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U.S. Department of Transportation 

Federal Aviation 

Administration

Advisory

Circular 

Subject: FUEL VENTING AND EXHAUST 

EMISSION REQUIREMENTS 

FOR TURBINE ENGINE 

POWERED AIRPLANES 

Date: 06/27/03

Initiated by: AEE-300

AC No: 34–1B 

Change: 

1. PURPOSE The intent of this advisory Circular (AC) is to promote uniformity of implementation of the 

emissions certification requirements of Part 34 of the Federal Aviation Regulations. FAR 34 is unusually 

complex in that it must reflect the requirements of the Clean Air Act, Sections 232 and 233, the EPA, 40 CFR 

Part 87 and ICAO Annex 16, Volume II, Second Edition, July 1993, as well the FAA’s mandated charter. This 

advisory circular brings these seemingly disparate requirements together to provide a single source of 

information and advice to individuals and agencies interested in FAR 34. 

a. Contents 

This revised Advisory Circular (AC) contains updated information, including anticipated adoption of ICAO 

CAPE 4 post December 31, 2003 rules, describing the standards and requirements for aircraft fuel venting and 

engine emission certification and presents explanatory and supplementary information, as necessary, to 

identify acceptable means of compliance. The information contained in this document sets forth acceptable 

means, but not the sole means, by which compliance may be shown with the requirements of Federal Aviation 

Regulations (FAR) Part 34 of the United States Code of Federal Regulations (CFR) Title 14. The regulation 

that this AC references is 14 CFR Part 34 and its Amendments (hereinafter referred to as “Part 34”). 

Pursuant to the Clean Air Act (CAA), Sections 231 and 232, Part 34 necessarily must conform to 

Environmental Protection Agency (EPA) Title 40, Part 87, “Control of Air Pollution From Aircraft and Aircraft 

Engines; Emission Standards and Test Procedures”. Therefore any change in procedures, of a substantive 

nature, must be discussed with, and approved by, the Administrator of the EPA. This is mentioned explicitly in 

Part 34 and in this AC for those areas of particular concern. In addition, users of this AC, as well as Part 34, 

must be aware of any changes to 40 CFR Part 87 which have not yet been included in either Part 34 or this 

AC. In such instances the requirements described in these documents must defer to 40 CFR Part 87, unless 

and until approval is obtained from the Administrator of the EPA. 

b. Advisory Nature

Like other Federal Aviation Administration (FAA) advisory circulars, the language within this document is 

intended to be permissive and advisory in nature, except for explanations of regulatory language that are 

mandatory. In addition, the compliance methods chosen by the applicant are voluntary within the framework of 

the regulation as written. Mandatory terms used in this AC, such as “must” and “shall”, are used only in the 

sense of ensuring the applicability of these particular methods of compliance when the acceptable means of 

compliance described herein are used. This AC does not change regulatory requirements and does not 

authorize changes in, or deviations from, regulatory requirements. 

c. Document Format 

This AC contains a section-by-section review and explanation of 14 CFR Part 34. In order to assist the user, 

each explanation is provided as a separate, sequentially numbered, paragraph. In general, each paragraph is 

presented as follows in Figure 1: 
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Paragraph Number: 

Easy to reference 

number for each 

section of Advisory 

Circular AC 34-1B 

that is addressed 

1. Citation Number: Number in 14 CFR Part 34 that 

is being addressed 

Actual regulatory text 

(italicized and indented) 

reproduced for better 

readability)

 19 § 34.61 Turbine Fuel Specification

 For exhaust emissions testing, fuel meeting the 

specifications listed below shall be used... 

 a. Explanation

The fuel specification in Part 34 matches the amended 

ICAO fuel specification in Annex 16, Vol. II, Second 

Edition, 1993. This specification is typical of Jet A 

Brief “Plain English” 

explanation of regulatory 

text (appears only if text is 

not self explanatory)

b. Supplemental Information

Aircraft gas turbine engines can and do use a variety of 

fuels. The specific fuel type and composition can and 

often does have a significant effect on engine 

emissions. ... 

Potentially useful 

supplementary information 

(included only if 

necessary)

2. DEFINITIONS 

Where the following expressions are used in this 

appendix, they have the meanings ascribed to them 

below: 

(1) Accuracy. The closeness with which a 

measurement approaches the true value established 

independently. 

Text reproduced from 

ICAO Annex 16, Volume II, 

Second Edition, 1993. 

 

FIGURE 1: Document Format 

In addition to the section-by-section explanations, this AC includes 3 additional chapters that explain specific 

appendices from ICAO, Annex 16, Volume II. Second Edition, July 1993. These have been included to make 

this AC relatively self contained, since these appendices are explicitly referenced within Part 34. Specifically: 

• FAR 34 Subpart G refers to ICAO Appendices 3, 5 and 6. 

• FAR 34 Subpart H refers to ICAO Appendices 2 and 6. 

These ICAO appendices, 3,5 and 6, deal with detailed technical issues regarding instrumentation and 

measurement techniques and statistically derived compliance procedures. As such they are relatively complex 

and have been kept distinct from the rest of the AC as separate chapters. Typically, only those readers who 

are interested in specific equations and/or details regarding measurement techniques and compliance 

procedures will need to read these sections. 
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d. Audience 

The intended audience for this AC includes engine specialists from the FAA (aircraft certification and flight 

standards), aircraft and aircraft engine industry, aircraft certification applicants, foreign governments, airline 

customers, airport operators, the scientific community, and other interested persons. 

e. AC Intent 

The intent of this AC is to establish a clear understanding between the regulatory authorities, aircraft engine 

users, local governments, and the aircraft engine industry of the engine emissions certification processes and 

to present historical policies, guidance material and interpretations that have been used in the aircraft engine 

certification process. 

f. Document Use 

Sequential paragraphs are indicated in this AC to improve usage. The regulatory section numbers, together 

with the regulatory language are indented and italicized. In addition, text from ICAO Annex 16 is included 

(shaded and italicized) where appropriate. 

g. Technical Advancement: 

Since the introduction of engine emission standards in 1973 (38 FR 19088, July 17, 1973), acceptable means 

and procedures for measurement, testing, data reduction, evaluation and compliance reporting have advanced 

considerably. For the purpose of certification and compliance, applicants have, over time, developed, 

evaluated and had approved engine specific alternate but equivalent testing, measurement and data reduction 

procedures. Approval, in these instances, is obtained through the FAA, Office of Environment and Energy 

(AEE) located in the FAA Headquarters in Washington DC. 

h. FAA Certification Process: 

The FAA administrative certification process is shown in Figure 2. Each step in the appropriate process must 

be completed before proceeding to the next step. Specific details of this process can be found in a 

memorandum “Inter-Office Management Plan for Aircraft Engine Fuel Venting and Exhaust Emissions”, 

appended to this Advisory Circular as Exhibit 1. As a part of its compliance responsibilities, FAA can either 

conduct the emission tests or delegate that responsibility to the engine manufacturer, which is then monitored 

by the FAA. Since the FAA does not have the resources or the funding to test engines themselves, FAA 

selects engineers at each plant to serves as representatives (called Designated Engineering Representatives 

or DERs) for the FAA while the manufacturer performs the test procedures. DER’s responsibilities include 

evaluating the test plan, the test engine, the test equipment, and the final testing report sent to the FAA. 

i. Exclusions 

There are no sections excluded from this AC. 

2. CANCELLATION 

Advisory Circular 34–1A, Fuel Venting and Exhaust Emission Requirements for Turbine Engine Powered 

Airplanes, dated June 30, 2001, is canceled. 
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 FIGURE 2. FAA Certification Process

Test

Post Test

Inspection

Test Report 

Approved

FAA Final Type

Board Meeting

Conformity

Inspection

Analysis Approved

by FAA

Analysis 

to FAA

Test Plan Approved

by FAA

Overall Test Plan/

Analysis

Outline to FAA

Detailed Test Plans

to FAA

Preliminary Type

Board with FAA

FAA Certification Process (Administrative)

New Model Certification Major Change Substantiation

Test Plan 

Submitted to FAA

Conformity

Inspection

Analysis

Approved by FAA

Test Plan

Approved by FAA

Analysis

Submitted to FAA

Major Change

Approved by FAA

Results Submitted

to FAA

Test

AND/OR OR

DER Responsible to local region
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3. TABLE OF CONTENTS 

1. PURPOSE........................................................................................................................................ 1 

a. Contents........................................................................................................................................... 1 

b. Advisory Nature................................................................................................................................ 1 

c. Document Format ............................................................................................................................ 1 

d. Audience .......................................................................................................................................... 3 

e. AC Intent .......................................................................................................................................... 3 

f. Document Use ................................................................................................................................. 3 

g. Technical Advancement:.................................................................................................................. 3 

h. FAA Certification Process: ............................................................................................................... 3 

FAA Certification Process - Figure 2............................................................................................................. 4 

i. Exclusions ........................................................................................................................................ 3 

2. CANCELLATION.............................................................................................................................. 3 

3. TABLE OF CONTENTS .................................................................................................................. 5 

4. REFERENCES................................................................................................................................. 7 

I. 14 CFR PART 34 Subpart A—General Provisions ........................................................................ 7 

5. §34.1 DEFINITIONS............................................................................................................................ 7 

6. §34.2 Abbrevations ....................................................................................................................... 10 

7. § 34.3 GENERAL REQUIREMENTS...................................................................................................... 12 

8. §34.4 [RESERVED] .......................................................................................................................... 17 

9. §34.5 SPECIAL TEST PROCEDURES.................................................................................................. 17 

10. §34.6 AIRCRAFT SAFETY.................................................................................................................. 18 

11. §34.7 EXEMPTIONS ......................................................................................................................... 18 

II. Subpart B — Engine Fuel Venting Emissions - (New and In-Use Aircraft Gas Turbine 

Engines)........................................................................................................................................ 21

12. §34.10 APPLICABILITY ..................................................................................................................... 21 

13. §34.11 STANDARD FOR FUEL VENTING EMISSIONS. ............................................................................ 21 

III. Subpart C — Exhaust Emissions (New Aircraft Gas Turbine Engines) ................................. 23
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14. § 34.20 APPLICABILITY ..................................................................................................................... 23 

15. § 34.21 STANDARDS FOR EXHAUST EMISSIONS .................................................................................. 23 

IV. Subpart D — Exhaust Emissions (In-Use Aircraft Gas Turbine Engines)Error! Bookmark not defined. 

16. § 34.30 APPLICABILITY ..................................................................................................................... 27 

17. § 34.31 STANDARDS FOR EXHAUST EMISSIONS .................................................................................. 27 

V. Subpart E — [Reserved].............................................................................................................. 28 

VI. Subpart F — [Reserved] .............................................................................................................. 29 

VII. Subpart G — Test Procedures for Engine Exhaust Gaseous Emissions (Aircraft and 

Aircraft Gas Turbine Engines) .................................................................................................... 30

18. §34.60 INTRODUCTION. ................................................................................................................... 30 

19. §34.61 TURBINE FUEL SPECIFICATION. ............................................................................................ 30 

20. §34.62 TEST PROCEDURE (PROPULSION ENGINES). .......................................................................... 32 

21. §34.63 [RESERVED] ......................................................................................................................... 33 

22. §34.64 SAMPLING AND ANALYTICAL PROCEDURES FOR MEASURING GASEOUS EXHAUST EMISSIONS..... 33 

23. §34.65—§34.70 [RESERVED] .......................................................................................................... 33 

24. § 34.71 COMPLIANCE WITH GASEOUS EMISSION STANDARDS.............................................................. 33 

VIII. Subpart H — Test Procedures for Engine Smoke Emissions (Aircraft and Aircraft Gas 

Turbine Engines).......................................................................................................................... 33

25. §34.80 INTRODUCTION. ................................................................................................................... 34 

26. §34.81 FUEL SPECIFICATIONS. ........................................................................................................ 35 

27. §34.82 SAMPLING AND ANALYTICAL PROCEDURES FOR MEASURING - SMOKE EXHAUST EMISSIONS....... 36 

28. §34.83 – §34.88 [RESERVED] ......................................................................................................... 36 

29. §34.89 COMPLIANCE WITH SMOKE EMISSION STANDARDS................................................................... 36 

IX. ICAO ANNEX 16, VOLUME II, Second Edition, July, 1993, APPENDIX 6................................ 38

X. ICAO ANNEX 16, VOLUME II, Second Edition, July, 1993, APPENDIX 3................................ 42

XI. ICAO ANNEX 16, VOLUME II, Second Edition, July, 1993, APPENDIX 5................................ 81

XII. ICAO ANNEX 16, VOLUME II, Second Edition, July, 1993, APPENDIX 2.............................. 121

30 EXHIBIT 1 Inter-Office Management Plan ................................................................................... 131 
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4. REFERENCES 

(1) Clean Air Act as amended, 42 U.S.C. 7571 and 7601. 

(2) 14 CFR ch. 1 (1-1-97 edition), Federal Aviation Administration, Department of Transportation, Subchapter 

A, Definitions. 

(3) 40 CFR Part 87, Environmental Protection Agency, Control of Air Pollution from Aircraft and Aircraft 

Engines; Emission Standards and Test Procedures; Final and Proposed Rule, Federal Register, Vol. 62, 

No. 89, Thursday, May 8, 1997. 

(4) Federal Aviation Regulations, Part 34, Fuel Venting and Exhaust Emission Requirements for Turbine 

Engine Powered Airplanes, February 3, 1999. 

(5) International Civil Aviation Organization, International Standards and Recommended Practices, 

Environmental Protection, Annex 16, Volume II, Aircraft Engine Emissions, Second Edition — July 1993. 

(6) SAE International, SAE AEROSPACE RECOMMENDED PRACTICE ARP 1256, Procedure for the 

Continuous Sampling and Measurement of Gaseous Emissions from Aircraft Turbine Engines. 

(7) SAE International, SAE AEROSPACE RECOMMENDED PRACTICE ARP 1179, Aircraft Gas Turbine 

Engine Exhaust Smoke Measurement. 

(8) SAE International, SAE AEROSPACE RECOMMENDED PRACTICE ARP 1533, Procedure for the 

Calculation of Gaseous Emissions from Aircraft Turbine Engines. 

I. 14 CFR 34 Subpart A General Provisions 

5. 34.1 Definitions 

As used in this AC, all terms not defined herein shall have the meaning given them in the Clean Air Act, as 

amended (42 U.S.C. 7401 et. seq.): 

Supplemental Information:

Section 232 of the Clean Air Act, as amended, directs the Secretary of Transportation to issue regulations to 

ensure compliance with 40 CFR part 87. 40 CFR part 87 calls out, by reference, specific sections of ICAO 

Annex 16, Volume II, Second edition, 1993. ICAO Annex 16 includes definitions which should be added to 

the definitions in Part 34 to provide understanding and completeness. Following is a combined list of 

definitions required when fulfilling the requirements of Part 34. The ICAO definitions are italicized and 

shaded. Some discussion is provided where further clarification is needed. 

Act means the Clean Air Act, as amended (42 U.S.C. 7401 et. seq.). 

Administrator means the Administrator of the Federal Aviation Administration or any person to whom he has 

delegated his authority in the matter concerned. 

Administrator of the EPA means the Administrator of the Environmental Protection Agency and any other 

officer or employee of the Environmental Protection Agency to whom the authority involved may be 

delegated. 

Aircraft as used in this part means any airplane as defined in 14 CFR part 1 for which a U.S. standard 

airworthiness certificate or equivalent foreign airworthiness certificate is issued. 

Aircraft engine means a propulsion engine which is installed in, or which is manufactured for installation in, an 

aircraft. 

Supplemental Information: This definition applies to those engines for which a U.S. standard airworthiness 

certificate or equivalent foreign airworthiness certificate is issued. 

Aircraft gas turbine engine means a turboprop, turbofan, or turbojet aircraft engine. 

Explanation:

As with the overall intent of this regulation piston engines are excluded. 
 

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Afterburning. A mode of engine operation wherein a combustion system fed (in whole or part) by vitiated air is 

used. 

Approach Phase. The operating phase defined by the time during which the engine is operated in the 

approach operating mode. 

Class TP means all aircraft turboprop engines. 

Class TF means all turbofan or turbojet aircraft engines or aircraft engines designed for applications that 

otherwise would have been fulfilled by turbojet and turbofan engines except engines of class T3, T8, and 

TSS. 

Explanation:

Applications, which could fulfill these requirements, are propfans, unducted fans, and advanced unducted 

fans. 

Class T3 means all aircraft gas turbine engines of the JT3D model family. 

Class T8 means all aircraft gas turbine engines of the JT8D model family. 

Class TSS means all aircraft gas turbine engines employed for propulsion of aircraft designed to operate at 

supersonic flight speeds. 

Climb phase: The operating phase defined by the time during which the engine is operated in the climb 

operating mode. 

Commercial aircraft engine means any aircraft engine used or intended for use by an "air carrier" (including 

those engaged in "intrastate air transportation") or a "commercial operator" (including those engaged in 

"intrastate air transportation") as these terms are defined in the Federal Aviation Act and the Federal Aviation 

Regulations. 

Commercial aircraft gas turbine engine means a turboprop, turbofan, or turbojet commercial aircraft engine. 

Date of manufacture of an engine is the date the inspection acceptance records reflect that the engine is 

complete and meets the FAA approved type design. 

Emission measurement system means all of the equipment necessary to transport the emission sample and 

measure the level of emissions. This includes the sample system and the instrumentation system. 

Explanation: 

The intention is to delineate all of the equipment and devices to extract, transport, condition, differentiate and 

measure the concentrations of “exhaust emissions” – see 4.a. (17). If inlet species are measured, for 

monitoring or corrections, as part of the certification process the equipment and devices used should be 

included as part of the “Emissions measurement system”. 

Engine model means all commercial aircraft turbine engines, which are of the same general series, 

displacement, and design characteristics and are approved under the same type certificate. 

Supplemental Information: 

For the purposes of a working definition, with respect to emissions certification, when considering the 

similarity or equivalence of engines, similar or equivalent engine models should be taken as those engines 

approved under the same type certificate. For example, from 14 CFR ch. 1 (1-1-97 edition), Federal Aviation 

Administration Department of Transportation, Subchapter A, Definitions: “Type”: (3) As used with respect to 

the certification of aircraft engines means those engines which are similar in design. For example, JT8D and 

JT8D-7 are engines of the same type, and JT9D-3A and JT9D-7 are engines of the same type. 

Exhaust emissions means substances emitted into the atmosphere from the exhaust discharge nozzle of an 

aircraft or aircraft engine. 
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Fuel venting emissions means raw fuel, exclusive of hydrocarbons in the exhaust emissions, discharged from 

aircraft gas turbine engines during all normal ground and flight operations. 

In-use aircraft gas turbine engine means an aircraft gas turbine engine, which is in service. 

New aircraft turbine engine means an aircraft gas turbine engine, which has never been in service. 

Explanation: 

This definition should be viewed with respect to “In-use aircraft gas turbine engine” and relative to the intent of 

40 CFR Part 87, Subpart B, Engine Fuel Venting emissions (New and In-Use Aircraft Gas Turbine Engines), 

Subpart C, Exhaust Emissions (New Aircraft Gas Turbine Engines), and Subpart D, Exhaust Emissions (InUse Aircraft Gas Turbine Engines). 

Any engine intended for revenue service but which has never been in service is by definition new and must 

meet the provisions of Subpart B and C for fuel venting, gaseous and smoke emissions. This sets the 

baseline for regulation and control of emissions from aircraft gas turbine engines. Alternatively the definition 

for in-use aircraft gas turbine engines is intended, for those engines in service, to prevent deterioration of fuel 

venting and/or smoke emissions beyond the maximum allowable for new engines. In other words, the first 

time a particular engine sees revenue service it is “new” and ever after it is “in-use”. The fact that a given 

engine model is in revenue service does not relieve a newly manufactured engine of this model of being 

considered as “new”. Although this interpretation could impose severe penalties on the engine manufacturer 

in the demonstration of compliance, the allowance, and universal use, of ICAO Annex 16, Volume II, 

Appendix 6, Compliance Procedure for Gaseous Emissions and Smoke solves the problem by specifying a 

limited engine preproduction compliance procedure which relieves the manufacturer from having to test every 

engine and, in effect, follows the engine in time, i.e., there is no requirement for the testing of engines in-use. 

Oxides of Nitrogen. The sum of the amounts of the nitric oxide and nitrogen dioxide contained in a gas 

sample calculated as if the nitric oxide were in the form of nitrogen dioxide. 

Power Setting: means the power or thrust output of an engine in terms of kilonewtons thrust for turbojet and 

turbofan engines or shaft power in terms of kilowatts for turboprop engines. 

Rated Output (rO): means the maximum power/thrust available for takeoff at standard day conditions as 

approved for the engine by the Federal Aviation Administration, including reheat contribution where 

applicable, but excluding any contribution due to water injection and excluding any emergency power/thrust 

rating. 

Explanation:

For the purpose of this regulation “maximum power/thrust available for takeoff” is taken to mean under normal

operating conditions. The definition as stated has caused some confusion because of a maximum thrust 

emergency rating even though the definition, as it appears in 14 CFR Part 34, excludes any emergency 

power/thrust rating. Some of the confusion may be due to the parent definition in 40 CFR 87, which does not 

explicitly exclude the emergency power/thrust rating. The intent is clear however from 40 CFR Part 87, 

Subpart G, 87.60 (c): “... determine mass emissions through calculations during a simulated aircraft landingtakeoff cycle (LTO). The LTO cycle is based on time in mode data during high activity periods at major 

airports.” The use of emergency power/thrust during takeoff would be an extraordinary and abnormal 

situation. Further, 40 CFR Part 87 (87.64) requires the use of ICAO Annex 16, Volume II, 1993, Appendix 3. 

Appendix 3 defines Rated Output, rO, as “ F00,” which is further defined as: “The maximum thrust available for 

take-off under normal operating conditions at ISA sea level static conditions, without the use of water 

injection, as approved by the applicable certificating authority”. 

Rated pressure ratio (rPR): means the ratio between the combustor inlet pressure and the engine inlet 

pressure achieved by an engine operation at rated output. 
 

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REFERENCE DAY CONDITIONS: MEANS THE REFERENCE AMBIENT CONDITIONS TO WHICH THE GASEOUS EMISSIONS (HC

AND SMOKE) ARE TO BE CORRECTED. THE REFERENCE DAY CONDITIONS ARE AS FOLLOWS: TEMPERATURE = 15 O C,

SPECIFIC HUMIDITY = 0.00629 KG H20/KG OF DRY AIR, AND PRESSURE = 101325 PA. 

Reference pressure ratio. The ratio of the mean total pressure at the last compressor discharge plane of the 

compressor to the mean total pressure at the compressor entry plane when the engine is developing take-off 

thrust rating in ISA sea level static conditions. 

Sample System: means the system, which provides for the transportation of the gaseous emissions sample 

from the sample probe to the inlet of the instrumentation system. 

Supplemental information:

A ‘Sample System’ is required for smoke emissions as well as for gaseous emission. Detailed specifications, 

for each, are described in ICAO Appendices 2 and 3. There are differences in requirements between the two 

systems but it is not unusual to satisfy the separate requirements with an appropriately designed single 

sample system. 

Shaft Power: means only the measured shaft power out put of a turboprop engine. 

Smoke: means the matter in exhaust emissions, which obscures the transmission of light. 

Smoke Number (SN): means the dimensionless term quantifying smoke emissions. 

Standard day conditions: means standard ambient conditions as described in the United States Standard 

Atmosphere 1976, (i.e., temperature = 15 o C, specific humidity = 0.00 kg H20/kg dry air, and pressure = 

101325 Pa.) 

Take-off phase. The operating phase defined by the time during which the engine is operated at the rated 

output. 

Taxi/idle (in): means those aircraft operations involving taxi and idle between the time of landing roll-out and 

final shutdown of all propulsion engines. 

Taxi/idle (out): means those aircraft operations involving taxi and idle between the time of initial starting of the 

propulsion engine(s) used for the taxi and the turn onto the duty runway. 

j. Unburned hydrocarbons. The total of hydrocarbon compounds of all classes and molecular weghts contained 

in a gas sample, calculated as if the were in the form of methane. 

6. §34.2 Abbreviations

The abbreviations used in this part have the following meanings in both upper and lower case 

CO Carbon Monoxide 

EPA United States Environmental Protection Agency 

FAA Federal Aviation Administration, United States Department of Transportation 

HC Hydrocarbons 

HP Horsepower 

hr Hour(s) 

H2O water 

kg Kilogram(s) 

kJ Kilojoule(s) 

LTO Landing and takeoff 

min Minute(s) 
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NO(X) Oxides of Nitrogen 

Pa Pascal(s) 

rO Rated Output 

rPR Rated pressure ratio 

sec Second(s) 

SP Shaft power 

SN Smoke number 

T Temperature, degrees Kelvin 

TIM Time in mode 

W Watt(s) 

Deg. C Degrees Celsius 

% Percent 

Supplemental information:

In addition to the abbreviations listed in §34.2 there are a large number of abbreviations from other sources 

that are used in AC 34. Those abbreviations listed in ICAO Annex 16 as Symbols are italicized and shaded. 

Only those Symbols from ICAO that are not duplicated in Part 34 are listed. 

AC FAA Advisory Circular 

ACO Local FAA Aircraft Certification Office 

AEE FAA Office of Environment and Energy 

AFM Airplane Flight Manual 

APP Approach 

APU Auxiliary Power Unit 

ARP Aerospace Recommended Practice 

CAA Clean Air Act 

CFR Code of Federal Regulations 

CI Confidence Interval (90%) 

CO2 Carbon Dioxide 

Dp The mass of any gaseous pollutant emitted during the reference emissions landing and take-off cycle 

DER Designated Engineering Representative 

EPA United States Environmental Protection Agency. 

EI Emission Index 

EPR Engine Pressure Ratio (Power Setting Parameter) 

Fn Thrust in International Standard Atmosphere (ISA), sea level conditions, for the given operating mode 

F00 Rated output 

F*

00 Rated output with afterburning applied

FAR Federal Aviation Regulation (CFR Title 14) 

FCAA Foreign Civil Aviation Authority 

FID Flame Ionization Detector 

FPR Fan Pressure Ratio 

ICAO International Civil Aviation Organization 

JAA Joint Airworthiness Authorities (of Europe) 

JAR Joint Airworthiness Requirements (of Europe) 

Log logarithmic value to base 10 

M meter 

MJ Mega Joules 

MSL Mean Sea Level altitude, feet 

N/A Not Applicable 

NIST National Institute of Standards and Technology 

NO Nitric oxide 

NO2 Nitrogen dioxide 

ppmC Parts per million carbon 

ref. Reference 

RH Relative Humidity, % 
 

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rms root-mean-square 

rpm Revolutions Per Minute 

SAE SAE International (formerly Society of Automotive Engineers) 

Sec Second(s) 

TC Type Certificate 

TIM Time in mode 

TO Takeoff 

VNTSC Volpe National Transportation System Center (D.O.T.) 

W Watt(s) 

oC Degrees Celsius. 

% Percent 

π00 Reference pressure ratio 

7. 34.3 General requirements: 

§ 34.3(a) 

(a) This part provides for the approval or acceptance by the Administrator or the Administrator of the EPA 

of testing and sampling methods, analytical techniques, and related equipment not identical to those 

specified in this part. Before either approves or accepts any such alternate, equivalent, or otherwise 

nonidentical procedures or equipment, the Administrator or the Administrator of the EPA shall consult 

with the other in determining whether or not the action requires rulemaking under sections 231 and 

232 of the Clean Air Act, as amended, consistent with the responsibilities of the Administrator of the 

EPA and the Secretary of Transportation under sections 231 and 232 of the Clean Air Act. 

Explanation

This part provides for the flexibility needed to accommodate changing engine designs and possible changes 

and/or improvements in testing, sampling methods, analytical techniques and related equipment. This part 

does not provide guidelines or any systematic means of demonstrating equivalence of non-identical 

procedures or equipment. 40 CFR part 87, calls out, by reference, those sampling and analytical procedures 

specified by ICAO. ICAO does not specify particular equipment but does detail accuracy, operational and 

performance requirements wherever possible. For example, ICAO states the method of detection for each of 

the pollutants along with details of calibration and operation but does not list specific pieces of equipment. 

Presumably each emissions certification test would require demonstration that each analytical technique and 

piece of equipment met the ICAO requirements. Similarly, it is the intent of 34.3(a) that any alternate method 

proposed demonstrate that it met the ICAO operational and performance requirements or their equivalent. 

Each such instance would, necessarily, need to be considered on its own merit. 

§ 34.3 (b) through (f):

(b) Under section 232 of the Act, the Secretary of Transportation issues regulations to ensure 

compliance with 40 CFR part 87. This authority has been delegated to the Administrator of the 

FAA (49 CFR 1.47). 

(c) U.S. airplanes. This Federal Aviation Regulation (FAR) applies to civil airplanes that are powered 

by aircraft gas turbine engines of the classes specified herein and that have U.S. standard 

airworthiness certificates. 

(d) Foreign airplanes. Pursuant to the definition of "aircraft" in 40 CFR 87.1(c), this FAR applies to 

civil airplanes that are powered by aircraft gas turbine engines of the classes specified herein and 

that have foreign airworthiness certificates that are equivalent to U.S. standard airworthiness 

certificates. This FAR applies only to those foreign civil airplanes that, if registered in the United 

States, would be required by applicable Federal Aviation Regulations to have a U.S. standard 

airworthiness certificate in order to conduct the operations intended for the airplane. Pursuant to 

40 CFR 87.3(c), this FAR does not apply where it would be inconsistent with an obligation 

assumed by the United States to a foreign country in a treaty, convention, or agreement. 
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(e) Reference in this regulation to 40 CFR part 87 refers to title 40 of the Code of Federal 

Regulations, chapter I--Environmental Protection Agency, part 87, Control of Air Pollution from 

Aircraft and Aircraft Engines (40 CFR part 87). 

(f) This part contains regulations to ensure compliance with certain standards contained in 40 CFR 

part 87. If EPA takes any action, including the issuance of an exemption or issuance of a revised 

or alternate procedure, test method, or other regulation, the effect of which is to relax or delay the 

effective date of any provision of 40 CFR part 87 that is made applicable to an aircraft under this 

FAR, the Administrator of FAA will grant a general administrative waiver of its more stringent 

requirements until this FAR is amended to reflect the more relaxed requirements prescribed by 

EPA. 

Explanation

Authority under Section 232, Clean Air Act, as amended, is to "insure compliance with all standards 

prescribed under section 231 by the Administrator" of the EPA. If the Administrator of the EPA takes any of 

the actions described in 34.3 (f) the Administrator of FAA must respond accordingly. In such instances some 

or all of Part 34 may not be applicable until such time as Part 34 is reissued. In the past any such action 

taken by the EPA has been reflected in the issuance of a revised or amended version of 40 CFR part 87. 

This would then serve as the primary reference for all substantive information. 

If the EPA changes 40 CFR Part 87 to relax any of the standards, and the relaxed standards apply to aircraft 

pursuant to Part 34, then the FAA Administrator will grant a general waiver to use the relaxed EPA standard 

until such time as Part 34 is reissued. It should be noted that a general waiver is not a waiver that can be 

applied for by an individual, but is a waiver that is issued by the Administrator to all persons subject to Part 34 

that is affected by the relaxed or changed 40 CFR Part 87 standards. 

§ 34.3(g)

(g) Unless otherwise stated, all terminology and abbreviations in this FAR that are defined in 40 CFR 

part 87 have the meaning specified in that part, and all terms in 40 CFR part 87 that are not 

defined in that part but that are used in this FAR have the meaning given them in the Clean Air 

Act, as amended by Public Law 91-604. 

Explanation

40 CFR part 87 specifies, by reference, selected sections of ICAO Annex 16, Volume II, Aircraft Engine 

Emissions, Second edition, 1993. Namely, Appendices 2, 3, 5, and 6 of Annex 16 provides definitions that 

are specifically applicable to these referenced appendices and are necessary to an understanding of the 

requirements described therein. These definitions can be considered to be part of 40 CFR Part 87. 

§ 34.3 (h), (i)

(h) All interpretations of 40 CFR part 87 that are rendered by the EPA also apply to this FAR. 

(i) If the EPA, under 40 CFR 87.3(a), approves or accepts any testing and sampling procedures or 

methods, analytical techniques, or related equipment not identical to those specified in that part, 

this FAR requires an applicant to show that such alternate, equivalent, or otherwise nonidentical 

procedures have been complied with, and that such alternate equipment was used to show 

compliance, unless the applicant elects to comply with those procedures, methods, techniques, 

and equipment specified in 40 CFR part 87. 
 

Page 14 

Explanation

Similar to 34.3 (a) any, individual or agency requesting acceptance and approval for testing, sampling 

procedures or methods, analytical techniques, or related equipment not identical to those specified, having 

demonstrated equivalency, must prove to the satisfaction of the FAA that the alternate, equivalent, or 

otherwise nonidentical procedures have been complied with, and the approved procedures, methods, 

analytical techniques and related equipment was used to show compliance. Once approval has been 

obtained from the EPA the requirement to prove that the alternate equivalent, or otherwise nonidentical 

procedures have been complied with are similar to the requirements for the standard procedures. If the 

individual or agency reconsiders this, they are free to use the standard testing procedures. The Request 

Process for §34.3, is shown graphically in FIGURE 3, “EXCEPTIONS TO FAR 34”. 
 Page 15 

Supplemental information for Sections 34.3 (h), (i), (k) and 34.5 

FIGURE 3 Request Process for Alternate, Equivalent or Otherwise Nonidentical Procedures 

FAA

AEE-300 

Grants or denies 

request

FAA

AEE – 300 

Receives and 

Reviews Request
 

Page 16 

§ 34.3 (j)

(j) If the EPA, under 40 CFR 87.5, prescribes special test procedures for any aircraft or aircraft 

engine that is not susceptible to satisfactory testing by the procedures in 40 CFR part 87, the 

applicant must show the Administrator that those special test procedures have been complied 

with. 

Explanation 

The FAA has this responsibility under Section 232, CAA as amended. As with 34.3 (a) and (i) the applicant 

must provide evidence to the FAA that the special test procedures have been complied with as approved. 

§ 34.3 (k) 

(k) Wherever 40 CFR part 87 requires agreement, acceptance, or approval by the Administrator of 

the EPA, this FAR requires a showing that such agreement or approval has been obtained. 

Explanation 

The FAA has this responsibility under Section 232, CAA as amended. The Request Process for Alternate, 

Equivalent or Otherwise Nonidentical Procedures is shown in Figure 3. 

§ 34.3 (l)

(l) Pursuant to 42 U.S.C. 7573, no state or political subdivision thereof may adopt or attempt to 

enforce any standard respecting emissions of any air pollutant from any aircraft or engine thereof 

unless that standard is identical to a standard made applicable to the aircraft by the terms of this 

FAR. 

Explanation

42 U.S.C. 7573 refers to Section 233 of the Clean Air Act as amended. Section 233 of the Clean Air Act as 

amended preempts the adoption or enforcement of any emissions standard not identical to the standards 

promulgated in 40 CFR part 87, and enforced through 14 CFR Part 34. 

§ 34.3 (m)

(m) If EPA, by regulation or exemption, relaxes a provision of 40 CFR part 87 that is implemented in 

this FAR, no state or political subdivision thereof may adopt or attempt to enforce the terms of this 

FAR that are superseded by the relaxed requirement. 

Explanation

Similar to 34.3 (l) above with authority from Section 233 of the Clean Air Act as amended. 

§ 34.3 (n)

(n) If any provision of this FAR is rendered inapplicable to a foreign aircraft as provided in 40 CFR 

87.3(c) (international agreements), and §34.3(d) of this FAR, that provision may not be adopted 

or enforced against that foreign aircraft by a state or political subdivision thereof. 
 Page 17 

Explanation

Similar to 34.3 (l) (m) above with authority from Section 233 of the Clean Air Act as amended. 

Standardization and control of emissions from commercial aircraft is the responsibility of the Federal 

government. 

§ 34.3 (o)

(o) For exhaust emissions requirements of this FAR that apply beginning February 1, 1974, January 

1, 1976, January 1, 1978, January 1, 1984, and August 9, 1985, continued compliance with those 

requirements is shown for engines for which the type design has been shown to meet those 

requirements, if the engine is maintained in accordance with applicable maintenance 

requirements for 14 CFR chapter I. All methods of demonstrating compliance and all model 

designations previously found acceptable to the Administrator shall be deemed to continue to be 

an acceptable demonstration of compliance with the specific standards for which they were 

approved. 

Explanation

With respect to emissions engines are not expected to deteriorate significantly in time so if they met 

emissions requirements in the past and are maintained in accordance with FAA requirements they will be 

considered to be in compliance. 

§ 34.3 (p)

(p) Each applicant must allow the Administrator to make, or witness, any test necessary to determine 

compliance with the applicable provisions of this FAR. 

Explanation

Emissions compliance testing is typically performed at the engine manufacturers’ facility. Because of the 

expense and complexity of emissions sampling and analytical equipment, engine manufacturers use the 

same procedures and equipment, to the extent possible, for all emissions certification testing. Once an 

emissions certification test has been witnessed and approved, future, similar tests, can be evaluated at little 

risk, by means of the engine certification test plan and the engine test and emissions measurement 

equipment operational documentation. Changes in test equipment and/or procedures should be evaluated for 

each situation. For example, changing an analytical instrument from one manufacturer to another without on 

site inspection would pose little risk, whereas changing from a single point, traversing, sampling probe to an 

integrating traversing sampling rake might warrant review and discussion and perhaps inspection of the 

equipment involved. 

8. §34.4 [Reserved] 

9. §34.5 Special Test Procedures:. 

The Administrator or the Administrator of the EPA may, upon written application by a manufacturer or 

operator of aircraft or aircraft engines, approve test procedures for any aircraft or aircraft engine that is 

not susceptible to satisfactory testing by the procedures set forth herein. Prior to taking action on any 

such application, the Administrator or the Administrator of the EPA shall consult with the other. 

Explanation

The particular configuration of a given engine may lend itself to testing by some means other than that implied 

in Part 34. For example it may be beneficial to sample, for emissions, a mixed fan flow engine from the core 
 

Page 18 

rather than from the standard co-annular core/fan flow discharge nozzle. Because of the restrictions placed 

on the location of the emissions sampling probe this would be difficult if not impossible. By adopting a 

scheme of separating the two flows, fan and core without adversely affecting engine performance, a viable 

core only sample could be taken. Such a scheme would have to be reviewed and approved by the FAA. The 

request process for approval is shown in Figure 3. 

10. §34.6 Aircraft safety

(a) The provisions of this part will be revised if at any time the Administrator determines that an 

emission standard cannot be met within the specified time without creating a safety hazard. 

Explanation

The Administrator must assure appropriate consideration of aircraft safety when considering meeting 

emissions standards within any time frame. 

(b) Consistent with 40 CFR 87.6, if the FAA Administrator determines that any emission control 

regulation in this part cannot be safely applied to an aircraft, that provision may not be adopted or 

enforced against that aircraft by any state or political subdivision thereof. 

Explanation

Authority for Part 34.6 (b) comes from Section 233, Clean Air Act as amended. In addition, aircraft, in 34.6(b) 

should be interpreted to mean “aircraft and aircraft engine”. 

11. §34.7 Exemptions

Notwithstanding part 11 of the Federal Aviation Regulations (14 CFR part 11), all petitions for rulemaking 

involving either the substance of an emission standard or test procedure prescribed by the EPA that is 

incorporated in this FAR, or the compliance date for such standard or procedure, must be submitted to 

the EPA. Information copies of such petitions are invited by the FAA. Petitions for rulemaking or 

exemption involving provisions of this FAR that do not affect the substance or the compliance date of an 

emission standard or test procedure that is prescribed by the EPA, and petitions for exemptions under the 

provisions for which the EPA has specifically granted exemption authority to the Secretary of 

Transportation are subject to part 11 of the Federal Aviation Regulations (14 CFR part 11). Petitions for 

rulemaking or exemptions involving these FARs must be submitted to the FAA. 

(a):

Exemptions based on flights for short durations at infrequent intervals. The emission standards of this 

part do not apply to engines which power aircraft operated in the United States for short durations at 

infrequent intervals. Such operations are limited to: 

(1) Flights of an aircraft for the purpose of export to a foreign country, including any flights essential to 

demonstrate the integrity of an aircraft prior to a flight to a point outside the United States. 

(2) Flights to a base where repairs, alterations or maintenance are to be performed, or to a point of 

storage, or for the purpose of returning an aircraft to service. 

(3) Official visits by representatives of foreign governments. 

(4) Other flights the Administrator determines, after consultation with the Administrator of the EPA, to 

be for short durations at infrequent intervals. A request for such a determination shall be made 

before the flight takes place. 
 Page 19 

(b) Exemptions for very low production engine models. The emissions standards of this part do not 

apply to engines of very low production after the date of applicability. For the purpose of this part, 

"very low production" is limited to a maximum total production for United States civil aviation 

applications of no more than 200 units covered by the same type certificate after January 1, 1984. 

Engines manufactured under this provision must be reported to the FAA by serial number on or 

before the date of manufacture and exemptions granted under this provision are not transferable 

to any other engine. 

(c) Exemptions for new engines in other categories. The emissions standards of this part do not 

apply to engines for which the Administrator determines, with the concurrence of the 

Administrator of the EPA, that application of any standard under Sec. 34.21 is not justified, based 

upon consideration of— 

(1) Adverse economic impact on the manufacturer; 

(2) Adverse economic impact on the aircraft and airline industries at large; 

(3) Equity in administering the standards among all economically competing parties; 

(4) Public health and welfare effects; and 

(5) Other factors which the Administrator, after consultation with the Administrator of the 

EPA, may deem relevant to the case in question. 

(d) Time-limited exemptions for in-use engines. The emissions standards of this part do not apply to 

aircraft or aircraft engines for time periods which the Administrator determines, with the 

concurrence of the Administrator of the EPA, that any applicable standard under Sec. 34.11(a), or 

Sec. 34.31(a), should not be applied based upon consideration of-- 

(1) Documentation demonstrating that all good faith efforts to achieve compliance with such 

standard have been made; 

(2) Documentation demonstrating that the inability to comply with such standard is due to 

circumstances beyond the control of the owner or operator of the aircraft; and 

(3) A plan in which the owner or operator of the aircraft shows that he will achieve 

compliance in the shortest time which is feasible. 

Explanation

The EPA is mandated to address all sources of air pollution which may endanger the public health or welfare. 

From Federal Register, Vol. 62, No. 89, Thursday, May 8, 1997, "Currently, aircraft are about 2 percent of the 

total U.S. mobile source NOx and CO ground level emissions inventory. Commercial aircraft emissions are 

about 70 and 30 percent respectively of these NOx and CO aircraft emissions inventories." While of concern, 

and determined by the Administrator of the EPA to be in need of regulatory control, commercial aircraft 

emissions constitute a relatively small fraction of the total mobile sources emissions burden. The likely 

contribution from the allowable exemptions listed in categories 34.7 (a) - (d) are a small fraction of an already 

small fraction. EPA has granted a blanket exemption from the standards for all models of engines which 

satisfy a criterion for low production engines. The FAA has been granted, by the EPA, responsibility for acting 

on petitions for exemptions of any sort. 

From ICAO Annex 16, Volume II, Second edition, 1993, Chapter 2, “TURBO-JET AND TURBOFAN 

ENGINES INTENDED FOR PROPULSION ONLY AT SUBSONIC SPEEDS”: 

Note: In considering exemptions, certificating authorities should take into account the probable numbers of 

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 future production of such engines for 

installation on new aircraft, although production of such engines as spares should be permitted indefinitely. 

(e)

Applications for exemption from this part shall be submitted in duplicate to the Administrator in accordance 

with the procedures established by the Administrator in part 11. 
 

Page 20 

Explanation

34.7 (e), and the prefacing remarks to this subsection, do not appear in 40 CFR Part 87, subsection 84.7. 

They are an addition and reflect the differing roles and responsibilities between the EPA which establishes the 

regulatory standards, and the FAA, which enforces these standards. Applications for exemptions which do 

not significantly impact or compromise the substance or compliance date of an emission standard or test 

procedure or for which the EPA has granted authority to the Secretary of Transportation should be submitted 

to the FAA subject to 14 CFR part 11. Petitions of a substantive nature relating to emission standards and 

test procedures must be submitted to the EPA with copies requested by the FAA. 

(g):

No state or political subdivision thereof may attempt to enforce a standard respecting emissions from an 

aircraft or engine if such aircraft or engine has been exempted from such standard under this part. 

Explanation

This is an interpretation of Section 233, Clean Air Act as amended, maintaining authority over aircraft and 

aircraft engine emissions while allowing exemptions for the reasons specified in 34.7 (a) - (d). 
 Page 21 

II Subpart B—Engine Fuel Venting Emissions 

(New and In-use Aircraft Gas Turbine Engines) 

12. §34.10 Applicability 

(a) The provisions of this subpart are applicable to all new aircraft gas turbine engines of classes T3, 

T8, TSS and TF equal to or greater than 36 kilonewton (8090 pounds) rated output, manufactured 

on or after January 1, 1974, and to all in-use aircraft gas turbine engines of classes T3, T8, TSS 

and TF equal to or greater than 36 kilonewtons (8090 pounds) rated output manufactured after 

February 1, 1974. 

(b) The provisions of this subpart are also applicable to all new aircraft gas turbine engines of class 

TF less than 36 kilonewtons (8090 pounds) rated output and class TP manufactured on or after 

January 1, 1975, and to all in-use aircraft gas turbine engines of class TF less than 36 

kilonewtons (8090 pounds) rated output and class TP manufactured after January 1, 1975. 

13. §34.11 Standard for fuel venting emissions:

(a) No fuel venting emissions shall be discharged into the atmosphere from any new or in-use aircraft 

gas turbine engine subject to the 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. 

(b) Conformity with the standard set forth in paragraph (a) of this section shall be determined by 

inspection of the method designed to eliminate these emissions. 

(c) As applied to an airframe or an engine, any manufacturer or operator may show compliance with 

the fuel venting and emissions requirements of this section that were effective beginning 

February 1, 1974 or January 1, 1975, by any means that prevents the intentional discharge of fuel 

from fuel nozzle manifolds after the engines are shut down. Acceptable means of compliance 

include one of the following: 

(1) Incorporation of an FAA approved system that recirculates the fuel back into the fuel 

system. 

(2) Capping or securing the pressurization and drain valves. 

(3) Manually draining the fuel from a holding tank into a container. 

Explanation

Table 1 summarizes the Engine Fuel Venting Emissions Standards as described in Part 34. 

It is normal for aircraft gas turbine engine fuel systems to operate in a pressurized condition. This pressure is 

relieved after the engines are shut down. Raw fuel allowed to drain uncontained or onto hot internal engine 

parts will result in the discharge of hydrocarbons from the aircraft into the environment. These hydrocarbons 

pass into the atmosphere, adding to the local air pollution burden. The objective of this regulation is to 

eliminate the intentional discharge, into the atmosphere, of fuel drained from the engine fuel manifolds after 

the engine is shut down following normal flight or ground operations. This regulation is not intended to apply 

to normal fuel seepage from shaft seals, joints and fittings. 
 

Page 22 

Compliance is by inspection of the method designed or chosen to prevent these emissions. Acceptable 

means of compliance include recirculating fuel back into the fuel system, by means of an FAA approved 

system, capping or securing the pressurization and drain valve or manually draining the fuel from a holding 

tank into a container. In the latter case this fuel must be disposed of in an environmentally sound manner. It 

should be noted that unlike meeting emissions levels which are clearly the responsibility of the engine 

manufacturer meeting fuel venting standards can be assigned to the operator depending upon which strategy 

is chosen to prevent the intentional discharge from the fuel manifold after the engine is shut down. Most, if 

not all, modern aircraft are designed and constructed to meet this regulation. 

As a point of observation, it should be noted that turboshaft engines are not included in these requirements. 

Table 1: ENGINE FUEL VENTING EMISSIONS 

(New and In-Use Aircraft Gas Turbine Engines) 

ENGINE CLASS EFFECTIVE DATE STANDARD

T3, T8, TSS, TF 

≥ 36 kilonewtons (8090 lbs.) 

All new aircraft gas turbine 

engines manufactured on or 

after January 1, 1974 

Prohibition of fuel venting 

emissions discharged into 

the atmosphere 

T3, T8, TSS, TF 

≥ 36 kilonewtons 

All in-use aircraft gas 

turbine engines 

manufactured after 

February 1, 1974 

Prohibition of fuel venting 

emissions discharged into 

the atmosphere 

TF < 36 kilonewtons 

TP 

All new and in-use aircraft 

gas turbine engines 

manufactured on or after 

January 1, 1975 

Prohibition of fuel venting 

emissions discharged into 

the atmosphere 
 Page 23 

III. Subpart C — Exhaust Emissions 

(New Aircraft Gas Turbine Engines) 

14. § 34.20 Applicability 

The provisions of this subpart are applicable to all aircraft gas turbine engines of the classes specified 

beginning on the dates specified in § 34.21. 

15. § 34.21 Standards for exhaust emissions

(a) Exhaust emissions of smoke from each new aircraft gas turbine engine of class T8 manufactured 

on or after February 1, 1974, shall not exceed a smoke number (SN) of 30. 

(b) Exhaust emissions of smoke from each new aircraft gas turbine engine of class TF and of rated 

output of 129 kilonewtons (29,000 pounds) thrust or greater, manufactured on or after January 1, 

1976, shall not exceed: 

SN = 83.6(rO)-0.274 (rO is in kilonewtons) 

(c) Exhaust emissions of smoke from each new aircraft gas turbine engine of class T3 manufactured 

on or after January 1, 1978, shall not exceed a smoke number (SN) of 25. 

(d) Gaseous exhaust emissions from each new commercial aircraft gas turbine engine shall not 

exceed: 

(1) Classes, TF, T3, T8 engines greater than 26.7 kilonewtons (kN) rated output: 

(i) Engines manufactured on or after January 1, 1984: 

Hydrocarbons: 19.6 grams/kilonewton rO. 

 

(ii) Engines manufactured on or after July 7, 1997. 

Carbon Monoxide: 118 grams/kilonewton rO. 

(iii) Engines of a type or model of which the date of manufacture of the first individual 

production model was on or before December 31, 1995 and for which the date of 

manufacture of the individual engine was on or before December 31, 1999. 

Oxides of Nitrogen: (40 + 2 (rPR)) grams/kilonewton rO. 

(iv) Engines of a type or model of which the date of manufacture of the first individual 

production model was after December 31, 1995 or for which the date of manufacture of 

the individual engine was after December 31, 1999: 

Oxides of Nitrogen: (32 + 1.6(rPR)) grams/kilonewton rO. 

(v) The emission standards prescribed in paragraphs (d)(1)(iii) and (iv) of this section 

apply as prescribed beginning July 7, 1997. 

(vi) Engines of type or model for which the date of manufacture of the first individual 

production model was after December 31, 2003: 

(A) For engines with a pressure ratio of 30 or less: 

(1) For Engines with a maximum rated thrust of more than 89.0 kN: 
 

Page 24 

Oxides of Nitrogen: (19 + 1.6 rPR) grams/kilonewton rO. 

(2) For engines with a maximum rated thrust of more than 26.7 kN but not 

more than 89.0 kN: 

Oxides of Nitrogen: (37.572 + 1.6 rPR – 0.2087 rO) grams/Kilonewton rO. 

(B) For engines with a pressure ratio of more than 30 but less than 62.5: 

(1) For engines with a maximum rated thrust of more than 89.0 kN: 

Oxides of Nitrogen: (7 + 2.0 rPR) grams/kilonewton rO. 

(2) For engines with a maximum rated thrust of more than 26.7 kN but more 

than 89.0 kN: 

Oxides of Nitrogen: (42.71 + 1.4286 rPR – 0.4013 rO + 0.00642 rPR(rO)) 

grams/kilonewton rO. 

(C) For engines with a pressure ratio of 62.5 or more: 

Oxides of Nitrogen: (32 + 1.6 rPR) grams/kilonewton rO. 

Explanation: The emission standards described in paragraphs (d)(1)(vi)(A), (B), and (C) of this section are 

contingent upon promulgation by EPA and FAA in their respective regulations and standards. They list the 

current ICAO CAPE 4 requirements and represent a continuation of the harmonization program with ICAO. 

Supplemental Information:

The date of the first individual production model is generally interpreted to mean the date of type certification. 

(2) Class TSS: Engines manufactured on or after January 1, 1984: 

Hydrocarbons = 140(0.92)rPR grams/kilonewton rO. 

(e) Smoke exhaust emissions from each gas turbine engine of the classes specified below shall not 

exceed: 

(1) Class TF of rated output less than 26.7 kilonewtons (6000 pounds) manufactured on or 

after August 9, 1985. 

SN = 83.6(rO)-0.274 (rO is in kilonewtons) not to exceed a maximum of SN = 50.

(2) Classes T3, T8, TSS, and TF of rated output equal to or greater than 26.7 kilonewtons 

(6000 pounds) manufactured on or after January 1, 1984. 

SN = 83.6(rO)-0.274 (rO is in kilonewtons) not to exceed a maximum of SN = 50.

(3) Class TP or rated output equal to or greater than 1,000 kilowatts (1340 Hp) manufactured 

on or after January 1, 1984. 

SN = 187(rO)-0.168 (rO is in kilowatts). 
 Page 25 

(f) The standards set forth in paragraphs (a), (b), (c), (d) and (e) of this section refer to a composite 

gaseous emission sample representing the operating cycles set forth in the applicable sections of 

subpart G of this part, and exhaust smoke emissions emitted during operations of the engine as 

specified in the applicable sections of subpart H of this part, measured and calculated in 

accordance with the procedures set forth in those subparts. 

Explanation

For TF, T3 and T8 engines the following chart (Figure 4) provides a graphical representation of the smoke 

emissions requirements. This chart reflects the requirements of Subpart D as well. In general, the threshold 

of plume visibility can be expected to lie between SN 25 and SN 30. However, visibility is a complex function 

of the tailpipe diameter, viewing angle, background and meteorological conditions. Differences in any one, or 

any combination, of these factors, from the average, can be expected to influence this relationship. For 

example, a plume which is not visible when viewed in a direction normal to its axis could appear to be visible 

when viewed at an angle more nearly parallel to its axis. In addition apparent plume visibility seems to vary 

with local ambient humidity. That is, when plumes can be seen they seem to become darker as humidity 

increases. The regulatory intent is to assure a non-visible plume when viewed in a direction normal to the 

plume axis. 

FIGURE 4: Smoke Emission Requirements For New or In Use TF, T3, and T8 Engines 

(3) – 49. Reserved 

10

15

20

25

30

35

40

45

50

0 50 100 150 200 250 300 350 400 450

Rated Output (rO) - kilonewtons

Smoke Number (SN)

.

SN=83.6(rO)-0.274

SN=50 - maximum allowed

SN=34 @ rO=26.7 kilonewtons

SN=22 @ rO=129 kilonewtons
Page 26 

Table 2: Exhaust Emissions - Summary of Requirements 

CLASS DATE STANDARD 

T8 Each aircraft gas turbine engine in use, or 

manufactured, on or after February 1, 1974 

SN ≤ 30 

TF ≥ 129 kN 

(29,000 pounds) 

Each aircraft gas turbine engine in use, or 

manufactured, on or after January 1, 1976 

SN ≤ 83.6×(rO)-0.274 

(rO in kN) 

T3 Each new aircraft gas turbine engine 

manufactured on or after January 1, 1978 

SN ≤ 25 

TF, T3, T8 >26.7 kN 

(6,000 pounds) 

Each new aircraft gas turbine engine 

manufactured on or after January 1, 1984 

Each new aircraft gas turbine engine 

manufactured on or after July 7, 1997 

HC ≤ 19.6 g/kN rO 

CO ≤ 118 g/kN rO 

TF, T3, T8 >26.7 kN Engines where the first production model 

was manufactured on or before December 

31, 1995 and where the date of 

manufacture of the engine was on or before 

December 31, 1999 - effective July 7, 1997 

NOX ≤ (40 + 2(rPR)) g/kN rO 

TF, T3, T8 >26.7 kN Engines where the first production model 

was manufactured after December 31, 1995 

and where date of manufacture of the 

engine was after December 31, 1999 - 

effective July 7, 1997 

NOX ≤ (32 + 1.6(rPR)) g/kN 

rO 

For rPR ≤ 30 and:

26.7 kN< TF, T3, T8≤ 89.0 kN 

TF, T3, T8 >89.0 kN 

Engines of a type or model for which the 

date of manufacture of the first individual 

production model was after December 31, 

2003 

NOX ≤ (37.572 + 1.6 rPR –

0.2087 rO) g/kN rO 

NOX ≤ (19 + 1.6 rPR) g/kN rO 

For 30< rPR< 62.5 and:

26.7 kN< TF, T3, T8≤ 89.0 kN 

TF, T3, T8>89.0 kN 

Engines of a type or model for which the 

date of manufacture of the first individual 

production model was after December 31, 

2003 

NOX ≤ (42.71 + 1.4286 rPR – 

0.4013 rO + 0.0642 rPR(rO) 

g/kN rO 

NOX ≤ (7 + 2.0 rPR) g/kN rO 

For rPR ≥ 62.5:

All engines Engines of a type or model for which the 

date of manufacture of the first individual 

production model was after December 31, 

2003 

NOX ≤ (32 + 1.6 rPR) g/kN rO 

TF < 26.7 kN Each gas turbine engine manufactured on 

or after August 9, 1985 

SN ≤ 83.6×(rO)-0.274 ≤ 50 

(rO in kN) 

T3, T8, TSS, TF ≥ 26.7 kN Each gas turbine engine manufactured on 

or after January 1, 1984 

SN ≤ 83.6×(rO)-0.274 ≤ 50 

(rO in kN) 

TSS Each gas turbine engine manufactured on 

or after January 1, 1984 

HC ≤ 140 (0.92)rPR g/kN rO 

TP ≥ 1,000 kW 

(1340 HP) 

Each gas turbine engine manufactured on 

or after January 1, 1984 

SN ≤ 187×(rO)-0.168 

(rO in kW) 
 Page 27 

Explanation:

Table 2, above, is a summary listing (by class of aircraft engine) of the smoke and gaseous emission 

regulatory levels for both new and in-use engines. Included as well are the ICAO CAPE 4 NOX standards 

effective after 12/31/2003, listed in terms of rated pressure ratio. 

IV. Subpart D — Exhaust Emissions 

(In-Use Aircraft Gas Turbine Engines) 

50. § 34.30 Applicability 

The provisions of this subpart are applicable to all aircraft gas turbine engines of the classes specified 

beginning on the dates specified in § 34.31.

(4) § 34.31 Standards for exhaust emissions

(a) Exhaust emissions of smoke from each in-use aircraft gas turbine engine of Class T8, 

beginning February 1, 1974 shall not exceed a smoke number (SN) of 30. 

(b) Exhaust emissions of smoke from each in-use aircraft gas turbine engine of Class TF and 

of rated output of 129 kilonewtons (29,000 pounds) thrust or greater, beginning January 

1, 1976, shall not exceed: 

SN = 83.6(rO)-0.274 (rO is in kilonewtons) 

(c) The standards set forth in paragraphs (a) and (b) of this section refer to exhaust smoke 

emissions emitted during operations of the engine as specified in the applicable section 

of subpart H of this part, and measured and calculated in accordance with the procedure 

set forth in this subpart. 

Explanation

Table 2, above lists by Class and by applicable date the smoke and gaseous emission regulatory 

levels. 

(Note: this table is attached to Subpart C of this AC as a composite C-D compilation of requirements) 
Page 28 

V Subpart E — [Reserved] 
 Page 29 

VI. Subpart F — 

[Reserved] 
Page 30 

VII. Subpart G — Test Procedures for Engine Exhaust Gaseous Emissions (Aircraft and Aircraft

Gas Turbine Engines) 

18. §34.60 Introduction 

(a) Except as provided under §34.5, the procedures described in this subpart shall constitute 

the test program used to determine the conformity of new aircraft gas turbine engines 

with the applicable standards set forth in this part. 

(b) The test consists of operating the engine at prescribed power settings on an engine 

dynamometer (for engines producing primarily shaft power) or thrust measuring test 

stand (for engines producing primarily thrust). The exhaust gases generated during 

engine operation must be sampled continuously for specific component analysis through 

the analytical train. 

(c) The exhaust emissions test is designed to measure hydrocarbons, carbon monoxide, 

carbon dioxide and oxides of nitrogen concentrations, and to determine mass emissions 

through calculations during a simulated aircraft landing-takeoff cycle (LTO). The LTO 

cycle is based on time in mode data during high activity periods at major airports. The 

test for propulsion engines consists of at least the following four modes of engine 

operation: taxi/idle, takeoff, climbout, and approach. The mass emissions for these 

modes are combined to yield the reported values. 

(d) When an engine is tested for exhaust emissions on an engine dynamometer or test 

stand, the complete engine shall be used with all accessories which might reasonably be 

expected to influence emissions to the atmosphere installed and functioning, if not 

otherwise prohibited by §34.62(a)(2). 

(e) Other gaseous emissions measurement systems may be used if shown to yield 

equivalent results and if approved in advance by the Administrator or the Administrator of 

the EPA. 

 Supplemental Information 

Engines have generally been tested without off-take bleeds and accessory loads other than those 

necessary for the engine’s basic operation, consistent with ICAO Annex 16, paragraph 2.1.5.2. 

Paragraph 34.60(d) is intended to be consistent with the procedures specified in Annex 16, with 

consideration for special cases where accessory loads might be large enough to influence emissions. 

19. §34.61 Turbine Fuel Specification 

For exhaust emissions testing, fuel meeting the specifications listed below shall be used. 

Additives used for the purpose of smoke suppression (such as organometallic compounds) shall 

not be present. 

Explanation:

The fuel specification in Part 34 matches the, amended, ICAO fuel specification in Annex 16, Vol. II, 

Second Edition, 1993. This specification is typical of Jet A aviation fuel. Although EPA chose to 

adopt, by reference, the measurement and compliance procedures of ICAO Annex 16, Vol. II, Second 

Edition, Appendix, 2, 3, 5 and 6, they chose not to adopt by reference the ICAO fuel specification. 

Instead they listed the fuel properties and allowable ranges of values. 
 Page 31 

Specification for Fuel to be Used in Aircraft 

Turbine Engine Emissions Testing 

Property Allowable range of 

values 

Density kg/m3 at 15°C 780 – 820 

Distillation temperature °C 

 10 % boiling point 155 – 201 

 Final boiling point 235 – 285 

Net heat of combustion MJ/kg 42.86 – 43.50 

Aromatics, volume % 15 – 23 

Naphthalenes, volume % 1.0 – 3.5 

Smoke point, mm 20 – 28 

Hydrogen, mass % 13.4 – 14.1 

Sulphur, mass % less than 0.3% 

Kinematic viscosity at -20°C, mm2/s 2.5 – 6.5 

 Supplemental information:

Aircraft gas turbine engines can and do use a variety of fuels. The specific fuel type and composition 

can and often does have a significant effect on engine emissions. Knowing the fuel types in general 

use is important in establishing a baseline of emissions from the existing and future fleet of 

commercial aircraft which affects regulatory requirements. It is important when comparing emission 

levels from one engine with those from another. It is particularly important in evaluating engine 

emission levels relative to a regulation that was based, in part, on an assumed fuel specification. 

Because fuel type and composition varies it was necessary to establish a fuel specification which 

fairly represented typical aircraft gas turbine engine fuels which are in use. The ICAO amended fuel 

specification is a reasonable international consensus specification, which was the result of over 

fifteen years of study and negotiation. 

In 1972 the EPA Proposed Rule Making specified ASTM D1655 as the requirement that test fuels 

must meet. They allowed the use of nonmetallic additives as specified in ASTM D1655 but prohibited 

the use of additives used for the purpose of smoke suppression. 

In 1981 ICAO published "International Standards and Recommended Practices Environmental 

Protection, Annex 16, Volume II, Aircraft Emissions, first edition, 1981" which included a specific 

detailed turbine engine test fuel specification. In 1982 the EPA adopted the 1981 ICAO fuel 

specification bringing the U.S. into alignment with ICAO. However, in 1984 the EPA changed its fuel 

specification, broadening the ranges of allowable test fuel naphthalenes, aromatics and hydrogen 

content, viscosity and final boiling point values in response to manufacturers difficulty in obtaining 

fuels meeting the ICAO test fuel specification. The EPA expected ICAO to amend its fuel 

specification to match the EPA specification. 

In 1988 ICAO did amend its fuel specification but rather than addressing the disparity between EPA 

and ICAO it further widened the range of acceptable fuels by broadening, again, the ranges of 

allowable test fuel naphthalenes, aromatics and hydrogen content, viscosity and final boiling point 

values. 

In 1993 ICAO, once again, amended its fuel specification substituting density for specific gravity and 

changing the units of net heat of combustion from kilojoule/kilogram (kJ/kg) to 

megajoule/kilogram(MJ/kg). EPA analyzed and evaluated the resulting ICAO fuel specification with 

respect to its effect on aircraft gas turbine engine emissions and on general fuel availability in the 
Page 32 

U.S. One particular concern was a decision by EPA to adopt the ICAO NOx standards. Fuel type and 

composition affect emissions and these standards were based on the latest ICAO fuel specification. 

If the EPA decided not to adopt the ICAO fuel specifications the U.S. and ICAO NOx standards would 

not be entirely consistent. 

EPA found that changing from specific gravity to density and kilojoules to megajoules would, 

obviously, not affect either emissions or fuel availability. In comparing actual U.S. jet fuel 

characteristics to differences between EPA and ICAO test fuel specifications EPA concluded that, for 

distillation temperatures and hydrogen content, where there were differences, the effect would be 

negligible, i.e., "not discernable". For the broader range of aromatics and naphthalenes, testing on 

the high end of the range would be more severe for emissions and would not effect in-use emissions. 

That is, based on current U.S. jet fuel characteristics, fuels used by in-use aircraft gas turbine engines 

would be likely to have lower values of aromatics and naphthalenes than used in testing and 

therefore lower emissions. As a result EPA adopted the 1993 ICAO test fuel specification for the 

purpose of certification emission testing. 

Part 34 reflects, as it must, the EPA standard. Although not spelled out in Part 34 the EPA states that 

manufacturers should, unless otherwise specified, comply with the latest version of the aviation test 

fuel specifications from the American Society for Testing and Materials, ASTM, "Standard 

Specifications for Aviation Turbine Fuels," D1655. There is no mention of the use of non metallic 

additives. Additives used for smoke suppression, such as organometallic compounds, shall not be 

present. 

20. §34.62 Test procedure (propulsion engines). 

(a)(1) The engine shall be tested in each of the following engine operating modes which 

simulate aircraft operation to determine its mass emission rates. The actual power 

setting, when corrected to standard day conditions, should correspond to the following 

percentages of rated output. Analytical correction for variations from reference day 

conditions and minor variations in actual power setting should be specified and/or 

approved by the Administrator: 

Class 

Mode TP TF, T3, T8 TSS 

Taxi/idle (*) (*) (*) 

Takeoff 100 100 100 

Climbout 90 85 65 

Descent NA NA 15 

Approach 30 30 34 

 * See paragraph (2) of this section 

 (2) The taxi/idle operating modes shall be carried out at a power setting of 7 percent 

rated thrust unless the Administrator determines that the unique characteristics of an 

engine model undergoing certification testing at 7 percent would result in substantially 

different HC and CO emissions than if the engine model were tested at the 

manufacturers' recommended idle power setting. In such cases the Administrator shall 

specify an alternative test condition. 
 Page 33 

 (3) The times in mode (TIM) shall be as specified below: 

Class 

Mode TP TF, T3, T8 TSS 

Taxi/idle 26.0 Min. 26.0 26.0 

Takeoff 0.5 0.7 1.2 

Climbout 2.5 2.2 2.0 

Descent N/A N/A 1.2 

Approach 4.5 4.0 2.3 

 (b) Emissions testing shall be conducted on warmed-up engines which have achieved a steady 

operating temperature. 

21. §34.63 [Reserved] 

22. §34.64 Sampling and analytical procedures for measuring gaseous exhaust emissions. 

The system and procedures for sampling and measurement of gaseous emissions shall be done 

in accordance with Appendices 3 and 5 to International Civil Aviation Organization (ICAO) Annex 

16, Environmental Protection, Volume II, Aircraft Engine Emissions, Second Edition, July 1993, 

which are incorporated herein by reference. This incorporation by reference was approved by the 

Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. This 

document can be obtained from the International Civil Aviation Organization (ICAO), Document 

Sales Unit, P.O. Box 400, Succursale: Place de L'Aviation Internationale, 1000 Sherbrooke Street 

West, Suite 400, Montreal, Quebec, Canada H3A 2R2. Copies may be reviewed at the FAA 

Office of the Chief Counsel, Rules Docket, Room 916, Federal Aviation Administration 

Headquarters Building, 800 Independence Avenue, SW., Washington, DC, or at the FAA New 

England Regional Offce, 12 New England Executive Park, Burlington, Massachusetts, or at the 

Office of the Federal Register, 800 North Capitol Street, NW., Suite 700, Washington, DC. 

23. § 34.65—34.70 [Reserved] 

24. § 34.71 Compliance with gaseous emission standards 

Compliance with each gaseous emission standard by an aircraft engine shall be determined by 

comparing the pollutant level in grams/kilonewton/thrust/cycle or grams/kilowatt/cycle as 

calculated pursuant to §34.64 with the applicable emission standard under this part. An 

acceptable alternative to testing every engine is described in Appendix 6 to ICAO Annex 16, 

Environmental Protection, Volume II—Aircraft Engine Emissions. Second Edition, July 1993, 

effective March 20, 1997. This incorporation by reference was approved by the Director of the 

Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. This document can be 

obtained from, and copies may be reviewed at the respective addresses listed in §34.64. Other 

methods of demonstrating compliance may be approved by the FAA Administrator with the 

concurrence of the Administrator of the EPA. 

[(Amdt. 34-2, Eff. 9/98)] 
Page 34 

VIII. Subpart H — Test Procedures for Engine Smoke Emissions (Aircraft and Aircraft Gas 

Turbine Engines) 

25. §34.80 Introduction 

Except as provided under §34.5, the procedures described in this subpart shall constitute the test 

program to be used to determine the conformity of new and in-use gas turbine engines with the 

applicable standards set forth in this part. The test is essentially the same as that described in 

§§34.60-34.62, except that the test is designed to determine the smoke emission level at various 

operating points representative of engine usage in aircraft. Other smoke measurement systems 

may be used if shown to yield equivalent results and if approved in advance by the Administrator 

or the Administrator of the EPA. 

Supplemental information

The regulatory smoke standards established by EPA and ICAO were set to ensure the invisibility of 

the engine exhaust when viewed across the plume. Smoke level is determined indirectly, by means 

of the loss of reflectance of a filter used to trap smoke particles from a prescribed mass of exhaust 

per unit area of filter. The result is a dimensionless number “SN.” Using generalized relationships 

between engine thrust and exhaust duct diameters, an empirically derived relationship between 

smoke number (SN) and engine thrust was developed. The information available to develop this 

relationship came from early gas turbine engines with straight jet or low bypass ratios. There was little 

or no dilution of the engine core exhaust gas which is not the case with modern, high bypass, 

engines. ICAO, which defines – by reference – the measurement standard, requires smoke to be 

measured at or near the engine exhaust nozzle exit plane, which is consistent with the requirements 

for using SN as an indicator of visibility for the early engines. Some current engine designs, however, 

extend the bypass cowling beyond the core nozzle and for these, by definition, the measurement 

plane includes the bypass airflow. This results in a lower SN, and some question about the 

relationship of SN to plume visibility for these designs. Introduction of ultra high bypass ratio 

engines, such as the ducted or unducted prop fan engines will serve to further complicate this 

situation. The measurement method itself has proven to be physically robust, repeatable and 

reliable, but time consuming and expensive – particularly for traverse testing. 

As a direct result of the narrowly defined smoke number, demanded by the prescribed method of 

measurement and its implied correlation with engine exhaust plume visibility, finding an alternate, 

equivalent smoke method has proven to be challenging. Such a method must necessarily correlate 

with smoke number, not with plume visibility, i.e., any measured value arrived at using an alternate 

method must be associated unambiguously with an equivalent smoke number. Some engine 

manufacturers use an optical device that provides continuous, almost real time smoke measurement. 

This device is patterned after the Hartridge optical smoke meter. Their experience has been that the 

optical measurements correlate well with in-house ICAO Appendix 2 stained filter measurements with 

considerable savings in engine test time. If an engine manufacturer wanted to use such a device for 

certification it would be allowed upon demonstration, by means of actual test data, that the device 

was equivalent to Appendix 2. It should be mentioned that the correction found at a single 

manufacturer’s facility has not been demonstrated between engine manufacturers facilities so some 

caution is advised when assessing equivalency. Because smoke measurement is time consuming, 

particularly during traversing, and places great demands on the engine, finding an alternate and less 

costly method is and will continue to be attractive. 

The smoke measurement standard was developed for engines that generated smoke at considerably 

higher levels than are seen today. This affects the relative accuracy of the method. The 

measurement is considered (by the SAE E-31 committee which developed the method) to be no more 

accurate than ±3 SN. At smoke levels of SN 50-60 this represents an accuracy of 6-5%. At 

regulatory standards of 30 and below, relative accuracy becomes 10-20% or more. 

 
 Page 35 

Also significant is the requirement to "...provide evidence to the certification authority, by means of 

detailed traverses, that the proposed probe design and position does provide a representative sample 

for each prescribed power setting." ICAO Appendix 2 does not provide a definition of "representative" 

nor does it specify any procedures by which conformance to this requirement can be demonstrated. 

Because traversing is time consuming, costly, and highly problematic with some new engine designs, 

this lack of definition and test of 'representativeness' is a serious problem and must be addressed, 

almost uniquely, for each emissions certification test for which there is a traversing requirement. As 

with gaseous emissions to a first approximation how well the exhaust was sampled can be estimated 

from a carbon balance which relates the total carbon measured (mostly CO2) to a measured value of 

fuel-air ratio. For engine modes above idle a necessary condition could be agreement between fuelair ratios arrived at from emissions and performance measurements within ± 10%. This would not, 

however, be a sufficient condition. The variability of smoke is typically greater than the variability of 

CO2, the dominant species, and so additional work needs to be done. Because smoke, as with the 

gaseous emissions, seems to be normally (gaussian) distributed, in the core at least, standard 

statistical techniques can be used to estimate the mean value for the exhaust and the number of 

sampling points necessary to arrive at the required confidence level. The information to do this can 

come from prior data or from trial traverses on the current or previous, similar, engines. Note that 

evidence of a satisfactory probe design can be as simple as having proven the design on a previous, 

similar, engine. Similarity would, then, need to be proven to the certificating authority. 

The smoke sampling and measurement procedures standardized in ICAO Annex 16, Volume II, 

second edition, 1993, Appendix 2, are derived from an SAE standard, SAE Aerospace 

Recommended Practice (ARP) 1179, Aircraft Gas Turbine Exhaust Smoke Measurement. ARP 

1179, first issued in 1971, is the result of a collaborative government/industry effort to develop a 

consensus standard for measuring smoke from these sources. It is a dynamic standard which is 

actively managed by the SAE E-31 committee but has changed little over the years. ICAO maintains 

an observer on the E-31 committee. Agreeable changes in ARP 1179 can be reflected in future 

versions of ICAO Appendix 2. With the ICAO procedures being called out by reference (40 CFR part 

87), any changes in Appendix 2 will necessarily be reflected in the requirements of Part 34. 

The relationship of CO2 to fuel is straight forward given the fuel formulation. For example, a typical 

kerosenic fuel in the middle of the specification for fuel hydrogen mass ration would have a 

formulation C12H23. Knowing the atomic weights of carbon (12) and Hydrogen (1.008) you calculate 

the relative mass of carbon in this fuel molecule to be 0.86, or 1 kg of fuel would contain 0.86 kg of 

carbon. Taking the atomic weight of oxygen to be 16, a similar calculation shows that 1 kg of fuel, 

upon complete combustion, would yield 3.16 kg of CO2 (these numbers are rounded for illustrative 

purposes). For an engine running at high power, say a fuel to air of 0.02 kg fuel/kg air the resulting 

CO2 mass ratio would be .02*3.16 or approximately .063 kg CO2 per kg of air. Taking the molecular 

weight of CO2 to be 44.01, air to be 28.96 and the specific weight of air to be 1.225 kg/m3

 the 

volumetric ratio is seen to be 0.0416 or 4.16%. Since CO2 instruments read in volumetric percent, 

this is the value the instrument should read when the engine is operating at 0.02 f/a. Obviously the 

reverse calculation, fuel to air ratio from measured volumetric CO2, proceeds in a similar fashion. 

This relationship is convenient as a nominal indicator of sampling status assuming you know the fuel 

to air ratio, i.e., by multiplying the fuel to air ratio by 200 you should arrive at an approximate value of 

CO2 in volumetric percent. 

26. §34.81 Fuel Specifications 

Fuel having specifications as provided in §34.61 shall be used in smoke emission testing. 

Supplemental information

The requirement for emissions certification testing with a fuel which meets a particular specification 

provides a fixed point of reference for the engine. It provides for some degree of control over the 

effect of fuel composition on smoke formation and emission. It also helps in the assessment of the 
Page 36 

effects of changing technology. It will not ensure continued conformance to the smoke emissions 

standards if a fuel outside of the ICAO fuel specification is used in practice. 

27. §34.82 Sampling and analytical procedures for measuring - smoke exhaust emissions 

The system and procedures for sampling and measurement of smoke emissions shall be done in 

accordance with Appendix 2 to International Civil Aviation Organization (ICAO) Annex 16, Volume 

II—Aircraft Engine Emissions, Second Edition, July 1993. This incorporation by reference was 

approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR 

part 51. These materials are incorporated as they exist on the date of the approval and a notice of 

any change in these materials will be published in the Federal Register. Frequent changes are 

not anticipated. This document can be obtained from the International Civil Aviation, P.O. Box 

400, Succursale: Place de L' Aviation Internationale, 1000 Sherbrooke Street West, Montreal, 

Quebec, Canada H3H 2R2. Copies may be inspected at the FAA Office of the Chief Counsel, 

Rules Docket, room 916, Federal Aviation Administration Headquarters Building, 800 

Independence Avenue, SW., Washington, DC, or at the FAA New England Regional Office, 12 

New England Executive Park, Burlington, Massachusetts, or at the Office of the Federal Register, 

800 North Capitol Street, NW., suite 700, Washington, DC. 

Supplemental information

ICAO Appendix 2 was derived, almost exclusively, from SAE Aerospace Recommended Practice 

ARP1179 “Aircraft Gas Turbine Engine Exhaust Smoke Measurement.” This Aerospace 

Recommended Practices and, by implication, ICAO Appendix 2 truly represents a significant cross 

section of the affected aircraft community. The U.S. government was represented by the EPA and 

precedents, the FAA, Bureau of Mines, NASA, Air Force and the Navy. The commercial sector 

included airlines, airframe manufacturers, engine manufacturers, fuel suppliers, calibration gas 

suppliers and instrument manufacturers. Over the years, as the methods evolved, many tests were 

conducted both by individual groups and as collaborative efforts. Data and information that resulted 

was freely shared, discussed and factored into this ARP as appropriate. The method that resulted, 

while not perfect, is well understood, repeatable and is robust. However there are some problems 

which have arisen due to changing engine designs and the intent of ensuring low visibility exhaust 

plumes. 

28. §34.83 – 34.88 [Reserved] 

29. §34.89 Compliance with smoke emission standards 

Compliance with each smoke emission standard shall be determined by comparing the plot of the 

smoke number as a function of power setting with the applicable emission standard under this 

part. The smoke number at every power setting must be such that there is a high degree of 

confidence that the standard will not be exceeded by any engine of the model being tested. An 

acceptable alternative to testing every engine is described in Appendix 6 to ICAO, Annex 16, 

Environmental Protection, Volume II, Aircraft Engine Emissions, Second Edition, July 1993. This 

incorporation by reference was approved by the Director of the Federal Register in accordance 

with 5 U.S.C. 552(a) and 1 CFR part 51. This document can be obtained from the address listed 

in 34.64. Other methods of demonstrating compliance may be approved by the Administrator with 

the concurrence of the Administrator of the EPA. 

Supplemental information

In agreeing to use the ICAO Compliance procedures, EPA has concluded, by implication, that the 

combination of the test and the compliance procedures will result in assurance that, with 90% 

confidence 100% of the engines produced, model and type, will meet the smoke standard if the 

engine or engines tested for smoke, meet the standard. 
 Page 37 

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Page 38 

IX. ICAO MANUAL APPENDIX 6 

ICAO MANUAL APPENDIX 6. COMPLIANCE PROCEDURE FOR 

GASEOUS EMISSIONS AND SMOKE 

1. GENERAL 

The following general principles shall be followed for compliance with the regulatory levels set 

forth in Volume II, Part III, 2.2, 2.3, 3.2 and 3.3 of this Annex: 

a) the manufacturer shall be allowed to select for certification testing any number of 

engines, including a single engine if so desired; 

b) all the results obtained during the certification tests shall be taken into account by the 

certification authority; 

c) a total of at least 3 engine tests shall be conducted, so that if a single engine is presented 

for certification it must be tested at least 3 times; 

d) if a given engine is tested several times, the arithmetic mean value of the tests shall be 

considered to be the mean value for that engine. The certification result (x) is then the mean of 

the values (X) obtained for each engine tested; 

e) the manufacturer shall provide to the certificating authority, the information specified in 

Volume II, Part III, 2.4 or 3.4 of this Annex as appropriate; 

f) the engines submitted for testing shall have emissions features representative of the 

engine type for which certification is sought. However, at least one of the engines shall be 

substantially configured to the production standard of the engine type and have fully 

representative operating and performance characteristics. One of these engines shall be declared 

to be the reference standard engine. The methods for correcting to this reference standard 

engine from any other engines tested shall have the approval of the national certificating 

authority. The methods for correcting test results for ambient effects shall be those outlined in 7 of 

Appendix 3 or 7 of Appendix 5, as applicable. 

2. COMPLIANCE PROCEDURES 

The certificating authority shall award a certificate of compliance if the mean of the values 

measured and corrected (to the reference standard engine and reference ambient 

conditions) for all the engines tested, when converted to a characteristic level using the 

appropriate factor which is determined by the number of engines tested (i) as shown in the table 

below, does not exceed the regulatory level. 

Note.- The characteristic level of the Smoke Number or gaseous pollutant emissions is 

the mean of the values of all the engines tested, measured and corrected to the reference 

standard engine and reference ambient conditions divided by the coefficient corresponding to the 

number of engines tested. as shown in the table below 
 Page 39 

Number 

of engines 

tested (i) CO HC NOX SN 

1 0.814 7 0.649 3 0.862 7 0.776 9 

2 0.877 7 0.768 5 0.909 4 0.852 7 

3 0.924 6 0.857 2 0 944 1 0.909 1 

4 0.934 7 0.876 4 0.951 6 0.921 3 

5 0.941 6 0.889 4 0.956 7 0.929 6 

6 0.946 7 0.899 0 0.960 5 0.935 8 

7 0.950 6 0.906 5 0.963 4 0.940 5 

8 0.953 8 0.912 6 0.965 8 0.944 4 

9 0.956 5 0.917 6 0.967 7 0.947 6 

10 0.958 7 0.921 8 0.969 4 0.950 2 

more 

than 10 1 0130 59 − .

i

1 0 247 24 − .

i

1 0 096 78 − .

i

1 0157 36 − .

i

3. PROCEDURE IN THE CASE 

OF FAILURE 

Note.- when a certification test fails, it does not necessarily mean that the engine type does not comply 

with the requirements, but it may mean that the confidence given to the certificating authority in 

compliance is not sufficiently high, i.e. less than 90 per cent. Consequently, the manufacturer should be 

allowed to present additional evidence of engine type compliance. 

3.1 If an engine type fails a certification test, the certificating authority shall permit the manufacturer, if 

he so wishes, to conduct additional tests on the certification engines. If the total results available 

still show that the engine type fails the certification requirements, the manufacturer shall be 

allowed to test as many additional engines as desired. The resulting test results shall then be 

considered with all previous data. 

3.2 If the result is still failure, the manufacturer shall be allowed to select one or more engines for 

modification. The results of the tests already made on the selected engine(s) while unmodified 

shall be inspected, and further testing shall be done so that at least three tests are available. The 

mean of these tests shall be determined for each engine and described as the "unmodified mean" 

3.3 The engine(s) may then be modified, and at least three tests shall he conducted on the modified 

engine(s), the mean of which shall be described as the "modified mean" in each case. This 

"modified mean" shall he compared to the "unmodified mean" to give a proportional improvement 

which shall then be applied to the previous certification test result to determine if compliance has 

been achieved. It shall be determined before testing of any modified engine is begun that the 

modification(s) comply with the appropriate airworthiness requirements. 

3.4 This procedure shall be repeated until compliance has been demonstrated or the engine type 

application is withdrawn. 
 

Page 40 

4. REPORTING OF DATA TO THE 

CERTIFICATING AUTHORITY 

The measured data shall be reported to the certificating authority. In addition the following data shall be 

reported for each test: 

a) sample temperature; 

b) sample pressure; 

c) actual sample volume at sampling conditions; 

d) actual sample flow rate as sampling conditions; and 

e) leak and cleanliness checks substantiation (see 2.5.2) 
 Page 41 

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Page 42 

X. ICAO MANUAL APPENDIX 3 

INSTRUMENTATION AND MEASUREMENT TECHNIQUES 

FOR GASEOUS EMISSIONS 

1. INTRODUCTION 

Note. —- The procedures specified in this appendix are concerned with the acquisition of representative 

exhaust samples and their transmission to, and analysis by, the emissions measuring system. The 

procedures do not apply to engines employing afterburning. The methods proposed are representative of 

the best readily available and most established practice. 

Variations in the procedure contained in this appendix shall only be allowed after prior application to and 

approval by the certificating authority. 

Supplemental Information

The methods recommended in ICAO Annex 16 Volume II, Second Edition, 1993 were adopted from SAE 

Aerospace Recommended Practice ARP 1256, "Procedure for the Continuous Sampling and Measurement of 

Gaseous Emissions from Aircraft Turbine Engines". ARP 1256 was first issued 10-1-71, by SAE committee E31, Aircraft Exhaust Emission Measurement. This ARP was developed by user groups in the aircraft industry 

who were interested in measuring and understanding emissions from aircraft gas turbine engines. Subsequent 

to the issuance of ARP 1256, in 1971, the methods proposed were, with the exception of NOx, adopted by the 

EPA in 40 CFR part 87, Part II, December 12, 1972. 

The exception in NOx measurement involved the adoption of chemiluminescence by the EPA in 40 CFR 87 and 

NDIR/NDUV by SAE E-31 in ARP 1256. Chemiluminescence, although a new technique at the time, was 

clearly the superior method and quickly adopted by the user community, incorporated into ARP 1256, replacing 

NDIR/NDUV, and recommended by ICAO in Annex 16, Volume II, first edition, 1981. The methods of 

measurement recommended in ICAO Annex 16, Volume II, first edition, 1981 were incorporated, by reference, 

into EPA 40 CFR 87, in 1982, Federal Register, Vol. 47, No. 251. These recommended methods represent the 

best readily available and most established practice. 

2. DEFINITIONS 

Where the following expressions are used in this appendix, they have the meanings ascribed to them 

below: 

(1) Accuracy. The closeness with which a measurement approaches the true value established 

independently. 

(2) Air/fuel ratio. The mass rate of airflow through the hot section of the engine divided by the mass 

rate of fuel flow to the engine. 

(3) Calibration gas. A high accuracy reference gas to be used for alignment, adjustment and periodic 

checks of instruments. 

(4) Concentration. The volume fraction of the component of interest in the gas mixture - expressed 

as volume percentage or as parts per million. 

(5) Exhaust nozzle. In the exhaust emissions sampling of gas turbine engines where the jet effluxes 

are not mixed (as in some turbofan engines for example) the nozzle considered is that for the gas 

generator (core) flow only. Where, however, the jet efflux is mixed the nozzle considered is the 

total exit nozzle. 

(6) Flame ionization detector. A hydrogen-air diffusion flame detector that produces a signal 

nominally proportional to the mass-flow rate of hydrocarbons entering the flame per unit of time - 
 Page 43 

generally assumed responsive to the number of carbon atoms entering the flame. 

(7) Interference. Instrument response due to presence of components other than the gas (or vapour) 

that is to be measured. 

(8) Noise. Random variation in instrument output not associated with characteristics of the sample to 

which the instrument is responding, and distinguishable from its drift characteristics. 

(9) Non-dispersive infra-red analyser. An instrument that by absorption of infra-red energy selectively 

measures specific components. 

(10) Parts per million (ppm). The unit volume concentration of a gas per million unit volume of the gas 

mixture of which it is a part. 

(11) Parts per million carbon (ppmC). The mole fraction of hydrocarbon multiplied by 106 measured on 

a methane-equivalence basis. Thus, 1 ppm of methane is indicated as 1 ppmC. To convert ppm 

concentration of any hydrocarbon to an equivalent ppmC value, multiply ppm concentration by 

the number of carbon atoms per molecule of the gas. For example, 1 ppm propane translates as 

3 ppmC hydrocarbon, 1 ppm hexane as 6 ppmC hydrocarbon. 

(12) Reference gas. A mixture of gases of specified and known composition used as the basis for 

interpreting instrument response in terms of the concentration of the gas to which the instrument 

is responding. 

(13) Repeatability. The closeness with which a measurement upon a given, invariant sample can be 

reproduced in short-term repetitions of the measurement with no intervening instrument 

adjustment. 

(14) Resolution. The smallest change in a measurement which can be detected. 

(15) Response. The change in instrument output signal that occurs with change in sample 

concentration. Also the output signal corresponding to a given sample concentration. 

(16) Stability. The closeness with which repeated measurements upon a given invariant sample can 

be maintained over a given period of time. 

(17) Zero drift. Time-related deviation of instrument output from zero set point when it is operating on 

gas free of the component to be measured. 

(19) Zero gas. A gas to be used in establishing the zero, or no-response, adjustment of an instrument. 

3. DATA REQUIRED 

3.1 Gaseous emissions 

Concentrations of the following emissions shall be determined: 

(a) Hydrocarbons (HC): a combined estimate of all hydrocarbon compounds present in the exhaust gas. 

Supplemental information

Gas turbine engine exhaust gases typically contain a variety of hydrocarbon compounds. The specific 

compounds present and their relative concentrations are usually unknown. Flame Ionization Detectors (FID), 

used to measure hydrocarbons, do not respond equally to all hydrocarbon compounds - differential 

hydrocarbon response. Although the differential hydrocarbon response is to be held within specific bounds, 

the resulting measurement is an estimate of the hydrocarbon compounds present in the exhaust gas. 
 

Page 44 

(b) Carbon monoxide (CO). 

(c) Carbon dioxide (CO2). 

Note.— CO2 is not considered a pollutant but its concentration is required for calculation and check 

purposes. 

(d) Oxides of nitrogen (NOX) an estimate of the sum of the two oxides, nitric oxide (NO) and nitrogen 

dioxide (NO2). 

(e) Nitric oxide (NO). 

Supplemental information

The measurement of oxides of nitrogen, using an NO specific device, requires the conversion of NO2 in the 

exhaust gas to NO. The conversion efficiency of the device used must be known and must be greater than 

90%. Measurements of NOx are adjusted for conversion efficiency. The resulting values are considered to 

be estimates of the NOx concentration in the exhaust gas. 

3.2 Other information 

In order to normalize the emissions measurement data and to quantify the engine test characteristics, the 

following additional information shall be provided: 

- inlet temperature; 

- inlet humidity; 

- atmospheric pressure; 

- hydrogen/carbon ratio of fuel; 

- other required engine parameters (for example, thrust, rotor speeds, turbine temperatures and 

gas-generator air flow). 

This data shall be obtained either by direct measurement or by calculation as presented in Attachment F 

to this appendix. 

4. GENERAL ARRANGEMENT OF THE SYSTEM 

No desiccants, dryers, water traps or related equipment shall be used to treat the exhaust sample flowing 

to the oxides of nitrogen and the hydrocarbon analysis instrumentation. Requirements for the various 

component sub-systems are given in 5, but the following list gives some qualifications and variations: 

a) it is assumed that each of the various individual sub-systems includes the necessary flow control, 

conditioning and measurement facilities; 

b) the necessity for a dump and/or a hot-sample pump will depend on ability to meet the sample 

transfer time and analysis sub-system sample flow rate requirements. This in turn depends on the 

exhaust sample driving pressure and line losses. It is considered that these pumps usually will be 

necessary at certain engine running conditions; and 

c) the position of the hot pump, relative to the gas analysis sub-systems, may be varied as required. 

(For example, some HC analysers contain hot pumps and so may be judged capable of being 

used upstream of the system hot pump.) 

Note.- Figure A3-1 is a schematic drawing of the exhaust gas sampling and analytical system and typifies 

the basic requirements for emissions testing. 
 Page 45 

Figure A3-1 Sampling and Analysis System 

Supplemental information

Water is a major product of combustion. Its removal upstream of the measuring instruments is desirable. 

Removal would minimize possible interference effects, where the instrument responds to the water present as 

well as to the gas or vapor being measured. It would also prevent or minimize water condensing in the 

instruments, which could cause erratic flow and/or contamination. In the worst case the instrument would be 

rendered inoperable until thoroughly cleaned. Some devices which remove water are known to remove 

hydrocarbons and oxides of nitrogen as well. 

For most aircraft gas turbine engines and most engine running modes, supplemental pumps will be needed to 

match the engine exhaust flow with the probe system pressure drop mandated requirement (80% at the probe 

entrance orifices), the sample line residence time and pressure drop, and the need to remove excess flow 

from the sampling system. In general the size and location of the pumps and the associated flow control 

devices are determined from the particular sampling system configuration. 

Pumps used for the purpose of sample transfer must be heated. Their location is determined by the particular 

test configuration. Usually, because of the sample gas physical properties and the need to maintain 

temperature and flow control within the FID used for hydrocarbon analysis, some instruments utilize internal 

heated, inert sample transfer pumps. If loss of hydrocarbons in the sampling system is a concern, the FID 

can be located upstream of the system hot pump as close as physical constraints will allow (temperature, 

noise, vibration). 
 

Page 46 

5. DESCRIPTION OF COMPONENT PARTS 

Note.— A general description and specification of the principal elements in the engine exhaust emissions 

measurement system follows. Greater detail, where necessary, will be found in Attachments A, B and C 

to this appendix. 

5.1 Sampling system 

5.1.1 Sampling probe 

a) The probe shall be made of stainless steel. If a mixing probe is used, all sampling orifices 

shall be of equal diameter; 

b) the probe design shall be such that at least 80 per cent of the pressure drop through the 

probe assembly is taken at the orifices; 

Supplemental information

While there is no need to approximate isokinetic conditions when sampling for non-particulates, good practice 

requires minimum disturbance to the sampled stream as practical. This is especially true when there is 

concern over spatial variability in gas species concentration, which is the case for the gas turbine engine 

exhaust plume. 

c) the number of sampling orifices shall not be less than 12; 

Supplemental information

12 sampling orifices, for an averaging probe, or 12 sampling points for a single point traversing probe, should 

be considered acceptable only in extreme circumstances or when this number of sampling points has clearly 

been demonstrated to yield a representative sample. 

d) the sampling plane shall be as close to the engine exhaust nozzle exit plane as permitted 

by considerations of engine performance but in any case shall be within 0.5 nozzle 

diameter of the exit plane; 

Supplemental information

For non-coplanar fan/core exhaust nozzles, care must be taken in locating the sampling plane within 0.5 

nozzle diameters of the exit plane inasmuch as there can be two exit planes. The exit plane, from which this 

distance is measured, is the plane of the final exhaust nozzle – usually the core. The distance allowed would 

be determined from the larger, fan exhaust nozzle. Further, for these engines, locating the sampling probe as 

close to the engine exhaust nozzle exit plane as permitted could compromise the requirement to make 

measurements of the 'total exit nozzle' as defined. Given this ambiguity and the requirement to determine the 

concentration of species generated by the engine – restricted to the core flow until mixed out – every effort 

should be made to sample core flow only. This may require a special extension to the core nozzle which will 

require FAA approval. 

and 

e) the applicant shall provide evidence to the certificating authority, by means of detailed traverses, 

that the proposed probe design and position does provide a representative sample for each 

prescribed power setting. 
 Page 47 

Supplemental information:

There are no standard definitions of representative sample for emissions from aircraft gas turbine engines nor 

is there a specification for detailed traverse. The most commonly used definition, arrived at from decades of 

testing and collaborative analytical exercises by user groups, seems to be the following: for engine modes 

above idle, (i.e., approach, climb-out and take-off) the integrated average of the measured species should 

agree with the true average within 10 %. For idle this agreement is ± 15%. 

This is similar to the values quoted in section 6.4 of this Appendix, for the carbon balance check. However 

there is a significant difference. For the carbon balance check, a comparison is made between sets of 

independently related measured values. With knowledge about the combustion process and the hydrogen to 

carbon ratio of the fuel used, an estimate can be made from the measured carbon containing species – most 

of which is CO2, – of the engine average fuel-to-air ratio. The engine fuel-to-air ratio can be independently 

arrived at from measured fuel and airflow. These two values can be compared and an estimate made of how 

well the exhaust stream was sampled for carbon containing compounds. However, as mentioned, CO2 far 

outweighs the influence of any other carbon bearing species in the calculation of fuel-to-air ratios. The spatial 

variability of CO2 will determine how many sampling points are required and how these sampling points 

should be distributed. CO2 has been found to consistently exhibit the least variability of all the species of 

interest – CO, HC, NOx, and smoke. This suggests that it would be possible to meet the criteria – for carbon 

balance without having obtained a representative sample – using the same 10 and 15% criteria, of the other 

species. In other words, obtaining a carbon balance, while a necessary condition for a representative sample, 

can not be considered to be a sufficient condition. 

Historically, each engine manufacturer or testing agency appears to have addressed this problem in unique 

and sometimes novel ways. The simplest method is as follows: 

• Recognizing that gas turbine engines are, for most emissions sampling purposes, axi-symmetric, sample 

the exhaust plume, point by point, with a sufficient number of points to be able to estimate, by statistical 

means, the true engine average species concentration for each of the species of interest. Engine 

exhaust species are close enough to normally (Gaussian) distributed to make simple statistical tools 

acceptable. 

• Using these sampling points and the measured concentration values, for each of the species of interest, 

analytically generate contour plots of constant concentration (isopleths) at each power setting tested. 

There are a number of computer programs available for workstations or desktop computers to do this. 

• For any given probe or rake design analytically overlay the design on the contour plots, estimate the 

average probe/rake values and compare to the estimated true average arrived at from the detailed 

traverse. 

If the comparisons match the carbon balance criteria, within 10% for engine powers above idle and ±15% at 

idle, the probe/rake can be considered to be representative. This process may be have to be repeated until 

an acceptable design is found. 

When applying this analytical technique (for core flow only), multiport rake designs which have proven most 

robust have four sampling arms spaced 90 degrees apart with sampling orifices located on centers of equal 

area. The sampling ports are equally distributed across the sampling arms. The analysis will determine the 

minimum number of sampling ports necessary to yield a representative sample. 

All data used in arriving at a probe/rake design should be made available to the certificating agency. 

5.2 HC analyser 
 

Page 48 

The measurement of total hydrocarbon sample content shall be made by an analyser using the heated 

flame ionization detector (FID), between the electrodes of which passes an ionization current proportional 

to the mass rate of hydrocarbon entering a hydrogen flame. The analyser shall be deemed to include 

components arranged to control temperature and flow rates of sample, sample bypass, fuel and diluent 

gases, and to enable effective span and zero calibration checks. 

Note. — An over-all specification is given in Attachment A to this appendix 

5.3 CO and CO2 analysers 

Non-dispersive infra-red analysers shall be used for the measurements of these components, and shall 

be of the design which utilizes differential energy absorption in parallel reference and sample gas cells, 

the cell or group of cells for each of these gas constituents being sensitized appropriately. This analysis 

sub-system shall include all necessary functions for the control and handling of sample, zero and span 

gas flows. Temperature control shall be that appropriate to whichever basis of measurement, wet or dry, 

is chosen. 

Note.—- An over-all specification is given in Attachment B to this appendix 

5.4 NOX analyser 

The measurement of NO concentration shall be by the chemiluminescent method in which the measure of 

the radiation intensity emitted during the reaction of the NO in the sample with added O3 is the measure 

of the NO concentration. The NO2 component shall be converted to NO in a converter of the requisite 

efficiency prior to measurement. The resultant NOX measurement system shall include all necessary flow, 

temperature and other controls and provide for routine zero and span calibration as well as for converter 

efficiency checks. 

Note. — An over-all specification is given in Attachment C to this appendix 

6. GENERAL TEST PROCEDURES 

6.1 Engine operation 

6.1.1 The engine shall be operated on a static test facility which is suitable and properly equipped for 

high accuracy performance testing. 

6.1.2 The emissions tests shall be made at the power settings prescribed by the certificating authority. 

The engine shall be stabilized at each setting. 

6.2 Major Instrument calibration 

Note. — The general objective of this calibration is to confirm stability and linearity. 

6.2.1 The applicant shall satisfy the certificating authority that the calibration of the analytical system is 

valid at the time of the test. 

6.2.2 For the hydrocarbon analyser this calibration shall include checks that the detector oxygen and 

differential hydrocarbon responses are within the limits specified, as laid down in Attachment A to 

this appendix. The efficiency of the NO2/NO converter shall also be checked and verified to meet 

the requirements in Attachment C to this appendix. 
 Page 49 

6.2.3 The procedure for checking the performance of each analyser shall be as follows (using the 

calibration and test gases as specified in Attachment D to this appendix): 

a) introduce zero gas and adjust instrument zero, recording setting as appropriate; 

b) for each range to be used operationally, introduce calibration gas of (nominally) 90 per cent 

range full-scale deflection (FSD) concentration; adjust instrument gain accordingly and record 

its setting; 

c) introduce approximately 30 per cent, 60 per cent, and 90 per cent range FSD concentration 

and record analyser readings; 

d) fit a least squares straight line to the zero, 30 per cent, 60 per cent and 90 per cent 

concentration points. For the CO and/or CO2 analyser used in their basic form without 

linearization of output, a least squares curve of appropriate mathematical formulation shall be 

fitted using additional calibration points if judged necessary. If any point deviates by more 

than 2 per cent of the full scale value (or ±l ppm*, whichever is greater) then a calibration 

curve shall be prepared for operational use. 

* Except for the CO2 analyser, for which the value shall be ±100 ppm. 

** A more comprehensive and precise alternative methodology which is acceptable is presented in 

Attachment E to this appendix. 

 Supplemental Information: 

For most, if not all modern analyzers, the adjustment and recording of settings is performed by an internal 

computer. When the computer stores the calibration coefficients and generates a least square curve for 

each operational range, this should be considered equivalent to those system controls performed 

manually in older systems as described in 6.2.3. 

6.3 Operation 

6.3.1 No measurements shall be made until all instruments and sample transfer lines are warmed up 

and stable and the following checks have been carried out: 

a) leakage check: prior to a series of tests the system shall be checked for leakage by isolating 

the probe and the analysers, connecting and operating a vacuum pump of equivalent 

performance to that used in the smoke measurement system to verify that the system 

leakage flow rate is less than 0.4 L/min referred to normal temperature and pressure; 

b) cleanliness check: isolate the gas sampling system from the probe and connect the end of 

the sampling line to a source of zero gas. Warm the system up to the operational temperature 

needed to perform hydrocarbon measurements. Operate the sample flow pump and set the 

flow rate to that used during engine emission testing. Record the hydrocarbon analyser 

reading. The reading shall not exceed 1 per cent of the engine idle emission level or 1 ppm 

(both expressed as methane), whichever is the greater. 

Note 1.— It is good practice to back-purge the sampling lines during engine running, while the probe is in 

the engine exhaust but emissions are not being measured. to ensure that no significant contamination 

occurs. 

Note. 2.— It is also good practice to monitor the inlet air quality at the start and end of testing and at least 

once per hour during a test. If levels are considered significant, then they should be taken into 

account. 

6.3.2 The following procedure shall be adopted for operational measurements: 
 

Page 50 

a) apply appropriate zero gas and make any necessary instrument adjustments; 

b) apply appropriate calibration gas at a nominal 90 per cent FSD concentration for the ranges 

to be used, adjust and record gain settings accordingly; 

c) when the engine has been stabilized at the requisite operating mode, continue to run it and 

observe pollutant concentrations until a stabilized reading is obtained, which shall be 

recorded; 

d) recheck zero and calibration points at the end of the test and also at intervals not greater than 

1 hour during tests. If either has changed by more than ±2 per cent of range FSD, the test 

shall be repeated after restoration of the instrument to within its specification. 

6.4 Carbon balance check 

Each test shall include a check that the air/fuel ratio as estimated from the integrated sample total carbon 

concentration exclusive of smoke, agrees with the estimate based on engine air/fuel ratio within ±15 per 

cent for the taxi/ground idle mode, and within 10 per cent for all other modes (see 7.1.2). 

7. CALCULATIONS 

7.1 Gaseous emissions 

7.1.1 General 

The analytical measurements made shall be the concentrations of the various classes of pollutant, as 

detected at their respective analysers for the several engine operation modes, and these values shall be 

reported. In addition, other parameters shall be computed and reported, as follows**. 

** A more comprehensive and precise alternative methodology which is acceptable is presented in 

Attachment E to this appendix. 

7.1.2 Basic parameters 

[ ]

[ ] [ ][ ] ( ) ( ) ( )

[ ]

[ ] [ ][ ] ( ) ( ) ( )

[ ]

[ ] [ ][ ] ( ) ( ) ( )

EI(CO) CO

CO CO HC

EI(HC) HC

CO CO HC

EI(NO ) NO

CO CO HC

2

CO

C H

2

HC

C H

X

X

2

NO

C H

X

= + +

⎛

⎝

⎜ ⎞

⎠

⎟

+

⎛

⎝

⎜

⎞

⎠

⎟ +

= + +

⎛

⎝

⎜ ⎞

⎠

⎟

+

⎛

⎝

⎜

⎞

⎠

⎟ +

= + +

⎛

⎝

⎜ ⎞

⎠

⎟

+

⎛

⎝

⎜

⎞

⎠

⎟ +

10 1

10 1

10 1

3

0

3

0

3

0

M

M nm M

TPm

M

M nm M

TPm

M

M nm M

TPm

Supplemental information: 

The basic descriptive parameter for gaseous emissions is the emission index (EI), defined as the mass of a 

product of combustion, in grams, divided by the mass of fuel used in kilograms, i.e., grams per kilogram. 
 Page 51 

0

AIR

C H

/ = (P / ) (/ ) Air fuel ratio m M

M n mM

⎡ ⎤ ⎢ ⎥ ⎣ ⎦ + 

 

where: 

( )

( ) o

2Z- / P/ =

4 1+ - TZ/2

n m

m

h ⎡ ⎤ ⎣ ⎦

and: 

[ ] ( ) [ ] [ ] [ ] [ ]

[ ][ ][ ]

2

2

2- CO - 2/ - /2 HC + NO

Z=

CO + CO + HC

x yx

MAIR Molecular mass of dry air = 28.966 g or, where appropriate, = (32 R + 28.156 4 S + 

44.011 T) g 

MHC molecular mass of exhaust hydrocarbon, taken as CH4 = 16.043 g 

MCO molecular mass of CO = 28.011 g 

MNO2 molecular mass of NO2 = 46.008 g 

MC molecular mass of carbon = 12.011 g 

MH molecular mass of hydrogen = 1.008 g 

R concentration of O2 in dry air, by volume = 0.209 5 normally 

S concentration of N2 + rare gases in dry air, by volume = 0.709 2 normally 

T concentration of CO2 in dry air, by volume = 0.000 3 normally 

[HC] mean concentration of exhaust hydrocarbons vol/vol, expressed as carbon 

[CO] mean concentration of CO vol/vol, wet 

[CO2] mean concentration of CO2 vol/vol, wet 

[NOX] mean concentration of NOX vol/vol, wet = [NO + NO2} 

[NO] mean concentration of NO in exhaust sample, vol/vol, wet 

[NO2] mean concentration of NO2 in exhaust sample, vol/vol, wet 

( ) [NO NO x ] [ ] c

η

− =

[NOX]c mean concentration of NO in exhaust sample after passing through the NO2/NO 

converter, vol/vol, wet 

η efficiency of NO2/NO converter 

h humidity of ambient air, vol water/vol dry air 

m number of C atoms in characteristic fuel molecule 

n number of H atoms in characteristic fuel molecule 

x number of C atoms in characteristic exhaust hydrocarbon molecule 

y number of H atoms in characteristic exhaust hydrocarbon molecule 
 

Page 52 

The value of n/m, the ratio of the atomic hydrogen to atomic carbon of the fuel used, is evaluated by fuel 

type analysis. The ambient air humidity, h, shall be measured at each set condition. In the absence of 

contrary evidence as to the characterization (x, y) of the exhaust hydrocarbons, the values x= 1, y=4 are 

to be used.1f dry or semi-dry CO and CO2 measurements are to be used then these shall first be 

converted to the equivalent wet concentration as shown in Attachment E to this appendix, which also 

contains interference correction formulas for use as required. 

7.1.3 Correction of emission indices 

to reference conditions 

Corrections shall be made to the measured engine emission indices for all pollutants in all relevant engine 

operating modes to account for deviations from the reference conditions (ISA at sea level) of the actual 

test inlet air conditions of temperature and pressure. The reference value for humidity shall be 0.00629 kg 

water/kg dry air. 

Thus, EI corrected = K x EI measured, where the generalized expression for K is: 

( )( ) / / exp | | / exp ( )( ) Bref B | -0.00629| a b

K P P FAR FAR d T T c d Bref B ref B = × × −× h

PB Combustor inlet pressure, measured 

TB Combustor inlet temperature, measured 

FARB Fuel/air ratio in the combustor 

h Ambient air humidity 

Pref ISA sea level pressure 

Tref ISA sea level temperature 

PBref Pressure at the combustor inlet of the engine tested (or the reference engine if the 

data is corrected to a reference engine) associated with TB under ISA sea level 

conditions 

TBref Temperature at the combustor inlet under ISA sea level conditions for the engine 

tested (or the reference engine if the data is corrected to a reference engine). This 

temperature is the temperature associated with each thrust level specified for each 

mode. 

FARref Fuel/air ratio in the combustor under ISA sea level conditions for the engine tested 

(or the reference engine if the data is to be corrected to a reference engine). 

a,b,c,d Specific constants which may vary for each pollutant and each engine type 

The combustor inlet parameters shall preferably be measured but may be calculated from ambient 

conditions by appropriate formulas. 

7.1.4 Using the recommended curve fitting technique to relate emission indices to combustor inlet 

temperature effectively eliminates the exp ((TBref - TB)/c) term from the generalized equation and 

for most cases the (FARref/FAR,) term may be considered unity. For the emissions indices of CO

and HC many testing facilities have determined that the humidity term is sufficiently close to unity 

to be eliminated from the expression and that the exponent of the (PBref /PB) term is close to unity. 

Thus, 

EI(CO) corrected = EI derived from 

(PB /PBref) EI(CO) v. TB, curve 

EI(HC) corrected = EI derived from 

(PB /PBref) EI(HC) v. TB, curve 
 Page 53 

EI(NOX) corrected = EI derived from 

EI(NOX) (PBref/PB)

0.5 exp (19 |h - 0.006 29|) v. TB curve 

If this recommended method for the CO and HC emissions index correction does not provide a 

satisfactory correlation, an alternative method using parameters derived from component tests may be 

used. 

Supplemental Information

In the generalized correction, for K the term (PB/PBref), (in the EI(CO) and EI(HC) expressions) should be 

(PBref/PB) 

Any other methods used for making corrections to CO, HC and NO, emission indices shall have the 

approval of the certificating authority. 

7.2 Control parameter functions 

(Dp , Foo , π) 

7.2.1 Definitions 

Dp The mass of any gaseous pollutant emitted during the reference emissions landing 

and take-off cycle. 

Foo The maximum thrust available for take-off under normal operating conditions at ISA 

sea level static conditions, without the use of water injection, as approved by the 

applicable certificating authority. 

π The ratio of the mean total pressure at the last compressor discharge plane of the 

compressor to the mean total pressure at the compressor entry plane when the 

engine is developing take-off thrust rating at ISA sea level static conditions. 

7.2.2 The emission indices (EI) for each pollutant, corrected for pressure and humidity (as appropriate) 

to the reference ambient atmospheric conditions as indicated in 7.1.4 and if necessary to the 

reference engine, shall be obtained for the required LTO engine operating mode settings (n) of 

idle, approach. climb-out and take-off, at each of the equivalent corrected thrust conditions. A 

minimum of three test points shall be required to define the idle mode. The following relationships 

shall be determined for each pollutant: 

a) between EI and TB; and 

b) between Wf (engine fuel mass flow rate) and TB; and 

c) between Fn,, (corrected to ISA sea level conditions) and TB, (corrected to ISA sea level 

conditions); 

Note. — These are illustrated, for example, by Figure 3-2 a), b) and c). 

When the engine being tested is not a "reference" engine, the data may be corrected to "reference" 

engine conditions using the relationships b) and c) obtained from a reference engine. A reference engine 

is defined as an engine substantially configured to the description of the engine to be certificated and 

accepted by the certificating authority to be representative of the engine type for which certification is 

sought. 
 

Page 54 

The manufacturer shall also supply to the certificating authority all of the necessary engine performance 

data to substantiate these relationships and for ISA sea level ambient conditions: 

d) maximum rated thrust (Foo); and 

e) engine pressure ratio (π) at maximum rated thrust. 

Note.— These are illustrated by Figure A3-2 d). 

7.2.3 The estimation of EI for each pollutant at each of the required engine mode settings, corrected to 

the reference ambient conditions, shall comply with the following general procedure: 

a) at each mode ISA thrust condition Fn determine the equivalent combustor inlet temperature 

(TB) (Figure 3-2 c)); 

b) from the EI/TB characteristic (Figure 3-2 a)), determine the EIn value corresponding to TB; 

c) from the Wf/TB characteristic (Figure 3-2 b)), determine the Wfn value corresponding to TB; 

Note the ISA maximum rated thrust and pressure ratio values. These are Foo and π respectively (Figure 

3-2 d)); 

calculate, for each pollutant Dp = Σ (EIn)(Wfn)(t) 

t time in LTO mode (minutes) 

Wfn fuel mass flow rate (kg/min) 

Σ is the summation for the set of modes comprising the reference LTO cycle. 

7.2.4 While the methodology described above is the recommended method, the certificating authority 

may accept equivalent mathematical procedures which utilize mathematical expressions 

representing the curves illustrated if the expression have been derived using an accepted curve 

fitting technique 

. 
 Page 55 

Figure A3-2 ICAO Calculation Procedure 

7.3 Exceptions to the 

proposed procedures 

In those cases where the configuration of the engine or other extenuating conditions exist which would 

prohibit the use of this procedure, the certificating authority, after receiving satisfactory technical evidence 

of equivalent results obtained by an alternative procedure, may approve an alternative procedure. 
 

Page 56 

ATTACHMENT A TO ICAO MANUAL APPENDIX 3. 

SPECIFICATION FOR HC ANALYSER

Note 1.- As outlined in 5.2 of Appendix 3, the measuring element in this analyser is the flame ionization 

detector (FID) in which the whole or a representative portion of the sample flow is admitted into a 

hydrogen-fueled flame. With suitably positioned electrodes an ionisation current can be established which 

is a function of the mass rate of hydrocarbon entering the flame. It is this current which, referred to an 

appropriate zero, is amplified and ranged to provide the output response as a measure of the 

hydrocarbon concentration expressed as ppmC equivalent. 

Note 2. — See Attachment D for information on calibration and test gases. 

1. GENERAL 

Precautions: The performance specifications indicated are generally for analyser full scale. Errors at 

part scale may be a significantly greater percentage of reading. The relevance and importance of such 

increases shall be considered when preparing to make measurements. If better performance is 

necessary, then appropriate precautions shall be taken. 

Supplemental information

The performance specifications for these analyzers, given in terms of full scale response, can have a 

significant and adverse impact on part scale measurements. In extreme instances, concentrations of HC at 

high power, such as take-off, can differ from concentrations at idle, by orders of magnitude e.g., 3,500 ppmC 

at idle and 10 ppmC at take-off. The FID specification suggests the high level can be 5,000 ppmC. For most 

modern engines the idle concentrations are considerably lower but still of concern when setting up the FID to 

maintain suitable accuracy of measurement. In general, where concentrations of species to be measured are 

known to vary this way, it is always good practice to use a multi-range instrument and to adjust ranges such 

as to keep the measurement in the upper 30% of the instrument response range. A measurement made at 

20% of full scale could result in an error 5 times the error specified as a percent of full scale. Calibrations 

should be performed on each range used as required. 

The instrument to be used shall be such as to maintain the temperature of the detector and samplehandling components at a set point temperature within the range 155o

C to 165oC to a stability of ±2°C. The 

leading specification points shall be as follows, the detector response having been optimized and the 

instrument generally having stabilized: 

Supplemental information

Stability is usually defined in terms of a time interval which, because this is a temperature control set point, 

can be taken as the duration of the test. 

a) Total range: 0 to 5 000 ppmC in appropriate ranges. 

Supplemental information

A total range of 0 to 5,000 ppmC, while appropriate for the engines in use when Annex 16 was published in 

1981, is broader than needed for today's engines. Given practical limitations on instrument design the result 

could restrict the number of appropriate instrument ranges available in any single instrument. Restricting the 

number of ranges available makes it difficult to follow good measurement practices by restricting 

measurements to the upper 30% of range. 

b) Resolution: better than 0.5 per cent of full scale of range used or 0.5 ppmC, whichever is 

greater. 
 Page 57 

c) Repeatability: better than ±1 per cent of full scale of range used. or ±0.5 ppmC. whichever is 

greater. 

d) Stability: better than ±2 per cent of full scale of range used or ±l.0 ppmC, whichever is 

greater, in a period of 1 hour. 

 

e) Zero drift: less than ±1 per cent of full scale of range used or ±0.5 ppmC, whichever is 

greater, in a period of 1 hour. 

 

f) Noise: 0.5 Hz and greater, less than ±1 per cent of full scale of range used or ±0.5 ppmC, 

whichever is greater. 

Supplemental information

The FID requires fuel and oxidant gases for operation. The fuel gas is typically either a mixture of hydrogen 

and nitrogen or hydrogen and helium. If the noise specification cannot be met and a hydrogen/nitrogen 

mixture is being used as the fuel gas, it sometimes helps to change to a hydrogen/helium mixture. 

g) Response time: shall not exceed 10 seconds from inlet of the sample to the analysis system, 

to the achievement of 90 per cent of the final reading. 

h) Linearity: response with propane in air shall be linear for each range within ±2 per cent of full 

scale, otherwise calibration corrections shall be used. 

Supplemental information

The performance specifications for the HC analyzer are typical of those analyzers offered by major instrument 

manufacturers. 

2. SYNERGISTIC EFFECTS 

Note.- In application there are two aspects of performance which can affect the accuracy of 

measurement: 

a) the oxygen effect (whereby differing proportions of oxygen present in the sample give 

differing indicated hydrocarbon concentration for constant actual HC concentrations); and 

b) the relative hydrocarbon response (whereby there is a different response to the same sample 

hydrocarbon concentrations expressed as equivalent ppmC, dependent on the class or 

admixture of classes of hydrocarbon compounds). 

The magnitude of the effects noted above shall be determined as follows and limited accordingly. 

Oxygen response: measure the response with two blends of propane, at approximately 500 ppmC 

concentration known to a relative accuracy of ±l per cent, as follows: 

1) propane in 10 ± 1 per cent O2, balance N2

2) propane in 21 ± 1 per cent O2, balance N2

If R1 and R2 are the respective normalized responses then (R1 - R2) shall be less than 3 per cent of R1. 
 

Page 58 

Supplemental information

The typical range of O2 concentrations in the core exhaust gas from idle to take-off, is approximately 18% at 

idle, to 15% (or somewhat less) at take-off. The specification for a response of <3% between samples of 10% 

and 21% is conservative, effectively limiting the differential response to <1% over the range of interest. If 

needed the O2 response can be minimized by adjusting the FID burner fuel/air ratio. 

Differential hydrocarbon response: measure the response with four blends of different hydrocarbons in 

air, at concentrations of approximately 500 ppmC, known to a relative accuracy of ±l per cent, as follows: 

 a) propane in zero air 

 b) propylene in zero air 

 c) toluene in zero air 

 d) n-hexane in zero air. 

If Ra, Rb, Rc and Rd are, respectively, the normalized responses (with respect to propane), then (Ra - Rb), 

(Ra - Rc) and (Ra - Rd) shall each be less than 5 per cent of Ra. 

Supplemental information

Although assumed to respond as a carbon number counter, for the purposes of testing engine exhaust, the 

FID response is known to vary somewhat with the particular hydrocarbon or class of hydrocarbons being 

measured. For example three molecules of methane, CH4, will not necessarily result in the same instrument 

response as one molecule of propane, C3H8. Because of this differential response it is sometimes helpful to 

think of the FID as responding to an “effective” carbon number. It is important to ensure the instrument 

responds acceptably to all of the hydrocarbons in the engine exhaust. This group of hydrocarbons – 

propylene, toluene, and n-hexane – with propane as a reference was chosen to represent, in terms of 

differential response, the range of hydrocarbons expected in the exhaust. 

3. OPTIMIZATION OF DETECTOR RESPONSE AND ALIGNMENT 

3.1 The manufacturer's instructions for initial setting up procedures and ancillary services and 

supplies required shall be implemented, and the instrument allowed to stabilize. All setting 

adjustments shall involve iterative zero checking, and correction as necessary. Using as sample a 

mixture of approximately 500 ppmC of propane in air, the response characteristics for variations 

first in fuel flow and then, near an optimum fuel flow, for variations in dilution air flow to select its 

optimum shall be determined. The oxygen and differential hydrocarbon responses shall then be 

determined as indicated above. 

Supplemental information

The FID detector response and alignment can be optimized by adjusting the FID burner fuel and air flow 

while sampling a mixture containing approximately 500 ppmC propane. Care should be taken when 

changing fuel flow that the instrument zero does not shift. If it does the instrument zero should be reset. 

Response curves, illustrating this process, shown below in Figures A3-3 and A3-4, were taken from 40 CFR 

Part 87, Control of Air Pollution from Aircraft and Aircraft Engines, Federal Register, Vol. 43, No. 58 — 

Friday, March 24, 1978. They were taken, in turn, from SAE ARP1256, "Procedure for the Continuous 

Sampling and Measurement of Gaseous Emissions from Aircraft Turbine Engines". 
 Page 59 

Figure A3-3 Typical Fuel Flow Response Curve 

Figure A3-4 Typical Airflow Response Curve 

The objective of this procedure is to select operating flow rates which will give near maximum response with 

least variation for minor fuel flow variations. It may be necessary to repeat this operation in an iterative 

fashion: 

• Adjust the fuel flow to maximize output; 

• Adjust zero if necessary; 

• Adjust the air flow to maximize output 

• Readjust the fuel flow, if necessary, and 

• Repeat until the burner output is optimized. 

3.2 The linearity of each analyser range shall be checked by applying propane in air samples at 

concentrations of approximately 30, 60 and 90 per cent of full scale. The maximum response 

deviation of any of these points from a least squares straight line (fitted to the points and zero) 

shall not exceed ±2 per cent of full scale value. If it does, a calibration curve shall be prepared for 

operational use. 
 

Page 60 

Explanation

Table A3-1 summarizes the performance specifications of an HC analyzer. 

Table A3-1 HC ANALYZER PERFORMANCE SPECIFICATIONS 

Parameter Value

Total Range 0 to 5,000 ppmC 

Resolution better than 0.5 percent full scale range 

used or 0.5 ppmC whichever is greater 

Repeatability better than ±1 percent full scale range 

used or ±0.5 ppmC whichever is greater 

Stability better than ±2 percent full scale range 

used or ±1 ppmC whichever is greater in 

a period of 1 hour 

Zero drift < ±1 percent full scale range used 

or ±0.5 ppmC, whichever is greater in a 

period of 1 hour 

Noise 0.5 Hz and greater, < than ±1 percent full 

scale range used or ±0.5 ppmC, 

whichever is greater 

Response time ≤ 10 seconds from inlet of sample to 

achieve 90 percent of final reading 

Linearity ±2 percent full scale to propane in air, for 

each range used, or calibration 

correction required 
 Page 61 

ATTACHMENT B TO ICAO MANUAL APPENDIX 3. 

SPECIFICATION FOR CO AND CO2 ANALYSERS 

Note 1.- Paragraph 5.3 of Appendix 3 summarizes the characteristics of the analysis sub-system to be 

employed for the individual measurements of CO and CO2 concentrations in the exhaust gas sample. The 

instruments are based on the principle of non-dispersive absorption of infra-red radiation in parallel 

reference and sample gas cells. The required ranges of sensitivity are obtained by use of stacked sample 

cells or changes in electronic circuitry or both. Interferences from gases with overlapping absorption 

bands may be minimised by gas absorption filters and/or optical filters. preferably the latter. 

Note 2. — See Attachment D for information on calibration and test gases. 

Precautions: The performance specifications indicated are generally for analyser full scale. Errors at part 

scale may be a significantly greater percentage of reading. The relevance and importance of such 

increases shall be considered when preparing to make measurements. If better performance is 

necessary, then appropriate precautions shall be taken. 

Supplemental information

The performance specifications for these analyzers, given in terms of full scale response, 

can have a significant and adverse impact on part scale measurements. This needs to be 

considered when planning and executing the test and in evaluating the accuracy of the 

measurements after the test. Concentrations of CO, when going from the idle mode to takeoff, can differ by orders of magnitude. In general, where concentrations of species to be 

measured are known to vary this way, it is always good practice to use a multi-range 

instrument and to choose ranges such as to keep the measurement in the upper 30% of 

scale on the range in use, where possible. A measurement made at 20% of full scale could 

result in an error 5 times the error specified as a percent of full scale. This is a general 

precaution. Some modern instruments with internal electronic ranging and calibration 

capability can be used over their entire range without penalty. Calibrations should be 

performed on each range used as required. Relative to the precautions mentioned above, ranges are 

chosen such that the instrument responds in the upper 30% of scale for the range in use. While this may not 

always be possible it should be a goal. 

The principal performance specification shall be as follows: 

CO Analyser 

a) Total range: 0 to 2 500 ppm in appropriate ranges. 

b) Resolution: better than 0.5 per cent of full scale of range used or 1 ppm, whichever is greater. 

c) Repeatability: better than ±1 per cent of full scale of range used, or ±2 ppm, whichever is greater. 

d) Stability: better than ±2 per cent of full scale of range used or ±2 ppm, whichever is greater, in a 

period of 1 hour. 

e) Zero drift: less than ±l per cent of full scale of range used or ±2 ppm. whichever is greater, in a period 

of 1 hour. 

f) Noise: 0.5 Hz and greater, less than ±l per cent of full scale of range used or ±l ppm, whichever is 

greater. 

g) Interferences: to be limited with respect to indicated CO concentration as follows: 
 

Page 62 

1) less than 500 ppm/per cent ethylene concentration 
 Page 63 

Supplemental information

It is unlikely that high concentrations of ethylene will be found in gas turbine engine exhaust. The highest 

concentration of hydrocarbons is found at idle, corresponding to the highest concentrations of CO. If all of the 

hydrocarbons were ethylene, C2H4, and the concentration were 100% of the maximum range, 5,000 ppmC, – 

corresponding to 2,500 ppm ethylene, the allowable interference would be less than 125 ppm, or less than 

5% of the highest CO range, 2,500 ppm. Since the interference limit is in absolute terms, the relative error 

will increase for measurements made at less than full scale. If ethylene is present in significant 

concentrations then corrections to the data are required. 

2) less than 2 ppm/per cent CO2 concentration 

3) less than 2 ppm/per cent water vapour.* 

Supplemental information

These two interferents, CO2 and water vapor, are additive. Being the major products of combustion they 

increase and decrease together and are at their highest levels at the highest power. Unfortunately 

concentrations of CO tend to be at their lowest concentrations at the highest power. This can cause 

significant problems in the accuracy of the measurement even if the interference limits are met. It is not 

unusual for tests to be conducted with the sample dried before measurement and the interference due to the 

remaining interferent, CO2, compensated for through use of gas or optical filters. It does bear mentioning that 

the contribution of high power CO concentrations to the total gross CO emission measured over the LTO 

cycle is relatively small. 

If the interference limitation(s) for CO2 and/or water vapour cannot be met, appropriate correction factors 

shall be determined, reported and applied. 

Note.- It is recommended as consistent with good practice that such correction procedures be adopted in 

all cases. 

*Need not apply where measurements are on a "dry" basis. 

CO2 Analyser 

a) Total range: 0 to 10 per cent in appropriate ranges. 

Supplemental information

Although the total range specified for CO2 is 0 to 10% concentrations most often will vary between 1% and 

5%. This range is considerably narrower than that for CO. Never-the-less good practice dictates using 

ranges that keep the instrument response in the upper 30% of the meter scale as appropriate. 

b) Resolution: better than 0.5 per cent of full scale of range used or 100 ppm, whichever is greater. 

c) Repeatability: better than ±1 per cent of full scale of range used or ±100 ppm, whichever is greater. 

d) Stability: better than ±2 per cent of full scale of range used or ±100 ppm, whichever is greater, in a 

period of 1 hour. 

e) Zero drift: less than ±l per cent of full scale of range used or ±l00 ppm, whichever is greater, in a 

period of 1 hour. 

f) Noise: 0.5 Hz and greater, less than ±1 per cent of full scale of range used or ±100 ppm, whichever is 

greater. 

g) The effect of oxygen (O2) on the CO2 analyser response shall be checked. For a change from 0 per 
 

Page 64 

cent O2 to 21 per cent O2, the response of a given CO2 concentration shall not change by more than 2 

per cent of reading. If this limit cannot be met an appropriate correction factor shall be applied. 

Supplemental information

Gas turbine engines use a considerable amount of internal cooling air that mixes with the combustion 

products before exiting the engine. Oxygen rich exhaust samples warrant close attention. 

Note.— It is recommended as consistent with good practice that such correction procedures be adopted 

in all cases. 

CO and CO2 Analysers 

a) Response time: shall not exceed 10 seconds from inlet of the sample to the analysis system, to the 

achievement of 90 per cent of the final reading. 

b) Sample temperature: the normal mode of operation is for analysis of the sample in its (untreated) 

"wet" condition. This requires that the sample cell and all other components in contact with the 

sample in this sub-system be maintained at a temperature of not less than 50°C, with a stability of 

±2°C. The option to measure CO and CO2 on a dry basis (with suitable water traps) is allowed, in 

which case unheated analysers are permissible and the interference limits for H2O vapour removed, 

and subsequent correction for inlet water vapour and water of combustion is required. 

Supplemental information

Stability is defined in terms of a time interval which, because this is a temperature control set point, can be 

taken as the duration of the test, or one hour to be consistent with the stability limits placed on the detection 

system. 

The temperature quoted for the CO and CO2 subsystems, 50°C, is on the low end of the sample line 

specification, 65°C ±15°C. Good practice would suggest that the subsystem temperature be approximately 

the same as the sample gas temperature. If the samples are dried and the analyzers unheated, it would be 

reasonable to lower the sample temperature to that of the analyzer. If water is removed prior to analysis, 

corrections must be applied to compensate for the loss of water of combustion and inlet water vapor. 

Correction procedures are detailed in Attachment F of this Appendix. 

c) Calibration curves: 

i) Analyzers with a linear signal output characteristic shall be checked on all working ranges using 

calibration gases at known concentrations of approximately 0, 30, 60 and 90 per cent of full scale. 

The maximum response deviation of any of these points from a least squares straight line, fitted 

to the points and the zero reading, shall not exceed ±2 per cent of the full scale value. If it does 

then a calibration curve shall be prepared for operational use. 

Supplemental information

Straight line fits to sets of linear data can be arrived at graphically or analytically. If graphically, the results are 

subject to interpretation, i.e., best estimate by ‘eye’ by individual. If analytically, there is assurance that each 

case and all data are handled the same way each time. The most appropriate technique is to perform a linear 

regression, or ‘least-squares fit’ for a line. The calibration gas values are the independent “variables and are 

assumed to be correct (to have negligible error) for the purpose of this analysis. The instrument response 

values are the “dependent” variables and are assumed to have errors and that these errors are normally 

(Gaussian) distributed about the true line. The equation describing the straight line is: 

yi

 = A + B*xi

true value for response yi

 = A (a constant) + B (another constant) * (calibration gas value xi) 
 Page 65 

For instruments which have been adjusted such that zero input results in zero output, and where the variance in known to 

be proportional to the reading the slope B can be shown to be equal to the ratio of the averages and can be expressed as: 

Often A and B are not such simple values for intercept and slope but must be calculated as if the variance 

were not known to be proportional to the instrument response. Again if we set the instrument to read zero for 

zero gas input then A = 0 which makes the calculation relatively simple. The generalized expression for B 

can be found in any elementary statistics or error analysis text and is: 

Where xi

 is the calibration gas value and yi is the instrument response and N refers to the number of points 

used in the analysis. 

With N = 4, corresponding to 0, 30, 60 and 90% of full scale, this equation can be rewritten as: 

A simple table, for the four sets of values, can be used for organizing the information thereby simplifying the 

calculation: 

Measurement 

number i 

xi

cal. gas value i

yi

response i xi

2 xiyi 

1 

 

2 

3 

4 

N = 4 Σxi Σyi Σxi

2 Σxi yi

If the instrument is not set to zero-zero (zero response for zero input) then A must be determined. The 

equation for A is (for N = 4) is: 

y

x
 

Page 66 

The table shown earlier can be used to organize the elements of this equation as well. 

Usually the next step would be to calculate the uncertainty in yi

 about this line. However, instead of 

controlling uncertainty about the line, ICAO chose to set an absolute limit of ±2% deviation of the full scale 

value for each point. This should make clear the advantage in using the upper region (top 30%) of the range 

for all measurements. 

ii) Analyzers with a non-linear signal output characteristic, and those that do not meet the 

requirements of linearity given above, shall have calibration curves prepared for all working 

ranges using calibration gases at known concentrations of approximately 0, 30, 60 and 90 per 

cent of full scale. Additional mixes shall be used, if necessary, to define the curve shape properly. 

Supplemental information

For analyzers with a non-linear signal output characteristic calibration curves shall be prepared, again using 

approximately 0, 30, 60 and 90% of full scale calibration gases. If a curve is substantially non-linear in shape, 

it is recommended that additional calibration gases be used with values between the ones specified. These 

calibration curves can be determined analytically using a least squares fit, but in this case the fit would be to a 

polynomial or exponential. The equations for doing this can be found in any basic text on statistics or error 

analysis. It should be noted that for exponential fits it is often convenient to work with the logarithm of the 

expression, which reduces the problem to a least-squares-fit about a line as is described above. (This 

technique is used in analyzing smoke filters as required in 3.0 of Appendix 2). Although not stated explicitly, 

the presumption is that the same ±2% of full scale response deviation is true for non-linear as well as linear 

instruments. The use of a gas divider is an acceptable alternative to acquiring and maintaining additional gas 

resources. 
 Page 67 

Table A3-2 summarizes the specifications for CO and CO2 analyzers. These are typical of those analyzers 

offered by major analyzer manufacturers. 

Table A3-2 NDIR ANALYZER PERFORMANCE SPECIFICATIONS 

Value 

Parameter CO2 CO

Total Range 0 to 10% in appropriate 

ranges 

0 to 2 500 ppm in 

appropriate ranges 

Resolution better than 0.5% fs 

range used or 100 ppm 

whichever greater 

better than 0.5% fs range 

used or 1 ppm whichever 

greater 

Repeatability better than ±1% fs 

range used or ±100 

ppm whichever greater 

better than ±1% fs range 

used or ±2 ppm whichever 

greater 

Stability better than ±2% fs 

range used or ±100 

ppm whichever greater 

period of 1 hr 

better than ±2% fs range 

used or ±2 ppm whichever 

greater period of 1 hr 

Zero Drift < ±1% fs range used or 

±100 ppm whichever 

greater period of 1 hr 

< ±1% fs range used or 

±2 ppm whichever greater 

period of 1 hr 

Noise ≥0.5 Hz, <±1% fs range 

used or ±100 ppm, 

whichever greater 

≥0.5 Hz, <±1% fs range 

used or ±1 ppm, 

whichever greater 

Interference ≤ 2% of reading for O2

between 0 and 21% 

<500 ppm/% ethylene 

<2 ppm/% CO2

<2 ppm/% water vapor 

Response 

Time 

≤10 seconds from 

instrument inlet to 

90% fs 

≤10 seconds from 

instrument inlet to 

 90% fs 

Sample 

Temperature 

wet samples ≥50°C 

stability ± 2°C 

wet samples ≥50°C 

stability ± 2°C 
 

Page 68 

ATTACHMENT C TO ICAO MANUAL APPENDIX 3. 

SPECIFICATION FOR NOX ANALYSER 

Note. — See Attachment D for information on calibration and test gases. 

1. As indicated in 5.4 of Appendix 3, the measurement of the oxides of nitrogen concentration. shall be 

by the chemiluminescent technique in which radiation emitted by the reaction of NO and O3 is 

measured. This method is not sensitive to NO2 and therefore the sample shall be passed through a 

converter in which NO2 is converted to NO before the measurement of total NOX is made. Both the 

original NO and the total NOX concentrations shall be recorded. Thus by difference, a measure of the 

NO2 concentration shall be obtained. 

2. The instrument to be used shall be complete with all necessary flow control components, such as 

regulators, valves, flowmeters, etc. Materials in contact with the sample gas shall be restricted to 

those, which are resistant to attack by oxides of nitrogen, such as stainless steel, glass, etc. The 

temperature of the sample shall everywhere be maintained at values, consistent with the local 

pressures, which avoid condensation of water. 

Precautions: The performance specifications indicated are generally for analyzer full scale. Errors at 

part scale may be a significantly greater percentage of reading. The relevance and importance of 

such increases shall be considered when preparing to make measurements. If better performance is 

necessary, then appropriate precautions shall be taken. 

Supplemental information

The performance specifications for these analyzers given in terms of full scale response can have a 

significant and adverse impact on part scale measurements. This needs to be considered when planning and 

executing the test and in evaluating the accuracy of the measurements after the test. Concentrations of NOX, 

when going from the idle mode to take-off, can differ by orders of magnitude. In general, where 

concentrations of species to be measured are known to vary this way, it is always good practice to use a 

multi-range instrument, and to choose ranges such as to keep the measurement in the upper 30% of scale on 

the range in use. A measurement made at 20% of full scale could result in an error 5 times the error specified 

as a percent of full scale. This is a general precaution. Some modern instruments with internal electronic 

ranging and calibration capability can be used over their entire range without penalty. Calibrations should be 

performed on each range used as required. 

3. The principal performance specification, determined for the instrument operated in an ambient 

temperature stable to within 2°

C, shall be as follows: 

a) Total range: 0 to 2 500 ppm in appropriate ranges. 

b) Resolution: better than 0.5 per cent of full scale of range used or 1 ppm, whichever is greater. 

c) Repeatability: better than ±l per cent of full scale of range used, or ±1 ppm, whichever is greater. 

d) Stability: better than ±2 per cent of full scale of range used or ±l ppm, whichever is greater, in a 

period of 1 hour. 

e) Zero drift: less than ±1 per cent of full scale of range used or ±1 ppm, whichever is greater, in a 

period of 1 hour. 

f) Noise: 0.5 Hz and greater, less than ±1.0 per cent of full scale of range used or ±l ppm, 

whichever is greater, in a period of 2 hours. 
 Page 69 

g) Interference: suppression for samples containing CO2 and water vapour shall be limited as 

follows: 

— less than 0.05 per cent reading/per cent CO2 concentration; 

— less than 0.1 per cent reading/per cent water vapour concentration. 

If the interference limitation(s) for CO2 and/or water vapour cannot be met, appropriate correction factors 

shall be determined, reported, and applied. 

Note.- It is recommended as consistent with good practice that such correction procedures be adopted in 

all cases. 

h) Response time: shall not exceed 10 seconds from inlet of the sample to the analysis system to 

the achievement of 90 per cent of the final reading. 

i) Linearity: better than ±2 per cent of full scale of range used or ±2 ppm, whichever is greater. 

j) Converter: this shall be designed and operated in such a matter as to reduce NO2 present in the 

sample to NO. The converter shall not affect the NO originally in the sample. 

Supplemental information

Correction: ...”in such a matter” ... “should read” ... “in such a manner” ... . 

The converter efficiency shall not be less than 90 per cent. 

This efficiency value shall be used to correct the measured sample NO2 value (i.e. [NOX]c - [NO]) to that 

which would have been obtained if the efficiency had not been 100 per cent. 

Supplemental information

The last sentence should read as follows: 

“This efficiency value shall be used to correct the measured sample NO2 value (i.e. [NOX]c –[NO]) to that 

which would have been obtained if the efficiency had been 100 per cent.” 

A procedure for determining the NO2 to NO conversion efficiency, in the absence of any specific 

manufacturer’s instructions, may be found in 40 CFR Part 87, Control of Air Pollution from Aircraft and Aircraft 

Engines, Federal Register, Vol. 43, No. 58 — Friday, March 24, 1978. It was taken, in turn, from SAE 

ARP1256, "Procedure for the Continuous Sampling and Measurement of Gaseous Emissions from Aircraft 

Turbine Engines". 
 

Page 70 

Figure A3-5: NOx Converter Efficiency Detector Schematic 

Figure A3-5 schematically depicts such a device. This device is intended for use with the NOX analyzer 

specified in Attachment C. It depends on the reaction: NO + O3 = NO2 + O2 

Starting with a known concentration of NO in N2, measurements are made through – and bypassing – the 

chemiluminsecence analyzer converter, the inlet to which is shown as “C3” in the diagram. With the NOX

converter ozonator alternately on, reducing the NO concentration by approximately 80%, and off, allowing 

100% of the NO to reach the analyzer the analyzer’s converter efficiency can be determined. This efficiency 

should be used to correct test data as required. 

The specific instructions for using this device, from 40 CFR part 87, are as follows: 

(i) Attach the NO/N2 supply (150-250 ppm.) at “C2”, the O2 supply at “C1”, and the analyzer inlet 

connection to the efficiency detector at C3. If lower concentrations of NO are used, air may be used in 

place of O2 to facilitate better control of the NO2 generated during step (iv). 

(ii) With the efficiency detector Variac (Note: SAE uses the term autotransformer) off, place the NOX

converter in bypass mode and close valve “V3”. Open valve “MV2” until sufficient flow and stable 

readings are obtained at the analyzer. Zero and span the analyzer output to indicate the value of the 

NO concentration being used. Record this concentration. 

(iii) Open valve V3 (on/off flow control solenoid valve for O2) and adjust valve “MV1” (O2 supply metering 

valve) to blend enough O2 to lower the NO concentration (ii) to about 10 percent. Record this 

concentration. 

(iv) Turn on the ozonator and increase its supply voltage until the NO concentration of (iii) is reduced to 

about 20 percent of (ii). NO is now being formed from the NO + O2 reaction. There must always be at 

least 10 percent unreacted NO at this point. Record this concentration. 

(v) When a stable reading has been obtained from (iv), place the NOX converter in the convert mode. The 

analyzer will now indicate the total NOX concentration. Record this concentration. 

(vi) Turn off the ozonator and allow the analyzer reading to stabilize. The mixture NO + O3 is still passing 

through the converter. This reading is the total NOX concentration of the dilute NO span gas used in 

step (iii). Record this concentration. 
 Page 71 

(vii) Close valve V3. The NO concentration should be equal to or greater than the reading of (ii) indicating 

whether the NO contains any NO2. 

Calculate the efficiency of the NOX converter by substituting the concentrations obtained during the test into 

the following equation: 

% . Eff = −

− × (v) (iv)

(vi) (iv)

100%

To improve the effectiveness of thermal converters, particularly those with efficiencies of less than 90%, it is 

sometimes helpful to raise the temperature of the converter. 

Table A3-3 NOX ANALYZER PERFORMANCE SPECIFICATION 

Parameter Value

Total Range 0 to 2 500 ppm in appropriate ranges 

Resolution better than 0.5 percent full scale range 

used or 1 ppm whichever is greater 

Repeatability better than ±1 percent full scale range 

used or 1 ppm whichever is greater 

Stability better than ±2 percent full scale range 

used or ±1 ppm whichever is greater in 

a period of 2 hours 

Zero Drift < ±1 percent full scale range used 

or ±1 ppm, whichever is greater in a 

period of 2 hours 

Noise ≥0.5 Hz, <±1 percent fs range used or ±1 

ppm, whichever greater period of 2 hours 

Interference < 0.05 percent reading/ percent CO2

< 0.1 percent reading/ percent water 

vapor 

Response Time ≤ 10 seconds from inlet of sample to 

achieve 90 percent of final reading 

Linearity better than ±2 percent full scale for each 

range used or ± 2ppm, whichever 

greater 

Converter 

Efficiency 

≥ 90 percent 

Table A3-3 summarizes the specifications for NOx analyzers. These are typical of those analyzers offered by 

major analyzer manufacturers. 
 

Page 72 

ATTACHMENT D TO ICAO MANUAL APPENDIX 3. 

CALIBRATION AND TEST GASES 

Table of calibration gases 

Analyzer Gas Accuracy* 

HC 

CO2 

CO

NOx

propane in zero air 

CO2 in zero air 

CO in zero air 

NOx in zero nitrogen 

±2 per cent or ±0.05 ppm** 

±2 per cent or ±100 ppm** 

±2 per cent or ±2 ppm** 

±2 per cent or ±1 ppm** 

* Taken over the 95 per cent confidence interval. 

 ** Whichever is greater 

The above gases are required to carry out the routine calibration of analyzers during normal operational use.

Analyzer Gas Accuracy* 

HC propane in l0 ±1 per 

cent O2 balance zero 

nitrogen 

±1 per cent 

HC propane in 21 ±1 per 

cent O2 balance zero 

nitrogen 

±l per cent 

HC propylene in zero air ±l per cent 

HC toluene in zero air ±l per cent 

HC n-hexane in zero air ±l per cent 

HC propane in zero air ±1 per cent 

CO2 CO2 in zero air ±1 per cent 

CO2 

CO 

CO2 in zero nitrogen 

CO in zero air 

±1 per cent 

±1 per cent 

NOx NO in zero nitrogen ±1 per cent 

* Taken over the 95 per cent confidence interval 

The above gases are required to carry out the tests of Attachments A, B, and C. 

Carbon monoxide and carbon dioxide calibration gases may be blended singly or as dual component mixtures. 

Three component mixtures of carbon monoxide, carbon dioxide, and propane in zero air may be used, provided the 

stability of the mixture is assured. 
 Page 73 

Zero gas as specified for the CO, CO2 , and HC analyzers shall be zero air (which includes "artificial" air with 20 to 

22 per cent O2 blended with N2). For the NOX analyzer zero nitrogen shall be used as the zero gas. Impurities in 

both kinds of zero gas shall be restricted to be less than the following concentrations: 

 1 ppm C

 1 ppm CO

 100 ppm CO2

 1 ppm NOx

The applicant shall ensure that commercial gases supplied to him do in fact meet this specification, or are 

so specified by the vendor. 

Supplemental information

Calibration and test gases are readily available, with traceability to the National Institute of Standards and 

Technology (NIST), from commercial suppliers. Gases with an accuracy of ± 1% are considered “primary” 

standards and intended for use where the highest accuracy and reliability are needed. Very tight controls 

over cylinder material, age, and history are considered good practice, if not essential. Periodic checks of the 

accuracy of assay for each cylinder is advisable. Gases such as CO, CO2, and propane with a certified 

accuracy of ± 2% can be obtained as multi-component mixtures. This will reduce the number of gas cylinders 

needed for testing. The importance of this becomes obvious when considering the calibration requirements 

for each instrument and each range. Managing just the minimum number of calibration and test gases can be 

challenging. For example, an average certification test, when backup gases are counted, can require 100 two 

component cylinders, or more. The stability of the components in each mixture should be checked 

periodically. If the assay no longer agrees with the certified analysis, the cylinder should be returned to the 

supplier or discarded as appropriate. 

Because of the accuracy required and the sophistication of the techniques necessary to produce and analyze 

gases to these standards, most testing laboratories rely on the commercial suppliers analysis and certification 

for primary accuracy and use in-house checks via instrument response for consistency of assay. It is good 

practice to recheck all calibration and working standard gases immediately prior to a certification test. 

All calibration gas monitoring data should be kept and made available to the certificating agency if required. 

Although not a calibration gas or, strictly speaking, a test gas, the FID analyzer fuel and oxidant gases should 

also meet a hydrocarbon specification. For hydrogen/nitrogen or hydrogen/helium fuel mixtures, total 

hydrocarbons present should be < 1 ppmC. The oxidant should be hydrocarbon free grade air, containing < 1 

ppmC hydrocarbon. The SAE in ARP 1256 restricts the FID fuel gas to a 40% hydrogen, 60% helium mixture 

which is required to meet this hydrocarbon level specification. 
 

Page 74 

ATTACHMENT E TO ICAO MANUAL APPENDIX 3. THE CALCULATION OF THE EMISSIONS 

PARAMETERS - BASIS, MEASUREMENT CORRECTIONS AND 

ALTERNATIVE NUMERICAL METHOD 

1. SYMBOLS P7 number of moles of NO2 in the exhaust 

sample per mole of fuel 

AFR air/fuel ratio, the ratio of the mass flow 

rate of dry air to that of the fuel 

P8 number of moles of NO in the exhaust 

sample per mole of fuel

El emission index; l03

 x mass flow rate of 

gaseous emission product in exhaust 

per unit mass flow rate of fuel 

PT P1 + P2 + P3 + P4 + P5 + P6 + P7 + P8

K ratio of concentration measured wet to 

that measured dry (after cold trap) 

R concentration of O2 in dry air, by volume 

= 0.2095 normally

L, L' analyzer interference coefficient for 

interference by CO2

S concentration of N2 + rare gases in dry 

air, by volume = 0.7902 normally

M, M' analyzer interference coefficient for 

interference by H2O

T concentration of CO2 in dry air, by 

volume = 0.0003 normally

MAIR molecular mass of dry air = 28.966 g 

or, where appropriate, = (32 R + 

28.156 4 S + 44.011 T) g 

P0 number of moles of air per mole of fuel in 

initial air/fuel mixture

MCO molecular mass of CO = 28.011 g Z symbol used and defined in 3.4

MHC molecular mass of exhaust 

hydrocarbon, taken as CH4 = 16.043 g 

[CO2] mean concentration of CO2 in exhaust 

sample, vol/vol

MNO2 molecular mass of NO2 = 46.008 g [CO] mean concentration of CO in exhaust 

sample, vol/vol 

MC atomic mass of carbon = 12.011 g [HC] mean concentration of HC in exhaust 

sample, vol C/vol 

MH atomic mass of hydrogen = 1.008 g [NO] mean concentration of NO in exhaust 

sample, vol/vol 

P1 number of moles of CO2 in the exhaust 

sample per mole of fuel

[NO2] mean concentration of NO2 in exhaust 

sample, vol/vol 

P2 number of moles of N2 in the exhaust 

sample per mole of fuel

[NOX] mean concentration of NO and NO2 in 

exhaust sample, vol/vol 

P3 number of moles of O2 in the exhaust 

sample per mole of fuel

[NOX]c mean concentration of NO in exhaust 

sample. after passing through the 

N02/NO converter, vol/vol 

P4 number of moles of H2O in the exhaust 

sample per mole of fuel 

[NO2] mean = ([NOX]c -[NO])

 η

P5 number of moles of CO in the exhaust 

sample per mole of fuel 

[ ]d mean concentration in exhaust sample 

after cold trap, vol/vol

P6 number of moles of CxHy in the 

exhaust sample per mole of fuel

[ ]m mean concentration measurement 

indicated before instrument correction 

applied, vol/vol
 Page 75 

h humidity of ambient air, vol water/vol dry air 

hd humidity of exhaust sample leaving "drier" or "cold trap", vol water/vol dry sample 

rn number of C atoms in characteristic fuel molecule 

n number of H atoms in characteristic fuel molecule 

x number of C atoms in characteristic exhaust hydrocarbon molecule 

y number of H atoms in characteristic exhaust hydrocarbon molecule 

η efficiency of NO2/NO converter 

2. BASIS OF CALCULATION OF El AND AFR PARAMETERS 

2.1 It is assumed that the balance between the original fuel and air mixture and the resultant state of 

the exhaust emissions as sampled can be represented by the following equation: 

CmHn + P0[R(O2) + S(N2) + T(CO2) + h(H2O)] 

 = P1(CO2) + P2(N2) + P3(O2) + P4(H2O) + P5(CO) + P6(CxHy) + P7(NO2) + P8(NO) 

from which the required parameters can, by definition, be expressed as 

expressed as methane equivalent 

( )

3 10

2 EI(NO ) X 78

M NO

P P

mM nM C H

⎡ ⎤

⎢ ⎥

= + ⎢ ⎥

⎢ ⎥ +

⎢ ⎥ ⎣ ⎦

expressed as NO2 equivalent 

AIR

0

C H

AFR M P

mM nM

⎛ ⎞ ⎜ ⎟ ⎝ ⎠ = =

3 10

EI(CO) 5

MCO P

mM nM C H

⎛ ⎞ ⎜ ⎟ = ⎜ ⎟ + ⎝ ⎠

3 10

EI(HC) 6

MHC xP

mM nM C H

⎛ ⎞ ⎜ ⎟ = ⎜ ⎟ + ⎝ ⎠
 

Page 76 

Supplemental information

This is a slightly different formulation for AFR than that stated in 7.1.2, “Basic parameters”. In this formulation 

m, the “number of C atoms in characteristic fuel molecule” is placed within the bracket. There is no particular 

advantage to using one formulation over the other. 

2.2 Values for fuel hydrocarbon composition (rn, n) are assigned by fuel specification or analysis. If only 

the ratio n/m is so determined, the value m = 12 may be assigned. The mole fractions of the dry air 

constituents (R, S, 7) are normally taken to be the recommended standard values but alternative 

values may be assigned, subject to the restriction R + S + T = 1 and the approval of the certificating 

authority. 

2.3 The ambient air humidity, h, is as measured at each test condition. It is recommended that, in the 

absence of contrary evidence as to the characterization (x, y) of the exhaust hydrocarbon, values of 

x = I and y = 4 are assigned. 

2.4 Determination of the remaining unknowns requires the solution of the following set of linear 

simultaneous equations, where (1) to (4) derive from the fundamental atomic conservation 

relationships and (5) to (9) represent the gaseous product concentration relationships. 

(1) M = TP0 = P1 + P5 + xP6

(2) n + 2hP0 = 2P4 + yP6

(3) (2R + 2T + h)P0 = 2P1 + 2P3 + P4 + P5 + 2P7 + P8

(4) 2SP0 = 2P2 + P7 + P8

(5) [CO2] PT = P1

(6) [CO] PT = P5

(7) [HC] PT = Xp6

(8) [NOX]C PT = P7 + P8

(9) [NO] PT = P8

(10) PT = P1 + P2 + P3 + P4 + P5 + P6 + P7 + P8

The above set of conditional equations is for the case where all measured concentrations are true ones, 

that is, not subject to interference effects or to the need to correct for sample drying. In practice, 

interference effects are usually present to a significant degree in the CO, NOX and NO

measurements, and the option to measure CO2 and CO on a dry or partially dry basis is often used. 

The necessary modifications to the relevant equations are described in 2.5 and 2.6. 

2.5 The interference effects are mainly caused by the presence of CO2 and H2O in the sample which can 

affect the CO and the NOX analysers in basically different ways. The CO analyzer is prone to a 

zero-shifting effect and the NOX analyzer to a sensitivity change, represented thus: 

[CO] = [CO]m + L[CO2] + M[H2O] 

and [NOX]c = [NOX]cm(1 + L'[CO2] + M'[H2O]) 
 Page 77 

which transform into the following alternative equations to (6), (8) and (9), when interference effects 

require to be corrected, 

(6A) [CO]m PT + LP1 + MP4 = P5

(8A) [NOX]cm (PT +L'P1 +M'P4) = P7 + P8

(9A) [NO]m (PT + L'P1 + M'P4) = P8

The option to measure CO2 and CO concentrations on a dry or partially dry sample basis, that is, with a 

sample humidity reduced to h,, requires the use of modified conditional equations as follows: 

(5A) [CO2]d(PT - P4)(1 + hd) = P1

and 

[CO]d (PT - P4)(1 + hd) + P5

 However, the CO analyzer may also be subject to interference effects as described in 2.5 above 

and so the complete alternative CO measurement concentration equation becomes 

(6B) [CO]md (PT - P4)(1 + hd) + LP1 + Mhd (PT - P4) = P5

3. ANALYTICAL FORMULATIONS 

3.1 General 

Equations (1) to (10) can be reduced to yield the analytical formulations for the EI and AFR parameters, 

as given in 7.1 to this appendix. This reduction is a process of progressive elimination of the roots P0, P1

through P8, PT making the assumptions that all concentration measurements are of the "wet" sample and 

do not require interference corrections or the like. In practice the option is often chosen to make the CO2

and CO concentration measurements on a "dry" or "semi-dry" basis; also it is often found necessary to 

make interference corrections. Formulations for use in these various circumstances are given in 3.2, 3.3 

and 3.4 below. 

3.2 Equation for conversion of 

dry concentration measurements 

to wet basis 

Concentration wet = K x concentration dry; that is. 

 [ ] = K [ ]d

The following expression for K applies when CO and CO2 are determined on a "dry" basis: 

{ ( ) ( )([ ] [] ( )) ( )( )[ ]}( )

( ) ( )( ) { } ( ) [ ] ( )( ) [ ]

2

2

4 / | | 2 NO 2 HC / 2 | | | HC 1

2 2 / 1 CO | | 2 1 |1 | CO

d

d d d d

n mT nmT h x h y x nm h

K

h n m h nmT h h

+ + − − ++ − + = + + + − − −+
 

Page 78 

3.3 Interference corrections 

The measurement of CO and/or NO may require corrections for interference by the sample CO2 and 

water concentrations before use in the above analytical equations. Such corrections can normally be 

expressed n the following general ways: 

[CO CO CO H O ] [ ] [ 2 2 ] [ ] m =+ + L M 

[][] [ ] CO CO CO2 1

d

d md d

d

h L M

h

⎛ ⎞

=+ + ⎜ ⎟ ⎝ ⎠ +

[NO NO 1 ' CO ' H O ] [ ] ( ) [ 2 2 ] [ ] m = ++ L M

[NO NO NO 1 ' CO ' H O 2X 2 2 ] ( ) [ ] [ ] ( [ ] [ ]) cm m η = − ++ L M

3.4 Equation for estimation of sample water content 

Water concentration in sample 

[ ] ( )([ ] [ ] [ ])

( ) ( )[ ] 0 2

2

0

| 2 | P | CO CO HC H O 2 HC

1 P

nmh m

y x T m

+ ++ = − +

Where 

( )

( ) 0

2

P

4 1 | 2|

Z nm

m

h TZ

− = + −

and 

[ ] ( )[ ] [ ]

[ ][ ][ ]

2

2

2 CO | 2 | | 2 | HC NO

CO CO HC

x yx Z−− − + = + +

It should be noted that this estimate is a function of the various analyses concentration readings, which 

may themselves require water interference correction. For better accuracy an iterative procedure is 

required in these cases with successive recalculation of the water concentration until the requisite stability 

is obtained. The use of the alternative numerical solution methodology (4) avoids this difficulty. 
 Page 79 

4. ALTERNATIVE METHODOLOGY -NUMERICAL SOLUTION 

4.1 As an alternative to the analytical procedures summarized in 3 above, it is possible to obtain 

readily the emissions indices, fuel/air ratio, corrected wet concentrations, etc., by a numerical 

solution of equations (1) to (10) for each set of measurements, using a digital computer. 

4.2 In the equation set (1) to (10) the actual concentration measurements are substituted using 

whichever of the alternative equations (5A), (6A), etc. applies for the particular measuring system, 

to take account of interference corrections and/or dried sample measurements. 

4.3 Suitable simple two-dimensional array equation-solving computer programmes are widely 

available and their use for this purpose is convenient and flexible, allowing ready incorporation 

and identification of any sample drying options and interference or other corrections. 

Supplemental information

Details explaining various calculation procedures can be found in AeroSpace Recommended Practice (ARP) 

1533, Procedure for the Calculation of Gaseous Emissions from Aircraft Turbine Engines. ARP 1533 

includes, among other things, the combustion chemical equations, the basic matrix solution with computer 

programs, derivation of equations and a sample calculation. 
 

Page 80 

[THIS PAGE INTENTIONALLY LEFT BLANK]
 Page 81 

XI. ICAO MANUAL APPENDIX 5 

INSTRUMENTATION AND MEASUREMENT TECHNIQUES 

FOR GASEOUS EMISSIONS FROM 

AFTERBURNING GAS TURBINE ENGINES 

1. INTRODUCTION 

Note.- The procedures specified in this appendix are concerned with the acquisition of 

representative exhaust samples and their transmission to, and analysis by, the emissions 

measuring system. These procedures only apply when afierburning is employed. The methods 

proposed are representative of the best readily available and most established modern practice. 

The need to correct for ambient conditions is recognized and a method will be specified when one 

becomes available. Meanwhile any correction methods used when afterburning is employed 

should be approved by the certificating authority. 

Variations in the procedure contained in this appendix shall only be allowed after prior application 

to and approval by the certificating authority. 

Supplemental information

This sampling and analytical procedure only applies to afterburning engines, while operating in the 

afterburning mode. Smoke and gaseous emissions levels in the exhaust plume of these engines, 

while in the non-afterburning mode, are determined using the standard procedures described in ICAO 

Annex 16, Volume II, Appendices 2 and 3. Smoke is not measured during afterburning operation. 

Experience in sampling and analyzing emissions in the plume of afterburning engines is sparse, and 

the resultant methodology not as well proven as for non-afterburning engines. In fact no effort, similar 

to that which resulted in SAE AeroSpace Recommended Practice ARP 1256, for non-afterburning 

engines, has emerged for the afterburning case. 

Sampling in the same region as required for non-afterburning engines would involve highly cooled 

and robust sampling probes, an understanding of the reaction chemistry in the exhaust plume and a 

detailed history of the gaseous species as they proceeded downstream to a point where the reaction 

could be considered complete or frozen. An alternative approach, and that adopted in ICAO Appendix 

5, is to sample sufficiently far downstream to be in the well mixed, turbulent and relatively cool region 

of the plume where all reactions, for all practical purposes, have ceased. Having taken this approach, 

ICAO does make allowance for alternatives, providing their viability can be demonstrated to the 

certificating authority. 

The analytical instrumentation used for non-afterburning engines has been found suitable for 

measuring gaseous emissions from afterburning engines with due care to be taken for measuring low 

concentration levels resulting from mixing the engine exhaust plume with ambient air. This mixing, 

with its resulting low concentrations suggests that close attention be paid to the ambient levels of CO, 

CO2, HC, and NOX. Proven methods for incorporating ambient corrections into these calculations 

have not been fully developed and are left to the testing agency to develop, use and validate. 

The sampling and analytical methods recommended in Appendix 5 were likely influenced by the work 

of T. F. Lyon, et al, on military engines, (under U.S. Air Force contract – AFAPL-TR-75-52, 

“Development of Emissions Measurement Techniques for Afterburning Turbine Engines”, T. F. Lyons, 

et al, General Electric Company, 1 1 Apr 73 – 31 Mar 75). Considerable insight can be gained from 

this report particularly in regard to sampling and validating the data. Validating data obtained in the 

far plume requires the assumption that the individual species CO, HC, and NOX, relative to CO2, form 
 

Page 82 

linearly related, bivariate Gaussian normal data sets to a high degree and for which correlation 

coefficient calculations are meaningful. The Lyon, et al, data seems to bear out this assumption. 

2. DEFINITIONS 

Where the following expressions are used without further explanation in this appendix, they have 

the meanings ascribed to them below: 

Accuracy. The closeness with which a measurement approaches the true value established 

independently. 

Calibration gas. A high accuracy reference gas to be used for alignment, adjustment and 

periodic checks of instruments. 

Concentration. The volume fraction of the component of interest in the gas mixture - expressed 

as volume percentage or as parts per million. 

Flame ionization detector. A hydrogen-air diffusion flame detector that produces a signal 

nominally proportional to the mass-flow rate of hydrocarbons entering the flame per unit of time - 

generally assumed responsive to the number of carbon atoms entering the flame. 

Interference. Instrument response due to presence of components other than the gas (or vapour) 

that is to be measured. 

Noise. Random variation in instrument output not associated with characteristics of the sample to 

which the instrument is responding, and distinguishable from its drift characteristics 

Non-dispersive infra-red analyzer. An instrument that by absorption of infra-red energy 

selectively measures specific components. 

Parts per million (ppm). The unit volume concentration of a gas per million unit volume of the 

gas mixture of which it is a part. 

Parts per million carbon (ppmC). The mole fraction of hydrocarbon multiplied by 106 measured 

on a methane-equivalence basis. Thus, 1 ppm of methane is indicated as 1 ppmC. To convert 

ppm concentration of any hydrocarbon to an equivalent ppmC value, multiply ppm concentration 

by the number of carbon atoms per molecule of the gas. For example, 1 ppm propane translates 

as 3 ppmC hydrocarbon; 1 ppm hexane as 6 ppmC hydrocarbon 

Plume. Total external engine exhaust flow, including any ambient air with which the exhaust 

mixes. 

Reference gas. A mixture of gases of specified and known composition used as the basis for 

interpreting instrument response in terms of the concentration of the gas to which the instrument 

is responding. 

Repeatability. The closeness with which a measurement upon a given, invariant sample can be 

reproduced in short-term repetitions of the measurement with no intervening instrument 

adjustment. 

Resolution. The smallest change in a measurement which can be detected. 

Response. The change in instrument output signal that occurs with change in sample 

concentration. Also the output signal corresponding to a given sample concentration. 
 Page 83 

Stability. The closeness with which repeated measurements upon a given invariant sample can 

be maintained over a given period of time. 

Zero drift Time-related deviation of instrument output from zero set point when it is operating on 

gas free of the component to be measured. 

Zero gas. A gas to be used in establishing the zero, or no-response, adjustment of an instrument. 

3.1 Gaseous emissions 

Concentrations of the following emissions shall be determined: 

a) Hydrocarbons (HC): a combined estimate of all hydrocarbon compounds present in the 

exhaust gas. 

b) Carbon monoxide (CO). 

c) Carbon dioxide (CO2)

Note.- CO2 is not considered a pollutant but its concentration is required for calculation and check 

purposes. 

d) Oxides of nitrogen (NOx): an estimate of the sum of the two oxides, nitric oxide (NO) and 

nitrogen dioxide (NO2). 

e) Nitric oxide (NO). 

3.2 Other information 

In order to normalize the emissions measurement data and to quantify the engine test 

characteristics, other information in addition to the requirements of Chapter 3, 3.4 shall be 

provided as follows: 

- inlet temperature; 

- inlet humidity; 

- atmospheric pressure; 

- wind vectors relative to engine exhaust axis; 

- hydrogen/carbon ratio of fuel; 

- engine installation details; 

- other required engine parameters (for example, thrust, rotor speeds, turbine 

temperatures); 

- pollutant concentration data and statistical validation parameters. 

This data shall be obtained either by direct measurement or by calculation, as presented in 

Attachment F to this appendix. 

4. GENERAL ARRANGEMENT OF THE SYSTEM 

Owing to the reactive nature of the exhaust plume from engines using afterburning, it is 

necessary to ensure that the measured emissions do in fact correspond to those actually emitted 

into the surrounding atmosphere. This is achieved by sampling the plume sufficiently far 

downstream from the engine that the exhaust gases have cooled to a temperature where 

reactions have ceased. No desiccants, dryers, water traps or related equipment shall be used to 

treat the exhaust sample flowing to the oxides of nitrogen and the hydrocarbon analysis 

instrumentation. Requirements for the various component sub-systems are given in 5, but the 
 

Page 84 

following list gives some qualifications and variations: 

a) it is assumed that each of the various individual subsystems includes the necessary flow 

control, conditioning and measurement facilities; 

b) the necessity for a dump and/or a hot-sample pump will depend on the ability to meet the 

sample transfer time and analysis sub-system sample flow rate requirements. This in turn 

depends on the exhaust sample-driving pressure and line losses. It is considered that 

these pumps usually will be necessary at certain engine running conditions; and 

c) the position of the hot pump, relative to the gas analysis sub-systems, may be varied as 

required. (For example, some HC analysers contain hot pumps and so may be judged 

capable of being used upstream of the system hot pump) 

Note.- Figures A5-1 and A5-2 are schematic drawings of the exhaust gas sampling and analytical 

system and typify the basic requirements for emissions testing 

Figure A5-1. Exhaust gas sampling system, schematic 
 Page 85 

Figure A5-2. Sample transfer and analysis system, schematic 

Supplemental information

In contrast to non-afterburning jet engine exhaust, local temperatures in the plume of an afterburning 

engine can be extremely high (in excess of 2,000° C) and very reactive. Measuring emissions in the 

hot, reactive part of the exhaust plume places a heavy burden on probe design and provides no 

assurance that the species measured are those which eventually contribute to atmospheric pollution. 

It is possible to calculate the final combustion products from species measured in the reacting flow. 

The methods however are complex, error prone, and the results subject to question. 

Additionally, the concentration profiles in the plane of the exhaust plume immediately downstream of 

the engine exhaust nozzle are highly variable and make obtaining a representative sample difficult, 

time consuming and costly. Sampling at some distance downstream of the nozzle exit takes 

advantage of the turbulent mixing in the plume which serves to cool the gases to the point where 

chemical reactions cease, and to smooth the concentration profiles, making sampling easier. This 

occurs through mixing of the exhaust gases with ambient air. This dilution must be accounted for 

when the data are analyzed and calculations are made. 

Depending on the amount of dilution, special care may be required in having suitable concentration 

ranges for the analytical instruments. This will be true of the calibration and standard gases as well. 

Because the products of combustion are the same for non-afterburning and afterburning engines, the 

same cautions apply to both. 
 

Page 86 

The following diagram, Figure A5-3, from AFAPL-TR-75-52, illustrates the degree of severity of the 

problem: 

Figure A5-3 Exhaust Concentration Profile 

5. DESCRIPTION OF COMPONENT PARTS 

Note.— A general description and specification of the principal elements in the engine exhaust 

emissions measurement system follows. Greater detail, where necessary, will be found in 

Attachments A, B and C to this appendix. 

5.1 Sampling system 

5.1.1 Sampling probe 

a) The probe shall be constructed so that individual samples can be withdrawn at 

various locations across a diameter of the plume. Mixed samples shall not be 

permitted. 

b) The material with which the sample is in contact shall be stainless steel and its 

temperature shall be maintained at a value not less than 600C. 

c) The sampling plane shall be perpendicular to the projected engine nozzle centre 

line, and shall be situated as close as possible to a position 18 nozzle diameters 

from the nozzle exit plane, consistent with 7.1.2, but in no case greater than 25 

nozzle diameters. The nozzle exit diameter shall be for the maximum engine 

power condition. Between and including exit and sampling planes there shall be 

an unobstructed region of at least 4 nozzle exit diameters in radial distance about 

the project engine nozzle centre line. 
 Page 87 

d) The minimum number of sampling points shall be equal to 11. The measurement 

plane, located at a distance X from the engine shall be divided into three sections 

demarcated by circles centred around the exhaust stream axis with radii 

R1 = 0.05X 

R2 = 0.09X 

and a minimum of 3 samples shall be taken from each section. The difference 

between the number of samples in each section must be less than 3. The sample 

taken at the most remote distance from the axis shall be from a point located at a 

radius of between 0.11X and 0.16X. 

5.1.2 Sampling lines 

The sample shall be transferred from the probe to the analysers via a line of 4.0 to 8.5 

mm inside diameter, taking the shortest route practicable and using a flow rate such that 

the transport time is less than 10 seconds. The line shall be maintained at a temperature 

of 1600C ±150C (with a stability of ±100C). When sampling to measure HC, CO, CO2 and 

NOx components, the line shall be constructed in stainless steel or carbon-loaded 

grounded PTFE. 

Supplemental information

To be consistent with appendix 5, Figure 5-2, “Sample transfer and analysis system, schematic”, this 

paragraph should be changed to read: 

“The sample shall be transferred from the probe to the analysers via a line of 4.0 to 8.5 mm inside 

diameter, taking the shortest route practicable and using a flow rate such that the transport time is 

less than 10 seconds. The line shall be maintained at a temperature of 1600

C ±150C (with a stability 

of ±100

C) except for the branch which supplies samples to the CO, CO2, and NOX analysers. This 

branch line shall be maintained at a temperature of 60°C ±150

C (with a stability of ±100C). When 

sampling to measure HC, CO, CO2 and NOx components, the line shall be constructed in stainless 

steel or carbon-loaded grounded PTFE.” 

5.2 HC analyzer 

The measurement of total hydrocarbon sample content shall be made by an analyzer using the 

heated flame ionization detector (FID), between the electrodes of which passes an ionization 

current proportional to the mass rate of hydrocarbon entering a hydrogen flame. The analyzer 

shall be deemed to include components arranged to control temperature and flow rates of 

sample, sample bypass, fuel and diluent gases, and to enable effective span and zero calibration 

checks. 

Note.- An over-all specification is given in Attachment A to this appendix. 

5.3 CO and CO2 analysers 

Non-dispersive infra-red analysers shall be used for the measurement of these components, and 

shall be of the design which utilizes differential energy absorption in parallel reference and 

sample gas cells, the cell or group of cells for each of these gas constituents being sensitized 

appropriately. This analysis sub-system shall include all necessary functions for the control and 

handling of sample, zero and span gas flows. Temperature control shall be that appropriate to 

whichever basis of measurement, wet or dry, is chosen. 

Note - An over-all specification is given in Attachment B to this appendix. 
 

Page 88 

5.4 NOX analyzer 

The measurement of NO concentration shall be by the chemiluminescent method in which the 

measure of the radiation intensity emitted during the reaction of the NO in the sample with added 

O3 is the measure of the NO concentration. The NO2 component shall be converted to NO in a 

converter of the requisite efficiency prior to measurement. The resultant NOX measurement 

system shall include all necessary flow, temperature and other controls and provide for routine 

zero and span calibration as well as for converter efficiency checks. 

Note.- An over-all specification is given in Attachment C to this appendix. 

6. GENERAL TEST PROCEDURES 

6.1 Engine operation 

The engine shall be operated on an open air static test facility which is suitable and properly 

equipped for high accuracy performance testing, and which conforms to the requirements for 

sampling probe installation as specified in 5.1. The emissions tests shall be made at the power 

settings prescribed by the certificating authority. The engine shall be stabilized at each setting. 

6.2 Ambient air conditions 

6.2.1 A check shall be made on the ambient concentrations of CO, HC, CO2 and NO, with the 

engine under test running at the test condition. Unusually high concentrations indicate 

abnormal conditions such as exhaust gas recirculation, fuel spillage or some other source 

of unwanted emissions in the test area and such situations shall be rectified or avoided 

as appropriate. 

Note.- For guidance, the normal ambient concentration of CO2 is 0.03 per cent, and ambient 

concentration levels for CO and HC of 5 ppm and NOX of 0.5 ppm are unlikely to be exceeded 

under normal conditions. 

6.2.2 Extreme climatic conditions, such a those involving precipitation or excessive wind speed 

shall also be avoided. 

6.3 Major instrument calibration 

Note.- The general objective of this calibration is to confirm stability and linearity. 

6.3.1 The applicant shall satisfy the certificating authority that the calibration of the analytical 

system is valid at the time of the test. 

6.3.2 For the hydrocarbon analyzer this calibration shall include checks that the detector 

oxygen and differential hydrocarbon responses are within the limits specified in 

Attachment A to this appendix. The efficiency of the NO2/NO converter shall also be 

checked and verified to meet the requirements in Attachment C to this appendix. 

6.3.3 The procedure for checking the performance of each analyzer shall be as follows (using 

the calibration and test gases as specified in Attachment D to this appendix): 

a) introduce zero gas and adjust instrument zero, recording setting as appropriate; 

b) for each range to be used operationally, introduce calibration gas of (nominally) 

90 per cent range full-scale deflection (FSD) concentration; adjust instrument 

gain accordingly and record its setting; 
 Page 89 

c) introduce approximately 30 per cent, 60 per cent, and 90 per cent range FSD 

concentrations and record analyzer readings; 

d) fit a least squares straight line to the zero, 30 per cent, 60 per cent and 90 per 

cent concentration points. For the CO and/or CO2 analyzer used in its basic form 

without linearization of output, a least squares curve of appropriate mathematical 

formulation shall be fitted using additional calibration points if judged necessary. 

If any point deviates by more than 2 per cent of the full scale value (or ±1 ppm*, 

whichever is greater) then a calibration curve shall be prepared for operational 

use 

* Except for the CO2 analyzer. for which the value shall be ±lOO ppm 

6.4 Operation 

6.4.1 No measurements shall be made until all instruments and sample transfer lines are 

warmed up and stable and the following checks have been carried out: 

a) leakage check: prior to a series of tests the system shall be checked for leakage 

by isolating the probe and the analysers, connecting and operating a vacuum 

pump of equivalent performance to that used in the smoke measurement system 

to verify that the system leakage flow rate is less than 0.4 L/min referred to 

normal temperature and pressure; 

b) cleanliness check: isolate the gas sampling system from the probe and connect 

the end of the sampling line to a source of zero gas. Warm the system up to the 

operational temperature needed to perform hydrocarbon measurements. Operate 

the sample flow pump and set the flow rate to that used during engine emission 

testing. Record the hydrocarbon analyzer reading. The reading shall not exceed I 

per cent of the engine idle emission level or 1 ppm (both expressed as methane), 

whichever is the greater. 

Note 1.-It is good practice to back-purge the sampling lines during engine running, while the 

probe is in the engine exhaust but emissions are not being measured, to ensure that no 

significant contamination occurs. 

Note. 2-It is also good practice to monitor the inlet air quality at the start and end of testing and at 

least once per hour during a test. If levels are considered significant, then they should be taken 

into account. 

6 4.2 The following procedure shall be adopted for operational measurements: 

a) apply appropriate zero gas and make any necessary instrument adjustments; 

b) apply appropriate calibration gas at a nominal 90 per cent FSD concentration for 

the ranges to be used, adjust and record gain settings accordingly; 

c) when the engine has been stabilized at the requisite operating conditions and 

sampling location, continue to run it and observe pollutant concentrations until a 

stabilized reading is obtained, which shall be recorded At the same engine 

operating condition repeat the measurement procedure for each of the remaining 

sampling locations; 

d) recheck zero and calibration points at the end of the test and also at intervals not 

greater than 1 hour during tests. If either has changed by more than ±2 per cent 
 

Page 90 

of full scale of range, the test shall be repeated after restoration of the instrument 

to within its specification. 

Supplemental information

Note 2: For significant levels in the inlet air, say 1% of full scale of appropriate range in use 

acceptable practice would allow subtracting out the inlet concentration from that measured in the 

exhaust. 

One objective of this sampling protocol is to take advantage of the relatively low spatial variability of 

the exhaust species by sampling in the fully turbulent free jet zone. Doing this requires a method of 

data analysis which accounts for dilution air which is well mixed with the core jet by calculating 

emission indices using a total carbon balance and ensuring – through a cross correlation calculation – 

that the CO2 correlates well with each of the other species, acceptable accuracy is achieved. 

7. CALCULATIONS 

7.1 Gaseous emissions 

7.1.1 General 

The analytical measurements made shall be the concentrations of the various classes of 

pollutant, at the relevant afterburning mode(s) of the engine, at the various locations in the 

sampling plane. In addition to the recording of these basic parameters, other parameters shall be 

computed and reported, as follows. 

7.1.2 Analysis and validation 

of measurements

a) At each engine setting, the concentrations measured at different probe sampling 

positions must be averaged as follows: 

C C i moy i j

j

n

= =

∑

1

where: 

j

n

=

∑

1

 Summation of the total number n of sampling positions used. 

Ci j Concentration of species i measured at the j th sampling position. 

Ci moy average or mean concentration of species i. 

All dry concentration measurements shall be converted into real wet concentrations. (See 

Attachment E to this appendix). 
 Page 91 

b) The quality of the measurements for each pollutant will be determined through a 

comparison with measurements of CO2, using the correlation coefficient: 

Values of ri which are near to 1 indicate that measurements taken over the entire sampling period 

are sufficiently stable and that the curves are Gaussian. In the event that ri is less than 0.95, 

measurements must be repeated in a sampling plane located at a more remote distance from the 

aircraft engine. The measurement process, per se, is then followed by the same calculations and 

the same demonstration as previously. 

7.1.3 Basic parameters 

[ ]

[ ] [ ][ ] ( ) ( ) ( )

[ ]

[ ] [ ][ ] ( ) ( ) ( )

[ ]

[ ] [ ][ ] ( ) ( ) ( )

EI(CO) CO

CO CO HC

EI(HC) HC

CO CO HC

EI(NO ) NO

CO CO HC

2

CO

C H

2

HC

C H

X

X

2

NO

C H

X

= + +

⎛

⎝

⎜ ⎞

⎠

⎟

+

⎛

⎝

⎜

⎞

⎠

⎟ +

= + +

⎛

⎝

⎜ ⎞

⎠

⎟

+

⎛

⎝

⎜

⎞

⎠

⎟ +

= + +

⎛

⎝

⎜ ⎞

⎠

⎟

+

⎛

⎝

⎜

⎞

⎠

⎟ +

10 1

10 1

10 1

3

0

3

0

3

0

M

M nm M

TPm

M

M nm M

TPm

M

M nm M

TPm

Supplemental information

The basic descriptive parameter for gaseous emissions is the emission index (EI), defined as the 

mass of a product of combustion, in grams, divided by the mass of fuel used in kilograms, i.e., grams 

per kilogram. 

where: 

( )

( ) [ ] 0

2

P

41 2

Z nm

m

h TZ

− = + −

and 

[ ] ( ) [ ] [ ] [ ] [ ]

[ ][ ][ ]

2

2

2 CO 2 2 HC NO

CO CO HC

x yx Z−− − + = + +
 

Page 92 

MAIR molecular mass of dry air = 28.966 g or, where appropriate, = (32 R + 28.156 4 S 

+ 44.011 T) g 

MHC molecular mass of exhaust hydrocarbon, taken as CH4 = 16.043 g 

MCO molecular mass of CO = 28.011 g 

MNO2 molecular mass of NO2 = 46.008 g 

MC molecular mass of carbon = 12.011 g 

MH molecular mass of hydrogen = 1.008 g 

R concentration of O2 in dry air, by volume = 0.209 5 normally 

S concentration of N2 + rare gases in dry air, by volume = 0.709 2 normally 

T concentration of CO2 in dry air, by volume = 0.000 3 normally 

[HC] mean concentration of exhaust hydrocarbons vol/vol, expressed as carbon 

[CO] mean concentration of CO vol/vol, wet 

[CO2] mean concentration of CO2 vol/vol, wet 

[NOX] mean concentration of NOX vol/vol, wet = [NO + NO2} 

[NO] mean concentration of NO in exhaust sample, vol/vol, wet 

([NO NO x ] ) [ ] c

η

− =

[NO2] mean concentration of NO2 in exhaust sample, vol/vol, wet 

[NOX]c mean concentration of NO in exhaust sample after passing through the NO2/NO

converter, vol/vol, wet 

η efficiency of NO2/NO converter 

h humidity of ambient air, vol water/vol dry air 

m number of C atoms in characteristic fuel molecule 

n number of H atoms in characteristic fuel molecule 

x number of C atoms in characteristic exhaust hydrocarbon molecule 

y number of H atoms in characteristic exhaust hydrocarbon molecule 

The value of n/m, the ratio of the atomic hydrogen to atomic carbon of the fuel used, is evaluated 

by fuel type analysis. The ambient air humidity, h, shall be measured at each set condition. In the 

absence of contrary evidence as to the characterization (x, y) of the exhaust hydrocarbons, the 

values x= 1, y=4 are to be used. If dry or semi-dry CO and CO2 measurements are to be used 

then these shall first be converted to the equivalent wet concentration as shown in Attachment E 

to this appendix, which also contains interference correction formulas for use as required. 

7.1.4 Correction of emission indices 

to reference conditions 

Corrections shall be made to the measured engine emission indices for all pollutants in all 

relevant engine operating modes to account for deviations from the reference conditions (ISA at 

sea level) of the actual test inlet air conditions of temperature and pressure. The reference value 

for humidity shall be 0.00629 kg water/kg dry air. 

Thus, EI corrected = K x EI measured, where the generalized expression for K is: 

( / / exp | / exp | 0.00629 | ) ( ) ( | ) ( ) a b

K P P FAR FAR T T c d h Bref B ref B Bref B − = × × ×−
 Page 93 

PB Combustor inlet pressure, measured 

TB Combustor inlet temperature, measured 

FARB Fuel/air ratio in the combustor 

h Ambient air humidity 

Pref ISA sea level pressure 

Tref ISA sea level temperature 

PBref Pressure at the combustor inlet of the engine tested (or the reference engine if the 

data is corrected to a reference engine) associated with TB under ISA sea level 

conditions 

TBref Temperature at the combustor inlet under ISA sea level conditions for the engine 

tested (or the reference engine if the data is corrected to a reference engine). This 

temperature is the temperature associated with each thrust level specified for each 

mode. 

FARref Fuel/air ratio in the combustor under ISA sea level conditions for the engine tested 

(or the reference engine if the data is to be corrected to a reference engine). 

a,b,c,d Specific constants which may vary for each pollutant and each engine type 

The combustor inlet parameters shall preferably be measured but may be calculated from 

ambient conditions by appropriate formulas. 

7.1.5 Using the recommended curve fitting technique to relate emission indices to combustor 

inlet temperature effectively eliminates the exp ((TBref - TB)/c) term from the generalized 

equation and for most cases the (FARref/FAR,) term may be considered unity. For the 

emissions indices of CO and HC many testing facilities have determined that the humidity 

term is sufficiently close to unity to be eliminated from the expression and that the 

exponent of the (PBref /PB) term is close to unity. 

Thus, 

EI(CO) corrected = EI derived from 

(PB /PBref) EI(CO) v. TB, curve 

EI(HC) corrected = EI derived from 

(PB /PBref) EI(HC) v. TB, curve 

EI(NOX) corrected = EI derived from 

EI(NOX) (PBref/PB)

0.5 exp (19 |h - 0.006 29|) v. TB curve 

Supplemental information

From the generalized correction for K, the term (PB/PBref) – in the EI(CO) and EI(HC) expressions – 

should be (PBref/PB). 

If this recommended method for the CO and HC emissions index correction does not provide a 

satisfactory correlation, an alternative method using parameters derived from component tests may 

be used. 

Any other methods used for making corrections to CO, HC and NO, emission indices shall have the 

approval of the certificating authority. 

7.2 Control parameter functions 
 

Page 94 

(Dp , Foo , π) 

7.2.1 Definitions 

Dp The mass of any gaseous pollutant emitted during the reference emissions 

landing and take-off cycle. 

Foo The maximum thrust available for take-off under normal operating conditions at 

ISA sea level static conditions, without the use of water injection, as approved by 

the applicable certificating authority. 

π The ratio of the mean total pressure at the last compressor discharge plane of the 

compressor to the mean total pressure at the compressor entry plane when the 

engine is developing take-off thrust rating at ISA sea level static conditions. 

7.2.2 The emission indices (EI) for each pollutant, corrected for pressure and humidity (as 

appropriate) to the reference ambient atmospheric conditions as indicated in 7.1.4 and if 

necessary to the reference engine, shall be obtained for the required LTO engine 

operating mode settings (n) of idle, approach. climb-out and take-off, at each of the 

equivalent corrected thrust conditions. A minimum of three test points shall be required to 

define the idle mode. The following relationships shall be determined for each pollutant: 

a) between EI and TB; and 

b) between Wf (engine fuel mass flow rate) and TB; and 

c) between Fn,, (corrected to ISA sea level conditions) and TB, (corrected to ISA sea 

level conditions); 

Note. — These are illustrated, for example, by Figure 5-3 a), b) and c). 

When the engine being tested is not a "reference" engine, the data may be corrected to 

"reference" engine conditions using the relationships b) and c) obtained from a reference engine. 

A reference engine is defined as an engine substantially configured to the description of the 

engine to be certificated and accepted by the certificating authority to be representative of the 

engine type for which certification is sought. 

The manufacturer shall also supply to the certificating authority all of the necessary engine 

performance data to substantiate these relationships and for ISA sea level ambient conditions: 

d) maximum rated thrust (Foo); and 

e) engine pressure ratio (%) at maximum rated thrust. 

Note.— These are illustrated by Figure A5-4 d). 

7.2.3 The estimation of EI for each pollutant at each of the required engine mode settings, 

corrected to the reference ambient conditions, shall comply with the following general 

procedure: 

a) at each mode ISA thrust condition Fn determine the equivalent combustor inlet 

temperature (TB) (Figure 3-2 c)); 

b) from the EI/TB characteristic (Figure 3-2 a)), determine the EIn value 

corresponding to TB; 
 Page 95 

c) from the Wf/TB characteristic (Figure 3-2 b)), determine the Wfn value 

corresponding to TB; 

note the ISA maximum rated thrust and pressure ratio values. These are Foo and π respectively 

(Figure 3-2 d)); 

calculate, for each pollutant Dp = Σ (EIn)(Wfn)(t) 

t time in LTO mode (minutes) 

Wfn fuel mass flow rate (kg/min) 

Σ is the summation for the set of modes comprising the reference LTO cycle. 

7.2.4 While the methodology described above is the recommended method, the certificating 

authority may accept equivalent mathematical procedures which utilize mathematical 

expressions representing the curves illustrated if the expression have been derived using 

an accepted curve fitting technique. 
 

Page 96 

Figure A5-4 Calculation Procedure 

7.3 Exceptions to the proposed procedures

In those cases where the configuration of the engine or other extenuating conditions exist which 

would prohibit the use of this procedure, the certificating authority, after receiving satisfactory 

technical evidence of equivalent results obtained by an alternative procedure, may approve an 

alternative procedure. 
 Page 97 

ATTACHMENT A TO ICAO MANUAL APPENDIX 5. SPECIFICATION 

FOR HC ANALYSER 

Note 1.- As outlined in 5.2 of Appendix 5, the measuring element in this analyzer is the flame 

ionization detector (FID) in which the whole or a representative portion of the sample flow is 

admitted into a hydrogen-fueled flame. With suitably positioned electrodes an ionisation current 

can be established which is a function of the mass rate of hydrocarbon entering the flame. It is 

this current which, referred to an appropriate zero, is amplified and ranged to provide the output 

response as a measure of the hydrocarbon concentration expressed as ppmC equivalent. 

Note 2.— See Attachment D for information on calibration and test gases. 

1. GENERAL 

Precautions: The performance specifications indicated are generally for analyzer full scale. 

Errors at part scale may be a significantly greater percentage of reading. The relevance and 

importance of such increases shall be considered when preparing to make measurements. If 

better performance is necessary, then appropriate precautions shall be taken. 

Supplemental information

The performance specifications for these analyzers, given in terms of full scale response, can have a 

significant and adverse impact on part scale measurements. If this instrument is used for both the 

afterburning and non afterburning modes, which is likely, then the comments made in Appendix 3, 

Attachment A apply here as well. In extreme instances, concentrations of HC at high power, such as 

take-off, can differ from concentrations at idle by orders of magnitude, e.g., 3,500 ppmC at idle and 

10 ppmC at take-off. The FID specification suggests the high level can be 5,000 ppmC. For most 

modern engines the idle concentrations are considerably lower, but still of concern when setting up 

the FID to maintain suitable accuracy of measurement. In general, where concentrations of species 

to be measured are known to vary this way it is always good practice to use a multi-range instrument 

and to adjust ranges such as to keep the measurement in the upper 30% of the instrument response 

range. A measurement made at 20% of full scale could result in an error 5 times the error specified 

as a percent of full scale. This is a general precaution. Some modern instruments with internal 

electronic ranging and calibration capability can be used over their entire range without penalty. 

Calibrations should be performed on each range used as required. 

The instrument to be used shall be such as to maintain the temperature of the detector and 

sample-handling components at a set point temperature within the range 155oC to 165oC to a 

stability of ±2°C. The leading specification points shall be as follows, the detector response having 

been optimized and the instrument generally having stabilized: 

Supplemental information

Stability is usually defined in terms of a time interval which, because this is a temperature control set 

point, can be taken as the duration of the test. 

a) Total range: 0 to 500 ppmC in appropriate ranges. 
 

Page 98 

Supplemental information

The total range of 0 – 500 ppmC reflects its singular use for testing afterburning engines. Since the 

operational range specified in Appendix 3, Attachment A, covers the non-afterburning range too, an 

instrument with a total range of 0 – 5,000 ppmC which incorporates a range of 0 – 500 ppmC is likely 

to be the instrument of choice. As far as possible, measurements should be restricted to the upper 

30% of full scale on the range or ranges used except as noted above. 

b) Resolution: better than 0.5 per cent of full scale of range used or 0.5 ppmC, 

whichever is greater. 

c) Repeatability: better than ±1 per cent of full scale of range used. or ±0.5 ppmC. 

whichever is greater. 

d) Stability: better than ±2 per cent of full scale of range used or ±l.0 ppmC, 

whichever is greater, in a period of 1 hour. 

 

e) Zero drift: less than ±1 per cent of full scale of range used or ±0.5 ppmC, 

whichever is greater, in a period of 1 hour. 

 

f) Noise: 0.5 Hz and greater, less than ±1 per cent of full scale of range used or 

±0.5 ppmC, whichever is greater. 

Supplemental information

The FID requires fuel and oxidant gases for operation. The fuel gas is typically either a mixture of 

hydrogen and nitrogen or hydrogen and helium. If the noise specification cannot be met and a 

hydrogen/nitrogen mixture is being used as the fuel gas, it sometimes helps to change to a 

hydrogen/helium mixture. 

g) Response time: shall not exceed 10 seconds from inlet of the sample to the 

analysis system, to the achievement of 90 per cent of the final reading. 

h) Linearity: response with propane in air shall be linear for each range within ±2 

per cent of full scale, otherwise calibration corrections shall be used.

2. SYNERGISTIC EFFECTS 

Note.- In application there are two aspects of performance which can affect the accuracy of 

measurement: 

a) the oxygen effect (whereby differing proportions of oxygen present in the sample give 

differing indicated hydrocarbon concentration for constant actual HC concentrations); and 

b) the relative hydrocarbon response (whereby there is a different response to the same 

sample hydrocarbon concentrations expressed as equivalent ppmC, dependent on the 

class or admixture of classes of hydrocarbon compounds). 

The magnitude of the effects noted above shall be determined as follows and limited 

accordingly. 

Oxygen response: measure the response with two blends of propane, at approximately 

500 ppmC concentration known to a relative accuracy of ±l per cent, as follows: 

1) propane in 10 ± 1 per cent O2, balance N2
 Page 99 

2) propane in 21 ± 1 per cent O2, balance N2

If R1 and R2 are the respective normalized responses then (R1 - R2) shall be less than 3 

per cent of R1. 

Supplemental information

Unlike the non-afterburning case, the range of oxygen values can vary over a fairly wide range. This 

will be influenced by the location of the sampling plane and the degree of mixing of ambient air with 

the reacted plume. If needed, the O2 response can be minimized by adjusting the FID burner fuel/air 

ratio. 

Differential hydrocarbon response: measure the response with four blends of different 

hydrocarbons in air, at concentrations of approximately 500 ppmC, known to a relative accuracy 

of ±l per cent, as follows: 

a) propane in zero air 

b) propylene in zero air 

c) toluene in zero air 

d) n-hexane in zero air. 

If Ra, Rb, Rc and Rd are, respectively, the normalized responses (with respect to propane), then 

(Ra - Rb), (Ra - Rc) and (Ra - Rd) shall each be less than 5 per cent of Ra. 

Supplemental information

Although assumed to respond as a carbon number counter, for the purposes of testing engine 

exhaust, the FID response is known to vary somewhat with the particular hydrocarbon or class of

hydrocarbons being measured. For example, three molecules of methane, (CH4), will not necessarily 

result in the same instrument response as one molecule of propane, (C3H8). Because of this 

differential response it is sometimes helpful to think of the FID as responding to an “effective” carbon 

number. It is important to ensure the instrument responds acceptably to all of the hydrocarbons in the 

engine exhaust. This group of hydrocarbons – propylene, toluene, and n-hexane, with propane as a 

reference – was chosen to represent, in terms of instrument response, the range of hydrocarbons 

expected in the exhaust. 

3. OPTIMIZATION OF DETECTOR RESPONSE AND ALIGNMENT 

3.1 The manufacturer's instructions for initial setting up procedures and ancillary services and 

supplies required shall be implemented, and the instrument allowed to stabilize. All 

setting adjustments shall involve iterative zero checking, and correction as necessary. 

Using as sample a mixture of approximately 500 ppmC of propane in air, the response 

characteristics for variations first in fuel flow and then, near an optimum fuel flow, for 

variations in dilution air flow to select its optimum shall be determined. The oxygen and 

differential hydrocarbon responses shall then be determined as indicated above. 

Supplemental procedure

The FID detector response and alignment can be optimized by adjusting the FID burner fuel and air 

flow while sampling a mixture containing approximately 500 ppmC propane. Care should be taken 

when changing fuel flow that the instrument zero response point does not shift. If it does, the 

instrument zero should be reset. Response curves illustrating this process, shown below in Figures 

A5-5 and A5-6, were taken from 40 CFR Part 87, Control of Air Pollution from Aircraft and Aircraft 

Engines, Federal Register, Vol. 43, No. 58 — Friday, March 24, 1978. They were taken, in turn, from 
 

Page 100 

SAE ARP1256, "Procedure for the Continuous Sampling and Measurement of Gaseous Emissions 

from Aircraft Turbine Engines". 

Figure A5-5 Typical Fuel Flow Response Curve 

Figure A5-6 Typical Airflow Response Curve 

The objective of this procedure is to select operating flow rates that will give near maximum response 

with least variation for minor changes in fuel flow. It may be necessary to repeat this operation in an 

iterative fashion: 

• Adjust the fuel flow to maximize output; 

• Adjust zero if necessary; 

• Adjust the air flow to maximize output; 

• Readjust the fuel flow, if necessary; and 

• Repeat until the burner output is optimized. 
 Page 101 

3.2 The linearity of each analyzer range shall be checked by applying propane in air samples 

at concentrations of approximately 30, 60 and 90 per cent of full scale. The maximum 

response deviation of any of these points from a least squares straight line (fitted to the 

points and zero) shall not exceed ±2 per cent of full scale value. If it does, a calibration 

curve shall be prepared for operational use. 

Table A5-1 HC ANALYZER PERFORMANCE SPECIFICATIONS 

Parameter Value

Total Range 0 to 500 ppmC (5 000ppmC for non AB) 

Resolution better than 0.5% full scale range used 

or 0.5 ppmC whichever is greater 

Repeatability better than ±1% full scale range used 

or ±0.5 ppmC whichever is greater 

Stability better than ±2% full scale range used 

or ±1 ppmC whichever is greater in a 

period of 1 hour 

Zero drift < ±1% full scale range used 

or ±0.5 ppmC, whichever is greater in a 

period of 1 hour 

Noise 0.5 Hz and greater, < than ±1% full scale 

range used or ±0.5 ppmC, whichever is 

greater 

Response time ≤ 10 seconds from inlet of sample to 

achieve 90% of final reading 

Linearity ±2% full scale to propane in air, for each 

range used, or calibration correction 

required 

The performance specifications shown in Table A5-1 are typical of those analyzers offered by major 

analyzer manufacturers. 
 

Page 102 

ATTACHMENT B TO ICAO MANUAL APPENDIX 5. 

SPECIFICATION FOR CO AND CO2 ANALYSERS 

Note 1.- Paragraph 5.3 of Appendix 5 summarizes the characteristics of the analysis sub-system 

to be employed for the individual measurements of CO and CO2 concentrations in the exhaust 

gas sample. The instruments are based on the principle of non-dispersive absorption of infra-red 

radiation in parallel reference and sample gas cells. The required ranges of sensitivity are 

obtained by use of stacked sample cells or changes in electronic circuitry or both. Interferences 

from gases with overlapping absorption bands may be minimised by gas absorption filters and/or 

optical filters. preferably the latter. 

Note 2.— See attachment D for information on calibration and test gases. 

Precautions: The performance specifications indicated are generally for analyzer full scale. 

Errors at part scale may be a significantly greater percentage of reading. The relevance and 

importance of such increases shall be considered when preparing to make measurements. If 

better performance is necessary, then appropriate precautions shall be taken. 

Supplemental information

The performance specifications for these analyzers given in terms of full scale response can have a 

significant and adverse impact on part scale measurements. This needs to be considered when 

planning and executing the test and in evaluating the accuracy of the measurements after the test. 

Concentrations of CO, when going from the idle mode to take-off, can differ by orders of magnitude. 

In general, where concentrations of species to be measured are known to vary this way, it is always 

good practice to use a multi-range instrument and to choose ranges such as to keep the 

measurement in the upper 30% of scale on the range in use. A measurement made at 20% of full 

scale could result in an error 5 times the error specified as a percent of full scale. This is a general 

precaution. Some modern instruments with internal electronic ranging and calibration capability can 

be used over their entire range without penalty. Calibrations should be performed on each range 

used as required. 

The principal performance specification shall be as follows: 

CO Analyzer 

b) Total range: 0 to 2 500 ppm in appropriate ranges. 

Relative to the precautions mentioned above ranges are chosen that the instrument responds in 

the upper 30% of scale for the range in use. While this may not always be possible it should be a 

goal. 

b) Resolution: better than 0.5 per cent of full scale of range used or 1 ppm, whichever is 

greater. 

c) Repeatability: better than ±1 per cent of full scale of range used, or ±2 ppm, whichever is 

greater. 

e) Stability: better than ±2 per cent of full scale of range used or ±2 ppm, whichever is 

greater, in a period of 1 hour. 

e) Zero drift: less than ±l per cent of full scale of range used or ±2 ppm. whichever is 

greater, in a period of 1 hour. 

f) Noise: 0.5 Hz and greater, less than ±l per cent of full scale of range used or ±l ppm, 

whichever is greater. 
 Page 103 

g) Interferences: to be limited with respect to indicated CO concentration as follows: 

1) less than 500 ppm/per cent ethylene concentration 

Supplemental information

It is unlikely that high concentrations of ethylene will be found in gas turbine engine exhaust. The 

highest concentration of hydrocarbons is found at idle, corresponding to the highest concentrations of 

CO. If all of the hydrocarbons were ethylene (C2H4), and the concentration were 100% of the 

maximum range, 5,000 ppmC, –corresponding to 2,500 ppm ethylene – the allowable interference 

would be less than 125 ppm, or less than 5% of the highest CO range, 2,500 ppm. Since the 

interference limit is in absolute terms, the relative error will increase for measurements made at less 

than full scale. If ethylene is suspected of being present in significant concentrations, then corrections 

to the data are required.

2) less than 2 ppm/per cent CO2 concentration 

4) less than 2 ppm/per cent water vapour.* 

Supplemental information

These two interferents, CO2 and water vapor, are additive. Being the major products of combustion 

they increase and decrease together, and are at their highest levels at the highest power. 

Unfortunately concentrations of CO tend to be at their lowest concentrations at the highest power. 

This can cause significant problems in the accuracy of the measurement even if the interference 

limits are met. It is not unusual for tests to be conducted with the sample dried before measurement 

and the interference due to the remaining interferent, CO2, compensated for through use of gas or 

optical filters. It does bear mentioning that the contribution of high power CO concentrations to the 

total gross CO emission measured over the LTO cycle is relatively small. 

If the interference limitation(s) for CO2 and/or water vapour cannot be met, appropriate correction 

factors shall be determined, reported and applied. 

Note.- It is recommended as consistent with good practice that such correction procedures be 

adopted in all cases. 

* Need not apply where measurements are on a "dry" basis. 

CO2 Analyzer 

d) Total range: 0 to 10 per cent in appropriate ranges. 

Supplemental information

Although the total range specified for CO2 is 0 to 10%, concentrations most often will vary between 

1% and 5%. This range is considerably narrower than that for CO. Never the less, good practice 

dictates using ranges that keep the instrument response in the upper 30% of the meter scale except 

as noted above. 

b) Resolution: better than 0.5 per cent of full scale of range used or 100 ppm, whichever is 

greater. 

c) Repeatability: better than ±1 per cent of full scale of range used or ±100 ppm, whichever 

is greater. 

d) Stability: better than ±2 per cent of full scale of range used or ±100 ppm, whichever is 
 

Page 104 

greater, in a period of 1 hour. 

e) Zero drift: less than ±l per cent of full scale of range used or ±l00 ppm, whichever is 

greater, in a period of 1 hour. 

f) Noise: 0.5 Hz and greater, less than ±1 per cent of full scale of range used or ±100 ppm, 

whichever is greater. 

h) The effect of oxygen (O2) on the CO2 analyzer response shall be checked. For a change 

from 0 per cent O2 to 21 per cent O2, the response of a given CO2 concentration shall not 

change by more than 2 per cent of reading. If this limit cannot be met an appropriate 

correction factor shall be applied. 

Supplemental information

Gas turbine engines use a considerable amount of internal cooling air that mixes with the combustion 

products before exiting the engine. This results in an oxygen rich exhaust sample that warrants close 

attention. 

Note.— It is recommended as consistent with good practice that such correction procedures be 

adopted in all cases. 

CO and CO2 Analysers 

a) Response time: shall not exceed 10 seconds from inlet of the sample to the analysis 

system, to the achievement of 90 per cent of the final reading. 

b) Sample temperature: the normal mode of operation is for analysis of the sample in its 

(untreated) "wet" condition. This requires that the sample cell and all other components in 

contact with the sample in this sub-system be maintained at a temperature of not less 

than 50°C, with a stability of ±2°C. The option to measure CO and CO2 on a dry basis 

(with suitable water traps) is allowed, in which case unheated analysers are permissible 

and the interference limits for H2O vapour removed, and subsequent correction for inlet 

water vapour and water of combustion is required. 

Supplemental information

Stability is defined in terms of a time interval which, because this is a temperature control set point, 

can be taken as the duration of the test, or one hour to be consistent with the stability limits placed on 

the detection system. 

The temperature quoted for the CO and CO2 subsystems, 50°C, is on the low end of the sample line 

specification, 65°C ±15°C. Good practice would suggest that the subsystem temperature be 

approximately the same as the sample gas temperature. If the samples are dried and the analyzers 

unheated it would be reasonable to lower the sample temperature to that of the analyzer. If water is 

removed prior to analysis corrections must be applied to compensate for the loss of water of 

combustion and inlet water vapor. Correction procedures are detailed in Attachment F of this 

Appendix. 

c) Calibration curves: 

j) Analysers with a linear signal output characteristic shall be checked on all working ranges 

using calibration gases at known concentrations of approximately 0, 30, 60 and 90 per 

cent of full scale. The maximum response deviation of any of these points from a least 

squares straight line, fitted to the points and the zero reading, shall not exceed ±2 per 

cent of the full scale value. If it does then a calibration curve shall be prepared for 

operational use. 
 Page 105 

Supplemental information

Straight line fits to sets of linear data can be arrived at graphically or analytically. If graphically, the 

results are subject to interpretation, i.e., best estimate by ‘eye’ by individual. If analytically, there is 

assurance that each case and all data are handled the same way each time. The technique is to 

perform a linear regression, or ‘least-squares fit’ for a line. The calibration gas values are the 

“independent” variables and are assumed to be correct, to have negligible error, for the purpose of 

this analysis. The instrument response values are the dependent variables and are assumed to have 

errors and that these errors are normally (Gaussian) distributed about the true line. The equation 

describing the straight line is: 

yi

 = A + B*xi

true value for response yi = A (a constant) + B (another constant) * (calibration gas value xi) 

For instruments which have been adjusted such that zero input results in zero output, and where the 

variance in known to be proportional to the reading the slope B can be shown to be equal to the ratio 

of the averages and can be expressed as: 

Often A and B are not such simple values for intercept and slope but must be calculated as if the 

variance were not known to be proportional to the instrument response. Again if we set the instrument 

to read zero for zero gas input then A = 0 which makes the calculation relatively simple. The 

generalized expression for B can be found in any elementary statistics or error analysis text and is: 

Where xi

 is the calibration gas value and yi is the instrument response and N refers to the number of 

points used in the analysis. 

With N = 4, corresponding to 0, 30, 60 and 90% of full scale, this equation can be rewritten as: 

A simple table, for the four sets of values, can be used for organizing the information, thereby 

simplifying the calculation: 

y

x
 

Page 106 

Measurement 

number i 

x 

cal. gas value i

y 

response i xi

2 xi

yi 

1 

 

2 

3 

4 

N = 4 Σxi Σyi Σxi

2 Σxi

 yi

If the instrument is not set to zero-zero (zero response for zero input), then A must be determined. 

The equation for A (for N = 4) is: 

The table shown earlier can be used to organize the elements of this equation as well. 

Usually the next step would be to calculate the uncertainty in yi

 about this line. However, instead of 

controlling uncertainty about the line, ICAO chose to set an absolute limit of ±2% deviation of the full 

scale value for each point. This should make clear the advantage in using the upper region (top 30%) 

of the range for all measurements. 

ii) Analysers with a non-linear signal output characteristic, and those that do not meet the 

requirements of linearity given above, shall have calibration curves prepared for all 

working ranges using calibration gases at known concentrations of approximately 0, 30, 

60 and 90 per cent of full scale. Additional mixes shall be used, if necessary, to define the 

curve shape properly. 

Supplemental information

For analyzers with a non-linear signal output characteristic, calibration curves shall be prepared, 

again using approximately 0, 30, 60 and 90% of full scale calibration gases. If a curve is 

substantially non-linear in shape, it is recommended that additional calibration gases be used with 

values between the ones specified. These calibration curves can be determined analytically using a 

least squares fit, but in this case the fit would be to a polynomial or exponential. The equations for 

doing this can be found in any basic text on statistics or error analysis. It should be noted that for 

exponential fits it is often convenient to work with the logarithm of the expression, which reduces the 

problem to a least-squares-fit about a line as is described above. This technique is used in 

analyzing smoke filters as required in 3. of Appendix 2. Although not stated explicitly, the 

presumption is that the same ±2% of full scale response deviation is true for non-linear as well as 

linear instruments. 
 Page 107 

Table A5-2 summarizes the specifications for CO and CO2 analyzers. These are typical of those 

analyzers offered by major analyzer manufacturers. 

Table A5-2 NDIR ANALYZER PERFORMANCE SPECIFICATIONS 

Value 

Parameter CO2 CO

Total Range 0 to 10% in appropriate 

ranges 

0 to 2 500 ppm in 

appropriate ranges 

Resolution better than 0.5% fs 

range used or 100 ppm 

whichever greater 

better than 0.5% fs range 

used or 1 ppm whichever 

greater 

Repeatability better than ±1% fs 

range used or ±100 

ppm whichever greater 

better than ±1% fs range 

used or ±2 ppm whichever 

greater 

Stability better than ±2% fs 

range used or ±100 

ppm whichever greater 

period of 1 hr 

better than ±2% fs range 

used or ±2 ppm whichever 

greater period of 1 hr 

Zero Drift < ±1% fs range used or 

±100 ppm whichever 

greater period of 1 hr 

< ±1% fs range used or 

±2 ppm whichever greater 

period of 1 hr 

Noise 

≥0.5 HZ, <±1% FS 

RANGE USED OR ±100

PPM, WHICHEVER 

GREATER

≥0.5 Hz, <±1% fs range 

used or ±1 ppm, 

whichever greater 

Interference ≤ 2% of reading for O2

between 0 and 21% 

<500 ppm/% ethylene 

<2 ppm/% CO2

<2 ppm/% water vapor 

Response 

Time 

≤10 seconds from 

instrument inlet to 

90% fs 

≤10 seconds from 

instrument inlet to 

 90% fs 

Sample 

Temperature 

wet samples ≥50°C 

stability ± 2°C 

wet samples ≥50°C 

stability ± 2°C 
 

Page 108 

ATTACHMENT C TO ICAO MANUAL APPENDIX 5. 

SPECIFICATION FOR NOX ANALYSER 

Note.— See attachment D for information on calibration and test gases. 

1. As indicated in 5.4 of Appendix 5, the measurement of the oxides of nitrogen 

concentration. shall be by the chemiluininescent technique in which radiation emitted by 

the reaction of NO and O3 is measured. This method is not sensitive to NO2 and therefore 

the sample shall be passed through a converter in which NO2 is converted to NO before 

the measurement of total NOX is made. Both the original NO and the total NOX

concentrations shall be recorded. Thus by difference, a measure of the NO2 

concentration shall be obtained. 

2. The instrument to be used shall be complete with all necessary flow control components, 

such as regulators, valves, flowmeters, etc. Materials in contact with the sample gas shall 

be restricted to those which are resistant to attack by oxides of nitrogen, such as 

stainless steel, glass, etc. The temperature of the sample shall everywhere be 

maintained at values, consistent with the local pressures, which avoid condensation of 

water. 

Precautions: The performance specifications indicated are generally for analyzer full scale. 

Errors at part scale may be a significantly greater percentage of reading. The relevance and 

importance of such increases shall be considered when preparing to make measurements. If 

better performance is necessary, then appropriate precautions shall be taken. 

Supplemental information

The performance specifications for these analyzers given in terms of full scale response can have a 

significant and adverse impact on part scale measurements. This needs to be considered when 

planning and executing the test, and in evaluating the accuracy of the measurements after the test. 

Concentrations of NOX, when going from the idle mode to take-off, can differ by orders of magnitude. 

In general, where concentrations of species to be measured are known to vary this way, it is always 

good practice to use a multi-range instrument, and to choose ranges such as to keep the 

measurement in the upper 30% of scale on the range in use. A measurement made at 20% of full 

scale could result in an error 5 times the error specified as a percent of full scale. This is a general 

precaution. Some modern instruments with internal electronic ranging and calibration capability can 

be used over their entire range without penalty. Calibrations should be performed on each range 

used as required. 

3. The principal performance specification, determined for the instrument operated in an 

ambient temperature stable to within 2°C, shall be as follows: 

a) Total range: 0 to 2 500 ppm in appropriate ranges. 

b) Resolution: better than 0.5 per cent of full scale of range used or 1 ppm, 

whichever is greater. 

c) Repeatability: better than ±l per cent of full scale of range used, or ±1 ppm, 

whichever is greater. 

d) Stability: better than ±2 per cent of full scale of range used or ±l ppm, whichever 

is greater, in a period of 1 hour. 
 Page 109 

e) Zero drift: less than ±1 per cent of full scale of range used or ±1 ppm, whichever 

is greater, in a period of 1 hour. 

f) Noise: 0.5 Hz and greater, less than ±1.0 per cent of full scale of range used or ±l 

ppm, whichever is greater, in a period of 2 hours. 

g) Interference: suppression for samples containing CO2 and water vapour, shall be 

limited as follows: 

— less than 0.05 per cent reading/per cent CO2 concentration; 

— less than 0.1 per cent reading/per cent water vapour concentration. 

If the interference limitation(s) for CO2 and/or water vapour cannot be met, appropriate 

correction factors shall be determined, reported and applied. 

Note.- It is recommended as consistent with good practice that such correction 

procedures be adopted in all cases. 

h) Response time: shall not exceed 10 seconds from inlet of the sample to the 

analysis system to the achievement of 90 per cent of the final reading. 

i) Linearity: better than ±2 per cent of full scale of range used or ±2 ppm, whichever 

is greater. 

j) Converter: this shall be designed and operated in such a matter as to reduce 

NO2 present in the sample to NO. The converter shall not affect the NO originally 

in the sample. 

Supplemental information

 ...”in such a matter” ... should read ... “in such a manner” ... . 

The converter efficiency shall not be less than 90 per cent. 

This efficiency value shall be used to correct the measured sample NO2 value (i.e. [NOX]c - [NO]) 

to that which would have been obtained if the efficiency had not been 100 per cent. 

Supplemental information

The last sentence should read as follows: 

“This efficiency value shall be used to correct the measured sample NO2 value (ie. [NOX]c –[NO]) to 

that which would have been obtained if the efficiency had been 100 per cent.” 

A procedure for determining the NO2 to NO conversion efficiency, in the absence of any specific 

manufacturer’s instructions, may be found in 40 CFR Part 87, Control of Air Pollution from Aircraft 

and Aircraft Engines, Federal Register, Vol. 43, No. 58 — Friday, March 24, 1978. It was taken, in 

turn, from SAE ARP1256, "Procedure for the Continuous Sampling and Measurement of Gaseous 

Emissions from Aircraft Turbine Engines". 
 

Page 110 

Figure A5-7: NOx Converter Efficiency Detector Schematic 

Figure A5-7 schematically depicts such a device. This device is intended for use with the NOX

analyzer specified in Attachment C. It depends on the reaction: 

NO + O3 = NO2 + O2 

Starting with a known concentration of NO in N2, measurements are made through – and bypassing – 

the chemiluminsecence analyzer converter, the inlet to which is shown as “C3” in the diagram. With 

the NOX converter ozonator alternately on, reducing the NO concentration by approximately 80%, and 

off, allowing 100% of the NO to reach the analyzer the analyzer’s converter efficiency can be 

determined. This efficiency should be used to correct test data as required. 

Note: it has been suggested that NO be mixed with Argon to avoid possible formation of NO in the 

ozonator. 

The specific instructions for using this device, from 40 CFR part 87, are as follows: 

(i) Attach the NO/N2 supply (150-250 ppm.) at “C2”, the O2 supply at “C1” and the analyzer inlet 

connection to the efficiency detector at C3. If lower concentrations of NO are used, air may be 

used in place of O2 to facilitate better control of the NO2 generated during step (iv). 

(ii) With the efficiency detector Variac (Note: SAE uses the term autotransformer) off, place the 

NOX converter in bypass mode and close valve “V3”. Open valve “MV2” until sufficient flow and 

stable readings are obtained at the analyzer. Zero and span the analyzer output to indicate the 

value of the NO concentration being used. Record this concentration. 

(iii) Open valve V3 (on/off flow control solenoid valve for O2) and adjust valve “MV1” (O2 supply 

metering valve) to blend enough O2 to lower the NO concentration (ii) to about 10 percent. 

Record this concentration. 

(iv) Turn on the ozonator and increase its supply voltage until the NO concentration of (iii) is 

reduced to about 20 percent of (ii). NO is now being formed from the NO + O2 reaction. There 

must always be at least 10 percent unreacted NO at this point. Record this concentration. 
 Page 111 

(v) When a stable reading has been obtained from (iv), place the NOX converter in the convert 

mode. The analyzer will now indicate the total NOX concentration. Record this concentration. 

(vi) Turn off the ozonator and allow the analyzer reading to stabilize. The mixture NO + O3 is still 

passing through the converter. This reading is the total NOX concentration of the dilute NO 

span gas used in step (iii). Record this concentration. 

(vii) Close valve V3. The NO concentration should be equal to or greater than the reading of (ii) 

indicating whether the NO contains any NO2. 

Calculate the efficiency of the NOX converter by substituting the concentrations obtained during the 

test into the following equation: 

% . Eff = −

− ×

v iv

vi iv

100%

To improve the effectiveness of thermal converters, particularly those with efficiencies of less than 

90%, it is sometimes helpful to raise the temperature of the converter. 

Table A5-3 NOX ANALYZER PERFORMANCE SPECIFICATION 

Parameter Value

Total Range 0 to 2 500 ppm in appropriate ranges 

Resolution 

BETTER THAN 0.5 PERCENT FULL SCALE 

RANGE USED OR 1 PPM WHICHEVER IS 

GREATER

Repeatability better than ±1 percent full scale range 

used or 1 ppm whichever is greater 

Stability better than ±2 percent% full scale range 

used or ±1 ppm whichever is greater in 

a period of 2 hours 

Zero Drift < ±1 percent% full scale range used or 

±1 ppm, whichever is greater in a period 

of 2 hours 

Noise ≥0.5 Hz, <±1 percent fs range used or ±1 

ppm, whichever greater period of 2 hours 

Interference < 0.05 percent reading/percent CO2

< 0.1 percent reading/percent water 

vapor 

Response Time ≤ 10 seconds from inlet of sample to 

achieve 90 percent of final reading 

Linearity better than ±2 percent full scale for each 

range used or ± 2ppm, whichever 

greater 

Converter 

Efficiency 

≥ 90 percent 

Table A5-3 summarizes the specifications shown are typical of those analyzers offered by major 

analyzer manufacturers. 
 

Page 112 

ATTACHMENT D TO ICAO MANUAL APPENDIX 5. 

CALIBRATION AND TEST GASES 

Table of calibration gases 

Analyser Gas Accuracy* 

HC 

CO2 

CO

NOx 

propane in zero air 

CO2 in zero air 

CO in zero air 

NOx in zero nitrogen 

±2 per cent or ±0.05 ppm** 

±2 per cent or ±100 ppm** 

±2 per cent or ±2 ppm** 

±2 per cent or ±1 ppm** 

* Taken over the 95 per cent confidence interval. 

 ** Whichever is greater 

The above gases are required to carry out the routine calibration of analysers during normal 

operational use. 

Analyser Gas Accuracy* 

HC propane in l0 ±1 per cent O2

balance zero nitrogen 

±1 per cent 

HC propane in 21 ±1 per cent O2

balance zero nitrogen 

±l per cent 

HC propylene in zero air ±l per cent 

HC toluene in zero air ±l per cent 

HC n-hexane in zero air ±l per cent 

HC propane in zero air ±1 per cent 

CO2 CO2 in zero air ±1 per cent 

CO2 

CO 

CO2 in zero nitrogen 

CO in zero air 

±1 per cent 

±1 per cent 

NOx NO in zero nitrogen ±1 per cent 

* Taken over the 95 per cent confidence interval 

The above gases are required to carry out the tests of Attachments A, B and C. 

Carbon monoxide and carbon dioxide calibration gases may be blended singly or as dual component 

mixtures. Three component mixtures of carbon monoxide, carbon dioxide and propane in zero air may be 

used, provided the stability of the mixture is assured. 
 Page 113 

Zero gas as specified for the CO, CO2 and HC analysers shall be zero air (which includes "artificial" air 

with 20 to 22 per cent O2 blended with N2). For the NOX analyser zero nitrogen shall be used as the zero 

gas. Impurities in both kinds of zero gas shall be restricted to be less than the following concentrations: 

 1 ppm C

 1 ppm CO

 100 ppm CO2

 1 ppm NOx

The applicant shall ensure that commercial gases supplied to him do in fact meet this 

specification, or are so specified by the vendor. 

Supplemental information

Calibration and test gases are readily available, with traceability to the National Institute of Standards 

and Technology (NIST), from commercial suppliers. Gases with an accuracy of ± 1% are considered 

“primary” standards and intended for use where the highest accuracy and reliability are needed. Very 

tight controls over cylinder material, age, and history are considered good practice, if not essential. 

Periodic checks of the accuracy of assay for each cylinder is advisable. Gases such as CO, CO2, and 

propane with a certified accuracy of ± 2% can be obtained as multi-component mixtures. This will 

reduce the number of gas cylinders needed for testing. The importance of this becomes obvious 

when considering the calibration requirements for each instrument and each range. Managing just 

the minimum number of calibration and test gases can be challenging. For example, an average 

certification test, when backup gases are counted, can require 100 two component cylinders, or more. 

The stability of the components in each mixture should be checked periodically. If the assay no 

longer agrees with the certified analysis, the cylinder should be returned to the supplier or discarded 

as appropriate. 

Because of the accuracy required and the sophistication of the techniques necessary to produce and 

analyze gases to these standards, most testing laboratories rely on the commercial suppliers analysis 

and certification for primary accuracy and use in-house checks via instrument response for 

consistency of assay. It is good practice to recheck all calibration and working standard gases 

immediately prior to a certification test. 

All calibration gas monitoring data should be kept and made available to the certificating agency if 

required. 

Although not a calibration gas or, strictly speaking, a test gas, the FID analyzer fuel and oxidant 

gases should also meet a hydrocarbon specification. For hydrogen/nitrogen or hydrogen/helium fuel 

mixtures, total hydrocarbons present should be < 1 ppmC. The oxidant should be hydrocarbon free 

grade air, containing < 1 ppmC hydrocarbon. The SAE in ARP 1256 restricts the FID fuel gas to a 

40% hydrogen, 60% helium mixture which is required to meet this hydrocarbon level specification. 
 

Page 114 

ATTACHMENT E TO ICAO MANUAL APPENDIX 5. 

THE CALCULATION OF THE EMISSIONS 

PARAMETERS - BASIS, MEASUREMENT CORRECTIONS AND 

ALTERNATIVE NUMERICAL METHOD

1. SYMBOLS P7 number of moles of NO2 in the exhaust 

sample per mole of fuel 

AFR air/fuel ratio, the ratio of the mass flow 

rate of dry air to that of the fuel 

P8 number of moles of NO in the exhaust 

sample per mole of fuel

El emission index; l03

 X mass flow rate of 

gaseous emission product in exhaust 

per unit mass flow rate of fuel 

PT P1 + P2 + P3 + P4 + P5 + P6 + P7 + P8

K ratio of concentration measured wet to 

that measured dry (after cold trap) 

R concentration of O2 in dry air, by 

volume = 0.2095 normally

L, L' analyser interference coefficient for 

interference by CO2 

S concentration of N2 + rare gases in dry 

air, by volume = 0.7902 normally

M, M' analyser interference coefficient for 

interference by H2O

T concentration of CO2 in dry air, by 

volume = 0.0003 normally

MAIR molecular mass of dry air = 28.966 g or, 

where appropriate, = (32 R + 28.156 4 

S + 44.011 T) g 

P0 number of moles of air per mole of fuel 

in initial air/fuel mixture

MCO molecular mass of CO = 28.011 g Z symbol used and defined in 3.4

MHC molecular mass of exhaust 

hydrocarbon, taken as CH4 = 16.043 g 

[CO2] mean concentration of CO2 in exhaust 

sample, vol/vol

MNO2 molecular mass of NO2 = 46.008 g [CO] mean concentration of CO in exhaust 

sample, vol/vol 

MC atomic mass of carbon = 12.011 g [HC] mean concentration of HC in exhaust 

sample, vol C/vol 

MH atomic mass of hydrogen = 1.008 g [NO] mean concentration of NO in exhaust 

sample, vol/vol 

P1 number of moles of CO2 in the exhaust 

sample per mole of fuel

[NO2] mean concentration of NO2 in exhaust 

sample, vol/vol 

P2 number of moles of N2 in the exhaust 

sample per mole of fuel

[NOX] mean concentration of NO and NO2 in 

exhaust sample, vol/vol 

P3 number of moles of O2 in the exhaust 

sample per mole of fuel

[NOX]c mean concentration of NO in exhaust 

sample. after passing through the 

N02/NO converter, vol/vol 

P4 number of moles of H2O in the exhaust 

sample per mole of fuel 

[NO2] mean = ([NOX]c -[NO])

 η

P5 number of moles of CO in the exhaust 

sample per mole of fuel 

[ ]d mean concentration in exhaust sample 

after cold trap, vol/vol

P6 number of moles of CxHy in the exhaust [ ]m mean concentration measurement 
 Page 115 

sample per mole of fuel indicated before instrument correction 

applied, vol/vol

h humidity of ambient air, vol water/vol dry air 

hd humidity of exhaust sample leaving "drier" or "cold trap", vol water/vol dry sample 

rn number of C atoms in characteristic fuel molecule 

n number of H atoms in characteristic fuel molecule 

x number of C atoms in characteristic exhaust hydrocarbon molecule 

y number of H atoms in characteristic exhaust hydrocarbon molecule 

η efficiency of NO2/NO converter 

2. BASIS OF CALCULATION OF El AND AFR PARAMETERS 

2.2 It is assumed that the balance between the original fuel and air mixture and the resultant 

state of the exhaust emissions as sampled can be represented by the following equation: 

CmHn + P0[R(O2) + S(N2) + T(CO2) + h(H2O)] 

 = P1(CO2) + P2(N2) + P3(O2) + P4(H2O) + P5(CO) + P6(CxHy) + P7(NO2) + P8(NO) 

from which the required parameters can, by definition, be expressed as 

( )

3

CO

3

C H

10 EI CO M P

mM nM

⎡ ⎤ = ⎢ ⎥ ⎣ ⎦ +

( )

3

HC

6

C H

10 EI HC M xP

mM nM

⎡ ⎤ = ⎢ ⎥ ⎣ ⎦ +

expressed as methane equivalent 

( )( ) 2

3

NO

X 78

C H

10

EI NO

M

P P

mM nM

⎡ ⎤

= + ⎢ ⎥ ⎢ ⎥ + ⎣ ⎦

AIR

0

C H

AFR M P

mM nM

⎡ ⎤ = ⎢ ⎥ ⎣ ⎦ +

expressed as NO2 equivalent 

Supplemental information

This is a slightly different formulation for AFR than that stated in 7.1.3, “Basic parameters”. In this 

formulation “m”, the number of C atoms in characteristic fuel molecule is placed within the 

bracket. There is no particular advantage to using one formulation over the other. 
 

Page 116 

2.2 Values for fuel hydrocarbon composition (rn, n) are assigned by fuel specification or 

analysis. If only the ratio n/m is so determined, the value m = 12 may be assigned. The 

mole fractions of the dry air constituents (R, S, T) are normally taken to be the 

recommended standard values but alternative values may be assigned, subject to the 

restriction R + S + T = 1 and the approval of the certificating authority. 

2.3 The ambient air humidity, h, is as measured at each test condition. It is recommended 

that, in the absence of contrary evidence as to the characterization (x, y) of the exhaust 

hydrocarbon, values of x = 1 and y = 4 are assigned. 

2.4 Determination of the remaining unknowns requires the solution of the following set of 

linear simultaneous equations, where (1) to (4) derive from the fundamental atomic 

conservation relationships and (5) to (9) represent the gaseous product concentration 

relationships. 

(1) M = TP0 = P1 + P5 + xP6

(2) n + 2hP0 = 2P4 + yP6

(3) (2R + 2T + h)P0 = 2P1 + 2P3 + P4 + P5 + 2P7 + P8

(4) 2SP0 = 2P2 + P7 + P8

(5) [CO2]PT = P1

(6) [CO]PT = P5

(7) [HC] PT = xP6

(8) [NOX]CPT = ηP7 + P8

(9) [NO]PT = P8

(10) PT = P1 + P2 + P3 + P4 + P5 + P6 + P7 + P8

The above set of conditional equations is for the case where all measured concentrations are true 

ones, that is, not subject to interference effects or to the need to correct for sample drying. In 

practice, interference effects are usually present to a significant degree in the CO, NOX and NO

measurements, and the option to measure CO2 and CO on a dry or partially dry basis is often 

used. The necessary modifications to the relevant equations are described in 2.5 and 2.6. 

2.5 The interference effects are mainly caused by the presence of CO2 and H2O in the 

sample which can affect the CO and the NOX analysers in basically different ways. The 

CO analyser is prone to a zero-shifting effect and the NOX analyser to a sensitivity 

change, represented thus: 

[CO] = [CO]m + L[CO2] + M[H2O] 

and [NOX]c = [NOX]cm(1 + L'[CO2] + M'[H2O])

which transform into the following alternative equations to (6), (8) and (9), when 

interference effects require to be corrected, 
 Page 117 

(6A) [CO]m PT + LP1 + MP4 = P5

(8A) [NOX]cm (PT +L'P1 +M'P4) = ηP7 + P8

(9A) [NO]m (PT + L'P1 + M'P4) = P8

The option to measure CO2 and CO concentrations on a dry or partially dry sample basis, that is, 

with a sample humidity reduced to h,, requires the use of modified conditional equations as 

follows: 

 (5A) [CO2]d(PT - P4)(1 + hd) = P1

and 

[CO]d (PT - P4)(1 + hd) = P5

However, the CO analyser may also be subject to interference effects as described in 2.5 above 

and so the complete alternative CO measurement concentration equation becomes 

(6B) [CO]md (PT - P4)(1 + hd) + LP1 + Mhd (PT - P4) = P5

3. ANALYTICAL FORMULATIONS 

3.1 General 

Equations (1) to (10) can be reduced to yield the analytical formulations for the EI and AFR

ameters, as given in 7.1 to this appendix. This reduction is a process of progressive elimination of 

the roots P0, P1 through P8, PT making the assumptions that all concentration measurements are 

of the "wet" sample and do not require interference corrections or the like. In practice the option is 

often chosen to make the CO2 and CO concentration measurements on a "dry" or "semi-dry" 

basis; also it is often found necessary to make interference corrections. Formulations for use in 

these various circumstances are given in 3.2, 3.3 and 3.4 below. 

3.2 Equation for conversion of 

dry concentration measurements 

to wet basis 

Concentration wet = K x concentration dry; that is. 

 [ ] = K [ ]d

The following expression for K applies when CO and CO2 are determined on a "dry" basis: 

{ ( )( )([ ] [] ( )) ( )( [ ])[ ]}( )

( ) ( )( ) { } ( ) [ ] ( )( ) [ ]

2

2

4 / | / | 2 NO 2 HC / 2 | / | / HC 1

2 2 / 1 CO | / | 2 1 |1 | CO

d

d d d d

n mT n mT h x h y x n m h

K

h nm h nmT h h

+ + − − ++ − + = + + + − − −+

3.3 Interference corrections 

The measurement of CO and/or NO may require corrections for interference by the sample CO2

and water concentrations before use in the above analytical equations. Such corrections can 

normally be expressed in the following general ways: 

[CO] = [CO]m + L[CO2} + M[H2O] 
 

Page 118 

[][] [ ] CO CO CO2 1

d

d md

d

h L M

h

⎛ ⎞

=+ + ⎜ ⎟ ⎝ ⎠ +

[NO] = [NO]m (1 + L'[CO2] + M'[H2O]) 

η[NO2] = ([NOX]cm - [NO]m)(1 + L'[CO2] + M'[H2O] 

3.4 Equation for estimation of sample water content 

Water concentration in sample 

[ ] ( )([ ] [ ] [ ])

( ) ( )[ ] 0 2

2

0

| / 2 | | P | CO CO HC H O 2 HC

1 P

nmh m

y x T m

+ ++ = − +

Where 

( )

( ) [ ] 0

2

P

41 2

Z nm

m

h TZ

− = + −

and 

[ ] ( )[ ] [ ]

[ ][ ][ ]

2

2

2 CO | 2 | | 2 | HC NO

CO + CO + HC

x yx Z−− − + =

It should be noted that this estimate is a function of the various analyses concentration readings, 

which may themselves require water interference correction. For better accuracy an iterative 

procedure is required in these cases with successive recalculation of the water concentration until 

the requisite stability is obtained. The use of the alternative numerical solution methodology (4) 

avoids this difficulty. 

4. ALTERNATIVE METHODOLOGY -NUMERICAL SOLUTION 

4.1 As an alternative to the analytical procedures summarized in 3 above, it is possible to 

obtain readily the emissions indices, fuel/air ratio, corrected wet concentrations, etc., by a 

numerical solution of equations (1) to (10) for each set of measurements, using a digital 

computer. 

4.2 In the equation set (1) to (10) the actual concentration measurements are substituted 

using whichever of the alternative equations (5A), (6A), etc. applies for the particular 

measuring system, to take account of interference corrections and/or dried sample 

measurements. 

4.3 Suitable simple two-dimensional array equation-solving computer programmes are widely 

available and their use for this purpose is convenient and flexible, allowing ready 

incorporation and identification of any sample drying options and interference or other 

corrections. 
 Page 119 

Supplemental information

Details explaining various calculation procedures, can be found in ARP 1533, “Procedure for the 

Calculation of Gaseous Emissions from Aircraft Turbine Engines.” ARP 1533 includes, among other 

things, the combustion chemical equation, the basic matrix solution with computer programs, 

derivation of equations and a sample calculation. 
 

Page 120 

ATTACHMENT F TO ICAO MANUAL APPENDIX 5. 

SPECIFICATIONS FOR ADDITIONAL DATA 

As required in 3.2 of Appendix 5, in addition to the measured sample constituent concentrations, 

the following data shall also be provided: 

a) inlet temperature: measured as the total temperature at a point within one diameter of the 

engine intake plane to an accuracy of ±0.5°C; 

b) inlet humidity (kg water/kg dry air): measured at a point within 15 m of the intake plane 

ahead of the engine to an accuracy of ±5 per cent of reading; 

c) atmospheric pressure: measured within 1 km of the engine test location and corrected as 

necessary to the test stand altitude to an accuracy of ±100 Pa; 

d) fuel mass flow: by direct measurement to an accuracy of ±2 per cent; 

e) fuel H/C ratio: defined as n/m, where CmHn is the equivalent hydrocarbon representation 

of the fuel used in the test and evaluated by reference to the engine fuel type analysis; 

f) engine parameters: 

1) thrust: by direct measurement to an accuracy of ±1 per cent at take-off power 

and ±5 per cent at the minimum thrust used in the certification test, with linear 

variation between these points; 

2) rotation speed(s): by direct measurement to an accuracy of at least ±0.5 per 

cent; 

3) gas generator airflow: determined to an accuracy of ±2 per cent by reference to 

engine performance calibration. 

The parameters a), b), d) and f) shall be determined at each engine emissions test setting, while 

c) shall be determined at intervals of not less than 1 hour over a period encompassing that of the 

emissions tests. 
 Page 121 

[THIS PAGE INTENTIONALLY LEFT BLANK] 
 

Page 122 

XII. ICAO MANUAL APPENDIX 2 

APPENDIX 2. SMOKE EMISSION EVALUATION 

Supplemental information

The smoke measurement standard described in ICAO Annex 16, Volume II, Second Edition, 1993, 

Appendix 2, is an indirect measure of smoke plume visibility which is obtained by using a filter to trap 

smoke particles contained in a predetermined mass of exhaust gas, and measuring the loss of 

reflectance, i.e., degree of staining, of this filter relative to the absolute reflectance of the filter when 

clean or free of stain. It is a reasonably repeatable, simple procedure, but does not provide a direct 

measure of either plume visibility or any properties of the smoke particles, size, size distribution or 

mass. The SAE estimates the practically achievable precision of the smoke number by this method 

to be within ±3 SN (smoke numbers). The equivalent SAE procedure is found in Aerospace 

Recommended Practice ARP1179, "Aircraft Gas Turbine Engine Exhaust Smoke Measurement". 

1. INTRODUCTION AND DEFINITIONS 

Note.- The procedures specified here are concerned with the acquisition of representative 

exhaust samples and their transmission to, and analysis by, the emissions measuring system. 

1.1 Variations in the procedure contained in this Appendix shall only be allowed after prior 

application to and approval by the certificating authority. 

1.2 Where the following expressions and symbols are used in this Appendix, they have the 

meanings ascribed to them below: 

Sampling reference size. The sample mass, 16.2 kg/m2 of stained filter area, which if 

passed through the filter material results in a change of reflectance which gives a value of 

the SN parameter. 

Sampling size. A chosen exhaust sample, the magnitude of whose mass (expressed in 

kilograms per square metre of stained filter surface area) lies in the range prescribed in 

2.5.3 h) of this Appendix which, when passed through the filter material, causes a change 

in reflectance yielding a value for the SN' parameter. 

Sampling volume. The chosen sample volume (expressed in cubic metres) whose 

equivalent mass, calculated as indicated in 3 of this Appendix, conforms to the above 

definition of sampling size. 

SN. Smoke Number; Dimensionless term quantifying smoke emission level based upon 

the staining of a filter by the reference mass of exhaust gas sample, and rated on a scale 

of 0 to 100 (see 3 of this Appendix). 

SN'. Smoke Number obtained from an individual smoke sample, not necessarily of the 

reference size, as defined in 3 of this Appendix. 

W.. Mass of individual exhaust gas smoke sample, in kilograms, calculated from the 

measurements of sample volume, pressure and temperature (see 3 of this Appendix). 
 Page 123 

2. MEASUREMENT OF SMOKE EMISSIONS 

2.1 Sampling probe for smoke emissions 

a) The probe shall be made of stainless steel. if a mixing probe is used, all sampling orifices 

shall be of equal diameter. 

b) The probe design shall be such that at least 80 per cent of the pressure drop through the 

probe assembly is taken at the orifices. 

c) The number of sampling orifices shall not be less than 12. 

d) The sampling plane shall be as close to the engine exhaust nozzle exit plane as 

permitted by considerations of engine performance but in any case shall be within 0.5 

nozzle diameters of the exit plane. 

e) The applicant shall provide evidence to the certificating authority, by means of detailed 

traverses, that the proposed probe design and position does provide a representative 

sample for each prescribed power setting. 

Supplemental information

The following diagram, Figure A2-1, is an artists rendition of an averaging probe in a cruciform 

configuration, with the minimum number of 12 orificies located on centers of equal area. While typical 

of averaging probes the actual design is not limited to a cruciform configuration. As with any design, 

this configuration would have to be proven by means of a detailed traverse. 

Supplemental Figure A2-1: 12 Point Cruciform Core Averaging Rake 
 

Page 124 

Sampling emissions from aircraft gas turbine engines is difficult and has been under continual study 

and development. Lacking a definition of representative or constraints on a traversing pattern or 

protocol, some technical guidance can be obtained from looking at the methods described in early 

versions of SAE ARP 1179 and the Federal Regulations, developed primarily from experience within 

the industry in testing turbojet engines. 

ARP 1179 stated that the tip of the sampling probe must be located between the engine exit plane 

and 6 inches downstream of the plane. The probe was to be oriented normal to this plane. 

An initial traverse was required to arrive at an appropriate probe location for subsequent testing and a 

minimum traverse pattern was defined. This was a requirement for any given engine model or 

installation and at each engine power setting. The traverse was to be made radially at two locations 

90 degrees apart, with 5 equal area sampling locations on each of the two radii. For each power 

setting, the point nearest the arithmetic average SN of the 10 points, was to be identified and entered 

as a permanent record of the particular engine or installation. All subsequent samples for that 

particular power setting were to be taken at this location. The sampling traverse needs to be repeated 

after any engine modification involving possible aerodynamic changes. 

Supplemental Figure A2-2: ARP1179 Early Traverse Pattern 

In the first version of 40 CFR Part 87, Federal Register, Vol. 38, No. 136, July 17, 1973, the sampling 

protocol required a minimum of 12 sampling points. Either mixing or individual probes were 

acceptable. At least three different radial positions were to be used in each of four sampling 

quadrants. If the minimum of 12 sampling points were used, the points in circumferentially adjacent 

sampling areas were to be separated in any direction by a distance not less than 0.1 tailpipe radius or 

0.1 annular height, as applicable; if the number of sampling points (n) was greater than 12, they were 

to be equal in number in each quadrant or sector, and the minimum separations were to be reduced 

by a factor of 12/n. 

The axial sampling plane had to be as close to the plane of the exit nozzle as engine performance 

parameters would permit, but in any case had to be within one exit nozzle diameter of the exit plane. 

In all cases, the probe had to be designed to obtain a representative sample over the area of the 

entire exhaust nozzle, on mixed fan engines, nonmixed fan engines, turbojets, turboprops, and 

auxiliary power engines. Finally, the multipoint probe had to be designed to minimize the errors due to 

pollutant stratification, whether the stratification was due to combustor design, mixing, lack of mixing, 

or engine design such as mixing of fan and core air. 

In Federal Register Vol. 43, No. 58, March 24, 1978, this sampling protocol was modified to include a 

specific angular reference, i.e., if the minimum of 12 sampling points were used, the points in 

circumferentially adjacent sampling areas were to be separated by at least 80° angular displacement. 

The most recent version of ARP 1179 has the axial location of the sampling plane as close to the exit 

nozzle as engine performance parameters permit, but in any case within 0.5 exit nozzle diameter of 

the exit plane. 
 Page 125 

The sampling points are to be arranged over the exhaust nozzle exit area for straight turbojet, 

turboprop, turboshaft, and mixed flow (or confluent flow) fan engines, and over the core nozzle exit 

area for nonmixed fan engines. In order to promote uniformity of smoke measurements, a specific 

probe design must be standardized for use with a given type or series of engines, and the suitability 

of this probe must be demonstrated, by means of detailed traverse measurements in the sampling 

plane. 

Sampling for smoke has been and continues to be a difficult problem to address and manage. If at all 

possible, samples should be taken from the core and analytically extended to the total exhaust plume. 

As with gaseous emissions, consensus seems to be that averaging probes sampling points should be 

located on centers of equal area rather than equal spacing. The number of sampling orifices should 

probably be more than the 12 minimum required. 

2.2 Sampling line for smoke emissions 

2.2.1 The sample shall be transferred from the probe to the sample collection system via a line 

of 4.0 to 8.5 mm inside diameter taking the shortest route practicable which shall in no 

case be greater than 25 m. The line temperature shall be maintained at a temperature 

between 600C and 1750C with a stability of ± l50C, except for the distance required to cool 

the gas from the engine exhaust temperature down to the line control temperature. 

2.2.2 Sampling lines shall be as "straight through" as possible. Any necessary bends shall 

have radii which are greater than 10 times the inside diameter of the lines. The material 

of the lines shall be such as to discourage build-up of particulate matter or static 

electricity. 

Note. — Stainless steel, copper or carbon-loaded grounded polytetrafuoroethylene (PTFE) meet 

these requirements. 

Supplemental information

The line from the probe to the sampling system should be heated to prevent water from condensing. 

It should be short and relatively straight to discourage loss of particulate matter to the walls and at 

bends. It should be of reasonably small diameter to keep the flow rate high, minimizing particle 

dropout and wall loss. It should be constructed of a material that discourages static buildup which can 

lead to particle loss. If carbon-loaded polytetrafluoroethylene (PTFE - Teflon) is used as a line 

material it is important that the sample gas have a chance to cool before entering the sample line to 

protect the Teflon from burning. 

2.3 Smoke analysis system 

Note. — The method prescribed herein is based upon the measurement of the reduction in 

reflectance of a filter when stained by a given mass flow of exhaust sample. 

The arrangement of the various components of the system for acquiring the necessary stained 

filter samples shall be as shown schematically in Figure 2-1. An optional bypass around the 

volume meter may be installed to facilitate meter reading. The major elements of the system 

shall meet the following requirements: 

a) sample size measurement: a wet or dry positive displacement volume meter shall be 

used to measure sample volume to an accuracy of ± 2 per cent. The pressure and 

temperature at entry to this meter shall also be measured to accuracies of 0.2 per cent 

and ± 2 oC respectively; 

b) sample flow rate measurement: the sample flow rate shall be maintained at a value of 14 

± 0.5 L/min and the flowmeter for this purpose shall be able to make this measurement 
 

Page 126 

with an accuracy of ± 5 per cent; 

c) filter and holder: the filter holder shall be constructed in corrosion-resistant material and 

shall have the flow channel configuration shown in Figure 2-1. The filter material shall be 

Whatman type No. 4, or any equivalent approved by the certificating authority; 

d) valves: four valve elements shall be provided as indicated in Figure 2-1: 

1) valve A shall be a quick-acting, full-flow, flow diverter enabling the incoming 

sample to be directed through the measuring filter or around the bypass circuits 

of shut off; 

2) Note. — Valve A may, if necessary, consist of two valves interlocked to give the 

requisite function. 

2) valves B and C shall be throttling valves used to establish the system flow rate; 

3) valve D shall be a shut-off valve to enable the filter holder to be isolated; 

all valves shall be made of corrosion-resistant material; 

e) vacuum pump: this pump shall have a no-flow vacuum capability of -75 kPa with respect 

to atmospheric pressure; its full-flow rate shall not be less than 28 L/min at normal 

temperature and pressure; 

f) temperature control: the incoming sample line through to the filter holder shall be 

maintained at a temperature between 60 °C and 175 °C with a stability of ± 15 °C; 

Note. — The objective is to prevent water condensation prior to reaching the filter holder and 

within it. 

g) If it is desired to draw a higher sample flow rate through the probe than through the filter 

holder, an optional flow splitter may be located between the probe and valve A (Figure 2-

1), to dump excess flow. The dump line shall be as close as possible to probe off-take 

and shall not affect the ability of the sampling system to maintain the required 80 per cent 

pressure drop across the probe assembly. The dump flow may also be sent to the CO2

analyser of complete emissions analysis system. 

h) If a flow splitter is used, a test shall be conducted to demonstrate that the flow splitter 

does not change the smoke level passing to the filter holder. This may be accomplished 

by reversing the outlet lines from the flow splitter and showing that, within the accuracy of 

the method, the smoke level does not change. 

i) leak performance: the sub-system shall meet the requirements of the following test: 

1) clamp clean filter material into holder, 

2) shut off valve A, fully open valves B, C and D. 

3) run vacuum pump for one minute to reach equilibrium conditions; 

4) continue to pump and measure the volume flow through the meter over a 

period of five minutes. This volume shall not exceed 5 L (referred to normal 

temperature and pressure)and the system shall not be used until this standard 

has been achieved. 

j) reflectometer: the measurements of the reflectance of the filter material shall be by an 

instrument conforming to the American National Standards Institute (ANSI) Standard No. 
 Page 127 

PH2.17/1977 for diffuse reflection density. The diameter of the reflectometer light beam 

on the filter paper shall not exceed D/2 nor be less than D/10 where D is the diameter of 

filter stained spot as defined in Figure 2-1. 

Supplemental information

Maintaining the diameter of the reflectometer light beam on the filter paper between these limits 

insures averaging over a reasonable area of the filter. This is most important for stained spots which 

are not uniform in consistency of stain due to edge effects at the boundary of the stain and graininess 

within the spot particularly for lightly loaded filters, i.e., low SN. 

Figure A2-3. Smoke analysis system 

2.4 Fuel specifications 

The fuel shall meet the specifications of Appendix 4. Additives used for the purpose of smoke 

suppression (such as organo-metallic compounds) shall not be present. 

Supplemental information

This fuel specification requirement is preempted by FAR 34 Subpart H, §34.81, Fuel specifications, 

which state “fuel having specifications as provided in §34.61 shall be used in smoke emission 

testing.“ 
 

Page 128 

2.5 Smoke measurement procedures 

2.51 Engine operation 

2.5.1.1 The engine shall be operated on a static test facility which is suitable and properly 

equipped for high accuracy performance testing. 

2.5.1.2 The tests shall be made at the power settings approved by the certificating authority. The 

engine shall be stabilized at each setting. 

2.5.2 Leakage and cleanliness checks 

No measurements shall be made until all sample transfer lines and valves are warmed up and 

stable. Prior to a series of tests the system shall be checked for leakage and cleanliness as 

follows: 

a) leakage check: isolate probe and close off end of sample line, perform leakage test 

as specified in 2.3g) with the exceptions that valve A is opened and set to "bypass", valve 

D is closed and that the leakage limit is 2 L. Restore probe and line interconnections; 

b) cleanliness check: 

1) open valves B, C and D; 

2) run vacuum pump and alternately set valve A to "bypass" and "sample" to purge 

the entire system with clean air for five minutes; 

3) set valve A to "bypass"; 

4) close valve D and clamp clean filter material into holder. Open valve D; 

5) set valve A to "sample" and reset back to "bypass" after 50 kg of air per square 

metre of filter has passed through the filter material; 

6) measure resultant filter spot SN' as described in paragraph 3 of this Appendix.; 

7) I f this SN' exceeds 3, the system shall be cleaned (or otherwise rectified) until a 

value lower than 3 is obtained. 

The system shall not be used until the requirements of these leakage and cleanliness checks 

have been met. 

Supplemental information

Leakage checks are to ensure clean air does not leak into the system, thereby diluting the sample 

and lowering the SN. Cleanliness checks ensure that the sample will not be contaminated, resulting 

in higher than warranted SN values. To minimize contamination problems, if the probe cannot be 

moved out of the sampling stream during engine start up, the probe and lines can be back pressured 

with a suitable clean gas. 

2.5.3 Smoke measurement 

Smoke measurement shall be made independently of other measurements unless the smoke 

values so measured are significantly below the limiting values, or unless it can be demonstrated 

that the smoke values from simultaneous smoke and gaseous emission measurements are valid, 

in which case smoke measurements made be made simultaneously with gaseous emissions 

measurements. In all cases the bend radius requirements for sampling lines detailed in 2.2.2 

shall be strictly observed. The smoke analysis sub-system shall be set up and conform to the 
 Page 129 

specifications of 2.3. Referring to Figure 2-1, the following shall be the major operations in 

acquiring the stained filter specimens: 

a) during engine operations with the probe in position, valve A shall not be placed in the noflow condition, otherwise particulate buildup in the lines might be encouraged; 

b) set valve A to "bypass" close valve D and clamp clean filter into holder. Continue to draw 

exhaust sample in the bypass setting for at least five minutes while the engine is at or 

near to the requisite operating mode, valve C being set to give a flow rate of 14 ± 0.5 

L/min; 

c) open valve D and set valve A to "sample", use valve B to set flow rate again to value set 

in b); 

d) set valve A to "bypass" and close valve D, clamp clean filter material into the holder; 

Supplemental procedure

As a result of the manufacturing process, Whatman type No. 4 filters will be found to be slightly 

different, one side to the other, when measured using a reflectometer. This difference can approach 

2 SN in value. During the filter cutting process, (filter disks are cut from larger sheets), the filters take 

on a slight set so there are distinct concave and convex sides. Filters seem to be cut, packaged and 

shipped in batches which preserves the top/bottom-concave/convex relationship. To eliminate 

unnecessary errors in measurement, it is advisable to load the filters in the filter holder in a consistent 

manner, i.e., always concave or convex side up. This should be kept in mind as well when 

determining the absolute reflectance of the clean filter, e.g., if the filter is placed in the filter holder 

concave side up, that is facing the sampling stream, then the absolute reflectance of the concave side 

is the reference measurement to be made. 

e) when the engine is stabilized on condition, allow one minute of sample flow with settings 

as at d); 

f) open valve D, set valve A to "sample", reset flow rate if necessary, and allow chosen 

sample volume (see h) to pass, before setting valve A back to "bypass" and close valve 

D; 

g) set aside stained filter for analysis, clamp clean filter into holder; 

h) the chosen sample sizes shall be such as to be within the range of 12 kg to 21 kg of 

exhaust gas per square metre of filter, and shall include samples which are either at the 

value of 16.2 kg of exhaust gas per square metre of filter or lie above and below that 

value. The number of samples at each engine operating condition shall not be less than 

3 and e) to g) shall be repeated as necessary. 

3. CALCULATION OF SMOKE NUMBER 

FROM MEASURED DATA 

The stained filter specimens obtained as outlined in 2.5.3 shall be analysed using a reflectometer 

as specified in 2.3. The backing material used shall be black with an absolute reflectance of less 

than 3 per cent. The absolute reflectance reading Rs of each stained filter shall be used to 

calculate the reduction in reflectance by 

SN' = 100(1-Rs/Rw) 

Where Rw is the absolute reflectance of clean filter material. 

Supplemental information
 

Page 130 

Reflectometers sometimes come equipped with a pseudo 'black body' cup like device which is used 

to set the meter zero response. It is not a good idea to use a device like this as backing material, 

although it does have an absolute reflectance of less than 3%. A solid surface, which applies light 

and equal pressure over the filter area to be measured, and which meets the less than 3% absolute 

reflectance requirement, is preferred. 

The masses of the various samples shall be calculated by 

W = 0.348 PV/T x 10-2 (kg) 

Where P and T are, respectively, the sample pressure in pascals and the temperature in kelvin, 

measured immediately upstream of the volume meter. V is the measured sample volume in cubic 

metres. 

For each engine condition in the case that the sample sizes range above and below the reference 

value, the various values of SN' and W shall be plotted as SN' versus log W/A, where A is the 

filter stain area (m2). Using a least squares straight line fit, the value of SN' for W/A=16.2 kg/m2

shall be estimated and reported as the Smoke Number (SN) for that engine mode. Where 

sampling at the reference size value only is employed, the reported SN shall be the arithmetic 

average of the various individual values of SN'. 

Supplemental information

Experience has shown that plotting the set of measured SN’s against the logarithm of the equivalent 

W/A’s results in a straight line. ICAO requires a least squares straight line fit to the SN’ vs. log W/A 

data, sometimes referred to as the regression of SN’ on log W/A. 

The calculation is straightforward, and for the limited data sets involved with jet engine testing, can be 

performed on a hand held calculator or by means of a desktop computer spreadsheet. The values to 

be calculated are the straight line intercept, a, and slope, b.. The equations to be solved for the least 

squares estimates of the intercept and slope, SN’≡ yi and log(W/A)≡xi, are: 

( )( )

( )

1

2

1

n

i i

i

n

i

i

x xy y

x x

b =

=

− −

=

−

∑

∑

x bar and y bar are the means of xi and yi respectively and i refers to the sample number. For the 

testing required a simple table with columns for sample number i, SN’,W/A, log (W/A) and [log(W/A)]2

 in 

collecting and organizing the data and intermediate calculations. 

For example, in the case where the minimum number of 3 smoke samples is taken a table might look like: 

y a bx = +
 Page 131 

Table A2-1 TABLE FOR CALCULATING SN

Sample number 

i

(SN'I ) Log(Wi

/A) log(Wi/A)*(SN'I) [log(Wi/A)]2

1 

2 

3 

Average 

Sum 

Using this table and the previously calculated values of SN prime and W/A, it is a simple matter to 

calculate the estimated slope and intercept, and from them the least squares straight line. The 

reporting value of SN can be estimated from a plot of this straight line or calculated from the equation. 
 

Page 132 

30. EXHIBIT 1

Engine and Propeller Directorate 

And 

Office of Environment and Energy 

Inter-Office Management Plan for Aircraft Engine

Fuel Venting and Exhaust Emissions

The Engine and Propeller Directorate (EPD) and the Office of Environment and Energy 

(AEE) agree that an inter-office management plan is needed to strengthen FAA's 

Participation in, and oversight of aircraft engine fuel venting and exhaust emission 

certification. The Participating entities believe that the actions and procedures identified 

in this document provide the foundation for a Fuel Venting and Exhaust Emissions 

Procedures management plan. 

The objective of this management plan is to define the roles and responsibilities of both 

entities, optimize the use of FAA resources, and provide adequate technical and 

procedural guidance for demonstrating compliance to 14 Code of Federal Regulations 

(CFR) Part 34. These actions are needed to: 

1. Strengthen the FAA's surveillance of aircraft engine fuel venting and exhaust 

emissions certification; 

2. Improve the application of technical guidance and procedural practices, and 

3. Promote improved inter-office communication and cooperation. 

Roles and Responsibilities: EPD and AEE agree that to achieve a step improvement in 

business practices between their respective organizations, the roles and responsibilities of 

Participating organizations need to be clearly defined. The following describes those 

roles and responsibilities: 

XIII. Organization Role Responsibility 

Office of Environment 

and Energy 

Regulatory and 

Standardization 

• Liaison with ICAO and CAEP 

• Coordinates with EPA (40 CFR Part 87) 

• Codifies fuel venting and exhaust 

emissions regulations (14 CFR 34) 

• Processes applications for Exemptions 

(14 CFR Part 11) 

• Audits and evaluates delegated functions 

• Approves new or equivalent test 

procedures (14 CFR 34) 

• Provides Policy and Guidance (AC-34) 
 Page 133 

Organization Role Responsibility 

Engine and Propeller 

Directorate (EPD) 

Implementation 

and Compliance 

• Provides resources 

ANE-110 Directorate 

Contact Point 

• Acts as EPD Focal Point for AEE on engine 

 technology issues and any other general 

 issues 

• Assures compliance to 14 CFR Part 

33.1(b). 

• Indirectly monitors all non-standard 

 certification requests (Exemptions & 

 Equivalent Safety Findings) as well as all 

 AEE guidance and policy publications. 

ACE/ECO Compliance • Issues type certificates 

• Reviews and approves engine fuel venting 

 and exhaust emissions test plans and test 

data 

• Determines compliance with 14 CFR Part 

34 

• Appoints Designated Engineering 

 Representatives (DERs) and assesses their 

 qualifications for witnessing tests and 

 reviewing test plans and test data, in 

 accordance with the DER appointment and 

 renewal process as defined within 14 CFR 

 Part 183. 

• Supervises DERs on the fuel venting and 

 exhaust emissions compliance requirements 

Delegation: Delegation of Authority to support the roles and responsibilities in fuel venting and exhaust 

emission certification programs is extended to the Participating entities and is defined by AEE as follows: 

1. AEE delegates the determination of compliance and acceptability of test plans, test 

 data and test reports to the cognizant ACO/ECO organization. 

2. AEE accepts the use of DERs as an extension of its delegation to the cognizant 

 ACE/ECO organization. 

Performance:

AEE will periodically evaluate the performance of its delegation to the ACOs/ECO by 
 

Page 134 

1. Observing the conduct of standard test practices and witnessing the conduct of 

 new or alternate methods of compliance, as deemed necessary. 

2. Conducting a random audit of smoke and emissions test plans for appropriate content. 

3. Notifying ACOs/ECO/ANE-110 in a timely manner of both the need for and the extent of 

Participation in the certification process. 

4. Reviewing DER oversight, such as qualifications and appointment. 

The ACOs will provide: 

1. Timely notification to AEE staff of upcoming smoke and emission test dates and locations. 

2. Timely responses to requests for test plans and test reports for audit purposes. 

Performance Metrics: AEE and EPD will implement the following performance metrics that will monitor 

fuel venting and exhaust emissions delegated functions: 

1. The elapsed time for AEE to respond to ACOs/ECO/ANE-110 requests for 

policy/guidance. 

2. The elapsed time for AEE to respond to requests for Exemptions. 

3. AEE attendance or Participation in DER Recurrent Seminars 

4. The percentage of recent emission compliance findings that comply with policy and guidance.