for emissions certification purposes, identify the original certificated engine model.
::Engine sub-model that received the original type certificate for the engine type certificate family;
::Production volume of the sub-model for the previous calendar year, or if zero, state that the engine model is not in production and list the date of manufacture (month and year) of the last engine produced;
::Regarding the above production volume report, specify (if known) the number of engines that are intended for use on new aircraft and the number intended for use as excepted spare engines on in-use aircraft;
::Reference pressure ratio (GHG);
::Combustor description (type of combustor where more than one type available on an engine);
::Engine maximum rated thrust output, in kilonewtons (kN)) or kilowatts (kW) (depending on engine type) (GHG);
::Unburned hydrocarbon (HC) mass (g) total (weighted) and over each segment of the Landing and Take-off Cycle (LTO), i.e. Take-off, Climb, Approach, Taxi / Ground Idle;
::Unburned hydrocarbon characteristic level (i.e. mass of hydrocarbons over LTO cycle / Rated Thrust (Dp/Foo);
::Carbon monoxide (CO) mass (g) total (weighted) and over each segment of the entire Landing and Take-off Cycle (LTO) (i.e. Take-off, Climb, Approach, Taxi / Ground Idle);
::Carbon monoxide (CO) characteristic level (i.e. mass of CO over LTO cycle / Rated Thrust (Dp/Foo));
::Nitrogen oxides (NOx) mass (g) total (weighted) and over each segment of the entire Landing and Take-off Cycle (LTO) (i.e. Take-off, Climb, Approach, Taxi/Ground Idle) (GHG);
::Nitrogen oxides (NOx) characteristic level (i.e. mass of NOx over LTO cycle / Rated Thrust (Dp/Foo))(GHG);
::Smoke number total and over each segment of the entire Landing and Take-off Cycle (LTO) (i.e. Take-off, Climb, Approach, Taxi / Ground Idle);
::Smoke number characteristic level;
::Carbon dioxide (CO2) mass (g) total (weighted) and over each segment of the entire Landing and Take-off Cycle (LTO), i.e. Take-off, Climb, Approach, Taxi / Ground Idle (GHG);
::Number of tests run per sub-model (GHG);
::Number of engines tested per sub-model (GHG);
::Fuel flow (grams / second) total (weighted) and over each segment of the Landing and Take-off Cycle (LTO) (i.e. Take-off, Climb, Approach, Taxi / Ground Idle) (GHG); and
::Any additional remarks to the EPA.
The proposed annual report wouldbe submitted for each calendar year in which a manufacturer produces any turbofan engine subject to emission standards as previously described.  These reports would be due by February 28 of each year,starting with the 2014calendar year, and cover the previous calendar year.This report wouldbe sent to the Designated EPA Program Officer.  Where information provided for anyprevious year remains valid and complete, the engine manufacturermay report the production figures and state that there are no changes instead of resubmitting the original information. To facilitate and standardize reporting, we expect to specify a particular format for this reporting in the form of a spreadsheet or database template that we provide to each manufacturer. As noted previously, we intendto use the proposed reports to help inform any further public policy approaches regarding aircraft engine emissions that we consider, including possible future emissions standards, as well as help provide transparency to the general public. Subject to the applicable requirements of 42 U.S.C. 7414(c), 18 U.S.C. 1905, and 40 CFR part 2, all data received by the Administrator that is not confidential business information may be posted on our website and would be updated annually. By collecting and publically posting this information on EPA's website, we will be able to calculate turbine exhaust emission rates and demonstrate to the public how the fleet meets the current emission requirements. We believe that this information will also be useful to the general public to help inform public knowledge regarding aircraft exhaust emissions.  We ask for comment on our proposed plan to post this information on our websiteand whether any of it should be omitted as confidential business information.  Such confidential information would be retained by EPA.  For guidance on how to preserve a claim of confidentiality and on how EPA would treat submitted information covered by such a claim, please see our earlier discussion in section VII. of this notice regarding how a public commenter on the proposed rule should submit information that the submitter considers to be confidential business information.

We have assessed the potential reporting burden associated with the proposed annual reporting requirement.  That assessment is presented in sections V. and IX.A. of this notice.E.  Proposed Standards for Supersonic Aircraft Turbine Engines
We are proposing CO and NOx emission standards for turbine engines that are used to propel aircraft at sustained supersonic speeds , i.e., supersonic aircraft to complement our existing HC standard for these engines.  These proposed standards were originally adopted by ICAO in the 1980s, and our adoption of NOx and CO standards for commercial engines in 1997 omitted coverage of these pollutants for supersonic commercial engines that were then in use.  The lack of EPA CO and NOx standards for engines used by supersonic aircraft has had no practical effect, because no such engines have been certified by the FAA.  Also, none of the engines used on these aircraft are currently in production.(See section III.G. for a brief discussion of potential revised emission standards for future engine designs that may be used on supersonic aircraft.)  However, to meet U.S.treaty obligations under the Convention on International Civil Aviation as previously described in section I.C., we believe it is necessary and appropriate to propose these conforming standards.Therefore, the proposed standard simply aligns EPA standards with the rest of the world.
F.  Amendments to Test and Measurement Procedures
We are proposing to incorporate by reference into the 40 CFR § 87.60 regulatory text, amendments to ICAO's International Standards and Recommended Practices for aircraft engine emissions testing and certification. These amendments to Annex 16, Volume II are mainly intended to ensure that the provisions reflect current certification practices.  The amendments make clarifications or add flexibilities for engine manufacturers. They aredescribed separatelybelow for the amendments that have already been adopted by ICAO[,] and those that have been recommended by CAEP for adoption by ICAO.
The amendments that have already been adopted by ICAO are:
::  Standardizing of the terminology relating to engine thrust/power;
::  Clarifying the need to correct measured results to standard reference day andreference engine conditions;
::  Allowing a certificating authority to approve the use of test fuels other than those specified during certification testing;
::  Allowing materials other than stainless steel in the sample collection equipment; and
::  Clarifying the appropriate value of fuel flow to be used at each LTO test	point.
The amendments that have been recommended for adoption by ICAO are:
::  Clarifying exhaust nozzle terminology for exhaust emissions sampling; and
::  Allowing an equivalent procedure for gaseous emission and smoke measurement if approved by the certificating authority.
The test procedure amendments that ICAO has already adopted became applicable on November 20, 2008.  The amendments that have been recommended to ICAO are expected to be adopted prior to the date of the final action on today's proposed rule.  Manufacturers are either already voluntarily complying with these changes or will be even in the absence of a final rule.  Our adoption of these test procedure amendments are,therefore,unlikely require new action by manufacturers beyond what they are already undertaking to meet ICAO's adopted and recommended amendments.