(2) The proposed alternative procedure is shown to be equivalent to, or more accurate or precise than, the specified procedure.
Examples of special test procedures include those for fuel composition, probe material, probe design or performance, or required calculations:
Applicants are advised to submit requests for special test procedures as early in the process as possible.
The review and approval process by the FAA and EPA can be lengthy, and approval as submitted is not guaranteed. Any approval of special test procedures should be documented by the applicant in its certification test plans and test reports.
Procedures that deviate from the regulatory test and measurement procedures that are not approved prior to their use may require that an engine be retested.
Note: The EPA requires the reporting of nvPM data for loss corrections in 40 CFR 1031.150(c)(6)(ii)(f) and (v). The procedures for calculating loss corrections are found in A16V2, Appendix 8, Procedures for estimating non-volatile particulate matter system loss corrections.
7.3. Section 34.7 Exemptions Petitioners for exemptions from any emissions regulation or test procedure of 14 CFR part 34 are encouraged to contact AEE prior to filing exemption requests. The FAA has the authority to grant exemptions from its regulations when doing so has been determined to be in the public interest.
Exemption requests should consider other requirements such as those found in 14 CFR parts 21, 25, 33 45, 91.203(d) where those parts require compliance with part 34. Exemptions are normally time-limited and require the applicant to achieve compliance to the exempted regulation at a future date.
Petitions for exemption from part 34 are subject to the rulemaking procedures of 14 CFR part 11.
Information required in a petition for exemption includes that specified in §11.81 and 40 CFR 1031.15 when consultation with the EPA is required. Petitions for exemption may be filed in electronic or hardcopy format following the instructions of §11.63.
For all part 34 exemption requests, denials, or grants, AEE will be the responsible FAA office and will coordinate with EPA’s Designated Program Officer and other FAA offices, as needed.
Temporary exemptions based on flights for short durations at infrequent intervals under 14 CFR 34.7(a) (40 CFR 1031.15(b)) require only FAA written approval to be effective.
Additional data on exempted engines is required in EPA annual production reports, as specified in 40 CFR 1031.150(d).
7.4. Section 34.9 Exceptions The regulations for spare engines contain an exception, as specified in §34.1, Definitions, and §34.9, Exceptions (40 CFR 1031.20, Exceptions).
Newly manufactured spare engines may only be installed on in-service aircraft to replace an existing engine and must be identical to a sub-model previously certificated for that aircraft. Newly manufactured, spare engines must meet Tier 4 regulations, or cleaner. An excepted spare engine must be certificated as having equal or lower regulated emissions than the engine it replaces. No written approval is needed from FAA to produce spare engines meeting these requirements. Records for excepted spare engines must indicate that the engine was produced as an excepted spare engine.
Excepted spare engines must be labelled as “EXCEPTED SPARE” as specified by 14 CFR 45.13 and manufacturers must provide annual reports to EPA for excepted spare engines for each engine model and engine sub-model, with the information specified in 40 CFR 1031.150(d). As specified in 40 CFR part 1031, “Engine manufacturers must submit an annual production report for each calendar year in which they produce any engines subject to emission standards under [part 1031].” These reports are due Page 12 of 57
to the Designated EPA Program Officer by February 28 of the following calendar year. The information that is required for the report is specified in 40 CFR 1031.150.
Part 34 contains no other exceptions to the emissions regulations. Manufacturers seeking relief from any other emissions regulation must follow the regulations and guidance specified for exemptions.
8. Part 34 Subpart B - Engine Fuel Venting Emissions (New and In- Use Aircraft Gas Turbine Engines)
8.1. Section 34.10 Applicability The following table provides a summary of engine classes to which the fuel venting regulations apply.
Engine Fuel Venting Emissions (new and in-use aircraft gas turbine engines)
8.2. Section 34.11 Regulations for Fuel Venting Emissions Aircraft gas turbine engine fuel systems operate in a pressurized condition, which may be relieved by various fuel system design features after engines are shut down. Raw, liquid fuel that drains uncontained or drips onto hot internal engine parts after shutting down may result in the discharge of fuel vapor into the atmosphere, adding to the local air pollution burden.
14 CFR 34.11(a) states the following:
“No liquid fuel venting emissions shall be discharged into the atmosphere from any new or in- use aircraft gas turbine engine subject to this subpart.” This paragraph is directed at the elimination of intentional discharge to the atmosphere of fuel drained from fuel nozzle manifolds after engines are shut down and does not apply to normal fuel seepage from shaft seals, joints and fittings.”
40 CFR 1031.30(b)(2) has equivalent, but not identical language:
“Engines may not discharge liquid fuel emissions into the atmosphere. This standard is directed at eliminating intentional discharge of liquid fuel drained from fuel nozzle manifolds after engines are shut down and does not apply to normal fuel seepage from shaft seals, joints, and fittings.
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Certification for the fuel venting standard will be based on an inspection of the method designed to eliminate these emissions.”
ICAO’s Annex 16 Volume II Environmental Technical Manual, hereafter referred to as “ETMV2”, Part II, Chapter 2 provides the following explanatory information for engine shutdown:
General:
The process of engine shutdown, following normal flight or ground operations, begins with the cut-off of fuel flow from the fuel control unit, and continues until a time when the design features of the engine and/or aircraft stop this flow. The engine and/or aircraft are required to be designed in such a way that this fuel cannot be discharged into the atmosphere.
Engine Shutdown process:
The process of engine shutdown is described as follows.
“The engine shutdown process begins when fuel cut-off is commanded by the pilot. Once fuel flow to the engine is cut-off, a process begins leading to engine shutdown. The amount of time for this process to take place is dependent upon the design features of the engine. As a generic description, this process involves the simultaneous movement of the liquid fuel that resides within the engine (whether from pressure and/or gravitational forces), into the combustion chamber, and/or settling in areas of the engine of lower potential energy (e.g., to a drain tank). The process may also include valves closing to prevent fuel flow into the combustor from the fuel manifold system, as well as trying to prevent residual fuel from vaporizing after engine shutdown. Any residual fuel that drains into the combustion chamber during engine shutdown is expected to be combusted, as the chamber remains at a high enough temperature to combust the fuel. Once the combustor temperature has cooled, any remaining un-combusted fuel is expected to be held
(e.g., fuel delivery system, ecology tank, etc.) and not susceptible to release to the atmosphere after engine shutdown.”
14 CFR 34.11(c) states that the manufacturer or operator may show compliance with liquid fuel venting regulations using any engine design feature(s) that prevents the intentional discharge of fuel from fuel nozzle manifolds after engine shutdown. 14 CFR 34.11(c)(1)-(3) describes three acceptable design features that comply with engine fuel venting regulations:
(1) Incorporation of an FAA-approved system that recirculates the fuel back into the fuel system Explanation: Some engine designs may use case drains or other mechanisms that collect residual fuel. The residual fuel is then directed back into aircraft-mounted tanks and recirculated back into the fuel system during the next engine operation.
(2) Capping or securing the pressurization and drain valve Explanation: Systems may be designed with multiple valves, sometimes within each fuel injector, to relieve manifold pressure within the system and prevent the manifold from draining residual fuel onto hot combustor surfaces when the engine is shut down.
(3) Manually draining the fuel from a holding tank into a container.
Explanation: Older systems may be designed to purge fuel from the manifolds and into a separate tank by using residual engine air pressure from the combustor, gravity, or a combination of gravity and pressure. The tanks may then be emptied manually on a periodic basis.
Certification to fuel venting regulations at the part 33 engine level does not guarantee engines will pass fuel venting certification requirements at the part 25 aircraft level after engines are installed. For this reason, part 25 requires compliance at the part 33 level. Examples of difficulties with fuel venting Page 14 of 57
requirements that arose at the part 25 certification level, after engines passed fuel venting requirements at the part 33 level, include the following:
Example: Heat Soak Effects Engines installed on a part 25 certification test aircraft released small quantities of fuel after engine shut down due to fuel expansion in the fuel manifold caused by heat soak effects that would intermittently open a pressure release valve under certain conditions. The released fuel would vaporize on contact with hot surfaces inside the engine. This would result in visible fuel vapors being emitted from either the inlet or the exit plane of the engine for up to 30 minutes after engine shutdown.
Finding: The Clean Air Act mandates that FAA coordinate with EPA on non-compliance emission issues. In this instance, the EPA analyzed the environmental effects of fuel releases of this magnitude and determined that the effects were minimal. However, EPA emphasized that the fuel venting regulation should be interpreted to mean zero liquid fuel release into the atmosphere.
EPA will not establish a minimum threshold for fuel venting or consider an alternative means of compliance. The FAA issued a time limited exemption to the part 25 certification on the basis that the part 34 certified engine fuel system be redesigned to eliminate the intermittent fuel release.
The time limited exemption required the engine manufacturer to redesign the fuel system for both newly built engines and retroactively modify the existing engines within two years. The design of the new fuel system relieves back pressure to the fuel nozzles by allowing fuel expansion to take place within the system and collecting in a chamber and recirculating within the system in compliance with § 34.11(c)(1).
9. Part 34 Subparts C and D - Exhaust Emissions (New and In-Use Aircraft Gas Turbine Engines)
9.1. Sections 34.10, 34.21, 34.23, 34.25, and 34.31 Applicability Dates The regulations in 14 CFR part 34 and 40 CFR part 1031 may apply to new types for which an application for certification will be made, newly manufactured engines under an existing type certificate, or engines that are currently in-use and include a subsequent compliance date such as “on or before” or “on and after” and, oftentimes, the class and rated output of the engine.
The applicability date for part 34 regulations is the date when the application for a type certificate for the engine is submitted to the FAA. Applications for design changes may also trigger the applicability of regulations which have been adopted subsequent to the original type certificate. For example, the new nvPM regulations may apply to engines for design changes that have not been previously certified to the nvPM regulations found in § 34.25 (see 9.5 of this AC).
9.2. Section 34.21(e) Smoke exhaust emissions SN regulations in 14 CFR 34.21(a), (b), and (c), (e)(1)-(3); 34.23(a)(1); and 34.31(a) and (b) (40 CFR 1031.60, 40 CFR 1031.40, and 40 CFR 1031.50) apply to all engine classes; TF, T3, T8, TP and TSS;
and are based on engine class, rated output (rO) and date of manufacture. A summary of the SN regulations is provided in the table below.
Smoke Number (SN) Regulations Regulation 14 CFR / 40 CFR Engine Class rO Manufacture Date Characteristic Value NTE
34.21(e)(1)(A) / 40 CFR 1031.50(a) TF < 26.7kN On or after 08/09/1985
83.6(rO)-0.274 or 50 max Page 15 of 57
14 CFR / 40 CFR Pollutant Manufacture Date Characteristic Value NTE
34.21(d)(1)(i) / 40 CFR 1031.60 HC On or after 01/01/1984
19.6 g/kN rO
34.21(d)(1)(ii) / 40 CFR 1031.60 CO On or after 07/07/1997 118 g/kN rO
and before 07/18/2012
34.21(e)(1)(B) / 40 CFR 1031.60 TF, T3, T8 < 26.7 kN On or after 07/18/2012 and before 01/01/2023
83.6(rO)−0.274 or
50.0, whichever is smaller
34.21(e)(1)(C) / 40 CFR 1031.60 TF, T3, T8 ≤ 26.7 kN On or after 01/01/2023
83.6(rO)−0.274 or
50.0, whichever is smaller
34.21(e)(2) / 40 CFR 1031.60 T3, T8, TSS, TF > 26.7 kN On or after 01/01/1984
83.6(rO)-0.274 or 50 max and before 01/01/2023
34.21(e)(3) / 40 CFR 1031.40 TP > 1,000 kW On or after 01/01/1984 187(rO)-0.168
34.21(e)(4) / 40 CFR 1031.90 TSS All On or after 01/01/2023
83.6(rO)-0.274 or 50 max The United States has a smoke number regulation that applies to turboprop (Class TP) engines, while ICAO has no smoke number or other emission standards that apply to turboprop engines. The FAA has therefore filed a difference with ICAO regarding the U.S. turboprop SN regulation (see 4 of this AC, Differences Between ICAO Annex 16 Volume II and 14 CFR Part 34).
For all turbofan engines with a rO greater than 26.7kN that are manufactured on or after January 1, 2023, the smoke number regulations in 14 CFR 34.21 (40 CFR 1031.60(a)) will no longer apply and are being replaced by the non-volatile particulate matter (nvPM) regulation for those aircraft engines. See 9.5 of this AC for additional information on the nvPM standard. As illustrated on the chart above, the smoke number requirements continue to apply to engines not converting to the nvPM standard.
9.3. Section 34.21 and 34.23 Hydrocarbon (HC) and Carbon Monoxide (CO) The HC and CO regulations in 14 CFR 34.21(d)(1)(i) and (ii) (40 CFR 1031.60) apply to TF, T3 and T8 engines with rO greater than 26.7 kN. HC and CO regulations are the following:
HC and CO Regulations for Class TF, T3 and T8 Engines with rO > 26.7 kN Page 16 of 57
9.4. Section 34.21 and 34.23 Oxides of Nitrogen (NOx) The NOx regulations in 14 CFR 34.23 apply to Class TF, T3 and T8 engines manufactured on or after July 18, 2012. The regulatory limits are based on the date of production of the first individual model (type certification date), rated pressure ratio (rPR) and rated output (rO) of the engine.
“Tier 6” and “Tier 8” in the NOx regulations corresponds to the ICAO Committee on Aviation Environmental Protection (CAEP) meeting number, CAEP/6 or CAEP/8 respectively, during which the NOx standards were adopted by ICAO.
In-production engines type certificated on or before December 31, 2013 must meet Tier 6 regulations in 14 CFR 34.23(a)(2) (40 CFR 1031.60(e)(4)). Tier 6 NOx regulations are defined in 34.23(a)(2) (40 CFR1031.60(e)(4)).)
All engines type certificated after December 31, 2013, must meet Tier 8 NOx regulations in 14 CFR
34.23(b)(1) (40 CFR 1031.60(e)(5)). Tier 8 NOx regulations are defined in 34.23(b)(1) (40 CFR1031.60(c)(5)i).
9.5. Section 34.25 Non-Volatile Particulate Emissions Standards (nvPM) On or after 1 January 2023, nvPM regulations apply to all TF, T3 and T8 engines with greater than 26.7 kN thrust, replacing the SN regulations for these engines. Any change in type design for engines that do not qualify as derivative engines under § 34.48 must demonstrate compliance with nvPM requirements, as applicable.
The nvPM requirement adopted in § 34.25 are not meant to affect the SN requirements for engines of any class having a rated output of 26.7 kN or less, for turboprop engines (Class TP), or for supersonic engines (Class TSS).
For Class TF, T3, or T8 engines (regulated classes of large turbofan engines) with a rated output greater than 26.7 kN, this rule replaces the SN requirement with a measurement of a maximum nvPM mass concentration (nvPMMC) limit in micrograms per cubic meter [μg/m3]. This action maintains the standard that aircraft engine exhaust plumes remain invisible, which was the intent of the ICAO standards adopted in the United States by the EPA. When determining nvPMMC, values must be obtained from measurements made across the entire thrust range of an engine. The characteristic level of the measured maximum nvPMMC value may not exceed the regulatory limit established using the formula in § 34.25.
The standards for nvPMmass and nvPMnum apply to all subsonic turbofan and turbojet engines that have a rated output greater than 26.7 kN. The nvPMmass limit is the mass of emissions of nvPM expressed in milligrams (mg) divided by kN of rated thrust, as determined over the LTO cycle. The nvPM num limit is the number of particles divided by kN of rated thrust, as determined over the LTO cycle.
An engine for which an application for an original type certificate is submitted on or after January 1, 2023 is subject to the nvPMmass and nvPMnum emission limits of § 34.25. An engine that was type certificated before January 1, 2023, for which an application for type design modification is submitted on or after January 1, 2023, is also subject to the nvPMmass and nvPMnum emission limits of § 34.25. This date is consistent with the effective date of the EPA final rule that adopted these standards.
When nvPM standards are expressed as a formula, § 34.25 requires that nvPMMC be rounded to the nearest 1.0 μg/m3, that nvPMmass be rounded to the nearest 0.1 mg/kN, and that nvPMnum be rounded to three significant figures.
The FAA is incorporating by reference into part 34 the nvPM test and measurement procedures of ICAO Annex 16, Volume II, Appendices 4, 6 and 7. The EPA incorporated these appendices and Appendix 8, Page 17 of 57
which is not relevant to FAA regulations.10 This incorporation by reference continues the FAA use of these procedures in part 34 to conform to accepted international standards.
9.6. Section 34.48 Emissions Test Requirements for Derivative Engines 14 CFR 34.48 specifies regulations to determine if design changes or cumulative design changes to derivative engines require retesting to determine new emissions characteristic levels. A derivative engine is defined in part 34 in terms of emissions certification and applies to modifications of already certificated engine types. Changes to a certificated engine which are considered major from an airworthiness perspective require an amendment or supplement to the Type Certificate. However, these same modifications may have no or very little effect on the emissions characteristics of that engine. Part 34 defines the limits to enable a determination of whether a modification can be classified as a “no emissions change” or if it would affect the emissions levels to such an extent that the modification to the engine type would need to be re-certificated to Annex 16, Volume II requirements. Of course, manufacturers may voluntarily apply for re-certification to the latest requirements at any time.
Section 34.48(a) states that a type certificate holder may request that the FAA determine if an engine configuration is considered a derivative engine for emissions certification purposes.
A derivative engine that has been derived from an original engine that was certificated to the requirements of part 33 does not have to be retested for emissions characteristics if it complies with one of the three criteria listed in § 34.48(a).
14 CFR 34.48(b)(2) requires that an applicant for a design change to an original certificated engine model (or any sub-models within the emission type certificate family tested for certification), must be retested to determine compliance with regulatory limits if any pollutant is at or above 95% of the applicable r egulatory limit before modification to the derived model. If the characteristic levels of the original certificated engine model (and all other sub-models within the emission type certificate family tested for certification) are below 95% of the applicable limit for each pollutant, the applicant may use engineering analysis, consistent with good engineering judgment11, to demonstrate that the derivative engine will not exceed applicable emissions limits for each pollutant. Applicants should submit substantiation of engineering analysis to AEE for approval if it is to be used in lieu of retesting.
The engineering analysis must address all modifications to the original engine including those approved for previous derivative engines. Analysis may consider areas such as cycle changes, combustor and fuel nozzle design, or large changes in combustor inlet velocity profile or turbine cooling flows. ETMV2, Part III, Chapter 2, 2.1.1. Paragraph 5 may be consulted for specific examples of design changes, including assessing design changes from an engineering analysis perspective such as for changes to engine cycles, combustor and fuel nozzles, and boundary conditions.
10 Control of Air Pollution From Aircraft Engines: Emission Standards and Test Procedures quotes “The EPA is incorporating by reference Appendix 8 of Annex 16, Volume II, which outlines procedures used to estimate measurement system losses, which are a required element of the reporting provisions.” page 72333 in FR Vol 87 No 225, November 23, 2022.
11 Good engineering judgement means judgement that is consistent with generally accepted scientific and engineering principles and all available relevant information.
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14 CFR / 40 CFR Pollutant Manufacture Date Characteristic Value NTE
34.10(a) / 1031.30(b) Fuel Venting After 1/1/1975
No fuel venting after engine shutdown
34.21(d)(2) / 1031.90(c) HC On or after 1/1/1984
140(0.92)rPR g/kN
34.21(e)(2) / 1031.90(a) SN On or after 1/1/1984
83.6(rO)-0.274 not to exceed 50
34.23(a)(4) / 1031.90(e) NOx On or after 7/18/2012
36 + 2.42(rPR) g/kN
34.23(a)(4) / 1031.90(d) CO On or after 7/18/2012
4,550(rPR)-1.03 g/kN
10. Sections 34.10 and 34.21 Supersonic Aircraft Engine Emissions Regulations The fuel venting and gaseous emissions regulations are applicable to all engines intended for use on aircraft that operate at supersonic speeds, turbo supersonic class (TSS).
Regulations applicable to TSS class engines are the following:
TSS Emissions Regulations
11. Engine Emissions Regulations for Unmanned Aircraft Systems (UAS) / Advanced Air Mobility (AAM) Engines for UAS/AAM that are defined as civil aircraft pursuant to 14 CFR 1.1 are subject to the same regulations as civil, manned aircraft under 14 CFR part 34. Therefore, if the civil UAS has a turbofan or turboprop engine, it is subject to the fuel venting requirements of 14 CFR 34.11 (40 CFR 1031.30). If the UAS has a turbofan engine with rated output greater than 26.7 kN, it is also subject to the SN, gaseous and nvPM emissions standards of 14 CFR 34.31 (40 CFR 1031.30), 14 CFR 34.21 (40 CFR 1031.50) and 14 CFR 34.23 (40 CFR 1031.60). If the UAS has a turboprop engine with thrust equal to or greater than 1,000 kW, it is subject to the smoke number requirements of 34.21(e)(3) (40 CFR 1031.40). None of the part 34 emissions requirements apply if the UAS/AAM has an electric or internal combustion engine.
12. Commercial Space Vehicle Emissions Part 34 applies to turbofan and turboprop engines for aircraft. There are no emission regulations applicable to commercial space vehicles or the engines that power these vehicles at the time of this publication.
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13. Part 34 Subpart G - Test Procedures for Engine Exhaust Gaseous Emissions (Aircraft and Aircraft Gas Turbine Engines)
13.1. Test Procedures Incorporated by Reference The system and procedure for sampling and measurement of gaseous and SN emissions are specified in Appendices 2, 3, 4, 5 and 6 to the International Civil Aviation Organization (ICAO) Annex 16, Environmental Protection, Volume II, Aircraft Engine Emissions, Third Edition, July 2008.
13.2. Section 34.60 Introduction 14 CFR part 34 and 40 CFR part 1031.1 require that the systems and procedure for sampling and measurement of gaseous emissions are specified by the various appendices of A16V2. 14 CFR 34.60(g) and 40 CFR 1031.30(a)(3) both state that engines comply with an applicable standard if the engine family’s characteristic level does not exceed the numerical level of that standard, as described in the applicable appendix of A16V2.
A16V2, Appendix 6, Compliance Procedure for Gaseous Emissions, Smoke and Particulate Matter Emissions, explains how to calculate characteristic emissions values (see 13.2.1 of this AC) to which the regulatory emissions limits apply.
13.2.1 of this AC further describes the calculation of characteristic engine emissions from measured data based on the number of actual engines tested and required curve fitting methods for determining maximum characteristic values for SN and nvPM.
13.2.1. Section 34.60(g) Calculation of Characteristic Emissions 14 CFR 34.60(g) states that, “engines comply with an applicable standard if the testing results show that the engine type certificate family’s characteristic level does not exceed the numerical level of that standard…” This statement is written regarding the applicable emissions standard and the characteristic emissions for an engine that are calculated following the procedures of A16V2, Appendix 6.
The characteristic level is calculated by dividing the measured and corrected mean emissions levels for CO, HC, NOx, SN and nvPM values by the coefficients listed in A16V2, Appendix 6, Table A6-1, which is provided as Attachment 3 to this AC. The coefficients are determined by the actual number of engines tested (i), with a minimum of three data sets averaged for each pollutant.
For example, a single engine test (i = 1) may be used to certify an engine based on a minimum of three data sets for each pollutant. The measured and corrected mean emissions levels from three or more data sets for each pollutant are then divided by the coefficients from A16V2 Appendix 6, Table A6-1 (Attachment 3) for i = 1 to determine the characteristic emissions for the engine. The coefficients for i = 1 are 0.8147 for CO, 0.6493 for HC, 0.8627 for NOx, 0.7769 for SN, and 0.7769 for nvPMMC and 0.7194 for both nvPMmass and nvPMnum.
If three engines are tested (i = 3) with data from a minimum of one test for each pollutant from each engine, the measured and corrected mean emissions levels for each pollutant from ICAO A16V2 Appendix 6, Table A6-1 (Attachment 3) for i = 3 are divided by 0.9246 for CO, 0.8572 for HC, 0.9441 for NOx, 0.9091 for SN, 0.9091 for nvPMmc,, and 0.8858 for both nvPMmass and nvPMnum.
Increasing the number of engines tested (i) reduces the reportable characteristic values for each pollutant by improving confidence in the averaged test data. The use of cycle deck data in lieu of an actual engine test to increase the value of engines tested (i) for calculating characteristic emissions is not permissible.
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14. Part 34 Subpart H - Test Procedures and Compliance Demonstration for Non-Volatile Particulate Matter Emissions Section 34.71 identifies the nvPMMC, nvPMmass and nvPMnum emissions test requirements applicable to Class TF, T3, or T8 engines manufactured on or after January 1, 2023, with rated output greater than
26.7 kN. The test procedures include the minimum number of emissions test runs required, the number of engines of the same type design that may be used to gather test data, and the operational conditions required for emissions certification (§§ 34.71 (b), (c), and (g)).
Section 34.71 also includes test fuel specifications (§ 37.71 (d)), a description of the LTO cycle (§
34.71(h)), and how to prepare and operate an engine for emissions certification (§ 34.71 (f)). Section
34.71(i) states how characteristic values, in conjunction with Table A6-1 of Annex 16 Vol II, Appendix 6, are to be calculated.
Section 34.71(e)(1) includes an incorporation by reference of ICAO Annex 16, Volume II, Appendices 1, 4, 6 and 7 requiring that the tests and procedures in the applicable Appendices be used when measuring and collecting nvPM emissions data.
Section 34.71(e)(2) provides instructions to the applicant interested in requesting an alternative to any of the test procedures of subpart H. In advance of conducting engine emissions certification tests, the FAA expects that any such written request would be pertaining to a procedure that was included in the approved test plan but was discovered to be unworkable. Any proposed alternative test procedure must be equivalent to, or more accurate than, the procedures specified in Subpart H. The proposed alternative procedure must be approved by the FAA before any emissions test is conducted. The FAA will consult with the EPA prior to making a written determination on any requested alternative procedure.
14.1. Determining Maximum nvPMMC Values The regulatory emissions levels for nvPMMC apply to the maximum values of nvPMMC throughout the entire thrust range of an engine, rather than the four LTO thrust settings as with gaseous emissions of HC, NOx, CO and nvPMmass and nvPMnum (see 5 of this AC for a discussion of maximum vs LTO values).
In either case, A16V2, Appendix 6 requires a minimum of three engine tests to be conducted, which may be on more than one engine, and the results averaged as explained below.
In determining the maximum nvPM mass concentration, an applicant is required to obtain measurements “at sufficient thrust settings, in such a way that the emissions maximum can be determined” (§ 34.71
(c)(1)). While there is no restriction on the number of thrust settings measured, a consistent set of measurement points and thrust settings should be chosen for each engine tested, typically encompassing low idle (less than 7% rated thrust) to thrusts greater than 100% rated thrust at ISA sea level conditions.
The resulting dataset should consist of nvPM mass concentration measurements made at each thrust setting across the thrust range chosen by the applicant for each engine.
The maximum nvPMMC standard is applicable to all engines with a rated thrust greater than 26.7kN produced on or after 1 January 2023. This includes derivative versions or modified engine models which are certified to the smoke number standard. These engines are no longer required to comply with the smoke number standard on or after 1 January 2023. Instead, they must comply with the maximum nvPMMC standard. Thus, beginning 1 January 2023, any modifications and changes to engines with rated thrust greater than 26.7 kN will not be assessed with the no change criteria for the smoke number standard, instead they will be assessed with the no emissions change criteria for nvPM as required by §
34.48 and described in 9.6 of this AC.
Because the requirements rely on data from multiple tests, and the nvPMMC regulations apply to maximums throughout the thrust range of an engine, there are various mathematical curve fitting and averaging approaches that may be applied to yield different maximum values for nvPM MC.
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Therefore, the FAA requires that one of the three individual methods, specified in § 34.73.(c)(1), and described below, be used for curve fitting and averaging to determine the maximum values for nvPM MC.
Engine manufacturers should report which of the methods was used in their test reports.
Method 1. The nvPMMC for individual data points is averaged to form an engine data point at a specific thrust setting then engine data points are averaged at common thrust settings in order to arrive at a single dataset which can then be curve fit from which the maximum may be determined to find the overall average maximum concentration. This approach requires common thrust settings. ( Data points falling within ±6° F of the combustor inlet temperatures may be considered the same thrust settings for averaging purposes, consistent with the “no emission change” criteria as described in § 34.48 and 9.6 of this AC). Method 1 is graphically illustrated, below.
Method 2. Develop curve fits of nvPMMC vs thrust range for all datasets combined for each engine and find the maximum for each engine. Then average all maximum engine values to find the overall average , maximum value for nvPMMC. Method 2 is graphically illustrated, below.
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Method 2 Y Engine 1 test run 1 data Engine 1 test run 2 data < Engine 2 test run 1 data Engine 1 test run 2 data Engine 1 curve fit Engine 2 curve fit Engine 1 curve fit maximum Engine 2 curve fit maximum nvPM Maximum nvPMc (kg/m3) Thrust(kN) Method 3. Develop curve fits of nvPM vs thrust range for each individual dataset and find the maximum for each individual curve fit. Average the individual curve fit maximums to get a maximum value for each engine. Average all of these maximum engine values to find the overall average, maximum value for nVP. Method 3 is graphically illustrated, below.
Method 3 Y Test run 1 data Test run 2 data Test run 3 data Test run 4 data Run 1 curve fit Run 2 curve fit Run 3 curve fit Run 4 curve fit X Run 1 curve fit maximum Run 2 curve fit maximum Run 3 curve fit maximum Run 4 curve fit maximum nvPM Max Thrust(kN) Page 23 of 57