33-05-003 Piston Engine Emissions_Swiss FOCA_Summary 

Report_070612_rit 

Federal Department of the Environment, Transport, Energy and 

Communications DETEC 

Federal Office of Civil Aviation FOCA 

Aviation Policy and Strategy 

Environmental Affairs 

AIRCRAFT PISTON ENGINE EMISSIONS 

SUMMARY REPORT 

Purpose of this paper: This paper aims to inform interested parties about the development of aircraft 

piston engine emission factors. These have been measured and are provided by Swiss FOCA for the 

primary purpose of emission inventory calculations. Furthermore, FOCA presents findings about emissions performance and in-flight operation of aircraft piston engines and recommendations for emissions reduction. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

FOCA, CH-3003 Bern

Reference: 0 / 3/33/33-05-003 ECERT 

Contact person: Theo Rindlisbacher 

Tel. +41 31 325 93 76, Fax +41 31 325 92 12, theo.rindlisbacher@bazl.admin.ch

This document has been released for publication by FOCA, Aviation Policy and Strategy, Director M. Zuckschwerdt, 13.06.2007 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

ABSTRACT 

According to Swiss aviation law (SR 748.0, LFG Art. 58), emissions from all engine powered aircraft 

have to be evaluated and tested. The legal requirement also incorporates aircraft engines that are 

currently unregulated and do not have an ICAO1

 emissions certification – like piston, helicopter, turboprop and small jet engines. Credible emissions data are necessary for emission and immission inventory purposes, environmental impact assessments and for issues directly related to environmental 

protection. 

Up to now, there have only been few emissions data available for aircraft piston engines. This report 

tries to fill this gap of knowledge in a comprehensive approach. The following aspects are documented 

in this report and in its Appendices: 

• Emissions performance for a wide range of existing aircraft piston engines. 

• A methodology for cost effective standardized on ground emission measurements of aircraft 

piston engines. 

• A methodology for the calculation of aircraft piston engine emissions. 

• General principles of aircraft piston engine combustion and the effect of pilot operations on 

emissions. 

• Research for emission reduction through optimization of pilot operations, new aircraft piston 

engine concepts, technological improvements and the use of cleaner AVGAS. 

The presented material serves FOCA for 

• Calculation of more complete aviation emission inventories in the context of legal national and 

international environmental requirements. 

• Observation of the environmental impact of piston engine aircraft. 

• Reduction of piston engine aircraft emissions. 

• Pilot education. 

As far as measurements are concerned, FOCA plans to increase the number of measured engines in 

the future. For other engine families without an ICAO emissions certification, like helicopter turbines 

and small jet engines, there is still a lack of emissions data and FOCA plans to work on respective 

packages, based on its aviation law. 

June, 2007 Theo Rindlisbacher

 

1 International Civil Aviation Organization
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

CONTENTS Page

1. General information 9 

 

1.1 Background 9 

1.2 Main scope and objectives of the project 10 

2. Summary of results 11 

2.1 FOCA data sheets and their practical application 11 

2.1.1 General methodology for emissions calculation 11 

2.1.2 Suggested times in mode for emissions calculation 11 

2.1.3 Cruise emissions factors 12 

2.1.4 Calculated LTO and 1 hour cruise emissions on data sheets 12 

2.1.5 Data quality and accuracy 13 

2.1.6 Data download 14 

2.2 General findings about aircraft piston engine emissions 15 

2.2.1 Combustion basics 15 

a) What goes in? Composition of AVGAS 100LL 15 

b) How much air to make the fire? 16 

c) What comes out? 17 

d) Properties of pollutants 17 

2.2.2 Air/fuel mixture adjustments 18 

a) Dominant “old tech” engines require manual mixture control 18 

b) Rich and lean mixture definition with lambda 19 

c) Mixer = lambda control 20 

d) Typical values for lambda 20 

e) Influence of mixer settings on engine temperatures and power 21 

f) Influence of mixer settings on emissions 22 

g) Influence of mixer settings summary 24 

h) Why “full rich” at high power for “old tech” engines? 24 

i) Why “rich” near idle power? 25 

j) Uneven distribution of mixture and temperature in “old tech” engines 25 

k) Investigated manual mixture setting procedures 28 

l) Mixture adjustment technique with fuel flow 29 

2.2.3 Typical emission factors and magnitude of emissions 30 

a) Pollutants of “old tech” engines during landing and take-off cycle (“full rich” mixture) 30 

b) Pollutants during cruise (at or near “peak EGT”) 33 

c) Emissions for aerodrome circuits (“old tech” engines) 34 

d) Emissions for landing and take-off cycle 35 

e) Emissions for cruise 36 
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f) Emissions of modern turbo diesel engines – a comparison 36 

g) Contribution of piston engines to total aviation emissions 38 

 

2.3 Optimization of fuel burn and emissions 38 

2.3.1 “Old tech” gasoline engines 38 

a) Use of unleaded AVGAS 38 

b) Power setting, choice of speed and altitude for lowest possible CO2 emissions in cruise 38 

c) Manual mixture management (Climb, Cruise, Descent/Approach) 43 

2.3.2 Choice of engine technology 44 

a) FADEC for gasoline engines 44 

b) Turbo Diesel engines 44 

 

3. Outlook – planned future work 45 

 

3.1 Number of measured aircraft piston engines 45 

3.1.1 “Old tech” engines and new engines concepts 45 

3.1.2 Modernized “old tech” engines with FADEC 45 

 

3.2 Unleaded AVGAS 45 

3.2 Emissions data for helicopter turbines and small turbofans 46 

3.3 International activities 46 

4. List of acronyms and abbreviations 47 

5. Bibliography 49 

Appendix 1: Measurement System 

a) Minimum requirements met by FOCA low cost gas measurement system 3 

b) Measurement Method 3 

c) Measured Gaseous Emissions 3 

d) Ranges 3

e) Illustration of FOCA low cost gas measurement system 4 

f) Measurement systems for total HC measurements (certification standard) 5 

g) Measurement systems for comparative gas measurements (certification standard) 5 

h) Measurement system for nanoparticle measurements (Appendix 4) 6 

Appendix 2: Documentation of in-flight Measurements 

1. The first in-flight tests 3 

1.a) Preparation of aircraft HBEYS 3 

1.b) Calculated emission factors for first test flight with HBEYS 5 

1.c) Discussion and general explanations 6 

2) Standard Flight Test Programme 7
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3) HBEYS (Carburated Engine Lyc O-360 Series) 8 

3.a) Results for simulated aerodrome circuits 8 

3.b) Discussion 11 

3.c) HC emission factors at flight idle 12 

3.d) Discussion 13 

3.e) Additional high altitude circuit flight testing 14 

3.f) Discussion 15 

3.g) Inventory: Total emissions in aerodrome circuits at different flight altitudes 15 

3.h) Full power and approach power settings 16 

3.i) Climb power and approach power settings 18 

3.j) Cruise power settings 20 

 

4) HBKEZ (Fuel Injected Engine Lyc IO-360 Series) 22

4.a) Results for simulated aerodrome circuits 25 

4.b) Discussion 27 

4.c) Full power and approach power settings 27 

4.d) Take-off, climb and approach power settings with mixture “full rich” 29 

4.e) Discussion 30 

4.f) Take-off, climb and approach power settings with mixture adjustment 31 

4.g) Discussion 33 

4.h) Inventory: Standard flight emission measurement 33 

5) HBKIA (Fuel Injected Engine TCM IO-550 B) 36 

5.a) Results for aerodrome circuits 39 

5.b) Discussion 43 

5.c) Inventory: Total emissions of HBKIA in aerodrome circuits 43 

5.d) Discussion 44 

5.e) Additional high altitude circuit flight testing 44 

5.f) Discussion 46 

5.g) Inventory: Total emissions of HBKIA in the low and high altitude aerodrome circuit 47 

5.h) Discussion 47 

5.i) Full power settings 47 

5.j) Discussion 50 

5.k) Climb power settings 50 

5.l) Approach power settings 53 

5.m) Standard flight profile emission measurement 55 

5.n) Discussion 57 

5.o) Inventory: Total emissions of HBKIA in standard flight, defined in 5.m) 59 

5.p) Emissions summary for a HBKIA mission, defined in 5.m) 64 

6) HBHFX (Carburated Engine Lyc O-320 Series) 64 

6.a) HBHFX high accuracy in-flight measurements: Installation of OBS2200 64 

6.b) Real time emission mass determination during flight 70 

6.c) OBS2200 confirms typical emission factors for Lycoming carbureted engines 75 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

6.d) OBS2200 time trend chart and confirmation of high HC at flight idle 76 

Appendix 3: Ground Measurement Power Settings 

1. The problem of piston engine power definitions 3 

2. Theoretical power calculation 3 

3. Engine manifold pressure (MAP) and RPM for power determination 3 

4. Correlation of fuel flow and propeller power 4 

5. Adjustment of ground measurement power settings (Fuel Flow Method) 7 

5.1 Step 1: Comparison of in-flight and static ground measurements of HBKEZ (example) 7 

5.2 Step 2: Power setting methodology for static ground measurements 8 

5.2.1 Determination of maximum fuel flow 8 

5.2.2 Power settings other than maximum propeller power 9 

5.3 Step 3: Application of the power setting methodology (step 2) 9 

5.3.1 Comparison of ground and later in-flight measurements 11 

5.3.2 Adjustments to the fuel flow method for complex aircraft/engines 14 

5.3.3 Temperature corrections for normally aspirated carburetted piston engines 15 

6. Recommended ground measurement power setting procedures for emission tests 17 

6.1 Selection of methodology 17 

6.2 Procedure for determination of maximum fuel flow 17 

6.2.1 Fuel flow calibration 17 

6.2.2 Preparing the aircraft for a maximum fuel flow (and emission) measurement 18 

6.3 Simple fuel flow method 19 

6.3.1 Fuel flow for all modes 19 

6.3.2 Recommended procedure 20 

6.4 Combined MAP & fuel flow method 21 

6.4.1 Preparations 21 

6.4.2 Recommended procedure 22 

7. Example for measurement documentation 23 

Appendix 4: Nanoparticle Measurements 

1. Background, motivation and project partners 3 

1.1 Research programme 3 

1.2 Research goals 3 

2. General results for nanoparticle emissions of an aircraft gasoline engine, running 3 

under rich air/fuel conditions (AVGAS 100 LL) 

2.1 Preparations 3 

2.2 SMPSTM system layout and description for particle measurements 4 

2.3 Results 6 

2.4 Picture documentation of first non-volatile nanoparticle measurements 9 
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3. Looking for particle emission improvements: First tests with unleaded 11 

AVGAS (AVGAS 91/96 UL) 

3. 1 Introduction and description of AVGAS 91/96 UL 11 

3.2 Composition of measured AVGAS 100LL (560 mg Pb / liter) 11 

3.3 Used aircraft 12 

3.4 Results for HB-EYS 12 

3.5 Conclusion for HB-EYS tests 13 

3.6 Results for SE-KEI 13 

3.7 Air/fuel mixture ratio for HB-EYS and SE-KEI 14 

3.8 Discussion 15 

3.9 Conclusions for AVGAS 91/96 UL 15 

4. Change from SMPSTM to Engine Exhaust Particle SizerTM (EEPS 3090TM) system for 15 

aircraft piston engine nanoparticle measurements 

4.1 Introduction 15 

4.2 EEPSTM system description 15 

4.3 Application of EEPSTM for aircraft piston engine measurements 16 

4.4 EEPSTM results 18 

4.5 First conclusions for EEPSTM measurements 19 

5. Research for AVGAS 100LL substitution and emission reduction 19 

5.1 Test fuels 20 

5.2 Test location 20 

5.3 Used aircraft 20 

5.4 Measurement systems 20 

5.5. Power settings 21 

5.6 Results 22 

5.7 Discussion 31 

5.8 First conclusions 32 

Appendix 5: Calculation of Emission Factors 

a) Introduction 3 

b) List of abbreviations 3 

c) Calculation of EF (Equations used for FOCA ground measurements and data sheets) 3 

d) Equations for "low cost" measurement system described in Appendix 1 for AVGAS 4 

 (used for FOCA in-flight measurements and comparative ground measurements) 

e) Equations for "low cost" measurement system described in Appendix 1 for DIESEL 6 

f) Correction of ambient air temperature influence on normally aspirated piston engines 7 

g) Statistical checks 7 

h) Fuel flow 7
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

1. General information

1.1 Background 

There are basically three propulsion concepts used for today’s engine powered civil aircraft: 

 

• Propulsion with „Turbofan“ (In everyday language, this is usually called “jet engine”), 

• Propulsion with „Turboprop“ (Turbojet engine, driving a propeller) and 

• Propulsion with piston engines (driving a propeller). 

Turbofans (jet engines) and turboprops burn jet fuel (kerosene), aircraft piston engines primarily burn 

aviation gasoline (AVGAS). The highest portion of aviation fuel is consumed by large aircraft with large 

engines (mostly turbofans). Large turbofans and jet engines are certified for compliance with tight 

emissions standards. 

Aircraft piston engines are mostly used for what might be called “small propeller aircraft”. On a global 

scale, such aircraft consume a relatively minor share of fuel. In Switzerland, the annual fuel consumption of aircraft piston engines is less than the fuel consumption for gardening activities2

. Basically, 

emissions from aircraft piston engines have not been seen as a significant problem when looking at 

the broad picture of total emissions, and when looking at measured pollutant concentrations in a country like Switzerland. This can vary when looking at the aviation sector only, as we will see later (section 

2.2.3 of this report). But assuming little to no influence, emissions from aircraft piston engines have not 

raised any interest, so far. Internationally, there have not been any efforts to consider work towards an 

emission certification for such engines. The disadvantage is that information about aircraft piston engine emissions performance is practically nonexistent. In Switzerland, this has sometimes caused 

problems, e.g. to produce a complete aircraft emissions inventory, or to provide credible data for an 

environmental impact assessment. 

According to Swiss aviation law (SR 748.0, LFG Art. 58), emissions from all engine powered aircraft 

have to be evaluated and tested. Therefore, the Swiss Federal Office of Civil Aviation (FOCA) has 

been looking for efficient means, to fill the ”black emission holes“. 

In autumn 2002, FOCA initiated project ECERT (Emission Certification). Although the project name 

incorporates the term “certification” it was clear from the beginning that the primary purpose of the 

project was to provide emission factors. This project would present the best available emissions data 

for aircraft piston engines but not necessarily at certification level, because of cost efficiency considerations. 

Project planning started with estimations of the aircraft piston engine emissions contribution to the total 

civil aviation emissions. First estimations were based on a handful of old data and generated a surprising result: Carbon monoxide (CO) and total hydrocarbon (HC) emissions could be significant in a 

landing and take-off cycle, compared to large aircraft. Despite a fuel burn that was several magnitudes 

lower, CO and HC emissions could reach the magnitude of large aircraft. Explanations were found: 

The combustion in engines used for today’s passenger aircraft has become exceptionally complete 

and clean, whereas aircraft piston engine technology – in general – has had a complete technology 

standstill since the 60’s. Emissions reduction has never been an issue. Reliability of simple piston 

engine concepts, high power-to-weight ratio (high HP per kg), and production costs for a comparatively low number of certified engines seemed to be the main drivers. A disadvantage of such concepts 

was high specific emissions. Additionally, about half of the global aircraft piston engine fleet must operate on leaded fuel, due to high octane requirements. 

It became clear to FOCA that it would be worth gathering a clear picture of aircraft piston engine emissions, and that new piston engine concepts would bear a high potential of emissions reduction within 

the aviation sector. 

 

2

 Swiss National Greenhouse Gas Inventory, Off Road Sector, INFRAS, January 2004. 
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From the beginning, the project was driven by the search for cost effective solutions. On the one hand, 

FOCA bought “low cost” equipment, which costs about 1/10 of a conventional certification level test 

equipment. This equipment was originally designed for automotive engine emissions testing (Appendix 

1). For the purpose of emission factor determination, several adaptations and further developments 

were needed (Appendix 5). On the other hand, most aircraft used for in-flight testing belong to the 

Swiss Confederation, with FOCA being the responsible operator having direct access to the fleet. 

(Robin DR400/180 HB-EYS, Robin DR400/500 HB-KEY and HB-KEZ, Raytheon A36 Bonanza HBKIA). 

In order to measure aircraft piston engine emissions in static conditions, directly on the ground, an 

appropriate ground measurement methodology had to be developed (Appendix 3). A special feature 

which most gasoline aircraft piston engines have in common is the manual air/fuel mixture control. 

Knowledge, necessary for standardization of the measurements could only be gained from in-flight 

emission tests (Appendix 2). These measurements were also leading to an improved insight in emissions optimized operations of manually tuned engines. With growing interest in fine particle emissions, 

particle measurements have been integrated into the project. Finally, after the first results for particles, 

FOCA intensified basic research into emissions reduction of AVGAS engines (Appendix 4). 

Since 2003, and through AERONET, there has been collaboration with the German Aerospace Centre 

(DLR), HJELMCO Oil Inc., BRP-ROTAX GmbH & Co, HORIBA Europe GmbH, TSI GmbH, ALPAIR, 

Swiss AIR FORCE, Prospective Concepts AG und GABUS SA. 

1.2 Main scope and objectives of the project 

- Development of a cost-effective ground based in-field measurement technique for aircraft piston engines (gaseous and non-volatile particle emissions) by using state of the art automotive 

testing equipment and by comparing in-flight to ground measurements. 

- Gather absolute emissions data of a variety of piston engines for emissions inventory purposes (some helicopter – and small jet engines will follow at a later step). 

- Development of operational guidelines for piston engines with manual mixture control which 

take engine durability and emission performance into account. 

- If feasible, use the basic research for the development of an emission certification for small 

engines, bearing in mind that certification costs should be reasonable. 

- Support basic research in order to replace leaded by unleaded AVGAS for aviation piston engines and to improve emissions performance. 

 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

2. Summary of results 

2.1 FOCA data sheets and their practical application

2.1.1 General Methodology for Emission Calculation 

Definition of Power Modes for Aircraft Piston Engines 

Typical power settings have been established by flight testing (Appendix 2) and ground measurement 

comparison. Table 1 below indicates five operating modes: Take-off, Climb out, Cruise, Approach 

and Taxi. For each mode, the table indicates typical power settings used in ground static tests. (Details are given in Appendix 3.) All FOCA data, established with ground static tests, are based on the 

suggested modes and power settings below. 

 

Table 1: Power Modes 

Mode % of max. Propeller HP

Take off 100 

Climb out 85 

Cruise 65 

Approach 45 

Taxi Operator’s Manual 

Calculation of emissions of an aircraft at and in vicinity of an airport 

(landing and take-off cycle, LTO) = 

Number of engines * 

(Taxi time * Taxi fuel flow * Taxi emission factor + 

Take-off time * Take-off fuel flow * Take-off emission factor + 

Climb out time * Climb out fuel flow * Climb out emission factor + 

Approach time * Approach fuel flow * Approach emission factor) 

Calculation of emissions of an aircraft during cruise = 

Number of engines* (Cruise time * Cruise fuel flow * Cruise emission factor) 

2.1.2 Suggested Times in Mode for Emission Calculation 

Table 2 suggests standard times in mode for piston engine LTO emission calculations according to the 

equation above. 

 Table 2: Standard Times in Mode for Piston Engines 

Mode Time (Minutes) 

Take off 0.3 

Climb out 2.5 

Cruise - 

Approach 3 

Taxi 12 

Remarks: 

1) Part of the piston engine powered aircraft are intensely used for training and school flights, 

where two movements (= 1 LTO) are reduced to one circuit around the airport. The times in 

mode try to take a representative mixture between LTO, circuit flying and the performance 

variability between different aircraft into account. This can be very country dependent. 

2) Cruise Time: Actual time outside LTO. In absence of such information FOCA suggests a 

mean cruising time of 20 minutes for small aircraft for central Europe, corresponding to a 

mean total flight time of 30 to 40 minutes per flight, when the LTO is included. 
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3) The time value for taxi (in and out) seems to be rather small but is considered appropriate 

for small airfields where most of piston aircraft operate. At airports, total taxi time might be 

higher and should be adjusted according to the local situation. 

4) At climb out up to 3000ft AGL, the majority of engines below 200 HP are operated at full 

power. In those cases, it would be more realistic to calculate the climb segment of the LTO 

with take-off emission factors and take-off fuel flow. 

Table 3 suggests times in mode for the LTO cycle, if circuit flying around airports is excluded. This is 

not suggested for full airport emissions inventories, however it can be used to compare piston engine 

emissions in the LTO band of 3000ft above ground level to other types of engines. 

 Table 3: Full LTO Times in Mode for Piston Engines 

Mode Time (Minutes) 

Take off 0.3 

Climb out 5 

Cruise - 

Approach 6 

Taxi 16 

2.1.3 Cruise Emission Factors 

Most of the piston engines which are dominating the market have manual air/fuel mixture control to 

adjust the engine to different altitudes (in fact to density altitude). This air/fuel mixture adjustment has 

to be done by the pilot during flight whenever the aircraft changes its power configuration and altitude. 

This adds a particular degree of complexity to representative emissions measurements, because 

emissions can vary strongly even if the same aircraft is flying at the same mass, same density altitude, 

same speed, configuration and attitude. The variation comes from different “leaning techniques” and is 

also dependent on the pilot’s experience, training and available engine cockpit instrumentation (sections 2.2, 2.3 and Appendix 2). For this reason and as a result of in-flight measurements, the cruise 

mode is given twice in the data sheet: 

Table 4: Extract of data sheet PF01. CRUISE and CRUISE LEAN values. EI = emission factors 

MODE

POWER

SETTING (%)

TIME

(minutes)

FUEL FLOW

(kg/s) EI HC (g/kg) EI CO (g/kg) EI NOx (g/kg)

PM

(...) (...)

TAKE-OFF 100 0.3 0.0182 12.7 818 6

CLIMB OUT 85 2.5 0.018 12.3 787 6

CRUISE 65 60 0.0152 6.9 750 8

APPROACH 45 3 0.0098 11.5 1055 2

TAXI 12 12 0.0038 42.6 1123 0

CRUISE LEAN 65 60 0.0138 5.4 473 23

CRUISE: Measured at very rich air/fuel mixture, called “full rich”. Well defined and for comparison only 

CRUISE LEAN: to be used for cruise emission calculations. The definition of the mixture comes 

from operator’s manuals and in-flight studies. “Cruise lean” values are the result of the most common 

“leaning technique”, where pilots manually adjust the air/fuel mixture to less rich conditions. ”Leaning” 

is a common term, however in most cases it means that the engine is run leaner than at full power but 

still at a rich air/fuel mixture (Details are given in sections 2.2, 2.3 and Appendix 2). 

Some of the engines do not have a manual mixture control. On the datasheet this is either indicated 

with remarks or with the same cruise values for CRUISE and CRUISE LEAN. 

2.1.4 Calculated LTO and 1 hour cruise emissions on data sheets 

Table 5 (below): Extract of data sheet PF01. LTO fuel consumption and total HC, CO and NOx emissions are marked in yellow. One hour cruise fuel consumption and emissions are marked in green. All 

values for LTO and CRUISE are calculated based on the suggestions made in sections 2.1.1 to 2.1.3 
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MODE

POWER

SETTING (%)

TIME

(minutes)

FUEL FLOW

(kg/s) EI HC (g/kg) EI CO (g/kg) EI NOx (g/kg)

PM

(...) (...)

TAKE-OFF 100 0.3 0.0182 12.7 818 6

CLIMB OUT 85 2.5 0.018 12.3 787 6

CRUISE 65 60 0.0152 6.9 750 8

APPROACH 45 3 0.0098 11.5 1055 2

TAXI 12 12 0.0038 42.6 1123 0

CRUISE LEAN 65 60 0.0138 5.4 473 23

LTO TOTAL FUEL (kg) or EMISSIONS (g) 7.53 174 7327 24

CRUISE 1HOUR FUEL (kg) or EMISSIONS (g) 49.7 268 23490 1149

2.1.5 Data Quality and Accuracy 

FOCA data sheets are primarily based on the "low cost" STARGAS 898 measurement system and the 

MEXA 1170 HFID (see Appendix 1). For each engine on ground static tests, a minimum of three 

measurements have been performed for every power mode. Data variability has been statistically 

checked with a T-test and 90% confidence interval (Example in Appendix 3). 

The particle emission measurements have been performed in collaboration with German DLR. Primary 

focus were the nanoparticle and carbonyl emissions. There is presently no "low cost" for such measurements. First measurements have been made with HBKEZ. The measurement results have been 

reproduced one year later with the DLR measurement system and the same aircraft (see Appendix 4 

for details). 

Swiss FOCA sees the primary purpose of the data collection in their application in emissions inventory 

calculations. The measurement system that has been used so far (STARGAS 898) does clearly not 

represent certification standard. However, the measurement quality achieved by requirements described in Appendix 1a/b) is considered sufficient for emissions inventories. This conclusion is based 

on the following comparisons: 

FOCA has started to use a total HC FID in parallel to the "low cost" STARGAS NDIR HC measurement and has done crosscheck measurements with a chemiluminescence (CLD) NOx analyzer. From 

comparative measurements with different systems, correction factors for the "low cost" gas analyzer 

with NDIR HC and electrochemical NO probe have been derived. (See Appendix 5 for details.) 

In addition to that, FOCA has been given the chance to use HORIBA OBS 2200. This system meets 

the requirements for high quality certification emissions measurements (THC FID, NO/NO2 CLD, 

heated sampling line at 191°C, exhaust flow measurement etc, see Appendix 1.g) and is very compact, originally designed and tested for on board measurements in cars and trucks under real operating conditions. The system has been used for comparative ground static tests in the ECERT project. It 

has then been installed for the first time in an aircraft and flown successfully, providing high quality real 

time mass emissions data at one second intervals, together with position, altitude, speed and flight 

time. Complete, 4-dimensional resolved emissions inventories have been measured and recorded, 

from taxi out to taxi in. Those real world data have been compared to the STARGAS data and to the 

existing LTO-modelling data. (Details are given in Appendix 2.) 

From the present experiences FOCA concludes that the results for a "low cost" measurement system 

described in Appendix 1a/b, as well as the calculations and corrections described in Appendix 5, 

would be in a systematic error band of +-15% for the measurement itself. This is considered acceptable because operational issues and individual engine tuning can change emission factors drastically 

(See Section 2.2.2 and Appendix 2) and because of the low system costs (approximately one tenth of 

a common measurement system, used for emission certification). In the opinion of FOCA, overall representation of emission factors mainly depends on the choice of operating points and on the real flight 

operations. FOCA has taken this into account by doing in-flight emission tests. 

Four aircraft have been used for basic testing (Appendix 2). The first two aircraft HBEYS and HBKEZ 

have been tested in-flight, followed by in-field static ground tests until it was possible to reproduce 

useful in-flight data on ground. The third aircraft HBKIA has been first tested on ground on the basis of 

the ground power setting procedure developed with the HBEYS and HBKEZ measurements. Once this 

had been completed, HBKIA has been tested in flight in order to validate the ground test procedure 

(Appendix 3). The HORIBA OBS 2200 has been used for cross check of HBKEZ static ground measurement data accuracy and for in-flight measurement of HBHFX in order to produce "real world" emissions inventories. 
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2.1.6 Data Download 

This report, as well as the full documentation (Appendices), available data and individual datasheets 

can be downloaded from the FOCA webpage. 

Download link: 

http://www.bazl.admin.ch -> for specialists -> environment -> engine emissions 

List of abbreviations, used in the data sheet table: 

FOCA UID: Unique identifier for piston engines which can be used as the key to link aircraft with 

engine data. “P” stands for piston engine, “F” stands for FOCA measurement. 

Rated HP: Rated Horse Power. Manufacturer declaration. The number may vary within certain 

engine model variants. If a certain engine model can not be found in the table, Horsepower, Combustion Tech, Cooling System and Technology Age can give hints to 

choose the nearest possible representative engine. 

Piston Engine Model: To simplify application of the table, only the basic model designations without 

derivative variants are given. Example: TCM IO-520 A, B, C, D, E, F, J, K & L are represented by TCM IO-520. In most cases the variants do not produce significant 

change of emission factors. The actual variant measured is indicated on the FOCA 

datasheet. 

Combustion Technology: If a certain engine model can not be found in the table, Combustion Tech 

can give hints to choose the nearest possible representative engine. 

Cooling System and Fuel Type: If a certain engine model can not be found in the table, Cooling System and Fuel Type can give hints to choose the nearest possible representative engine. Piston engine particle emissions are highly influenced by fuel type. Some of the 

engines that have been measured with AVGAS100LL are allowed to run on unleaded 

fuel. This has not yet been incorporated in the database. 

Technology Age: If a certain engine model can not be found in the table, Technology Age can give 

hints to choose the nearest possible representative engine. 1960 technology engines 

are currently dominating the market. 

Data Source: For completeness, the FAEED3

 data that Swiss FOCA has been used so far are incorporated in the table. Comparison with FOCA ECERT measurements has shown 

that existing FAEED data seem to be reasonable for the purpose of LTO-emission 

calculation. Therefore ECERT has primarily focused on missing and more modern engines to complete the picture. 

 

3

 FAEED = US Federal Aviation Engine Emissions Databank 
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2.2 General findings about aircraft piston engine emissions

2.2.1 Combustion basics 

a) What goes in? Composition of AVGAS 100LL 

AVGAS (aviation gasoline) is a complex mixture of hydrocarbons (HC) plus additives. The fuel must 

comply with the specification of the US standard ASTM D-910 which ensures safe engine operation at 

the whole ambient temperature and pressure range, as far as the fuel is concerned. 

Additives: 

• Most of the AVGAS available is AVGAS 100LL, a leaded fuel. The “LL” stands for “Low Lead” 

which is a relative term. AVGAS 100LL can contain up to 0.8 g lead (tetra ethyl lead) per kg 

fuel! The lead additive is used to get the high octane rating of 100/130. Lead additives have 

been introduced many decades ago, mainly to improve the power to weight ratio of aircraft 

piston engines by increasing the compression ratio in the cylinders. FOCA assumes that about 

30% of the global gasoline aircraft piston engine fleet still needs such high octane fuel to suppress knocking or self-detonation at high compression ratios and at suboptimal air/fuel ratios 

and ignition timings. 

• If the fuel is leaded, it contains a similar amount of ethylene dibromide. This substance is used 

to remove lead deposits from the combustion parts of the engine. Otherwise spark plugs can 

be destroyed and deposits on valves can obstruct their proper operation. As lead, the scavenger is an environmentally harmful substance, believed to be carcinogenic and contributing to 

stratospheric ozone depletion. 

• Dyes (to colour code the fuel): The blue dye in AVGAS 100LL (1,4 – dialkylaminoantraquinone) is causing skin irritation and allergic reactions. 

• Antioxidants (preventing gums and sediments) 

• Icing inhibitor (optional) 

• Electrical conductivity additive (optional) 

Like car gasoline, AVGAS 100LL contains some amount of benzene, a toxic substance known to be 

carcinogenic. 

Note: There are much cleaner alternatives to AVGAS 100LL, even cleaner than car gasoline. During 

the project, FOCA has started collaboration with Swedish Hjelmco Oil, the producer of a synthetic, 

very pure unleaded AVGAS, meeting ASTM-D910 specifications. (See Appendix 4 for details.) 

Figure 1: Composition of AVGAS 100LL, used for part of the FOCA emission tests. The composition 

analysis has been done with gas chromatography and mass spectrometry at DLR Stuttgart/Germany. 

[C. Wahl/DLR] 
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Some aircraft/engine combinations are certified to use motorcar gasoline (MOGAS). In Europe, this 

fuel is lead free but with the high bandwidth of possible composition and some alcohol content, there 

are limitations for its safe use. Besides this, not only the engine (which is in many cases not the problem) but also the airframe must be certified to use that fuel, which basically comes from requirements 

for the fuel system. 

For theoretical calculations of the fuel combustion, it is useful to look at a representative AVGAS (or 

MOGAS) hydrocarbon molecule. Figure 2 below shows a typical distribution of the carbon number in 

AVGAS molecules. 

A “mean” AVGAS molecule is considered to be composed of 7 Carbon atoms and 13 Hydrogen

atoms (C7H13). For all standard mass emission calculations of FOCA, this molecule is used (see Appendix 5). 

Figure 2: Carbon number distribution of the hydrocarbon molecules in AVGAS 100LL [Chevron]. 

b) How much air to make the fire? 

Fuel and air are needed to ignite a fire. Generally, the more of both there is, the hotter the flame. But 

the combustion will only be “optimal” at certain fuel/air ratios. 

The combustion conditions at which the fuel/air ratio is, such that there is neither an excess of fuel 

nor of air, is called the stoichiometric mixture within a cylinder. At this condition, all of the reactants 

are present in the chemically ideal amounts for combustion and the greatest amount of total combustion heat per unit of air is produced. 

At stoichiometric mixture, the cylinder is running at “peak EGT” (peak Exhaust Gas Temperature). 

Peak EGT mixture can be seen as the “maximum-heat mixture point”. 

In order to estimate the amount of air that is needed to burn a defined amount of fuel at stoichiometric 

mixture, the chemical reaction equation is used. Note, that in a combustion process the mass of all 

reactants going into the process is conserved. Molecules are reformulated but nothing is lost. The fuel 

and air have been reformed to other substances, giving heat during the formation process. Intake 

mass equals exhaust mass. 
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Calculation with reaction equation for complete combustion: 

 

1 C7H13 (AVGAS) + 10.25 O2 (Oxygen from Air) + 39 N2 (Nitrogen from Air) react to (“burn” to):

7 CO2 (Carbon dioxide) + 6.5 H2O (Water vapour) + 39 N2 

Taking the number of necessary molecules for the complete combustion from the equation above and 

multiplying them with the molar masses of the molecules, then, for 1 Mol of AVGAS the result is: 

97.18g C7H13 + 328.0g O2 + 1092g N2 react to 308.07g CO2 + 117.13g H2O + 1092g N2 (1) 

Therefore, 97.18 g fuel is reacting with 1420 g Air (O2 + N2). This is a mass ratio of 1 : 14.6 

The conclusion is that for complete combustion of 1 kg fuel, about 15 kg air is necessary! 

Fuel / Air ratio 1kg / 15 kg = 0.067 (for stoichiometric combustion) 

 

c) What comes out? 

From the chemical mass equation (1) above it can also be seen that for complete combustion: 

1 kg fuel (AVGAS) produces 

• 3.17 kg CO2 (Carbon dioxide) 

• 1.21 kg H2O (Water vapour) 

CO2 and H2O are no pollutants, but are both atmospheric green house gases due to their infrared (= 

heat) absorption properties. Most of the N2 (78Vol% in ambient air) passes combustion unchanged. 

Hot air: N2, CO2 and H2O are dominating the exhaust gas. 

Besides hot air, pollutants are formed. 

Causes for the production of pollutants can be:

Oxygen deficiency: 

There is too little oxygen to react the C from the fuel to CO2 (Carbon dioxide). It will react to CO (Carbon monoxide) only. 

The fuel can not react completely to CO2 and H2O (water) and a complex mixture of hydrocarbon 

molecules (CxHy) will be exhausted, also named HC. 

 

High combustion temperatures and pressures with short chemical reaction times: 

The nitrogen (N2) contained in ambient air (78Vol%) together with the oxygen (O2) from ambient air 

(21Vol%) start to react in the combustion chamber (cylinder) to form nitrogen oxides (NO and NO2, 

named as NOx)

Pollutants: CO, HC, NOx, soot, lead bromides (AVGAS 100LL) 

FOCA measurements concentrated on CO, total HC and NOx emissions, which are reported in FOCA 

data sheets. Soot and other particles were measured by DLR Institute of Combustion Technology, 

Stuttgart, in collaborative projects (Appendix 4). 

d) Properties of pollutants 

Carbon monoxide (CO): 

• Toxic gas, e.g. blocking oxygen transport in blood. 

• Chemically unstable, normally converted to CO2 after a few days in the free atmosphere. 
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Hydrocarbons (HC): 

• Hundreds of possible H-C-molecules (e.g. formaldehyde) with different health impacts, some 

carcinogenic. 

• Some are converted with sunlight (UV) to radicals, contributing to ground level ozone production. In the troposphere, ozone is able to strongly react on different substances. Ozone is able 

to “clean” the troposphere (+), but it is itself toxic with increasing concentrations (-). 

Nitrogen Oxides (NOx): 

• NO converts to NO2 within minutes to hours in free atmosphere. 

• NO2 (yellowish colour) is toxic for the respiratory system. 

• With sunlight (UV), NO/ NO2 contributes strongly to the low level ozone production

2.2.2 Air/fuel mixture adjustments 

a) Dominant “old tech” engines require manual air/fuel mixture control 

Around 70% of all aircraft piston engines which can be found in the global market have the following 

general concept: 

- Opposed cylinders in boxer configuration 

- Big cylinder volume, relatively low RPM, no reduction gear for the propeller 

- Air cooled (direct air cooled cylinders, indirect via oil cooler) 

- Carburettors without ambient conditions or combustion sensing devices 

- Most injection systems without ambient conditions or combustion sensing devices 

- Injection systems not timed with cylinder valve movements 

- Constant ignition timing, not taking into account engine RPM (except for start-up) 

- Everything mechanical, no electronic devices 

This general concept, which is called here “old tech” or “conventional”, has not changed for many 

decades. Contributing factors were the very good power to weight ratio, the “simplicity” (compared to a 

modern car engine) and very good reliability and durability of such engines. Keeping in mind that aircraft engines have to pass an airworthiness certification process, it must be understood how costly it 

is, to certify a complex engine. At the same time, the market of aircraft piston engines is rather small. 

This situation is completely different from that of car engines, which are sold in millions with less demanding requirements. In addition to that, as long as leaded AVGAS can not be completely replaced, 

it is difficult to install electronic mixture control devices. 

 

Figure 3: Basic design parameters of an “old tech” aircraft piston engine 

The disadvantage of the “old tech” engine is: 

- High specific fuel consumption (at least at high power settings)

- High specific emissions

Increasing flight altitude (decreasing air density) increases the fuel/air ratio (of normally aspirated engines.) 

Reliability

“Simplicity” 

Light weight 

Durability 

Proven Concept 

Reasonable engine costs 
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Because carburettors and fuel injectors of “old tech” aircraft piston engines can not sense air density 

and resulting fuel/air ratio, the air/fuel mixture has to be adjusted manually. Without correction, the 

engine runs increasingly richer, the lower the air density is, and besides waste of fuel and excessive 

emissions, it may finally quit. 

Picture 1: Throttle (black), propeller (blue) and mixture handle (red). 

In addition to the throttle, the mixer handle controls 

- Engine power 

- Engine temperature 

- Emissions performance 

- Specific fuel consumption 

The mixer position plays a vital role for the resulting emissions. That is why any measurement 

of aircraft piston engine emissions requires proper investigation of mixer operation. 

b) Rich and lean mixture definition with lambda (λ)

It is convenient to indicate actual air/fuel mixtures, obtained with a certain setting of the mixer handle 

at certain ambient conditions, by comparison with the stoichiometric air/fuel mixture. The term “lambda 

probe” is known from gasoline car engines with catalyst .The word “lambda” comes from the greek 

letter λ. The “lambda probe” (“λ – probe”) actually measures the oxygen content in the exhaust. The 

probe signal is used to control the air/fuel mixture in the injection system of a car engine to be near 

stoichiometric. If the air/fuel mixture is stoichiometric, λ equals 1. If there is too much fuel for the combustion (oxygen deficiency), λ is smaller than 1. If there is excess oxygen for the combustion, λ is 

bigger than 1. 

Definition of λ : 

lean mixture rich mixture

 AVGAS :

1: 1:

:

14.6 ( )

: ( )

: ( )

: ( )

> <

=

=

λ λ

λ

λ

Note

stoichiometric

Airmass Fuelmass measured

for

Airmass Fuelmass stoichiometric

Airmass Fuelmass measured

 

“lean” = poor in fuel (excess oxygen), “rich” = fuel excess (oxygen deficiency) 

Example: If a carburettor is mixing air and fuel in a ratio of 10 kg to 1 kg, then 

λ = (10 : 1) : (14.6 : 1) = 10 : 14.6 = 0.68 -> The engine is running rich, with oxygen deficiency. 
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c) Mixer = lambda control 

Figure 4 below shows lambda values in function of percent maximum continuous power for a TCM IO550B engine. The grey shaded area shows the “full rich” lambda region for that engine. This is the 

lambda region, obtained at mixture “full rich” for sea level ISA conditions. At taxi power, the engine 

runs at about lambda = 0.70, getting richer up to 20% power. With increasing power, if the mixer is left 

at “full rich”, the engine runs slightly less rich (lambda = 0.78) and towards maximum continuous 

power again richer with lambda around 0.74. 

If the mixer handle is pulled back at a certain throttle setting, for example at 45% power (as shown in 

figure 4, red line), lambda increases (in most cases while reducing the fuel pressure). The engine 

runs less and less rich. Still rich, the best power point is passed. Pulling the mixer handle further 

back, the stoichiometric mixture is reached, which gives the highest exhaust gas temperature (EGT 

peak). If that point is trespassed, the engine runs lean and the best economy point is approached. As 

the pilot pulls further, the engine may run rough and quit. At the maximum pulled position of the mixer 

handle, fuel is cut off and the engine will definitely quit. 

It must be noted that during the mixer operation, the engine power changes. So, for the measurement 

shown below, also throttle corrections had to be made, in order to maintain constant power. FOCA 

chose a low power setting for this measurement to keep engine temperatures of the air cooled engine 

well below the limit, as the aircraft was standing. But the variations of lambda with the mixer positions 

are valid for all possible power settings and are not limited to the measured engine (example). 

Mixture

Full rich

Lean

Rich

Fuel cut off

Figure 4: Lambda values in function of the mixer handle position, from full rich to lean, measured with 

TCM IO-550B engine at 45% maximum continuous propeller power. The measurement of lambda is 

described in Appendix 5. EGT = Exhaust Gas Temperature. 

d) Typical values for lambda 

λ = 1 EGT peak (maximum-heat mixture point) 

λ = 0.85 approx. 100°F rich of EGT peak (maximum-pressure mixture point, best power) 

λ = 0.95 approx. 25 - 50°F rich of EGT peak (still a rich air/fuel mixture) 

λ = 1.15 approx. 50°F lean of EGT peak (lean mixture, lowest specific fuel consumption) 
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e) Influence of mixer settings on engine temperature and power 

Mixture

Fuel cut off

Lean

Rich

Full rich

Figure 5: Influence of mixer position (lambda) on engine temperature, power and specific fuel consumption for a certain fixed throttle setting. Note: This chart has to be read for one single cylinder and 

not for the whole engine. 1 = full rich, 2 = peak EGT, 3 = peak CHT, 4 = standard cruise mixture, 5 = 

lean mixture setting. CHT = Cylinder Head Temperature. [Adapted from TextronTM LycomingTM] 

Discussion: 

At a fixed throttle setting, pulling the mixer from “full rich” (Position 1) first increases CHT, EGT and 

power and improves SFC (Specific Fuel Consumption). 

At EGT around 100 °F rich of EGT peak, the best power mixture is obtained. 

With further pulling the mixer, with still rich air/fuel mixture, EGT and CHT further increase. At 50° to 

25°F rich of EGT peak point (Position 4), the CHT is around the maximum (Position 3) for the 

given throttle setting. Interestingly, this is the most common cruise power mixture setting for conven-
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tional “old tech” aircraft piston engines (also obtained with the “feel-the-RPM-drop-and-push-back-themixture-1cm-rule”4

 for fixed pitch propeller aircraft, see section k). 

With further pulling the mixer, the air/fuel mixture gets stoichiometric (λ =1) and peak EGT is reached 

(Position 2). CHT has already fallen a little bit. Power and SFC are both decreasing. 

Past peak EGT, with further pulling the mixer, the air/fuel mixture gets lean (λ > 1). EGT is decreasing, CHT is significantly decreasing, power is decreasing and SFC reaches the minimum value. This 

drop of CHT at lean conditions seems to be contradictory to practical experience of pilots and mechanics, reporting engine overheat damage, when operated at lean conditions. This will be discussed in 

section j). 

Best power: 

• Best power is obtained at a fuel/air mixture with slight oxygen deficiency (at about 100°F below and rich of peak EGT.

• At this condition, from incomplete combustion, an excess of combustion gases is produced 

(mainly CO). 

• The extra gas produced increases the pressure in the cylinder which contributes more to piston movement. 

• “Best power mixture” can be seen as the “maximum-pressure mixture point” 

• Remember: Piston movement, not heat per se is what results in power. 

• Best power is generally about 5 to 7% above power at “full rich” (sea level) mixture. 

• At best power, the mixture is giving the most power per unit of air, not per unit of fuel. 

Best economy: 

• When the mixture is leaned past EGT peak, fuel consumption drops off faster than 

power production, up to a certain point. 

• This point is called the best-sfc point or best economy mixture and occurs at or near 50°F 

lean of EGT peak 

• Note: At best economy setting the fuel consumption can be 40% lower than at “best 

power”! 

f) Influence of mixer settings on emissions 

The FOCA instrumentation for measurement and calculation of emission factors is described in Appendix 1 and 5. Based on this instrumentation, in-flight testing with different mixer settings has been 

performed. In order to get emissions (in mass units), measured emissions concentrations (respectively 

emission factors) have to be multiplied with the fuel burn, as explained in section 2.1.1 of this report. 

Figure 6 below shows the exhaust CO2 and pollutant concentrations in function of the mixer position at 

a fixed throttle setting. The concentrations have been measured on a TCM IO-550B engine of the 

aircraft HB-KIA. 

Note: 

1) The shapes of the curves in figure 6 are representative for all combustion engines (piston engines, 

jet engines (turbofans), etc.). 

2) If on the one hand, the concentration (respectively emission factor) of a certain pollutant in the 

exhaust and the fuel burn are both high, resulting emissions are high. On the other hand, a fuel burn 

reduction can reduce emissions, even if the concentration (or emission factor) of a pollutant is not 

lowered. 

Taking the concentrations shown in figure 6 and the decreasing fuel flow from right to left into account: 

• At mixture “full rich”, CO is extremely high, HC high, NOx low. Direct CO2 is fairly low, but taking the later recombination of pollutants (mainly CO) to CO2 into account, total CO2 will be very 

high (corresponding to the very high fuel burn). 

 

4

 This is a standard rule, taught in many flight schools, applied for engines without EGT probe. With fixed pitch propeller, any

change in engine power will be noticed by an engine RPM change. 
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• At mixture “best power”, CO and HC become lower, NOx becomes higher with increasing engine efficiency, total CO2 high. 

• At “standard cruise mixture” (rich of EGT peak), CO and HC are further reduced, NOx sharply 

increases and total CO2 is still high. 

• At “peak EGT”, CO is very low, HC low and NOx near the maximum value (complete combustion with NOx “trade-off”). Total CO2 starts to decrease. 

• At “mixture lean” (around λ = 1.15), CO and HC are very low, NOx relatively low and CO2 is 

lower. The engine is at its best specific fuel consumption. Low pollutant concentrations and 

low fuel burn lead to lowest possible emissions. If not highest possible power is needed, then 

this would be the preferred mixture setting. 

In conclusion, the preferred mixture setting 

• For lowest emissions 

• For lowest fuel consumption per flight distance (in many cases) 

• For reasonable cylinder operating temperatures (see also figure 7) 

Would be 50°F Lean of EGT peak, at λ around 1.2 

It is known from AFM and engine operating manuals that this mixture setting 

• Must not be applied with most of “old technology” engines 

• Does not work with most of “old technology” engines 

The reason and possible solutions will be discussed in section j) 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6

Mixer position (lambda)

Relative Exhaust Concentration

Rel. Vol% CO2

Rel. Vol% CO

Rel. ppm HC

Rel. ppm NOx

Mixture

Full rich

Lean

Rich

Fuel cut off

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6

Mixer position (lambda)

Relative Exhaust Concentration

Rel. Vol% CO2

Rel. Vol% CO

Rel. ppm HC

Rel. ppm NOx

Mixture

Full rich

Lean

Rich

Fuel cut off

Figure 6: The figure shows the change of exhaust CO2 and pollutant concentration in function of the 

mixer position (lambda). The concentrations are given in a relative scale in order to show them all in 

the same figure. 
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g) Influence of mixer settings summary 

• CO emissions

• HC emissions

• NOx emissions

• Particle mass1)

• Power2)

• SFC

• CHT4)

• EGT

• Combustion

Stability3)

Full richMixture

Lean

Fuel cut off

Rich

Peak EGT

Full richMixture

Lean

Fuel cut off

Rich

Peak EGT

Figure 7: Influence of mixer position on emissions, power, specific fuel consumption, engine temperatures and combustion stability at a fixed throttle setting for one cylinder. 

Note1): Particle mass (and number) emissions are generally high. Emissions are at the same magnitude as a car diesel engine without particle filter, mainly for two reasons: Extremely rich mixtures at 

high power (black carbon emissions) and leaded fuel, producing a lot of lead bromide particles. With 

unleaded AVGAS, at lean conditions, particle mass emissions would be very low (Appendix 4). 

Note2): At lean conditions, there is a significant power drop, if the throttle is fixed. In the times of piston 

engine driven airliners, after lean mixture had been established in the cruise, throttle was increased to 

compensate for the power drop. This changed the mixture and temperature distribution again and in 

an iterative process, the lean mixture at the same power level as the rich mixture was established. 

This technique can still be used today, if the engine and instrumentation allow. 

Note3): Combustion stability is lost, if the mixture is too rich (engine flooded with fuel) or too lean 

(combustion temperature too low and combustion reaction too slow). The combustion stability range is 

wide for rich mixtures and narrow for lean mixtures. 

Note4): Lean mixture in the cylinder is not only beneficial for lowest emissions but also for lower CHT. 

Final note: Diesel piston engines always run lean on steady-state conditions over the whole operating 

range. 

h) Why “full rich” at high power for “old tech” engines? 

• Most “old tech” aircraft piston engines are air cooled. 

• At full power, the cooling performance of air cooled engines is often too weak. There is 

generally less cooling air flow in climb than in cruise or descent, because the aircraft flies 

slower and has a different attitude. But in climb, the engine is working at the highest load. 

Therefore, additional cooling is required: Incomplete combustion at very rich mixtures 

(lambda 0.7) reduces combustion temperatures, thus keeping cylinder head temperatures 

relatively low. This is internal combustion cooling by wasting fuel. 

• At high power settings, some excess fuel may be necessary to suppress detonation also due to invariable ignition timing. 

Note: Lean mixtures reduce combustion temperatures as well, but with greater loss of power. 
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i) Why “rich” near idle power? 

• “Rich mixture” ensures safe engine operation in engine transient conditions: 

When the throttle is opened, the engine experiences a sudden inrush of air. Therefore, a transient lean mixture condition exists. The mixture must be rich enough, so that suddenly opening 

the throttle does not kill the engine. 

• “Rich mixture” (λ around 0.7) is necessary for cold-weather starting ability. 

• Air-cooled engines need a “fudge factor” for possible too lean conditions of single cylinders 

under worst case conditions. 

Note: “Rich mixture” can be any mixture with λ < 1 (mixture rich of EGT peak). It is not necessarily 

the “full rich” carburettor setting. 

j) Uneven distribution of mixture and temperature in “old tech” engines 

From measurements and investigation, the author thinks that the primary cause for problems with 

running “old tech” piston engines lean in cruise is the uneven mixture and temperature distribution in 

the different cylinders. Figure 8 shows, what temperature and mixture distribution would be required, in 

order to be able to run the engine lean as a whole. All cylinders would have their temperature peaks at 

exactly the same mixer position. In that case, 50°F lean of EGT peak would be a clearly defined operating point for the engine, with all cylinder head temperatures lower than for the same power at rich 

mixture. If the cylinders run like this, the engine can be run lean at low temperature, low SFC and lowest emissions! 

Note: The temperature can vary in absolute terms from cylinder to cylinder, due to differences in cylinder charge and piston compression. Mixture Fuel cut off Lean Rich Full rich

Figure 8: Requested mixture distribution in four cylinders for a certain mixture position. All four cylinders pass peak temperature at the same mixture position. 

In reality, all cylinders of “old technology” aircraft piston engines normally have their individual peak 

temperature at different mixture settings (figure 9)! Additionally, peak temperature can vary significantly from cylinder to cylinder.
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Reasons for this (not to be considered complete): 

• Different distances from carburettor to cylinders 

• Cooling air distribution causes cooling differences. 

• Fuel droplets that have to travel “uphill”, against gravity in the induction system tend to reach 

the nearer cylinder more easily. 

• Fuel injectors: Bad nozzle tuning 

• Airflow anomalies 

Many intake systems are so poorly tuned that lean misfire begins in the leanest cylinder(s) well before 

peak EGT is reached in the richest cylinder(s). 

• Recall: It takes fuel and air to make the fire. The more fuel and air, generally, the hotter the 

flame. This can be expressed by the term “cylinder charge”. Cylinders normally are differently charged. 

• Also, the more compression a cylinder has during combustion, the higher the final temperature. 

• As the mixture handle is pulled back, the richest cylinder will be the last one to reach the peak 

EGT (figure 9). It is well possible that this cylinder can reach the highest EGT of all cylinders: 

It is possible for the richest cylinder to give the highest peak EGT. 

Mixture

Fuel cut off

Lean ??

Rich

Full rich

Figure 9: Uneven distribution of mixture and temperature in an “old tech” engine. At a certain mixture 

position, all cylinders have a different lambda and different temperatures! 
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In the example of figure 9 above, it is assumed that mixture is set to 50°F lean of EGT peak (left black 

line) with reference to cylinder 1.

The leanest cylinder is that one, which first reaches “EGT peak”, when the mixer is pulled. In the 

example, it is cylinder no. 4. 

At the selected mixture setting (for cylinder 1), the cylinder 4 can already be so lean that it reaches the 

lean misfire condition. In practice this can sometimes be noticed by a slightly rough running engine. 

Of course, this condition is negative for engine life. And note in this example, no 4 is running cooler 

than cylinders 1 and 2. 

The richest cylinder is no 2. All other cylinders have passed EGT peak and this one just reached it. 

The coolest cylinder, in absolute terms, is cylinder no 3, despite the fact, that it is running near EGT 

peak. 

The hottest cylinder, in absolute terms, is cylinder no 1. This one has e.g. the best charge and/or 

compression of all four cylinders. 

Do not confuse “leanest” and “hottest” cylinder. 

• The leanest cylinder is that one, which first reaches “EGT peak”, when the mixer is pulled 

back 

 

• The richest cylinder is that one, which last reaches “EGT peak”, when the mixer is pulled 

back 

• The hottest cylinder, can be the richest e.g. if combined with best charge and/or compression. 

Conclusions 

• If all cylinders together are running lean, temperatures can be lower than with rich of EGT 

peak or best power point. 

• At lean mixture, the combustion process is slowed down and the combustion pressure on the 

piston and on the cylinder head is distributed over a longer period of time, reducing material 

stress. 

• At lean mixture, the engine reaches the lowest specific fuel consumption and the lowest 

possible emissions. 

• Rich mixtures have a much larger bandwidth of lambda for engine operations than lean mixtures (figure 7). Lean mixtures require better mixture control. 

• Altitude changes (e.g. descent) are sometimes less critical with rich mixtures. 

• For engine transient power conditions, rich mixtures are needed. 

• Most “old tech” engines have a higher risk of one ore more cylinder(s) being at high internal 

temperatures, without noticing it. Therefore such engines must not be run lean. 

• Going very lean with “old tech” engines can cause one ore more cylinder(s) to reach the lean 

misfire condition. Therefore such engines must not be run lean. 

 

Picture 2: Running lean for thousands of hours is nothing new: The 

Wright R-3350 engine (DC7 etc.) has been operated on lean 

mixture during cruise (historical example). As explained above, 

lean mixture requires better mixture control. In former times this 

was assured e.g. by symmetrical engine design (equal distances 

for air intake, symmetrical cooling air flow etc) and a fuel flow and 

power based leaning technique. A flight engineer was looking after 

the engines all the time during flight. 

In a modernized piston engine aircraft, lean operation is 

possible by use of a fuel injection system with carefully 

tuned injection nozzles and/or with FADEC, controlling 

each cylinder separately. 
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 k) Investigated manual mixture setting procedures 

Setting the air/fuel mixture without EGT: Many “old tech” piston engine aircraft with fixed pitch propeller do not have any exhaust gas temperature instrumentation. Therefore no information about exhaust gas (and internal combustion) temperatures is available. To handle the mixer of such aircraft, 

pilots are often instructed to adjust the mixture with a "rule of thumb": At a fixed throttle setting, the 

pilot pulls the mixture lever slowly back and leans the mixture until a slight RPM drop of the fixed pitch 

propeller is recognized. At this condition, the engine is running slightly lean. After that, the pilot pushes 

the mixture lever slightly forward (about 1 cm) and the engine is running slightly rich. After a while, 

the pilot checks cylinder head and oil temperature. 

Rule for fixed pitch propeller engines without EGT for cruise below 75% propeller power: 

“feel-the-RPM-drop-and-push-back-the-mixture-1cm”. This mixture adjustment for cruise should 

be done at every altitude with engine propeller power not exceeding 75% (refer to AFM). 

The effect of the rule was studied with FOCA aircraft HB-EYS (In-flight measurements with application 

of the above rule are documented in Appendix 2, sections 1 and 3). The measurement system showed 

the resulting lambda for a certain mixer setting on a small TV-monitor. In doing so, during the flight, the 

effect of a certain mixer setting on lambda and emissions could be immediately observed. 

With a fixed pitch propeller engine, without EGT and the aircraft at constant climb angle, best 

power mixture is obtained with the mixer position giving the highest engine RPM. Usually, from 

this mixer position, the mixture is slightly enriched for better engine cooling. For a normally aspirated 

engine, this adjustment should usually be done in climb above 5000 ft density altitude (refer to AFM). 

General findings for the rule: 

• If the pilot applies the rule slowly and tries to sense possible engine vibrations5

 with feet on 

the floor, the resulting lambda is around 0.93 to 0.95 which corresponds quite nicely to a 50°F 

rich of EGT peak setting. 

• With increasing density altitude, the “rule of thumb” leads to increasingly richer mixture. 

• Adjusting the mixture in static aircraft condition, e.g. prior to take-off at high density altitude 

(mix for highest static RPM (best power) and enrich) leads to a richer mixture than applying 

the rule during flight. 

• Strictly speaking, the rule is only applicable for cruise but can be used to a lesser extend to 

climb. For descent, at a fixed mixer position, the mixture gets leaner, and eventually, the engine may quit. Therefore many AFM call for mixture “full rich” in the descent, which is very far 

from optimum for the engine (see 2.3.1 c). 

Setting the air/fuel mixture with EGT: 

The standard setting is often 25 to 50°F rich of EGT peak during cruise. 

Some engines may – according to AFM – run lean of EGT peak. In fact, the engine installed on HBKIA, does not seem to have an extremely uneven mixture distribution and it is not surprising as the 

AFM describes lean of peak operation. But in spite of that, during an in-flight measurement at lean 

conditions with HB-KIA, one or more cylinders were clearly running hot (high NOx emissions) without 

being noticed by cockpit instrumentation (see previous section j and Appendix 2, section 5)! 

General findings for EGT mixture setting: 

• Proper mixture adjustment with EGT needs time (5 minutes easily). The temperature probe 

(which is a thermocouple in many cases) is reacting slowly and the engine needs time to stabilize temperature at a certain throttle/mixer setting. 

• Most EGT leaning techniques start with finding EGT peak. This means that at least the measured cylinder has to run on EGT peak for a certain time, which may in fact not be beneficial for 

cylinder life, if by chance, this is the hottest cylinder. 

 

5

 Additional vibrations can be caused, if one or more cylinders are in a very different mixture state compared to others, as shown 

in section j) of this report. A mixer position with increased engine vibrations should be avoided. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

• A single probe for EGT (and CHT!) on a four or six cylinder “old tech” piston engine is considered not sufficient for proper mixture adjustment (see previous section j). Certified instruments, showing all cylinders and exhaust temperatures simultaneously, would be preferred. 

General findings for all “old tech” engines: 

• For every change of power configuration and altitude (air density change), the mixer position 

should be changed. 

• Applying “carburettor heat” at a fixed throttle position enriches the mixture. The hotter air in 

the intake is less dense and this has the same effect as flying higher. Therefore, the mixture 

should be adjusted to less rich conditions after applying carburettor heat. 

• Mixer adjustments, if done properly during flight, can consume a considerable amount of pilot 

concentration and can distract considerably from primary tasks (fly the aircraft, look out, etc.), 

especially, if pilots are not well trained. 

l) Mixture adjustment technique with fuel flow 

• Whenever possible, install (certified) EGT and CHT on every cylinder exhaust and cylinder 

head. 

• Whenever possible, install a (certified) fuel flow transducer in the fuel line(s) and a corresponding fuel flow instrument. 

Fuel flow method: 

• Record the indicated fuel flow for defined power settings at different flight pressure altitudes, 

with the engine perfectly leaned according AFM (preparation) 

. 

• Once this table is ready, the engine is leaned at a defined throttle (and RPM setting) based 

on the fuel flow. Example for a variable pitch propeller aircraft: 

For 65% power at 5500 ft PA the setting may be 22.5 InHg and 2350 RPM, 

The corresponding tabulated fuel flow for 50°F rich of EGT peak is 9.5 GAL 

Î Pull back the mixer handle to read 9.5 GAL on the fuel flow instrument instantly 

Î Check EGT and CHT values after a couple of minutes 

Setting the mixture by fuel flow goes very fast, does not distract too much from primary tasks. It may 

also be an advantage for engine life: There is no need to go to peak EGT values every time leaning 

starts. 

Picture 3: Mixture setting investigation with aircraft HB-EYS with Lycoming O-360 series engine 
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2.2.3 Typical emission factors and magnitude of emissions 

a) Pollutants of “old tech” engines during landing and take-off cycle (“full rich” mixture) 

In most cases, “full rich” is set during the whole landing and take-off cycle (LTO). Because of oxygen deficiency, the fuel combustion is very incomplete with a lot of CO, HC and particle emissions. 

CO Emission Factors 

1280

1300

1320

1340

1360

1380

1400

Mode

Mass (g/kg Fuel)

CO 1330 1364 1393 1420 1441 1430 1397 1374 1359

TO 

3000ft_4124

TO 

4000ft_5004

TO 

5000ft_5884

TO 

6000ft_6764

TO 

7000ft_7884

AP 

7000ft_7884

AP 

6000ft_6884

AP 

5000ft_5764

AP 

4000ft_4764

Figure 10: Example of CO emission factors, measured in-flight at full throttle between 3000 and 7000ft 

pressure altitude and at approach power (about 45% of maximum propeller power) between 7000 and 

4000ft pressure altitude. The second number to the right of the pressure altitude indicates the density 

altitude. The measurements were made with HB-KEZ and a Lyc IO-360 engine, which has an extremely rich “full rich” mixture. It can also be seen from the figure that increasing altitude leads to 

higher CO emission factors, which means that the engine gets increasingly richer, if it is not leaned. 

Generally, “old tech” engines will produce between 600 and 1200 g CO per kg fuel under “full rich” 

conditions. Note: The CO emission factor of a jet engine is generally a factor of 1000 lower! 

HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel)

HC NDIR 32 32 31 32 32 34 32 31 31

TO 

3000ft_4124

TO 

4000ft_5004

TO 

5000ft_5884

TO 

6000ft_6764

TO 

7000ft_7884

AP 

7000ft_7884

AP 

6000ft_6884

AP 

5000ft_5764

AP 

4000ft_4764

Figure 11: Example of HC emission factors, measured in-flight at full throttle between 3000 and 7000ft 

pressure altitude and at approach power (about 45% of maximum propeller power) between 7000 and 

4000ft pressure altitude. (Example HB-KEZ) 

Generally, “old tech” engines will produce between 12 and 30 g HC per kg fuel under “full rich” conditions. Note: The HC emission factor for a jet engine at high power is around zero! (Complete combustion). Only at taxi/idle it will be higher and be of the same magnitude. 
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Figure 12: Example of NOx emission factors, measured in-flight at full throttle between 3000 and 

7000ft pressure altitude and at approach power (about 45% of maximum propeller power) between 

7000 and 4000ft pressure altitude. (Example HB-KEZ) 

Generally, “old tech” engines will produce only a few g NOx per kg fuel under “full rich” conditions. 

Note: The NOx emission factor of current jet engines at high power is in the order of 20 to 30 g / kg 

fuel, because of high efficiency and slightly rich mixture at the fuel nozzle. At taxi/idle the NOx emission factor is down at a few g / kg fuel. 

Non-volatile particles and soot emission factors: 

Figure 13 shows a typical example of a particle number - size distribution from an aircraft gasoline 

piston engine, running on AVGAS 100LL (leaded fuel) under full rich air/fuel ratio at approach setting 

(HB-KEZ). 

For the different power modes, 

•

 the mean particle diameter6 varied between 49 and 108 nm and 

•

 the total particle concentration varied between 5.7 to 8.6 times 10 million particles per cubic centimetre.

With an assumed specific density for soot of 1.2, 

•

 the estimated particle mass concentration was around 10 000 μg/m3 (micro grams per cubic meter).

Generally, particle emissions of aircraft gasoline “old tech” piston engines, running on leaded AVGAS 

at “full rich” conditions, seem to be comparable to diesel car engine particle emissions (see figure 14). 

Details of these measurements are given in Appendix 4. 

 

6

 Most of the particles are ultra fine: 100 nm = 0.00001 mm 

NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) NOx 111001111

TO 

3000ft_4124

TO 

4000ft_5004

TO 

5000ft_5884

TO 

6000ft_6764

TO 

7000ft_7884

AP 

7000ft_7884

AP 

6000ft_6884

AP 

5000ft_5764

AP 

4000ft_4764
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

 

Figure 13: Number-size distribution of HB-KEZ engine at approach mode. The mean particle diameter 

is around 100 nm and the total concentration is in the order of 10 million particles per cubic centimetre 

(cm3

). 

 

Figure 14: Number-size distribution of a typical diesel passenger car (CDI) at 2000 RPM (increased 

idle) for comparison to the HB-KEZ measurements [C. Wahl/DLR 2004l] 

Based on the measurement of two typical “old tech” aircraft gasoline piston engines (150 and 180HP) 

the following soot emission factors are suggested (Appendix 4): 

Soot Emission Factors (mg soot / kg fuel)

Fuel TA AP CL TO

AVGAS 100LL (leaded) 50 40 70 100

AVGAS 91/96UL (unleaded) 1 1 2 3
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b) Pollutants during cruise (at or near “peak EGT”) 

In most cases, a mixture setting near peak EGT is chosen for cruise conditions. At peak EGT, the 

combustion is complete and theoretically, no partially burned fuel products should be produced. In 

reality, because of inhomogeneous mixture and temperature distribution in a cylinder, there are still 

small amounts of CO (carbon monoxide) and HC (hydrocarbons) in the exhaust gas. 

Due to maximum combustion heat and short reaction time at peak EGT, the nitrogen from air (N2) 

reacts with the oxygen from air (O2) in the combustion chamber to form NO (and to a lesser extent 

NO2), called nitrogen oxides NOx, as explained in section 2.2.2 f). This is the classical “fuel burn – 

NOx“ trade-off: Increased engine efficiency (less fuel burn) can lead to higher NOx emissions. The 

trade-off is normally discussed in the context of aircraft turbofan engines, but of course it exists also 

for piston engines, if they are run more efficiently. Automotive engines have exhaust after treatment 

systems with catalysts to reduce NOx. For aircraft gasoline piston engines, this would also be an option – if the fuel was not leaded. 

NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel)

NOx 8 46 6 43 5 44 5 44 4 39 9 45 6 43 7 42 4 41 3 39

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft

Figure 15: Example of NOx emission factors, measured in-flight during cruise between 3000 and 

7000ft pressure altitude and at about 65% of maximum propeller power. The measurements have 

been repeated between cruise “full rich” (indicated with CR, low NOx) and cruise peak EGT mixture 

(indicated with CR L, high NOx). At “full rich”, NOx emission factors decrease with increasing altitude. 

The measurement also shows reproducibility of the results (Example HB-EYS). 

Generally, “old tech” engines will produce between 30 and 40 g NOx per kg fuel near “EGT peak” 

conditions during cruise. 

CO Emission Factors 

0

200

400

600

800

1000

1200

Mode

Mass (g/kg Fuel)

CO 799 128 818 160 956 142 982 147 978 166 746 94 839 140 850 132 963 138 1013 144

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Figure 16: Example of CO emission factors, measured in-flight during cruise between 3000 and 7000ft 

pressure altitude and at about 65% of maximum propeller power. The measurements have been repeated during cruise “full rich” (indicated with CR, low NOx) and cruise peak EGT mixture (indicated 

with CR L, high NOx). At “full rich”, CO emission factors increase with increasing altitude. The measurement also shows reproducibility of the results (Example HB-EYS). 

Generally, “old tech” engines will produce around 200 g CO per kg fuel near “EGT peak” conditions 

during cruise. 

HC Emission Factors 

0

5

10

15

20

25

Mode

Mass (g/kg Fuel)

HC NDIR 13 5 14 3 16 5 16 6 21 5 13 3 14 5 16 6 16 5 19 4

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft

Figure 17: Example of HC emission factors, measured in-flight during cruise between 3000 and 7000ft 

pressure altitude and at about 65% of maximum propeller power. The measurements have been repeated during cruise “full rich” (indicated with CR, low NOx) and cruise peak EGT mixture (indicated 

with CR L, high NOx). At “full rich”, HC emission factors increase with increasing altitude. The measurement also shows reproducibility of the results (Example HB-EYS). 

Generally, “old tech” engines will produce between 6 and 12 g HC per kg fuel near “EGT peak” conditions during cruise. 

Based on the measurement of two typical “old tech” aircraft gasoline piston engines (150 and 180HP) 

the following soot emission factors for cruise are suggested (Appendix 4): 

Soot Emission Factors (mg soot / kg fuel)

Fuel CR 

AVGAS 100LL (leaded) 40

AVGAS 91/96UL (unleaded) 1

c) Emissions for aerodrome circuits (“old tech” engines) 

A circuit is a flight pattern that is flown at an airport e.g. for aircraft doing a sequence of landings for 

training purposes. A high percentage of piston engine aircraft are flying in aerodrome circuit patterns, 

because those aircraft are often used for pilot basic training and education. 

For a typical 4 seat piston engine aircraft, circuit emissions for low level circuits (1500 ft PA) and high 

level circuits (5600ft PA, with mixture adjustment) are given in tables 1 and 2 (from Appendix 2, section 3 g). For a high performance single engine piston aircraft, suggested mean values are given in 

table 3. 
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Normally, for CO2 emissions calculation, complete combustion is assumed, which means to multiply 

the kg fuel by 3.17 to get kg of CO2 (section 2.2.1.c). As shown before, “old tech” piston engine have 

an extremely incomplete combustion during circuit flying. In Tables 1 and 2, this has been taken into 

account with a lower value for CO2 emissions. So it is possible to sum up all emissions of different 

species to get the total emissions. 

However, in emissions inventory work, the general principle is to calculate the mass of CO2 (and H2O) 

as if they were resulting from complete combustion. The pollutants have to be seen as part of 

CO2 and H2O mass emissions. This makes a certain sense in the context of climate impact assessments, because most CO and HC pollutants will later be transformed in CO2 and H2O after being released into the atmosphere. 

Tables 1 and 2: Circuit emissions for a typical 4 seat single engine piston aircraft (180HP). (Appendix 2, section 3 g). Please note: CO2 emissions have been indicated here as measured directly in 

the exhaust gas (see text above for explanation). 

Total circuit emissions (taxi-in, 1 circuit, taxi-out)

Elevation fuel (kg) CO (g) HC (g) NOx (g) CO2 (kg) H20 (kg) lead (g)

2000ft 2.83 3305 73 3 5.66 3.40 2.25

5600ft (Samedan) 2.76 2562 67 8 5.51 3.31 2.19

Total circuit emissions (1 circuit without taxi)

Elevation fuel (kg) CO (g) HC (g) NOx (g) CO2 (kg) H20 (kg) lead (g)

2000ft 1.90 2200 45 3 3.79 2.28 1.51

5600ft (Samedan) 1.82 1898 44 5 3.65 2.19 1.45

Table 3: Circuit emissions for a typical high performance single engine piston aircraft (300HP), 

fitted with automatic mixture adjustment (best power mixture). (Appendix 2, section 5 h). Please note: 

CO2 emissions have been indicated here as measured directly in the exhaust gas (see text above for 

explanation). 

TCM IO-550 B fuel (kg) CO (g) HC (g) NOx (g) CO2 (kg) H20 (kg) lead (g)

1 Aerodrome circuit 3.9 3300 60 22 7.8 4.6 3.1

d) Emissions for landing and take-off cycle 

Emissions in the landing and take-off cycle (LTO) are based on the suggestions of section 2.1.2 and 

on the data contained in the individual FOCA engine data sheets. 

Table 4: LTO fuel and emissions for a typical microlight aircraft (Switzerland: Ecolight), if fitted with 

a four stroke engine. Note: No lead and no bromide emissions. The soot value is estimated. 

ECOLIGHT (MICROLIGHT 4 - STROKE) Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

LTO TOTAL FUEL (kg) or EMISSIONS (g) 1.4 47 940 33 0.002 0.0

Table 5: LTO fuel and emissions for a typical flying school single engine piston aircraft (150HP). 

The soot value is estimated. 

SINGLE EGINE PISTON AIRCRAFT 150HP Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

LTO TOTAL FUEL (kg) or EMISSIONS (g) 3.2 47 2397 28 0.17 2.5

Table 6: LTO fuel and emissions for a turbo diesel single engine piston aircraft (135HP). The soot 

value is estimated. 

SINGLE ENGINE TURBO DIESEL 135HP Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

LTO TOTAL FUEL (kg) or EMISSIONS (g) 1.6 5 19 30 0.09 0.0

Table 7: LTO fuel and emissions for a typical 4 seat single engine piston aircraft (180HP). The soot 

value is estimated. 

SINGLE EGINE PISTON AIRCRAFT 180HP Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

LTO TOTAL FUEL (kg) or EMISSIONS (g) 3.9 71 3930 12 0.20 3.1
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Table 8: LTO fuel and emissions for a single engine piston high performance aircraft (300HP). The 

soot value is estimated. 

SINGLE EGINE PISTON AIRCRAFT 300HP Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

LTO TOTAL FUEL (kg) or EMISSIONS (g) 7.5 174 7327 24 0.39 6.0

Table 9: LTO fuel and emissions for a twin engine piston high performance aircraft (2 x 325HP). 

The soot value is estimated. 

TWIN EGINE PISTON AIRCRAFT 2 X 325HP Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

LTO TOTAL FUEL (kg) or EMISSIONS (g) 21.6 244 19330 46 1.12 17.2

e) Emissions for cruise 

The tables below show fuel consumption (in kg) and gaseous pollutants mass emissions for cruise 

during one hour flight. The cruise setting has been chosen according to engine technology as described in Appendix 3. 

Table 10: One hour fuel and emissions for a typical microlight aircraft (Switzerland: Ecolight), if 

fitted with a four stroke engine. Note: No lead and no bromide emissions. The soot value is estimated. 

Ecolight Aircraft (Microlight 4-Stroke) Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

CRUISE 1HOUR FUEL (kg) or EMISSIONS (g) 8.7 67 1090 243 0.009 0.0

Table 11: One hour fuel and emissions for a typical flying school single engine piston aircraft 

(150HP). The soot value is estimated. 

SINGLE ENGINE PISTON AIRCRAFT 150HP Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

CRUISE 1HOUR FUEL (kg) or EMISSIONS (g) 20.9 243 8557 772 1.09 16.6

Table 12: One hour fuel and emissions for a turbodiesel single engine piston aircraft (135HP). The 

soot value is estimated. 

SINGLE ENGINE TURBO DIESEL 135HP Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

CRUISE 1HOUR FUEL (kg) or EMISSIONS (g) 14.1 22 91 373 0.8 0.0

Table 13: One hour fuel and emissions for a typical 4 seat single engine piston aircraft (180HP). 

The soot value is estimated. 

SINGLE ENGINE PISTON AIRCRAFT 180HP Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

CRUISE 1HOUR FUEL (kg) or EMISSIONS (g) 23.0 197 6743 903 1.20 18.3

Table 14: One hour fuel and emissions for a single engine piston high performance aircraft 

(300HP). The soot value is estimated. 

SINGLE ENGINE PISTON AIRCRAFT 300HP Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

CRUISE 1HOUR FUEL (kg) or EMISSIONS (g) 49.7 268 23490 1149 2.58 39.5

Table 15: One hour fuel and emissions for a twin engine piston high performance aircraft (2 x 

325HP). The soot value is estimated. 

TWIN ENGINE PISTON AIRCRAFT 2 x 325HP Fuel (kg) HC (g) CO (g) NOx (g) Soot (g) Lead (g)

CRUISE 1HOUR FUEL (kg) or EMISSIONS (g) 106.0 766 60088 1648 5.51 84.2

f) Emissions of modern turbo diesel engines – a comparison 

By design, diesel engines are lean burn engines, working with a lot of excess air (= a lot of excess 

oxygen)! The TAE-125-01 Centurion 1.7 engine, which FOCA has measured, had a minimal λ of at 

least 1.3. In every continuous operating condition (take-off, climb, cruise, approach), the FADEC controlled engine is running lean. With section 2.2.2 f) it is directly understandable, what this means in 

terms of gaseous emissions: Emissions are minimal in comparison to “old tech” gasoline piston 
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engines of the same power. Depending on the operating conditions, the emissions of the diesel 

can be a factor of 100 lower, compared to “old tech”! (See tables 6 and 12, figures 18 and 19).

Total gaseous pollutants in a landing and take-off cycle

0

500

1000

1500

2000

2500

3000

Conv. Piston (Lyc O-320) Diesel (TAE-125) Ecolight (Rotax 912)

Sum of pollutants (g)

Figure 18: Sum of gaseous emissions during a landing and take-off cycle, based on FOCA measurements, for a conventional “old tech”, a turbo diesel of similar power and a four stroke microlight engine 

(Swiss microlight = Ecolight). 

Total gaseous pollutants for a 1 hour cruise

0

2000

4000

6000

8000

10000

12000

Conv. Piston (Lyc O-320) Diesel (TAE-125) Ecolight (Rotax 912)

Sum of pollutants (g)

Figure 19: Sum of gaseous emissions during one hour cruise, based on FOCA measurements, for a 

conventional “old tech”, a turbodiesel of similar power and a four stroke microlight engine (Swiss microlight = Ecolight). 

Particle Emissions: At approach (full rich), the mean diameter of emitted particles from an “old tech” 

engine (an aviation gasoline engine) was around 100 nm and the concentration around 10 million nonvolatile particles in 1 cubic-centimetre (cm3

) of exhaust air. This is very similar to a diesel engine without particle filter (see section 2.2.3 a). 

From present knowledge it is concluded that the size, number and mass of emitted particles from the 

measured turbo diesel engine is not worse than with the rich burn gasoline aircraft piston engine, using leaded fuel. However, the chemical composition of the particles can be different with possibly different health effects, if particles are directly inhaled. 
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g) Contribution of piston engines to total aviation emissions 

FOCA is providing aircraft emissions data to external bodies e.g. for environmental impact assessments. FOCA is legally bound to calculate annual emissions inventories based on different principles, 

and has developed advanced models, taking every aircraft movement and destination into account, 

with actual flying engines . 

One of the models calculates the fuel (CO2) and emissions for all flights from A to B in Switzerland and 

all flights from A in Switzerland to the first destination B abroad during one year. This modelling corresponds approximately to the fuel sold in Switzerland during one year, which is used as a quality control for the bottom up calculated fuel consumption. This model has been used for the comparison below. 

For total CO2 emissions, based on the fuel sold, no modelling would be necessary, as for aviation fuel, 

every kg of fuel translates approximately into 3.15 kg CO2 (This is the value for jet fuel, not for AVGAS). Pollutants emissions depend on engine technology and therefore on the actual engines that are 

flying. From point of view of fuel burn (CO2), piston engines can be completely neglected. In Switzerland, AVGAS consumption is lower than fuel consumption for gardening (off road sector). Even in 

comparison with jet fuel only, the AVGAS consumption is not significant (see below). But from point of 

view of pollutants emissions, for the first time, FOCA was able to generate a clear picture of the contribution from aircraft piston engines to total aviation emissions in Switzerland. 

The results of pollutants mass emissions have been generated based on the computation of around 

700’000 flight records of the year 2004, using actual engine data as far as possible for all operations 

that took place in Switzerland during that year. 

Piston aircraft emissions have the following shares on civil aviation emissions in Switzerland: 

• Less than 1% share on total aviation fuel and CO2 

• 1% share on NOx 

• 10% share on HC 

• 40% share on CO 

• 100% share on lead and bromides (the only lead source!)* 

*about 5 metric tons of lead and a similar amount of bromides per year in Switzerland 

 

2.3 Optimization of fuel burn and emissions 

2.3.1 “Old tech” gasoline engines 

a) Use of unleaded AVGAS 

FOCA and DLR measurements have proven a significant reduction of gasoline piston aircraft emissions by use of the unleaded Swedish AVGAS 91/96 UL. Besides this, the fuel meets the same aviation standard as the leaded AVGAS. The engine manufacturer Textron Lycoming has included AVGAS 

91/96UL as an approved alternate aviation gasoline for a large number of its engines already since 

1995. The engines with type numbers are listed in service instruction No. SI 1070. Bombardier-Rotax 

explicitly recommends the use of this fuel for its engines. 

b) Power setting, choice of speed and altitude for lowest possible CO2 emissions in cruise 

Lowest possible CO2 emissions will be the result of lowest possible fuel burn (section 2.2.1 c). If CO2

emissions shall be minimized, a mission has therefore to be optimized for best range. In order to find 

an optimal speed and altitude for best range in cruise, a theoretical approach is outlined below. Please 

note that distances, speeds and forces are in fact vectors. Because of parallel vector situations, the 

notation of vectors is simplified with the size of the scalar. 

Definition of terms for theoretical considerations: 
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(5)

(3)

(1) (2)

specific fuel consumption 

available power (from engine at full throttle)

 required power (for airframe) required thrust true airspeed (4)

 engine power

fuelmass

distance specific range

true airspeed time

fuelmass fuelflow

t P

m

P

t

m

P

FF SFC

P

P F TAS

P

FF

TAS

t

m

t

d

m

d S

and TAS

t

m

FF

f

f

avail

req req

f f

R

f

⋅ = = = =

=

= = ⋅ = ⋅

=

= = = = =

= = = =

The speed for best range (v_best_range) is the speed, where the ratio between forward speed (a true air 

speed TAS) and the fuel flow (FF) is the best possible (equation 3). 

The term TAS : FF is called specific range. The specific range for a given aircraft depends on 

• power management 

• cleanness of the airframe 

• aircraft mass 

• density altitude 

At v_best_range, the specific range is highest. 

How can v_best_range be found? 

One practical solution is the permanent automatic computing of TAS : FF (or better: Ground Speed : FF,

which takes wind into account). This can be done with a fuel flow measurement unit, which is coupled 

to GPS and constantly provides the nautical miles (NM) per fuel ratio. With experience, the NM per 

fuel ratio can be maximized, adjusting engine power and altitude accordingly (therefore Ground Speed)

during flight. 

Theoretical approach: 

For the usual power range of an aircraft piston engine, the fuel flow is proportional to the (propellershaft) power Pavail. With (5), the fuel flow can be written as: 

P SFC P (6) P

FF FF = ⋅ = ⋅

Equation (6) in (3) gives the following specific range formula: 

 (7) SFC P

TAS SR ⋅ =

The term SFC describes engine resp. propulsion efficiency. The term TAS : Preq is an expression for 

the aerodynamic efficiency of the airframe. More precisely, the maximum specific range will be obtained at highest TAS with lowest SFC and minimum required engine power. 

max. max. (8)

req

R SFC P

TAS S ⋅ =

In order to make things easier, the considerations are made step by step: 

1) Looking at aerodynamic efficiency and aircraft mass (keeping propulsion efficiency constant) 

2) Looking at propulsion efficiency alone 

3) Altitude considerations 

4) Summary and “Rules of Thumb” 
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1) Aerodynamic efficiency term, with equation (4) 

(9) 1 

req Freq TAS Freq

TAS

P

TAS = ⋅ =

Equation (9) expresses the fact that aerodynamic efficiency is best, if the required thrust is least. In 

steady state conditions, level flight at constant speed, the required thrust exactly compensates drag. 

Therefore, the number of Newtons for the required thrust equals the number of Newtons of the drag. 

Hence, for best aerodynamic efficiency, drag must be minimal. Besides others, the drag of a given 

aircraft is dependent on the aircraft mass. During cruise, the aircraft burns fuel and gets lighter, which 

reduces the mass, therefore reduces the necessary lift (reduces the lift coefficient) and the resulting 

drag. 

From the lift and drag equations (which we are not writing down here), it follows that the minimum drag 

occurs at the maximum lift-to-drag ratio. The true air speed for minimum drag, vmin_drag, , can be found 

(theoretically) by using the function of required power to fly at a certain TAS for a given aircraft and 

mass: 

Figure 20: Required power for a given aircraft in function of TAS for two different aircraft masses. The 

highest possible value for equation (9) is given with the tangent from the origin to the power required 

curve. This represents the minimum for Preq : TAS which is the same as the maximum of TAS : Preq. The 

corresponding speed for minimum drag is v_min_drag. The two power curves have been plotted based on 

a generic airframe. The tangent in the figure shows the example for v_min_drag determination in the lower 

mass case. 

Figure 21: Required power for a given aircraft in function of TAS for two different aircraft masses. With 

increasing mass, v_min_drag increases. 
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• For best range (at constant SFC), v_best_range is equal to v_min_drag. 

• With decreasing aircraft weight, v_min_drag decreases. 

• With headwind, v_min_drag increases. (The origin of the tangent in figure 20 moves to the right.) 

• v_min_drag is a very low cruising speed compared to “conventional” cruising speeds. 

• Drag reduction in general is not only achieved by approaching v_min_drag, but also by cleaning 

the airframe and the propeller from insects and dirt, reducing edges between engine cowling 

and airframe, etc. 

2) Propulsion efficiency 

In general, aircraft piston engines will run more efficiently (SFC gets smaller, improves): 

• If the required power to fly at a certain TAS is generated with the throttle fully open. 

• If engine RPM are as low as possible to generate the required power. 

• If the engine runs with more than 40% and less than 70% of the maximum sea level power. 

• If the air/fuel mixture is properly adjusted (summary in next section c). 

At low engine RPM, cylinder charge with air/fuel mixture is better and there are less friction losses. At 

full throttle, the intake system works more efficiently. However, there is a lower limit for efficient engine 

power generation, as well. 

Low engine RPM can be achieved with a variable pitch propeller. In fact, the propeller efficiency of a 

variable pitch propeller is very good at low RPM, which can combine to a good efficiency of the whole 

propulsion system at relatively low RPM. 

Output of the required power at low RPM needs relatively higher Manifold Pressure (MAP), respectively torque. For many engines, the MAP (in InHg) must not exceed engine RPM/100. The limitations 

are given by engine manufacturers and/or stated in the AFM/EOM and must be known. 

Apart from a better achievable SFC at lowered RPM (not lowest power), the propeller noise can be 

significantly reduced. A drop of only 100 RPM will reduce the propeller tip mach number with an impressively positive effect on noise reduction. This is an environmental win-win situation (noise and 

emission reduction). 

For a fixed pitch propeller aircraft, to fly on lowest possible RPM is normally not feasible. The effects 

depend on the chosen fixed propeller pitch and are therefore extremely aircraft dependent. 

3) Altitude considerations 

Before talking about altitude effects, it is worth understanding, that the speed indicator in most piston 

engine aircraft is essentially a pressure gauge, calibrated in speed units. The speed is called “Indicated Air Speed” IAS. At sea level standard conditions IAS will equal TAS. TAS is the only speed in the 

narrow sense. 

• With increasing altitude, IAS will be less than TAS. If IAS is kept constant during climb, TAS will 

increase. 

• 

The dynamic pressure used for moving the needle of the speed indicator is the same as the dynamic 

pressure in the drag formula. Therefore, 

• if IAS is kept constant during climb, the drag will remain the same, but TAS will increase. From 

equation (4) follows, that the required power increases. 

• If TAS shall be kept constant with increasing altitude, IAS has to be reduced. At higher altitude, 

the drag and the required power will then be less. 

With increasing density altitude, normally aspirated piston engines lose power, due to the lower oxygen partial pressure. Flying at high density altitudes can reduce the available power at full throttle 

down to 55% or even below. With medium available power at full throttle, properly mixed and at reduced RPM, the engine is at best SFC. Despite lower drag and higher achievable TAS at higher altitude, the relatively low available power (around 50%) holds the TAS at a relatively low level, not very 

far above v_min_drag. This means that the airframe is near to its best aerodynamic efficiency. Both effects, good SFC and TAS near v_min_drag combine to best specific range. 
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During cruise, the aircraft gets lighter by fuel burn. Figure 22 suggests reducing TAS accordingly. This 

can be done by successively climbing higher, as the loss of power will eventually reduce TAS, despite 

a lower drag at higher altitude. 

In turbocharged engines, at higher altitude, a relatively high air pressure (enough oxygen per volume) 

can be maintained in the manifold. For turbocharged engines, the altitude for best specific range 

could be further increased compared to the normally aspirated engine, because the engine provides 

the required power at higher altitude. The lower ambient air density causes less drag, with the effect 

of a higher achievable TAS, which increases specific range (equations 4 and 8). 

High cruising altitude does not necessarily result in best specific range for a piston engine aircraft. 

The fuel for a climb to higher altitudes and the wind components have to be taken into account. Additionally, the SFC of the piston engine is not very altitude and speed dependent, compared to a jet 

engine. Therefore, high specific range can be obtained also at lower altitudes with sufficient power 

reduction at maximum allowed MAP and low RPM (around 50% of maximum sea level power), which 

results in a TAS not very far above v_min_drag

High cruising altitude does not necessarily result in best specific range for a piston engine aircraft. 

The fuel for a climb to higher altitudes and the wind components have to be taken into account. Additionally, the SFC of the piston engine is not very altitude and speed dependent, compared to a jet 

engine. Therefore, high specific range can be obtained with sufficient power reduction at maximum 

allowed MAP and low RPM, around 50% of maximum sea level power, which results in a TAS not very 

far above v_min_drag

4) Summary and “Rules of Thumb” 

The speed for best range is not very far above v_min_drag.. In any case, the AFM has to be consulted. 

Additionally, the following “rules of thumb” may be considered: 

The least CO2 emissions during cruise may be achievable with: 

• v_best_range (no wind) = TAS for best rate of climb + 15% 

• v_best_range + 1/4 of head wind component (for headwind) 

• v_best_range – 1/5 of tail wind component (for tailwind) 

• v_best_range – 4% for every 100 kg below MTOM 

• Required power not below 45% and seldom above 55% 

• Required power at lowest possible RPM with highest allowed MAP 

• Proper mixture adjustment (High contribution, Appendix 2, summary in section c below) 
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”Holding position” during flight 

If an aircraft has to hold position during flight (e.g. during an approach), the best range criteria is not 

important. In this case, the aircraft should burn the fuel at the slowest rate possible, in order to minimize CO2 emissions. This is a power setting for best endurance. As explained before, the fuel burn for a 

piston engine is practically proportional to the power. The least fuel burn per time can therefore be 

achieved with a speed that requires the least power to keep the aircraft flying. This speed is at the 

minimum of the required power: 

Figure 22: Determination of speed for maximum endurance. It is the speed at minimum required power 

(the lowest point of the curve), shown for two aircraft masses. With increasing mass, the speed for 

maximum endurance increases. The lowest required power equals the lowest energy consumption per 

time to keep the aircraft flying. The speed where this occurs corresponds to the speed for minimum 

sink rate with engine off (v_min_sink). 

Usually, v_min_sink is not directly indicated in a piston engine aircraft AFM. But it is very near vy, the 

speed for best rate of climb. The best rate of climb will be achieved at a speed where the difference 

between available power and required power for the climb will be biggest. Because the required power 

is lowest at v_min_sink, the best rate of climb will usually be around that speed. 

The least CO2 emissions in a holding may be achieved with: 

• Flying slightly higher than or at vy (AFM restrictions may apply) 

• Required power at lowest possible RPM with highest allowed MAP 

c) Manual mixture management (Climb, Cruise, Descent/Approach) 

Climb 

• At climb, the engine may be leaned according to AFM to best power if AFM/EOM allows and 

CHT limits can be maintained. Again, the fuel flow method (as described in section 2.2.2 l) 

may be useful. 

Cruise “rich of EGT peak” 

• At cruise, flying slightly “rich of EGT peak” is still better than flying best power or very rich from 

point of view of emissions, although there will be more NOx emissions. There will be less fuel 

consumption (less total CO2), less CO and HC emissions and less particle mass emissions. 
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Cruise at “50°F lean of EGT peak” 

• Flying lean would be the optimum from point of view of emissions. With the specific fuel consumption at the minimum for a certain power setting, range can be maximized and at the 

same time, all emissions will be minimized as shown in section 2.2.2 f). In addition, the engine 

can run cooler. Minimum requirements for safe engine operation at this condition are considered like: 

- The engine manual and AFM explicitly describe lean mixture setting as an option. 

- The engine has a well balanced mixture and temperature distribution between the different 

cylinders. 

Descent / Approach 

• During descent at a fixed mixer position, the engine will normally get less rich (or leaner) due 

to increasing air density. If the mixture is set slightly rich before descent, the cylinders are approaching peak EGT when the aircraft descends. With a lean setting before descent, the cylinders are approaching lean misfire condition and may flame out during descent. Therefore, 

pilots are told to go to “full rich” for descent or approach. This makes operation simple. 

• FOCA measurements have shown that with the simple “full rich” operation, more fuel per distance is burnt during descent and approach than during cruise! The combination with a very 

incomplete combustion at “full rich” often leads to higher total emissions during descent than 

during cruise (Appendix 2). 

• Instead of going standard “full rich”, the author tested alternatives: Engine propeller power is 

down at around 45%. If the mixture is set to 100°F rich of EGT peak (best power, safety margin) just before descent, and if the 100°F during descent are maintained by stepwise enriching 

the mixture, considerable amounts of fuel and emissions can be saved. The 100°F have 

proven to be practical also for the case, when a sudden increase of power is required during 

descent. “Full rich” is set later, at mid downwind and checked in the final check, because “full 

rich” is necessary in the event of a go around. 

2.3.2 Choice of engine technology 

a) FADEC for gasoline engines 

In the opinion of the author, certified FADEC systems for “old tech” fuel injected aircraft gasoline piston 

engines are a valuable means of significantly reducing emissions (including fuel burn). A FADEC system is able to control the air/fuel mixture of every single cylinder and therefore, the engine can be run 

lean during cruise. 

b) Turbo Diesel engine 

At the time of completing this FOCA report, the turbo diesel engine has shown by far the lowest gaseous emissions per unit of power. From point of view of emissions, the turbo diesel technology brings 

the greatest reduction of aircraft piston engine emissions. This includes CO2 and pollutants. From 

point of view of particle emissions, the turbo diesel is not considered worse than the “old tech” gasoline piston engine, running on AVGAS100LL. 
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3. Outlook – planned future work 

3.1 Number of measured aircraft piston engines 

3.1.1 “Old tech” engines and new engine concepts 

Some of the FOCA data are based on the measurements of one particular engine of a certain engine 

type. Significant variations between one and another engine of the same type exist and therefore 

FOCA plans to improve data representation with more measurements of different engines of a particular engine type. The database will also be completed with engine emissions data for still missing engines. 

3.1.2 Modernized “old tech” engines with FADEC 

During the last couple of years, options for fuel injected engines have been brought into the market 

and have been certified for certain airframe/engine combinations. 

From present knowledge, the author concludes that FADEC equipped aircraft piston engines (with 

individual cylinder control) can have substantially improved emissions performance. More measurement data are needed. 

3.2 Unleaded AVGAS 

In Europe, AVGAS 100LL is the only leaded fuel in the market. Besides lead-tetraethyl, this fuel contains bromides which are harmful to the stratospheric ozone layer. The scientific research programme 

documented in Appendix 4 has revealed that the use of an unleaded fuel like AVGAS 91/96 UL can 

dramatically improve emissions performance of existing aircraft piston engines. Therefore, whenever 

feasible and applicable, FOCA supports the transition from leaded AVGAS to a cleaner unleaded AVGAS for aircraft piston engines. Unfortunately, AVGAS 91/96 UL can not yet replace AVGAS 100LL in 

any case, due to the slightly lower octane rating. Tested unleaded AVGAS with still better environmental performance than 100LL, like type C and G (Appendix 4) are alternatives that will be evaluated 

in the future. 

Unleaded motor gasoline (MOGAS) has strong limitations for use in aircraft. Existing “old tech” piston 

engine aircraft designs – if possible at all - require a supplemental type certificate (STC) to ensure safe 

operation when using MOGAS. For safety reasons, such a STC normally prescribes very low ethanol 

content. The increasing ethanol content in motor gasoline may lead to difficulties in aircraft MOGAS 

supply in the future. Besides this, instead of lead components, MOGAS can contain substances, which 

create a certain risk for contamination of drinking water7

. 

Picture 4: Research on unleaded AVGAS, St. Stephan, Switzerland, May 2006. From left to right: C. 

Wahl, M. Kapernaum (both DLR), L. Hjelmberg (Hjelmco), T. Rindlisbacher, W. Bula (both FOCA) 

 

7

 MOGAS sold in Switzerland and analyzed in 2006 contained quite large amounts of MTBE. 
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3.3 Emissions data for helicopter turbines and small turbofans 

For other engine families, like helicopter turbines and small jet 

engines, without an ICAO emissions certification, there is still a 

lack of emissions data and FOCA plans to work on two 

respective packages, based on its aviation law (SR 748.0, LFG 

Art. 58): 

• Helicopter engine emissions, project HELEN (starting 

mid 2007) 

• Small turbofan engine emissions, project STUF

(planned to start in 2008). 

A first feasibility study for application of the FOCA “low cost” measurement system has been done on 

a typical business jet turbofan in summer 2006. Measurements of gaseous exhaust components have 

been combined with a sophisticated particle measurement system (as described in Appendix 4, section 4). Measured gaseous emissions have been compared to certification level data kindly provided 

by the engine manufacturer. The data matched quite nicely. 

3.4 International activities 

Due to environmental legislation of different countries, and also to the increase of interest at international level, the improvement of knowledge about non-certified engine emissions data has become 

more and more important. FOCA is supporting the further development of ICAO guidance material for 

the calculation of emissions caused by the aviation sector and for calculations in relation to environmental impact assessments. 

- END -
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4. List of acronyms and abbreviations

AFM Airplane Flight Manual 

AMSL Above mean sea level 

AP Approach mode 

ASTM American Society for Testing and Materials, one of the largest voluntary standards development organizations in the world 

AVGAS Aviation gasoline 

AVGAS 100LL leaded AVGAS with 100/130 aviation octane rating 

AVGAS 91/96 UL unleaded AVGAS with 91/96 aviation octane rating 

BHP Brake Horse Power 

°C Temperature in degrees Celsius 

CAEP Committee on Aviation Environmental Protection 

CHT Cylinder head temperature 

CL Climb mode 

CLD Chemiluminescence 

CO Carbon monoxide 

CO2 Carbon dioxide 

CPC Condensation Particle Counter 

CR Cruise mode 

CR L Cruise mode with adjusted mixture to lambda = 0.95 

CR LL Cruise mode with adjusted mixture to lambda = 1.3 

CR R Cruise mode at mixture "full rich" 

Density Altitude DA Height in the International Standard Atmosphere at which the prevailing air 

density occurs. Key parameter for aircraft and engine performance 

DLR German Aerospace Centre 

DWD Downwind (part of the approach pattern at the airport) 

EEPS Engine Exhaust Particle Sizer 

EF Emission Factor (sometimes also indicated as EI, emission index) 

EGT Exhaust Gas Temperature 

ELT Emergency Localizer Transmitter 

EOM Engine Operating Manual 

°F Temperature in degrees Farenheit 

FADEC Full Authority Digital Engine Control 

FF Fuel Flow 

FID Flame Ionization Detector 

Final Final approach (last segment of approach before touchdown) 

FOCA Federal Office of Civil Aviation (the Swiss Civil Aviation Authority) 

ft feet 

FT Full Throttle 

GPS Global Positioning System 

H2 Hydrogen 

H2O Water(vapour) 

HBEYS FOCA aircraft Robin DR400-180 with Lycoming O-360 series engine 

HBHFX Aircraft AS 2002 Bravo with Lycoming O-320 series engine 

HBKEY FOCA aircraft Robin DR400/500 with Lycoming IO-360 series engine 

HBKEZ FOCA aircraft Robin DR400/500 with Lycoming IO-360 series engine 

HBKIA FOCA aircraft Bonanza A35 with Teledyne Continental IO-550 series engine 

HBWAD Aircraft Ikarus C22-B with Rotax 912S engine 

HC (total) hydrocarbon emissions 

HC6NDIR NDIR HC reading in Hexane ppm 

He Helium 

HP (Propeller) Horsepower 

ICAO International Civil Aviation Organization 

InHg Pressure Unit in inches of mercury column, e.g. 23 InHg = 779 hPa 

ISA International Standard Atmosphere 

λ Number, expressing how rich or lean an air/fuel mixture is 

Lambda Number, expressing how rich or lean an air/fuel mixture is 

Lean Air/fuel mixture which is poor in fuel (excess oxygen) in relation to stoichiometric mixture 

LTO Landing and take-off cycle 

M Torque 

MAP Manifold Air Pressure 
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Mixer Lever in the cockpit to adjust air/fuel mixture 

Mixture Air/fuel mixture 

Mode Flight phase and attitude with certain power setting 

MOGAS Motorcar Gasoline 

MPH Miles per Hour 

MTBE Methyl tert-butyl ether 

N2 Nitrogen 

Nanoparticles Ultra fine combustion particles with diameters between 10 and 500 nanometers 

NDIR Non-Dispersive Infrared Sensor 

NOx Nitrogen oxides 

"Old tech" Market dominant aircraft piston engine concept 

P Power 

PM Particle Mass 

Pressure Altitude PA Height in the International Standard Atmosphere at which the prevailing air 

pressure occurs, obtained by setting the subscale of a pressure altimeter to 

1013.2 hPa 

QNH Ambient air pressure corrected to sea level with ISA temperatures 

Rich Air/fuel mixture which is rich in fuel (oxygen deficiency) in relation to 

stoichiometric mixture 

RPM Revolutions per Minute 

RWY Runway 

SEKEI Aircraft Piper PA-28 Warrior with Lycoming O-320 series engine 

SMPS Scanning Mobility Particle Sizer 

STC Supplemental Type Certificate 

stoichiometric Combustion condition at which the air/fuel ratio is such that there is neither an 

excess of fuel nor of air 

TA Taxi mode (aircraft taxi out and in at the airport) 

THC Total hydrocarbon emissions (often simply indicated as HC) 

TO Take-off mode 

UV Ultraviolet radiation 

VFR Visual Flight Rules 

Vne Never-exceed speed 
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5. Bibliography 

1) Bombardier-Rotax, engine test stand data, property of Rotax, 2005 

2) Chevron Products Company, Technical Review "aviation fuels", 2000 

3) DLR, German Aerospace Centre, Institute of Combustion Technology, C. Wahl/M. Kapernaum, written and oral communication, 2004 – 2007 

4) Hjelmco Oil, Aviation Gasolines, AVGAS 91/96UL description, Edition V, 1997 

5) Hjelmco Oil, Aviation Gasolines, turbo fuels & lubricants, Fuel Certificate, 2005 

6) HORIBA, Mexa 1170 HFID manual, 2006 

7) ICAO Annex 16, volume 2, aircraft emissions, second edition, July 1993, amendment 5 

8) Intertek Caleb Brett, C-H relation measurements for test fuels, FOCA property, 2006 

9) Kas Thomas, Light Plane Maintenance, 2000, ISBN 0-965196-0-6 

10) Porsche, PFM3200, Abgaskonzentrationen, BAZL, 1988 

11) Technotest, Stargas 898 manual, 2003 

12) Textron-Lycoming, Power Curves O-360 and IO-360 series engines, provided hand written 

documents 

13) TSI Incorporated, SMPS and EEPS functional drawings, 2007 

14) US EPA, Control of air pollution from aircraft and aircraft engines, federal register, volume 38, 

number 136, July 17, 1973 

15) US FAA, Advisory Circular AC34-1A 

16) US FAA, Federal Aviation Engine Emissions Databank, November 26, 1991 
Federal Department of the Environment, Transport, Energy and 

Communications DETEC 

Federal Office of Civil Aviation FOCA 

Aviation Policy and Strategy 

Environmental Affairs 

AIRCRAFT PISTON ENGINE EMISSIONS 

Appendix 1: Measurement System 

 

FOCA, CH-3003 Bern

Reference: 0 / 3/33/33-05-003 ECERT 

Contact person: Theo Rindlisbacher 

Tel. +41 31 325 93 76, Fax +41 31 325 92 12, theo.rindlisbacher@bazl.admin.ch

This document has been released for publication by FOCA, Aviation Policy and Strategy, Director M. Zuckschwerdt, 11.06.2007 

33-05-003 Piston Engine Emissions_Swiss FOCA_Appendix1_070605_rit 
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Contents Page

a) Minimum requirements met by FOCA low cost gas measurement system 3 

b) Measurement Method 

c) Measured Gaseous Emissions 

d) Ranges 

 e) Illustration of FOCA low cost gas measurement system 4 

f) Measurement systems for total HC measurements (certification standard) 5 

 g) Measurement systems for comparative gas measurements (certification standard) 

 h) Measurement system for nanoparticle measurements (Appendix 4) 6 
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a) Minimum requirements that are met by FOCA low cost gas measurement system 

- Class 0 of OIML R99 1

- Capable of NO measurements with electrochemical cell 

- Calibration Intervals three months ore more 

- Condensation water separation, capable of cold sampling line measurement 

- Capable of direct λ monitoring 

- Ambient temperature range of +1 to +40°C 

- Ambient relative humidity range 0 to 95% 

- Ambient pressure compensation between 770 and 1030 hPa (for in-flight tests) 

- Portable, no calibration gases and fuel during operation necessary (for in-flight tests) 

- Battery power possible (for in-flight tests) 

- Aviation fuel flow meter FAA TSO/STC approved 

FOCA uses Tecnotest S.r.l STARGAS 898 with implemented NO sensor (Andros) and jp fuel scan 450 with 

corresponding fuel flow transducers. 

b) Measurement Method 

NDIR (Non-dispersive Infrared Spectroscopy) for HC, CO, CO2

Electrochemical detection for O2 and NO 

c) Measured Gaseous Emissions 

HC calibrated with propane, results given as ppm n-hexane (see Appendix 4 for corrections to ppmC) 

CO, CO2; O2, NO 

d) Ranges Resolution Accuracy

CO 0 - 15 Vol% 0.001 0..10 l% +-0.02% abs. / +-3% rel. 

 10.01..15 % +-5% rel. 

CO2 0 - 20 Vol% 0.01 0.00..16.00 % +-0.03% abs. / +-3% rel. 

 16.01..20.00 % +-5% rel. 

HC 0 - 30000 ppm 1 0..2000 ppm +-4ppm abs. / +-3% rel. 

 2001..15000 ppm +-5% rel. 

 15001..30000 ppm +-8% rel. 

O2 0 - 25 Vol% 0.01 0.00..25.00 % +-0.1% abs. / +-3% rel. 

NO 0 - 5000 ppm 1 0..4000 ppm +-25ppm abs. / +-4% rel. 

 4001..5000 ppm +-5% rel. 

λ 0.5 - 2.000 0.01 +-0.3% abs.2

jp fuel flow 

 0 – 60 GPH 1% +- 1 liter / hour (test result)

 

 

1

 Organisation Internationale de Métrologie : „Instruments de mesure de gaz d’échappement des véhicules“ 2

 Roberto Amadasi, Tecnotest S.r.l, Sala Bagaza, Italy 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

e) Illustration of FOCA low cost gas measurement system 

Probe Design 

Exhaust In to analyzer 

The exhaust probe which goes into the exhaust pipe has a length of 30 cm (left part of the probe). The 

tip of the probe is closed and has four small holes, drilled sidewards into the probe. 

Normally, aircraft piston engines have rather short exhaust pipes. Therefore a cooling device as seen 

on the right hand side is necessary for cooling the exhaust gas in the probe from around 600°C to 

200°C measuring temperature. 

Gaz Analyzer STARGAS 898, MEXA 1170 HFID, calibration gas and FID operating gas installed 

in FOCA environmental measurement car 

Optional RPM 

Probe 

Automobile Gas Analyzer 

Fuel Flow 

Calibration Gas 
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f) Measurement systems for total HC measurements (certification standard) 

FOCA uses HORIBA Model MEXA-1170-HFID (Hot Flame Ionization Detector) for total HC measurements. The MEXA-1170-HFID is a stand-alone total HC analyzer with heated sample line at 191°C. 

This system is very accurate but not suitable for in-flight tests. It is used for static on ground total HC 

emission measurements. On ground, FOCA uses both the low cost NDIR HC and the HFID in parallel. 

However, HC data on FOCA data sheets (and CO, NOx corrections) are solely based on the 

more accurate HFID measurements.

g) Measurement systems for comparative gas measurements (certification standard) 

HORIBA OBS 2200 (provided by HORIBA, not owned by FOCA): 

All in one system. Dimensions: 40 x 35 x 50 cm Utilizing HFID for total HC measurement, HCLD (hot 

chemiluminescence) for NOx measurement, HNDIR (hot NDIR) for CO and CO2 measurement. GPS, 

Temp./Humidity, Engine Control Unit Interface, patented exhaust flow meters, heated sampling line at 

191°C. System mass (incl. batteries, calibration and utility gases): 120 kg 

This system has been used by FOCA in order to compare in-flight tests results with very sophisticated 

gas analyzer data. At the same time, the provider was able to demonstrate that its system even works 

in an aircraft up to 7000ft. 

Performance: 

THC HFID (0 – 100 ~10 000 ppm) 

NOx HCLD (0 – 100 ~3000 ppm) 

CO2 HNDIR (0 – 5 ~ 20vol%) 

CO HNDIR (0 – 0.5 ~ 12vol%) 

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Illustration: OBS 2200 pitot exhaust flow meter, ready for installation in light aircraft (AS02, HB-HFX) 

for in-flight measurements (see Appendix 2). 

Exhaust flow meter, heated sampling line and installation on backseat of HB-HFX 

h) Measurement system for nanoparticle measurements 

The measurement system and expertise is provided by German DLR, Institute of Combustion Technology. The 2004 measurement system consists of 

- TSITM SMPS (Scanning Mobility Particle Sizer) System 

- 4.5 meter stainless steel sampling line at 150°C, calibrated sampling line loss 

- Dekati Diluter 1:10 

In 2005 the SMPS has been replaced by a TSITM EEPS (Engine Exhaust Particle Sizer), providing fast 

response number-size distributions (see Appendix 4). 
33-05-003 Piston Engine Emissions_Swiss FOCA_Appendix2_070605_rit 

Federal Department of the Environment, Transport, Energy and 

Communications DETEC 

Federal Office of Civil Aviation FOCA 

Aviation Policy and Strategy 

Environmental Affairs 

AIRCRAFT PISTON ENGINE EMISSIONS 

Appendix 2: In-flight Measurements 

 

FOCA, CH-3003 Bern

Reference: 0 / 3/33/33-05-003 ECERT 

Contact person: Theo Rindlisbacher 

Tel. +41 31 325 93 76, Fax +41 31 325 92 12, theo.rindlisbacher@bazl.admin.ch

This document has been released for publication by FOCA, Aviation Policy and Strategy, Director M. Zuckschwerdt, 11.06.2007 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Contents 

 Page 

1. The first in-flight tests 3 

1.a) Preparation of aircraft HBEYS 3 

1.b) Calculated emission factors for first test flight with HBEYS 5 

1.c) Discussion and general explanations 6 

2) Standard Flight Test Programme 7

3) HBEYS (Carburated Engine Lyc O-360 Series) 8 

3.a) Results for simulated aerodrome circuits 8 

3.b) Discussion 11 

3.c) HC emission factors at flight idle 12 

3.d) Discussion 13 

3.e) Additional high altitude circuit flight testing 14 

3.f) Discussion 15 

3.g) Inventory: Total emissions in aerodrome circuits at different flight altitudes 15 

3.h) Full power and approach power settings 16 

3.i) Climb power and approach power settings 18 

3.j) Cruise power settings 20 

4) HBKEZ (Fuel Injected Engine Lyc IO-360 Series) 22 

4.a) Results for simulated aerodrome circuits 25 

4.b) Discussion 27 

4.c) Full power and approach power settings 27 

4.d) Take-off, climb and approach power settings with mixture “full rich” 29 

4.e) Discussion 30 

4.f) Take-off, climb and approach power settings with mixture adjustment 31 

4.g) Discussion 33 

4.h) Inventory: Standard flight emission measurement 33 

5) HBKIA (Fuel Injected Engine TCM IO-550 B) 36 

5.a) Results for aerodrome circuits 39 

5.b) Discussion 43 

5.c) Inventory: Total emissions of HBKIA in aerodrome circuits 43 

5.d) Discussion 44 

5.e) Additional high altitude circuit flight testing 44 

5.f) Discussion 46 

5.g) Inventory: Total emissions of HBKIA in the low and high altitude aerodrome circuit 47 

5.h) Discussion 47 

5.i) Full power settings 47 

5.j) Discussion 50 

5.k) Climb power settings 50 

5.l) Approach power settings 53 

5.m) Standard flight profile emission measurement 55 

5.n) Discussion 57 

5.o) Inventory: Total emissions of HBKIA in standard flight, defined in 5.m) 59 

5.p) Emissions summary for a HBKIA mission, defined in 5.m) 64 

6) HBHFX (Carburated Engine Lyc O-320 Series) 64 

6.a) HBHFX high accuracy in-flight measurements: Installation of OBS2200 64 

6.b) Real time emission mass determination during flight 70 

6.c) OBS2200 confirms typical emission factors for Lycoming carbureted engines 75 

6.d) OBS2200 time trend chart and confirmation of high HC at flight idle 76 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

1. The first in-flight tests 

1.a) Preparation of aircraft HBEYS 

July 2003: The FOCA measurement system was installed in HBEYS for the first time. After successful 

ground testing, documentation for airworthiness validation of such a major aircraft modification (aircraft 

category “restricted”) was completed. 

 

 

Picture 1: Electronic RPM and fuel flow Picture 2: Sampling lines in and out 

installation 

Picture 3: Installation of the remote controlled gas analyzer in the luggage compartment of HBEYS. 

The exhaust sample flows through the black line to the analyzer. Because of high CO concentrations 

in the exhaust, all sample gas has to be pumped outside the cabin (white line). Water condensate is 

separated from the sample and trapped in a small bottle at the bottom. To check cabin CO concentration level, a CO detector is installed, which is independent from the analyzer. 

The fuel scan box, which indicates the fuel flow, is placed on the knees of the copilot. 

The exhaust probe installation has been tested during many hours of ground operation prior to the first 

flight. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

 

Picture 4: Exhaust probe Picture 5: Cockpit of HBEYS with 12VDC/70W 

power supply for the gas analyzer on the right. 

 Picture 6: Taxiing for the first flight Picture 7: Those tapes have proven reliable... 

Installation steps HBEYS 

1. Mount exhaust probe 

2. Mount RPM detector (Engine cowling, electric line) 

3. Connect Fuel Scan 

4. Remove back seat, ELT OFF during work 

5. Fix Stargas in baggage compartment, install H2O line 

6. ELT ON 

7. Install 12DC lines and extern TV-screen 

8. Install exhaust sample lines IN and OUT (via fresh air vents on starboard, which are removed) 

9. Install lines for thermocouple 

10. Scotch all lines (exhaust sampling lines, PET, 12VDC and RPM detector lines) 

Operational Changes 

Installation moves the centre of gravity aft, which has to be considered in „Weight and Balance“ 

At engine start up there is an additional checklist for measurement system start up. 

If one of the cockpit CO detectors changes the colour to green or even blue, the canopy must be 

immediately opened by about 10 cm. 

 

Maximum continuous vertical acceleration is limited to +2g. Avoid negative vertical accelerations. 

Maximum pressure altitude is limited to 7000 ft AMSL. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Checklist Stargas 898 

Preparing for operation 

Paper roll Check 

Operation supply switch Chose „Battery“ 

Robin Checklist Engine in warming up phase 

Robin Checklist Radio Master ON 

Main switch Stargas ON 

External monitor ON 

Revolution counter Red LED ON 

Pump In function 

Menu Pump OFF 

Revolution counter Green LED ON, if negative: Vary Engine revolutions betw. taxi idle and 2000 RPM 

Clock Stargas Check 

Menu Exhaust measurement Standard 

Before measurement 

Warming phase > 30 seconds 

Pump ON 

Automatic calibration in function 

Value for O2 

(with probe pipe disconnected) 

21% 

Other values 

(with probe pipe disconnected) 

0 (HC few ppm) 

Fuel Flow in function 

1.b) Calculated emission factors for first test flight with HBEYS 

All calculations are done according Appendix 5. Abbreviations used in the figures: 

TO = Take off roll, CL = Climb, CR = Cruise, AP = Approach, L = air fuel mixture manually leaned 

3700_6748 = Altitude 3700ft QNH and Density Altitude 6748ft etc. 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 1224 1137 975 279 436 479 1124 1199

TO 3700_6748 CL 4700_7748 CR 5000_7880 CRL 

5000_8000

CRL 

6000_8880

CRL 

6000_8880 CR 6000_8760 AP 3000_5520

Figure 1: CO emission factors for take-off, climb, cruise and approach. TO, CL, CR5000_7748, 

CR6000_8760 and AP have been flown with air-fuel mixture “full rich”. CRL has been flown with 

manually adjusted engine air-fuel mixture. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

HC Emission Factors 

0

5

10

15

20

25

30

Mode

Mass (g/kg Fuel)

HC NDIR 22 21 19 8 10 9 19 28

TO 3700_6748 CL 4700_7748 CR 5000_7880 CRL 

5000_8000

CRL 

6000_8880

CRL 

6000_8880 CR 6000_8760 AP 3000_5520

Figure 2: HC emission factors for take-off, climb, cruise and approach. TO, CL, CR5000_7748, 

CR6000_8760 and AP have been flown with air-fuel mixture “full rich”. CRL has been flown with 

manually adjusted air-fuel mixture. 

NOx Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel)

NOx 2 2 6 43 28 27 3 1

TO 3700_6748 CL 4700_7748 CR 5000_7880 CRL 5000_8000 CRL 6000_8880 CRL 6000_8880 CR 6000_8760 AP 3000_5520

Figure 3: NOx emission factors for take-off, climb, cruise and approach. TO, CL, CR5000_7748, 

CR6000_8760 and AP have been flown with air-fuel mixture “full rich”. CRL has been flown with 

manually adjusted air-fuel mixture. 

1.c) Discussion and general explanations 

The engine tested (like the majority of existing aircraft piston engines) is air cooled. Cooling requirements are best met in cruise, when the air flow is rather high and the power is reduced. 

Take-off and Climb: At full power and climb power, such engines would overheat, if they were operated at high combustion efficiency (at high combustion temperatures). For that reason, the standard 

air-fuel mixture ratio is set far on the rich side. This means that in the combustion chamber, too much 

fuel is mixed to the air. The excess fuel takes heat in the process of vaporization and combustion temperatures in the combustion chamber remain low, although the engine produces high power. The system can be described as “internal combustion chamber cooling by using excess fuel”. In that operating 

condition, the air-fuel mixture setting is normally described as “full rich”. The actual air-fuel mixture 

compared to the stoichiometric mixture (when oxygen meats exactly the demand for complete combustion) is described with the term “lambda” (see Appendix 5). It is clear that “full rich” conditions result 

in very low fuel efficiency and very incomplete combustion. This can be seen in the extraordinary high 

CO and rather high HC emission factors for take-off and climb power settings. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Manual air/fuel mixture control: Most of these engines do not have an 

automatic mixture control. For reduced power (normally below 75% 

maximum brake horse power), the mixture has to be manually set to less 

rich conditions, according to the flight altitude (density altitude) as 

described in the engine and aircraft operating manual. In many cases of 

normal aspirated engines (as with the tested aircraft), the manual mixture 

adjustment to less richer conditions should start during climb at about 

5000ft pressure altitude, because the engine maximum power has fallen to around 75% of maximum 

sea level brake horse power. 

Cruise: During cruise, below 75% of maximum brake horse power, the manual mixture adjustment 

should normally be done for every flight altitude. During the first test flight, when reaching 5000ft, the 

pilot established cruise configuration. First, the mixture has been left at “full rich” position (CR 

5000_7880). Then, the pilot adjusted the mixture to less rich conditions: 

Setting the air/fuel mixture: This test aircraft (like many others) does not have exhaust gas temperature gauges, therefore no information about peak exhaust gas (and internal combustion) temperatures 

(EGT) is available. Therefore the pilot adjusts the mixture with a "rule of thumb": Normally the pilot 

pulls the mixture lever and leans the mixture until a slight RPM drop of the fixed pitch propeller is recognized. At this condition, the engine is running slightly lean. After that, the pilot pushes the mixture 

lever slightly back (about 1 cm) and the engine is running slightly rich. After a while, the pilot checks 

cylinder head and oil temperature. The result on emission factors of the described setting can be seen 

in CRL 5000_8000. Because of higher combustion efficiency, CO and HC emission factors are significantly lower. However, with increasing combustion temperatures, the NOx emission factors drastically 

increase. This is the classical trade-off, (fuel efficiency versus NOx) also known from rich burn jet engines. 

The same mixture adjustment has been repeated at 6000ft cruising altitude. From this first test we had 

the impression that the "rule of thumb" resulted in a richer mixture than at 5000ft. (CRL 6000_8800) 

which was confirmed later. 

Descent and approach: 

During descent, the air/fuel mixture should be enriched gradually. For simplicity - and to make sure 

pilots do not forget – the AFM of the test aircraft (and of many similar aircrafts) suggests pushing the 

mixture lever directly to the “full rich” position. The effect of this operation can be seen in CR 

6000_8760, where the mixture has been set to full rich just before descent and during approach (AP 

3000_5520). Again, we see very high CO and HC emission factors, resulting from much too rich 

air/fuel mixture, causing very incomplete combustion. 

2) Standard flight test programme 

The first flight test had shown the tremendous influence of pilot operations on emission factors. A lot of 

in – flight data would be needed for the development of ground based static tests. For the purpose of 

calculating emission inventories, the measurement of aerodrome circuits and the study of flight altitude 

on emissions were necessary. 

• Aerodrome circuits (VFR traffic departure and arrival pattern) simulated outside aerodrome 

airspace, starting at 2000, 4000 and 6000ft. Mixture full rich and leaned (standard leaning procedure as described in 1.c)). 

• Climb at full power (within permitted engine limits) with measurements at 3000, 4000, 5000, 

6000 and 7000ft. Descent (Approach) at around 45% engine load with measurements at 7000, 

6000, 5000, 4000 and 3000ft. Mixture full rich and leaned (standard leaning procedure as described in 1.c)). 

• Climb at reduced power (at around 85% engine load) with measurements at 3000, 4000, 

5000, 6000 und 7000f. Mixture full rich and leaned (standard leaning procedure as described 

in 1.c)). 

• Cruise at 3000, 4000, 5000, 6000 und 7000ft between 65 and 75% engine load. Controlled 

leaning (via emission measurements) and standard leaning procedure as described in 1.c). 

• Predefined flight profiles. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

3) HBEYS (Carburated Engine Lyc O-360 Series) 

3.a) Results for simulated aerodrome circuits, flown at 2000 to 6000ft 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 1237 1204 1208 1164 353 1215 1150 1171 1162 1104 1211 633 1162

Take off 

roll

Take off 

vy

Take off 

curve

Downwin

d Base Long 

Final

Short 

Final

Take off 

vy

Take off 

curve

Downwin

d Base Long 

Final

Short 

Final

Figure 4: CO emission factors during two aerodrome circuits, starting at 2000ft, downwind at 2800ft. (ECERT 4, 

HBEYS). The first base leg was measured during power adjustments and is not considered valid. 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 1285 1231 1170 1242 1201 200 159 387 478 705 391 118

Take off 

vy_4000

Take off 

curve

Downwind

_4800 Base Long Final Short 

Final

Take off vy 

L_4000

Take off 

curve L

Downwind 

L_4800 Base L Long Final 

L

Short 

Final L

Figure 5: CO emission factors during two aerodrome circuits, starting at 4000ft, downwind at 4800ft. The second 

circuit has been flown with leaned mixture as described in 1.c. (ECERT 4.2 HBEYS) 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 1346 1350 1277 707 593 1130 682 524 602 935 991 1201

Take off 

vy_6000

Take off 

curve

Downwind

_6800 Base Long Final Short Final

Take off vy 

L_6000

Take off 

curve L

Downwind 

L_6800 Base L Long Final L

Short 

Final L

Figure 6: CO emission factors during two aerodrome circuits, starting at 6000ft, downwind at 6800ft. The second 

circuit has been flown with leaned mixture as described in 1.c. (ECERT 4.3 HBEYS) The first base leg was measured during power adjustments and is not considered valid. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel) HC NDIR 27 23 22 27 15 30 496 22 21 25 27 20 562

Take off 

roll

Take off 

vy

Take off 

curve

Downwin

d Base Long Final

Short 

Final

Take off 

vy

Take off 

curve

Downwin

d Base Long Final

Short 

Final

Figure 7: HC emission factors during two aerodrome circuits, starting at 2000ft, downwind at 2800ft. (ECERT 4, 

HBEYS). The first base leg was measured during power adjustments and is not considered valid. 

HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel) HC NDIR 22 22 25 30 31 9 9 9 11 17 12 6

Take off 

vy_4000

Take off 

curve

Downwin

d_4800 Base Long Final

Short 

Final

Take off vy 

L_4000

Take off 

curve L

Downwin

d L_4800 Base L Long Final L

Short 

Final L

Figure 8: HC emission factors during two aerodrome circuits, starting at 4000ft, downwind at 4800ft. The second 

circuit has been flown with leaned mixture as described in 1.c. (ECERT 4.2, HBEYS) 

HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel) HC NDIR 25 26 32 20 14 1276 13 12 15 21 29 961

Take off 

vy_6000

Take off 

curve

Downwin

d_6800 Base Long Final

Short 

Final

Take off vy 

L_6000

Take off 

curve L

Downwin

d L_6800 Base L Long Final L

Short 

Final L

Figure 9: HC emission factors during two aerodrome circuits, starting at 6000ft, downwind at 6800ft. The second 

circuit has been flown with leaned mixture as described in 1.c. (ECERT 4.3, HBEYS). The first base leg was 

measured during power adjustments and is not considered valid.
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) NOx 2222812222121

Take off 

roll Take off vy Take off curve Dow nw ind Base Long Final Short Final Take off vy Take off curve Dow nw ind Base Long Final Short Final

Figure 10: NOx emission factors during two aerodrome circuits, starting at 2000ft, downwind at 2800ft. 

(ECERT 4, HBEYS). The first base leg was measured during power adjustments and is not considered 

valid. 

NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) NOx 1 2 2 1 1 11 62 36 23 7 6 10

Take off 

vy_4000

Take off 

curve

Downwind

_4800 Base Long Final Short Final Take off vy L_4000

Take off 

curve L

Downwind 

L_4800 Base L Long Final L

Short Final 

L

Figure 11: NOx emission factors during two aerodrome circuits, starting at 4000ft, downwind at 4800ft. The second circuit has been flown with leaned mixture as described in 1.c. (ECERT 4.2, HBEYS) 

NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) NOx 1 1 1 4 3 1 14 23 17 4 5 1

Take off 

vy_6000

Take off 

curve

Downwind

_6800 Base Long Final Short Final Take off vy L_6000

Take off 

curve L

Downwind 

L_6800 Base L Long Final L

Short Final 

L

Figure 12: NOx emission factors during two aerodrome circuits, starting at 6000ft, downwind at 6800ft. The second circuit has been flown with leaned mixture as described in 1.c. (ECERT 4.3, HBEYS). The first base leg was 

measured during power adjustments and is not considered valid.
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Lambda 

0

0.2

0.4

0.6

0.8

1

1.2

Mode

Lambda

Lambda 0.68 0.689 0.687 0.713 0.949 0.705 1.463 0.7 0.703 0.732 0.706 0.881 1.637

Take off 

roll Take off vy Take off curve Dow nw ind Base Long Final Short Final Take off vy Take off curve Dow nw ind Base Long Final Short Final

Figure 13: Lambda (=actual air/fuel ratio to stoichiometric air/fuel ratio) during two circuits, starting at 2000ft, 

downwind at 2800ft. (ECERT 4, HBEYS). The first base leg was measured during power adjustments and is not 

considered valid. 

 

Lambda 

0

0.2

0.4

0.6

0.8

1

1.2

Mode

Lambda

Lambda 0.663 0.681 0.71 0.693 0.708 1.009 0.981 0.916 0.906 0.853 0.947 1.027

Take off vy Take off 

curve Dow nw ind Base Long Final Short Final Take off vy L

Take off 

curve L

Dow nw ind 

L Base L Long Final L Short Final L

Figure 14: Lambda during two circuits, starting at 4000ft, downwind at 4800ft. The second circuit has been flown 

with leaned mixture as described in 1.c) (ECERT 4.2, HBEYS). 

Lambda 

0

0.2

0.4

0.6

0.8

1

1.2

Mode

Lambda

Lambda 0.642 0.64 0.674 0.856 0.882 1.771 0.841 0.882 0.874 0.79 0.831 1.501

Take off vy Take off 

curve Dow nw ind Base Long Final Short Final Take off vy L

Take off 

curve L

Dow nw ind 

L Base L Long Final L Short Final L

Figure 15: Lambda during two circuits, starting at 6000ft, downwind at 6800ft. The second circuit has been flown 

with leaned mixture as described in 1.c) (ECERT 4.3, HBEYS). The first base leg was measured during power 

adjustments and is not considered valid. 

3.b) Discussion 

CO emission factors remain rather constant at an extremely high value of around 1200 g/kg fuel, if the 

engine is operated at standard “full rich” mixture setting (figure 4). If the circuit is flown at higher altitude, the CO emission factors gets even worse at “full rich” condition. This can also be seen in the 

lambda value, which drops, the higher the aircraft flies (minimum lambda at around 0.64, figure 15). At 

this condition the engine swallows around 36% more fuel mass than necessary for efficient combus-
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tion. The additional enrichment of the air/fuel mixture with higher altitude can be explained by the fact 

that the air density becomes smaller with increasing altitude, thus the carburetor mixes even less air 

mass to the fuel than with higher air density at lower altitude. 

Below 5000ft and at full throttle, the engine air-fuel mixture is generally not adjusted to leaner conditions. For the circuit flying with moderate outside air temperature, we decided to start leaning at 4000ft 

and did not see any engine temperature problems with that particular aircraft. The effect of the mixture 

adjustment can be clearly seen in figure 5. CO emission factors drop by a factor of 2 to 8. However, at 

a fixed mixture lever setting, the air/fuel mixture seems to become richer again, as power is reduced 

(see CO emission factor increase on the right of figure 5 between take-off L (=lean) and base L, and 

lambda drop in figure 14, from take-off L to base L). 

Comparison of figure 5 and figure 6 shows that the standard “rule of thumb” leaning procedure seems 

to lead to higher CO emission factors at higher altitude, thus to richer air/fuel mixture than at 4000ft. 

This can also be seen in figures 14 and 15, right hand side, with lower values for lambda at 6000ft. 

Similar findings result for HC emission factors (figures 7 to 9) with values around 25 g/kg fuel at “full 

rich” mixture setting and half the value at less rich conditions. However, a dramatic increase in HC 

emission factors can be seen in short final measurements (figures 7 and 9) when the engine throttle is 

in idle position just before simulated touch down. In figure 8, this effect does not occur. A comparison 

between fuel flows and RPM in the measurements of figures 7, 8 and 9 showed that the engine was 

not really at idle setting in the short final at 4000ft (figure 8). So in fact, this difference between figure 8 

and figures 7 and 9 can be explained. The remaining question about the reason for the high HC emission factors at “flight idle”1

 remained unsolved and we decided to investigate this in a separate flight 

test (see section 3.c). 

NOx emission factors behave vice versa to CO and HC as can be seen in figures 10, 11 and 12. At 

“full rich” mixture, hardly any NOx can build up. Values are around 1 to 2 g / kg fuel. At less rich conditions, NOx emission factors grow. The highest factor of 62 g/kg fuel was measured during take-off at 

4000ft (figure 11). At this high power and hot condition, the engine was running nearly stoichiometric 

(figure 14, take-off L, lambda = 0.981). 

From FOCA experience it is well known that aerodrome circuits are mostly flown at mixture setting “full 

rich”. Exceptions are high (density) altitude airports, like Samedan airport in Switzerland (Elevation 

5600ft). The effect of mixture adjustment on emission factors (and fuel flow) is very big and therefore 

we decided to do additional “high” altitude flight tests in Samedan (see section 3.e). 

3.c) HC emission factors at flight idle 

In order to study the effect of high HC emission factors in flight idle (figures 7 and 9) we climbed several times to 4500ft and started descent with engine idle at different indicated air speeds: normal final 

approach speed of 115 km/h, and higher speeds of 140, 160 and 180 km/h. Measurements were performed each time when descending through 4000ft. 

RPM 

0

500

1000

1500

2000

2500

3000

Mode

RPM (1/Min.)

RPM 2520 2440 2330 880 1150 1290 1500

Take off vy cruise cruise L idle v=115 idle v=140 idle v=160 idle v=180

Figure 16: Engine RPM (Revolutions per Minute) at take-off and cruise (for comparison) and with engine idle at an 

indicated airspeed of 115, 140, 160 and 180 km/h. Idle RPM increases with increasing airspeed. (ECERT 4.4) 

 

1

 „flight idle“ is used here as short expression for „engine throttle fully pulled back to idle position during flight“. This does not in 

any case correspond to the term “flight idle” used for turboprops or jet engines. 
Reference: 0 / 3/33/33-05-003.022 

13/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

HC Emission Factors 

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Mode

Mass (g/kg Fuel)

HC NDIR 21 17 6 812 1115 1275 1716

Take off vy cruise_4300 cruise L_4300 idle v=115 idle v=140 idle v=160 idle v=180

Figure 17: HC emission factors for engine idle at an indicated airspeed of 115, 140, 160 and 180 km/h (take-off 

and cruise for comparison and system check). HC emission factors increase drastically with increasing airspeed 

at engine idle. Note that the absolute scale of HC emission factors at engine flight idle may have a considerable 

error. (ECERT 4.4) 

Lambda 

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Mode

Lambda

Lambda 0.696 0.787 0.993 1.426 1.637 1.534 1.616

Take off vy cruise cruise L idle v=115 idle v=140 idle v=160 idle v=180

Figure 18: Lambda for engine idle at an indicated airspeed of 115, 140, 160 and 180 km/h (take-off and cruise for 

comparison and system check). Lambda increases far above 1 at engine flight idle condition, which shows the 

presence of excess oxygen in the combustion chambers of the engine, producing very lean conditions. (ECERT 

4.4) 

3.d) Discussion 

The findings presented in figure 7 and 9 have been confirmed. The flight test showed that HC emission factors increase drastically at flight idle. The effect increases with increasing airspeed (and therefore increasing engine idle RPM). Figure 18 proves the presence of excess oxygen in the combustion 

chambers of that engine at these flight conditions. Standing on ground, the engine idles at about 650 

RPM. At normal approach speed, idle RPM is around 900. The RPM increase comes from the air 

stream, pushing the propeller to elevated RPM, working like a propeller of a windmill. One possible 

explanation for the measured effect on HC emission factors might be that the engine “pumps” air 

through the intake into the combustion chambers due to the elevated RPM from the propeller windmill. 

At the same time the throttle is nearly closed, therefore dispersing very little fuel. The little fuel quantity 

at idle setting is not burnt anymore, which causes extremely high HC emission factors. In fact the engine has practically a “flame out”. This is normally not observed by the pilots because the air stream 

turns the propeller. 

From point of view of emissions inventory calculation, the measured effect can be neglected in simple 

method or first order calculations. Normally, flight idle occurs only in short final, just before touch 

down. Duration of this event and fuel flow are both very small, resulting in a small emission change. 

However, if such an aircraft/engine was operated at long flight idle descents, HC total emissions increase would be considerable. 
Reference: 0 / 3/33/33-05-003.022 

14/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

3.e) Additional high altitude circuit flight testing at Samedan Airport (5600ft AMSL), Switzerland 

At this high altitude airport, the engine air/fuel 

mixture should be adjusted to less rich 

conditions already prior to take-off. We wanted to 

compare the resulting emission factors when the 

mixture was adjusted on ground and not during 

flight, as we had done in the simulated circuits at 

6000ft (figures 6, 9, 12 and 15). 

The “rule of thumb” procedure consisted of 

- going to full throttle, full rich, static aircraft. 

- pulling the mixture lever until maximum RPM 

was noted (with fixed pitch propeller). This can 

be described as best power mixture, still rich. 

- Slightly pushing the mixture lever, thus 

enriching the mixture again (for engine internal 

cooling reasons at high power). 

CO Emission Factors 

0

200

400

600

800

1000

1200

Mode

Mass (g/kg Fuel)

CO 1092 1082 1089 903 1083 1066 1084 1051 778 991

Take Off 

Roll_5600 Take Off Vy Take Off Turn

Downwind_

6600 Long Final Short Final Take Off Vy_5600

Downwind_

6600 Long Final Short Final

Figure 19: CO emission factors, measured during two circuits at Samedan airport. (ECERT 13) 

HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel) HC NDIR 22 19 19 25 29 43 25 27 27 39

Take Off 

Roll_5600 Take Off Vy Take Off Turn

Downwind_

6600 Long Final Short Final Take Off Vy_5600

Downwind_

6600 Long Final Short Final

Figure 20: HC emission factors, measured during two circuits at Samedan airport. (ECERT 13) 
Reference: 0 / 3/33/33-05-003.022 

15/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) NOx 3333322252

Take Off 

Roll_5600 Take Off Vy Take Off Turn Dow nw ind_6600 Long Final Short Final Take Off Vy_5600

Dow nw ind_66

00 Long Final Short Final

Figure 21: NOx emission factors, measured during two circuits at Samedan airport. (ECERT 13) 

Lambda 

0

0.2

0.4

0.6

0.8

1

1.2

Mode

Lambda

Lambda 0.733 0.728 0.726 0.788 0.738 0.748 0.726 0.744 0.824 0.706

Take Off Roll Take Off Vy Take Off Turn Dow nw ind Long Final Short Final Take Off Vy Dow nw ind Long Final Short Final

Figure 22: Lambda, measured during two circuits, starting at 5600ft, downwind at 6600ft. (ECERT 13) 

3.f) Discussion 

From comparison between figure 22 and figure 15, one can see that the mixture adjustment which had 

been prepared on ground was richer than that of the simulated circuit. But it had the same magnitude 

as “full rich” mixture on sea level. With the described mixture adjustment, the engine can be brought 

back to approximately the same rich mixture level which those types of engines normally have at sea 

level at “full rich” position. If the mixture adjustment is done properly at high altitude airports, emission 

factors will be similar to low altitude airports (figures 19, 20, 21 and 6, 9, 12). However, the fuel flow is 

lower at high altitude airports (as the power). A comparison of total emissions in the circuits at different 

airport levels is done in the next section. 

3.g) Inventory: Total emissions in aerodrome circuits at different flight altitudes 

For this comparison of total emissions in the circuits, we use the mean circuit times measured at Bern 

airport (LSZB). 

Table 1: 

Mode Times in Mode (s) 

TAXI OUT 467 

TAKE-OFF 20 

CLIMB OUT 75 

DOWNWIND 90 

BASE 105 

FINAL 20 

TAXI IN 200 

 
Reference: 0 / 3/33/33-05-003.022 

16/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Emission factors were taken from the previously discussed measurements, with “full rich” emission 

factors for 2000 and 4000ft and less rich conditions for 6000ft as presented in section 3.e). Because of 

very incomplete combustion, the mean emission factor for CO2 is far below the theoretical 3.17 kg / kg 

fuel. For this calculation we assume a conservative factor of 2 kg CO2 / kg fuel and 1.2 kg H2O / kg 

fuel. The lead content in AVGAS 100LL is considered 0.794 g / kg fuel, the fuel density 0.72 kg / liter. 

Tables 2 and 3 (emissionsinventar.volten.HBEYS_060825_rit): 

Total circuit emissions (taxi-in, 1 circuit, taxi-out)

Elevation fuel (kg) CO (g) HC (g) NOx (g) CO2 (kg) H20 (kg) lead (g)

2000ft 2.83 3305 73 3 5.66 3.40 2.25

5600ft (Samedan) 2.76 2562 67 8 5.51 3.31 2.19

Total circuit emissions (1 circuit without taxi)

Elevation fuel (kg) CO (g) HC (g) NOx (g) CO2 (kg) H20 (kg) lead (g)

2000ft 1.90 2200 45 3 3.79 2.28 1.51

5600ft (Samedan) 1.82 1898 44 5 3.65 2.19 1.45

3.h) Systematic measurements at full power and approach power settings between 3000 and 

7000ft flight altitude 

Lambda 

0

0.2

0.4

0.6

0.8

1

1.2

Mode

Lambda

Lambda 0.713 0.712 0.692 0.674 0.667 0.734 0.743 0.74 0.741 0.775

TO 3000ft TO 4000ft TO 5000ft TO 6000ft TO 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 23: Change of lambda during full power climb and approach at 45% engine load. All measurements with 

mixture “full rich”. Lambda decreases with increasing aircraft height. The air/fuel mixture gets richer the higher the 

aircraft flies. At approach power, the mixture is less rich than at climb full power. (ECERT 8) 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 1127 1130 1191 1249 1267 1096 1073 1106 1111 994

TO 3000ft TO 4000ft TO 5000ft TO 6000ft TO 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 24: Effect on CO emission factor. With increasing height, the CO emission factor gets even worse (without 

mixture adjustment). (ECERT 8) 
Reference: 0 / 3/33/33-05-003.022 

17/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel) HC NDIR 14 16 19 20 23 29 28 27 28 25

TO 3000ft TO 4000ft TO 5000ft TO 6000ft TO 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 25: Effect on HC emission factor. With increasing height, the HC emission factor gets even worse (without 

mixture adjustment). At approach power (45% engine load), HC emission factors are higher than at full power. 

(ECERT 8) 

NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) NOx 2221111112

TO 3000ft TO 4000ft TO 5000ft TO 6000ft TO 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 26: NOx emission factors are very low due to low internal combustion temperatures. With increasing 

height, the NOx emission factor decreases (no mixture adjustment). (ECERT 8) 

Fuel Flow 

0

10

20

30

40

50

60

Mode

Fuel Flow (l/h)

Fuel 60 58 57 58 55 25 26 26 26 27

TO 3000ft TO 4000ft TO 5000ft TO 6000ft TO 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 27: The fuel flow decreases with increasing height. During descent (45% engine load), the fuel flow has 

been kept constant. (ECERT 8) 
Reference: 0 / 3/33/33-05-003.022 

18/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Manifold Pressure 

0

5

10

15

20

25

30

Mode

Manifold Pressure (in Hg)

Man. Pr. 26.5 25.5 24.5 24 23 15 15 14.5 14.5 14.5

TO 3000ft TO 4000ft TO 5000ft TO 6000ft TO 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 28: Manifold Pressure (air inlet pressure between carburetor and cylinder inlet): Manifold pressure is a 

good indicator for engine power. It drops with increasing altitude due to decreasing ambient air pressure. Accordingly, engine power drops. During descent, engine power has been kept constant. (ECERT 8) 

3.i) Systematic measurements at climb power and approach power settings between 3000 and 

7000ft flight altitude 

Lambda 

0

0.2

0.4

0.6

0.8

1

1.2

Mode

Lambda

Lambda 0.739 0.737 0.715 0.706 0.685 0.712 0.723 0.743 0.746 0.779

CL 3000ft CL 4000ft CL 5000ft CL 6000ft CL 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 29: Change of lambda during climb at reduced power (85% engine load below 4000ft) and descent (45% 

engine load). All measurements with mixture “full rich”. (ECERT 11) 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 1046 1049 1122 1149 1216 1159 1136 1075 1058 943

CL 3000ft CL 4000ft CL 5000ft CL 6000ft CL 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 30: Effect on CO emission factor. With increasing height, the CO emission factor gets even worse (without 

mixture adjustment). (ECERT 11) 
Reference: 0 / 3/33/33-05-003.022 

19/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel) HC NDIR 18 25 21 22 24 33 31 27 25 22

CL 3000ft CL 4000ft CL 5000ft CL 6000ft CL 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 31: Effect on HC emission factor. At approach power, HC emission factors are higher than at climb power 

(ECERT 11). During descent, approach power has been slightly increased above 45% engine load, compared to 

ECERT 8 (figure 25). In spite of that, HC emission factors for approach show similar values between 22 and 33 

g/kg fuel. 

NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) NOx 3322112223

CL 3000ft CL 4000ft CL 5000ft CL 6000ft CL 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 32: NOx emission factors are very low and comparable to figure 26 due to low internal combustion temperatures. With increasing height, the NOx emission factor decreases (without mixture adjustment). (ECERT 11) 

Fuel Flow 

0

10

20

30

40

50

60

Mode

Fuel Flow (l/h)

Fuel 53 53 52 50 49 25 24 26 26 27

CL 3000ft CL 4000ft CL 5000ft CL 6000ft CL 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 33: The fuel flow decreases with increasing height. During descent, the fuel flow has slightly increased 

(ECERT 11). Approach power has been higher at 3000ft than at 7000ft (see figure 34). 
Reference: 0 / 3/33/33-05-003.022 

20/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Manifold Pressure 

0

5

10

15

20

25

30

Mode

Manifold Pressure (in Hg)

Man. Pr. 25 23.6 23.1 22.8 21.9 15 14.9 15.5 16.2 17.4

CL 3000ft CL 4000ft CL 5000ft CL 6000ft CL 7000ft AP 7000ft AP 6000ft AP 5000ft AP 4000ft AP 3000ft

Figure 34: 85% engine load could not be kept above 3000ft. With a manifold pressure of 23.6 at 4000ft, the engine load was already below 85%. During descent, manifold pressure has not been kept constant. Engine load 

increased slightly with decreasing altitude. Therefore, the results for descent can not be compared to the results 

of the previous section one to one. (ECERT 11) 

3.j) Systematic measurements for cruise power settings at flight altitudes between 3000 and 

7000ft 

Cruise power emissions have been measured with two flights (ECERT 9/10). The same flight test program as described in section 2, has been used for both flights, starting at 3000ft, mixture “full rich” and 

65% of maximum engine fuel flow, followed by a mixture adjustment to lambda = 1 (stoichiometric). 

The same procedure has been repeated at 4000, 5000, 6000 and 7000ft. 

Lambda 

0

0.2

0.4

0.6

0.8

1

1.2

Mode

Lambda

Lambda 0.812 1.011 0.806 0.999 0.766 1.003 0.759 0.999 0.759 0.996 0.826 1.034 0.799 1 0.796 1.003 0.763 1.001 0.749 1.003

CR 3kft CR L 

3kft CR 4kft CR L 4kft CR 5kft CR L 5kft CR 6kft CR L 6kft CR 7kft CR L 7kft CR 3kft CR L 3kft CR 4kft CR L 4kft CR 5kft CR L 5kft CR 6kft CR L 6kft CR 7kft CR L 7kft

Figure 35: Lambda at “full rich” condition in function of flight altitude (e.g. CR 3 kft = cruise at 3000ft full rich), 

followed by stoichiometric mixture (e.g. CR L 3kft = cruise leaned at 3000ft). Lambda at “full rich” setting is decreasing with altitude, as usual. Lambda for leaned condition has been set directly by on line reading of emission 

concentrations during flight. Therefore lambda at CR L could be kept constant around 1. (ECERT 9/10) 

Fuel Flow 

0

10

20

30

40

50

60

Mode

Fuel Flow (l/h)

Fuel 40 32 40 31 40 31 39 30 38 29 40 31 40 30 39 30 39 31 39 30

CR 3kft CR L 

3kft CR 4kft CR L 4kft CR 5kft CR L 5kft CR 6kft CR L 6kft CR 7kft CR L 7kft CR 3kft CR L 3kft CR 4kft CR L 4kft CR 5kft CR L 5kft CR 6kft CR L 6kft CR 7kft CR L 7kft

Figure 36: Reproducible fuel flows in both flights. (ECERT 9/10) 
Reference: 0 / 3/33/33-05-003.022 

21/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

CO Emission Factors 

0

200

400

600

800

1000

1200

Mode

Mass (g/kg Fuel)

CO 799 128 818 160 956 142 982 147 978 166 746 94 839 140 850 132 963 138 1013 144

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft

Figure 37: CO emission factors are very high and increasing with altitude without mixture adjustment. At 

stoichiometric mixture, the values vary around 140 g / kg fuel. In terms of typical emission measurement accuracies, the values are considered reproducible. (ECERT 9/10)

HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel) HC NDIR 13 5 14 3 16 5 16 6 21 5 13 3 14 5 16 6 16 5 19 4

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft

Figure 38: HC emission factors increasing with altitude without mixture adjustment. At stoichiometric mixture, the 

values vary around 5 g / kg fuel. In terms of typical emission measurement accuracies, the values are considered 

reproducible. (ECERT 9/10)

NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) NOx 8 46 6 43 5 44 5 44 4 39 9 45 6 43 7 42 4 41 3 39

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft

CR 

3kft

CR L 

3kft

CR 

4kft

CR L 

4kft

CR 

5kft

CR L 

5kft

CR 

6kft

CR L 

6kft

CR 

7kft

CR L 

7kft

Figure 39: NOx emission factors decreasing with altitude without mixture adjustment. At stoichiometric mixture, 

the values get high (trade off with CO and HC) and are around 42 g / kg fuel. In terms of typical emission measurement accuracies, the values are considered reproducible. (ECERT 9/10)
Reference: 0 / 3/33/33-05-003.022 

22/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

4) HBKEZ (Fuel Injected Engine Lyc IO-360 Series) 

Basically, installation of the exhaust emission 

measurement system in HBKEZ was identical to 

that of HBEYS. 

In addition to HBEYS, this aircraft is equipped 

with a variable pitch, constant speed propeller. At 

a given propeller RPM, the propeller governor 

will keep propeller RPM constant as long as 

possible (by automatic pitch adjustment) if 

engine power or aircraft speed change, thus 

leading to increased propulsion efficiency 

compared to the fixed pitch propeller. 

Power management complexity is increased, 

with propulsion power depending on throttle, 

mixture and propeller pitch adjustment! 

Installation of fuel flow transducer2

 for fuel flow measurement: 

 

2

 JPI Type 201 
Reference: 0 / 3/33/33-05-003.022 

23/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Documentation of sampling probe and measurement system installation: 
Reference: 0 / 3/33/33-05-003.022 

24/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 
Reference: 0 / 3/33/33-05-003.022 

25/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

4.a) Results for simulated aerodrome circuits, flown at 2000 to 6000ft 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 1273 1319 1345 1381 1370 1172 1355 1377 1394 1407 1420 1199 293 417 479 591 835 1116

TO vy 

2300ft

_3644

TO 

curve_

Down

wind_

4272

Base_

Long 

Final_

3652

Short 

Final_

TO vy 

4300ft

_5524

TO 

curve_

Down

wind_

6392

Base_

Long 

Final_

5652

Short 

Final_

TO vy 

6300ft

_7404

TO 

curve_

Down

wind_

8272

Base_

Long 

Final_

7652

Short 

Final_

Figure 40: Record braking CO emission factors in three simulated circuits, starting at 2300ft, 4300ft and 6300ft. 

The first two circuits were flown with air/fuel mixture “full rich”, the circuit above 6300ft with leaned mixture (right 

hand side). (ECERT22, HBKEZ) 
Reference: 0 / 3/33/33-05-003.022 

26/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel) HC NDIR 24 24 29 32 30 554 26 27 30 32 34 1616 13 12 12 13 25 1614

TO vy 

2300ft

TO 

curve_

Down

wind_ Base_ Long Final_

Short 

Final_

TO vy 

4300ft

TO 

curve_

Down

wind_ Base_ Long Final_

Short 

Final_

TO vy 

6300ft

TO 

curve_

Down

wind_ Base_ Long Final_

Short 

Final_

Figure 41: HC emission factors in three simulated circuits, starting at 2300ft, 4300ft and 6300ft. The first two circuits were flown with air/fuel mixture “full rich”, the circuit above 6300ft with leaned mixture (right hand side). 

Again, the same effect at engine idle, described in sections 3.c/d) can be seen. (ECERT22, HBKEZ) 

NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) NOx 1 1 1 1 1 0 1 1 1 1 1 1 42 33 25 17 7 1

TO vy 

2300ft

_3644

TO 

curve_

Down

wind_

4272

Base_

Long 

Final_

3652

Short 

Final_

TO vy 

4300ft

_5524

TO 

curve_

Down

wind_

6392

Base_

Long 

Final_

5652

Short 

Final_

TO vy 

6300ft

_7404

TO 

curve_

Down

wind_

8272

Base_

Long 

Final_

7652

Short 

Final_

Figure 42: NOx emission factors in three simulated circuits, starting at 2300ft, 4300ft and 6300ft. The first two 

circuits were flown with air/fuel mixture “full rich”, the circuit above 6300ft with leaned mixture (right hand side). 

(ECERT22, HBKEZ) 

Lambda 

0

0.2

0.4

0.6

0.8

1

1.2

Mode

Lambda

Lambda 0.665 0.649 0.64 0.628 0.632 0.883 0.636 0.628 0.622 0.618 0.613 1.066 0.936 0.904 0.889 0.861 0.798 0.909

TO vy 

2300ft_

TO 

curve_

Dow nw

ind_ Base_ Long Final_

Short 

Final_

TO vy 

4300ft_

TO 

curve_

Dow nw

ind_ Base_ Long Final_

Short 

Final_

TO vy 

6300ft_

TO 

curve_

Dow nw

ind_ Base_ Long Final_

Short 

Final_

Figure 43: Lambda values in three simulated circuits, starting at 2300ft, 4300ft and 6300ft. The first two circuits 

were flown with air/fuel mixture “full rich”, the circuit above 6300ft with leaned mixture (right hand side). This engine shows even richer combustion (lower lambda) than that of HBEYS at “full rich” setting. (ECERT22, HBKEZ) 
Reference: 0 / 3/33/33-05-003.022 

27/77

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Fuel Flow 

0

10

20

30

40

50

60

70

80

Mode

Fuel Flow (l/h)

Fuel 70 70 44 29 12 6 67 66 44 30 30 5 43 41 29 21 17 5

TO vy 

2300ft_

TO 

curve_

Dow nw

ind_ Base_ Long Final_

Short 

Final_

TO vy 

4300ft_

TO 

curve_

Dow nw

ind_ Base_ Long Final_

Short 

Final_

TO vy 

6300ft_

TO 

curve_

Dow nw

ind_ Base_ Long Final_

Short 

Final_

Figure 44: Fuel flows in three simulated circuits, starting at 2300ft, 4300ft and 6300ft. The first two circuits were 

flown with air/fuel mixture “full rich”, the circuit above 6300ft with leaned mixture (right hand side). (ECERT22, 

HBKEZ) 

4.b) Discussion 

The fuel injected engine of HBKEZ has an even richer standard air/fuel mixture setting than the carburated one of HBEYS, resulting in CO emission factors up to 1400 g / kg fuel. The reason for this extremely rich setting is not clear – engine cylinder and oil temperatures remained far below threshold 

values for all observed engine operations. However the aircraft AFM describes a leaning procedure, 

starting already shortly after lift off, when take-off power is reduced to climb power. This is rather 

unique for such engines but makes sense, as can be seen from the measurements. Mixture adjustment is easily possible to standard values according to AFM with help from fuel flow indicator and 

exhaust gas temperature control. 

In a conservative approach, we supposed that pilots would not always lean that particular engine on 

climb. For that reason, the following measurements were made at mixture “full rich”. 

4.c) Systematic measurements at full power and approach power settings between 3000 and 

7000ft flight altitude 

CO Emission Factors 

1280

1300

1320

1340

1360

1380

1400

Mode

Mass (g/kg Fuel)

CO 1330 1364 1393 1420 1441 1430 1397 1374 1359

TO 

3000ft_4124

TO 

4000ft_5004

TO 

5000ft_5884

TO 

6000ft_6764

TO 

7000ft_7884

AP 

7000ft_7884

AP 

6000ft_6884

AP 

5000ft_5764

AP 

4000ft_4764

Figure 45: CO emission factors during climb at full power (TO) from 3000 to 7000ft and during descent from 7000 

to 3000ft (AP). The second number after aircraft altitude in feet is the density altitude. (ECERT27, HBKEZ) 
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HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel) HC NDIR 32 32 31 32 32 34 32 31 31

TO 

3000ft_4124

TO 

4000ft_5004

TO 

5000ft_5884

TO 

6000ft_6764

TO 

7000ft_7884

AP 

7000ft_7884

AP 

6000ft_6884

AP 

5000ft_5764

AP 

4000ft_4764

Figure 46: HC emission factors during climb at full power (TO) from 3000 to 7000ft and during descent from 7000 

to 3000ft (AP). With the very rich mixture, they vary around 32 g / kg fuel. (ECERT27, HBKEZ) 

NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel)

NOx 111001111

TO 

3000ft_4124

TO 

4000ft_5004

TO 

5000ft_5884

TO 

6000ft_6764

TO 

7000ft_7884

AP 

7000ft_7884

AP 

6000ft_6884

AP 

5000ft_5764

AP 

4000ft_4764

Figure 47: NOx emission factors during climb at full power (TO) from 3000 to 7000ft and during descent from 7000 

to 3000ft (AP). With the very rich mixture, practically no NOx is built up. (ECERT27, HBKEZ) 

Fuel Flow 

0

10

20

30

40

50

60

70

80

Mode

Fuel Flow (l/h)

Fuel 70 69 68 67 66 47 46 45 44

TO 3000ft_ TO 4000ft_ TO 5000ft_ TO 6000ft_ TO 7000ft_ AP 7000ft_ AP 6000ft_ AP 5000ft_ AP 4000ft_

Figure 48: Fuel flow during climb at full power (TO) from 3000 to 7000ft and during descent from 7000 to 3000ft 

(AP). (ECERT27, HBKEZ) 
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Lambda 

0.58

0.59

0.6

0.61

0.62

0.63

0.64

0.65

Mode

Lambda

Lambda 0.644 0.631 0.621 0.612 0.603 0.609 0.622 0.631 0.635

TO 3000ft_ TO 4000ft_ TO 5000ft_ TO 6000ft_ TO 7000ft_ AP 7000ft_ AP 6000ft_ AP 5000ft_ AP 4000ft_

Figure 49: Lambda during climb at full power (TO) from 3000 to 7000ft and during descent from 7000 to 3000ft 

(AP). It can be seen, how the engine gets even richer without mixture adjustment during climb. At 7800ft density 

altitude (TO 7000ft), lambda stays at 0.6 and the engine swallows 40% more fuel than necessary for efficient 

combustion. (ECERT27, HBKEZ) 

4.d) Systematic measurements at take-off, climb and approach power at 3500ft flight altitude, 

mixture “full rich” 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 1315 1317 1321 1295 1291 1285 1316 1312 1310 1301 1304 1303 1281 1274 1279 1283 1274 1277

TO 

3500ft

_2840

TO 

3500ft

_2840

TO 

3500ft

_2840

CL 

3500ft

_2840

CL 

3500ft

_2840

CL 

3500ft

_2840

AP 

3500ft

_2840

AP 

3500ft

_2840

AP 

3500ft

_2840

TO 

3500ft

_2720

TO 

3500ft

_2720

TO 

3500ft

_2720

CL 

3500ft

_2720

CL 

3500ft

_2720

CL 

3500ft

_2720

AP 

3500ft

_2720

AP 

3500ft

_2720

AP 

3500ft

_2720

Figure 50: CO emission factors during take-off, climb and approach, when passing 3500ft (2800ft density altitude.) Two flights at different days. (ECERT48+49, HBKEZ) 

HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel) HC NDIR 25 26 26 25 26 26 28 28 29 24 27 26 27 27 27 29 28 29

TO 

3500ft

TO 

3500ft

TO 

3500ft

CL 

3500ft

CL 

3500ft

CL 

3500ft

AP 

3500ft

AP 

3500ft

AP 

3500ft

TO 

3500ft

TO 

3500ft

TO 

3500ft

CL 

3500ft

CL 

3500ft

CL 

3500ft

AP 

3500ft

AP 

3500ft

AP 

3500ft

Figure 51: HC emission factors during take-off, climb and approach, when passing 3500ft (2800ft density altitude.) 

Two flights at different days. (ECERT48+49, HBKEZ) 
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NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) NOx 111111111111111111

TO 

3500ft

_2840

TO 

3500ft

_2840

TO 

3500ft

_2840

CL 

3500ft

_2840

CL 

3500ft

_2840

CL 

3500ft

_2840

AP 

3500ft

_2840

AP 

3500ft

_2840

AP 

3500ft

_2840

TO 

3500ft

_2720

TO 

3500ft

_2720

TO 

3500ft

_2720

CL 

3500ft

_2720

CL 

3500ft

_2720

CL 

3500ft

_2720

AP 

3500ft

_2720

AP 

3500ft

_2720

AP 

3500ft

_2720

Figure 52: NOx emission factors during take-off, climb and approach, when passing 3500ft (2800ft density altitude.) Two flights at different days. (ECERT48+49, HBKEZ) 

Fuel Flow 

0

10

20

30

40

50

60

70

80

Mode

Fuel Flow (l/h)

Fuel 70 70 70 59 60 59 37 36 35 70 70 70 60 60 60 36 37 37

TO 

3500ft_

TO 

3500ft_

TO 

3500ft_

CL 

3500ft_

CL 

3500ft_

CL 

3500ft_

AP 

3500ft_

AP 

3500ft_

AP 

3500ft_

TO 

3500ft_

TO 

3500ft_

TO 

3500ft_

CL 

3500ft_

CL 

3500ft_

CL 

3500ft_

AP 

3500ft_

AP 

3500ft_

AP 

3500ft_

Figure 53: Fuel flow during take-off, climb and approach, when passing 3500ft (2800ft density altitude.) Two 

flights at different days. (ECERT48+49, HBKEZ) 

Manifold Pressure 

0

5

10

15

20

25

30

Mode

Manifold Pressure (in Hg)

Man. Pr. 26.3 26.3 26.3 25 25 25 17 17 17 26.3 26.2 26.2 25 25 25 16.9 16.9 16.8

TO 

3500ft_

TO 

3500ft_

TO 

3500ft_

CL 

3500ft_

CL 

3500ft_

CL 

3500ft_

AP 

3500ft_

AP 

3500ft_

AP 

3500ft_

TO 

3500ft_

TO 

3500ft_

TO 

3500ft_

CL 

3500ft_

CL 

3500ft_

CL 

3500ft_

AP 

3500ft_

AP 

3500ft_

AP 

3500ft_

Figure 54: Manifold pressure during take-off, climb and approach, when passing 3500ft (2800ft density altitude.) 

Two flights at different days. (ECERT48+49, HBKEZ) 

4.e) Discussion 

The two measurement series have been made with comparable power settings (figure 54) and fuel 

flows (figure 53). At the extremely rich air/fuel mixture condition of that engine, emission factors do not 

change significantly from one power condition to the other. It can also be seen that the data can be 
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considered reproducible in the context of emission measurements. CO emission factors stay around 

1300 g/kg fuel, HC emission factors around 26 g/kg fuel and NOx emission factors around 1 g / kg fuel. 

These are worst case scenario values, assuming that pilots do not lean the engine. 

4.f) Systematic measurements at take-off, climb and approach power at 3500ft flight altitude 

with mixture adjustment according to the aircraft flight manual (AFM). 

According to the AFM of HBKEZ, the engine air/fuel mixture 

should be leaned after obstacle clearance in the following 

way (normal procedure): 

Reduce angle of climb to reach 84 kt 

Reduce throttle to 25 InHg 

Reduce propeller RPM to 2500 RPM 

Mixture: Reduce fuel flow to 12 US gal/h 

The mixture setting can be checked with exhaust gas 

temperature (EGT) and cylinder head temperature (CHT). The obtained mixture setting results in an 

EGT about 150°F rich of EGT peak, which corresponds approximately to best power mixture (at sea 

level). For descent, mixture has to be set to “full rich” again, according to the AFM. 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 1290 1294 1300 584 811 817 1330 1301 1285 1294 1291

TO 

3500ft_264

4

TO 

3500ft_264

4

TO 

3500ft_264

4

CL 

3500ft_264

4

CL 

3500ft_264

4

CL 

3500ft_264

4

AP 

3500ft_264

4

AP 

3500ft_264

4

AP 

3500ft_264

4

AP 

3500ft_264

4

AP 

3500ft_264

4

Figure 55: CO emission factors when leaning during climb. (ECERT47, HBKEZ) 

HC Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel) HC NDIR 24 25 24 16 16 15 27 29 28 30 28

TO 

3500ft_264

TO 

3500ft_264

TO 

3500ft_264

CL 

3500ft_264

CL 

3500ft_264

CL 

3500ft_264

AP 

3500ft_264

AP 

3500ft_264

AP 

3500ft_264

AP 

3500ft_264

AP 

3500ft_264

Figure 56: HC emission factors when leaning during climb. (ECERT47, HBKEZ) 
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NOx Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) NOx 1 1 1 10 6 6 1 1 1 1 1

TO 

3500ft_264

4

TO 

3500ft_264

4

TO 

3500ft_264

4

CL 

3500ft_264

4

CL 

3500ft_264

4

CL 

3500ft_264

4

AP 

3500ft_264

4

AP 

3500ft_264

4

AP 

3500ft_264

4

AP 

3500ft_264

4

AP 

3500ft_264

4

Figure 57: NOx emission factors when leaning during climb. (ECERT47, HBKEZ) 

Fuel Flow 

0

10

20

30

40

50

60

70

80

Mode

Fuel Flow (l/h)

Fuel 71 71 71 46 48 48 32 35 34 34 33

TO 3500ft_ TO 3500ft_ TO 3500ft_ CL 3500ft_ CL 3500ft_ CL 3500ft_ AP 3500ft_ AP 3500ft_ AP 3500ft_ AP 3500ft_ AP 3500ft_

Figure 58: Fuel flow when leaning during climb. (ECERT47, HBKEZ) The engine is still running rich all the time, 

however consuming about 15% less fuel during climb than at the “full rich” setting (figure 53). 

Manifold Pressure 

0

5

10

15

20

25

30

Mode

Manifold Pressure (in Hg)

Man. Pr. 27 26.8 26.8 25 25 25 17 17 17 17 17

TO 3500ft_ TO 3500ft_ TO 3500ft_ CL 3500ft_ CL 3500ft_ CL 3500ft_ AP 3500ft_ AP 3500ft_ AP 3500ft_ AP 3500ft_ AP 3500ft_

Figure 59: Manifold pressure values. (ECERT47, HBKEZ) The throttle setting can be compared to the flights of 

section 4.d) 
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Lambda 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Mode

Lambda

Lambda 0.659 0.657 0.656 0.863 0.803 0.802 0.646 0.656 0.661 0.658 0.66

TO 3500ft_ TO 3500ft_ TO 3500ft_ CL 3500ft_ CL 3500ft_ CL 3500ft_ AP 3500ft_ AP 3500ft_ AP 3500ft_ AP 3500ft_ AP 3500ft_

Figure 60: Lambda values: The leaning procedure in climb according AFM leads to lambda values around 0.85 

(ECERT 47, HBKEZ). 

4.g) Discussion 

The leaning procedure during climb of that particular aircraft/engine combination leads to slightly better 

combustion and better engine power (lambda around 0.85). At all of those measurements, engine 

cylinder and oil temperatures were staying far below maximum allowed values. 

From present experience it is however not fully understood, why the mixture should be immediately set 

to “full rich” during descent, as described in the AFM. One explanation could be that pilots might forget 

to gradually enrich the mixture during descent and therefore are asked to go to “full rich” as a general 

procedure. Note that during descent, the fuel flow at “full rich” is only 30% below the fuel flow at leaned 

climb power (figure 58)! 

The values have shown to be reproducible (see section 4.d). 

4.h) Inventory: Standard flight emission measurement from Bern (LSZB) to Grenchen (LSZG) 

What we see in this section is the result of a real measured emission inventory for a half an hour VFR3

flight from Bern (LSZB) to Grenchen (LSZG) with HBKEZ. 

The pilot got the following route briefing: 

- Bern outbound route E – Hasle 

- Direct WIL VOR 

- Climb to 5500ft QNH4

 and level off 

- Cruising altitude 5500ft QNH 

- Grenchen approach Aarwangen, G-E 

- E altitude 3200ft QNH 

- RWY 25 in use 

The actual take-off mass of HBKEZ was 1040 

kg (+- 10 kg). 

The picture on the left shows the route flown 

with HBKEZ on 16th July 2004 (red line). 

 

3

 VFR = Visual Flight Rules 

4

 QNH = actual barometric air pressure in hPa, calculated to sea level & standard atmosphere, used for altimeter setting 
Reference: 0 / 3/33/33-05-003.022 

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Flight-Profile LSZB - LSZG, HB-KEZ, 16.07.2004

1000

2000

3000

4000

5000

6000

7000

0 5 10 15 20 25 30 35 40

Time (Min)

Index

Flightprofile RPM Man. Pressure Fuel Flow LTO 1 LTO 2 CR 1 CR 2

LTO 1 (Climb) (Descent) Cruise LTO 2 (including all taxi)

Figure 61: Altitude profile (dark blue), fuel flow (light blue), engine RPM (violet) and manifold pressure (brown) 

during flight from Bern to Grenchen. The taxi time which was spent in Bern has been added to the end of the flight 

for calculation purposes. 

The altitude profile on the left shows the climb phase to 5500ft. Most of this phase is spent in the LTO 1 (if the 

upper limit of the LTO is 3000ft AGL). During cruise, the flight altitude is kept constant and after 16 minutes flight 

time, the pilot starts the descent. 

Looking at the fuel flow: A first significant reduction of fuel flow is obtained when the pilot starts to lean the engine 

in climb, about two minutes after brake release (see also section 4.f ). The second reduction appears after top of 

climb (TOC), when the pilot sets cruise power, cruise propeller pitch and adjusts the air/fuel mixture (line CR 1). 

At top of descent (TOD, line CR 2), power is reduced (manifold pressure is dropping) but the fuel flow is increasing and higher as in cruise until around 24 minutes, when power is further reduced. The increasing fuel burn 

comes from the mixture adjustment, as described in sections 4.f/g). At about 23 minutes flight time, at the approach check, the mixture is set to “full rich”. (ECERT 29, HBKEZ) 

Cumulative Fuel Consumption

0

2

4

6

8

10

12

14

16

0 5 10 15 20 25 30 35 40

Time (Min)

Fuel (kg)

Fuel Consumption LTO 1 LTO2 CR 1 CR 2

Figure 62: Integrated fuel burn over time (ECERT 29, HBKEZ) 

Cumulative CO Emissions

0

2000

4000

6000

8000

10000

12000

0 5 10 15 20 25 30 35 40

Time (Min)

CO (g)

CO Emissions LTO 1 LTO 2 CR 1 CR 2

Figure 63: Integrated CO emissions over time (ECERT 29, HBKEZ) 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Cumulative HC Emissions

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35 40

Time (Min)

HC (g)

HC Emissions LTO 1 LTO 2 CR 1 CR 2

Figure 64: Integrated HC emissions over time (ECERT 29, HBKEZ) 

Cumulative NOx Emissions

0

50

100

150

200

250

300

350

0 5 10 15 20 25 30 35 40

Time (Min)

NOx (g)

NOx Emissions LTO 1 LTO 2 CR 1 CR 2

Figure 65: Integrated NOx emissions over time (ECERT 29, HBKEZ) 

CO Emission Factor Variation During Flight

0

200

400

600

800

1000

1200

1400

1600

0 5 10 15 20 25 30 35 40

Time (Min)

EI CO (g/kg)

EI CO LTO 1 LTO 2 CR 1 CR 2

Figure 66: Variation of CO emission factor over time (ECERT 29, HBKEZ) 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

HC Emission Factor Variation During Flight

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30 35 40

Time (Min)

EI HC (g/kg)

EI HC LTO 1 LTO 2 CR 1 CR 2

Figure 67: Variation of HC emission factor over time (ECERT 29, HBKEZ) 

NOx Emission Factor Variation During Flight

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

0 5 10 15 20 25 30 35 40

Time (Min)

EI NOx (g/kg)

EI NOx LTO 1 LTO 2 CR 1 CR 2

Figure 68: Variation of NOx emission factor over time (ECERT 29, HBKEZ) 

5) HBKIA (Fuel Injected Engine TCM IO-550 B) 

Basically, installation of the exhaust emission 

measurement system in HBKIA was similar to that of 

HBEYS and HBKEZ. 

As HBKEZ, this aircraft is equipped with a variable 

pitch, constant speed propeller. At a given propeller 

RPM, the propeller governor will keep propeller RPM 

constant as long as possible (by automatic pitch 

adjustment) if engine power or aircraft speed change, 

thus leading to increased propulsion efficiency 

compared to the fixed pitch propeller. The complexity of 

the aircraft is increased with the relatively high power 

six cylinder engine, higher speed and retractable gear. 

Not many pilots seem to know that this type of engine has auto-leaning capabilities. There is 

still a manual mixture handle but the fuel pump has what appears to be an aneroid that senses 

changes in ambient pressures. Ambient pressures are routed to the aneroid through the drain fitting 

via a bolt hole channel in the pump body. High rpm pressures are set by means of a tapered needle 

(like those seen on naturally aspirated models) housed in a brass boss on the side of the pump. So in 

fact, this air cooled engine is always automatically leaned even during climb and therefore engine 

temperatures should be watched with additional care. 

So, this type of engine added a further degree of complexity to representative measurements, because of the auto-leaning effects on emissions which could only be measured and “seen” in flight. 

In addition to previous flights with HBEYS and HBKEZ, repetitive patterns were flown by different pilots 

in order to study the effect on emissions depending on different pilot operations.
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Installation of FOCA emissions measurement unit in HBKIA: 
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5.a) Results for aerodrome circuits, flown at LSZG (Grenchen Airport, Switzerland) 

In Grenchen, high performance single engine 

piston aircraft like HBKIA have to fly the outer 

circuit No.1 (see picture). Runway in use 

during the measurements was 07. Take-off 

measurements took place shortly before liftoff. After departure, the pilot had to fly a slight 

right turn to avoid Altreu village, for noise 

abatement. The first climb measurement took 

place abeam ALTREU, the second (if 

possible) between Leuzigen and 

Nennigkofen. The downwind measurement 

was performed abeam tower (if possible) and 

the base measurement when crossing the 

river. The final measurement took place approximately in the middle between turning 

final and touch down points. Two sets of 

circuit patterns have been flown (ECERT 56 and 62), with the same aircraft at the same initial take-off 

mass and comparable meteorological conditions. But the second set of measurements was flown by a 

different pilot (ECERT 62). 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 621 713 746 860 844 1167 714 656 782 724 806 698 725 861 887 1301

TO CL CL DWD Base Final TO CL CL DWD Base TO CL DWD Base Final

Figure 69: CO emission factors during three aerodrome circuits (TO = Take off roll, CL = Climb at vy5, DWD = 

downwind). No “Final” measurement at the second circuit. (ECERT 56, HBKIA) 

HC Emission Factors 

0

5

10

15

20

25

Mode

Mass (g/kg Fuel) HC NDIR 23 17 17 9 11 13 21 13 14 8 9 22 16 9 10 18

TO CL CL DWD Base Final TO CL CL DWD Base TO CL DWD Base Final

Figure 70: HC emission factors during three aerodrome circuits (TO = Take off roll, CL = Climb at vy, DWD = 

downwind). No “Final” measurement at the second circuit. (ECERT 56, HBKIA) 

 

5

 Vy = indicated airspeed for best rate of climb 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

NOx Emission Factors 

0

2

4

6

8

10

12

Mode

Mass (g/kg Fuel) NOx 12 9 7 4 4 2 10 10 3 6 7 8 8 4 5 1

TO CL CL DWD Base Final TO CL CL DWD Base TO CL DWD Base Final

Figure 71: NOx emission factors during three aerodrome circuits (TO = Take off roll, CL = Climb at vy, DWD = 

downwind). No “Final” measurement at the second circuit. (ECERT 56, HBKIA) 

Fuel Flow 

0

10

20

30

40

50

60

70

80

90

100

Mode

Fuel Flow (l/h)

Fuel 91 87 83 58 58 49 91 81 83 64 57 91 83 60 57 44

TO CL CL DWD Base Final TO CL CL DWD Base TO CL DWD Base Final

Figure 72: Fuel flow during three aerodrome circuits (TO = Take off roll, CL = Climb at vy, DWD = downwind). No 

“Final” measurement at the second circuit. (ECERT 56, HBKIA) 

Manifold Pressure 

0

5

10

15

20

25

30

Mode

Manifold Pressure (in Hg)

Man. Pr. 27 27 25.5 20 20 15.5 27 25 25.2 23 19.2 27.2 25.8 20 19 14

TO CL CL DWD Base Final TO CL CL DWD Base TO CL DWD Base Final

Figure 73: Manifold pressure during three aerodrome circuits (TO = Take off roll, CL = Climb at vy, DWD = downwind). No “Final” measurement at the second circuit. (ECERT 56, HBKIA) 
Reference: 0 / 3/33/33-05-003.022 

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Lambda 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Mode

Lambda

Lambda 0.851 0.826 0.817 0.788 0.792 0.701 0.828 0.841 0.807 0.83 0.803 0.844 0.829 0.798 0.781 0.656

TO CL CL DWD Base Final TO CL CL DWD Base TO CL DWD Base Final

Figure 74: Lambda during three aerodrome circuits (TO = Take off roll, CL = Climb at vy, DWD = downwind). No 

“Final” measurement at the second circuit. (ECERT 56, HBKIA) 

Second set, flown by different pilot: 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 671 783 876 1165 678 724 945 1115 665 732 1021 982 662 740 1002 1217

TO CL DWD Final TO CL DWD Final TO CL DWD Final TO CL DWD Final

 Figure 75: CO emission factors during four aerodrome circuits (TO = Take off roll, CL = Climb at vy6

, DWD = 

downwind), flown with second pilot (ECERT 62, HBKIA) 

HC Emission Factors 

0

5

10

15

20

25

Mode

Mass (g/kg Fuel) HC NDIR 22 18 13 13 23 17 14 14 24 20 13 11 24 19 13 10

TO CL DWD Final TO CL DWD Final TO CL DWD Final TO CL DWD Final

Figure 76: HC emission factors during four aerodrome circuits (TO = Take off roll, CL = Climb at vy, DWD = downwind), flown with second pilot (ECERT 62, HBKIA) 

 

6

 Vy = indicated airspeed for best rate of climb 
Reference: 0 / 3/33/33-05-003.022 

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NOx Emission Factors 

0

2

4

6

8

10

12

Mode

Mass (g/kg Fuel) NOx 11 5 3 3 11 8 3 2 11 8 3 4 11 8 3 2

TO CL DWD Final TO CL DWD Final TO CL DWD Final TO CL DWD Final

Figure 77: NOx emission factors during four aerodrome circuits (TO = Take off roll, CL = Climb at vy, DWD = 

downwind), flown with second pilot (ECERT 62, HBKIA)

Fuel Flow 

0

10

20

30

40

50

60

70

80

90

100

Mode

Fuel Flow (l/h)

Fuel 93 87 58 53 93 87 57 53 94 88 57 53 94 87 34 33

TO CL DWD Final TO CL DWD Final TO CL DWD Final TO CL DWD Final

Figure 78: Fuel flow during four aerodrome circuits (TO = Take off roll, CL = Climb at vy, DWD = downwind), flown 

with second pilot (ECERT 62, HBKIA) 

Manifold Pressure 

0

5

10

15

20

25

30

Mode

Manifold Pressure (in Hg)

Man. Pr. 27 24.5 19 16 27 26.8 18 15 27.5 26.8 18 17 26.5 26.8 17 15

TO CL DWD Final TO CL DWD Final TO CL DWD Final TO CL DWD Final

Figure 79: Manifold pressure during four aerodrome circuits (TO = Take off roll, CL = Climb at vy, DWD = downwind), flown with second pilot (ECERT 62, HBKIA) 
Reference: 0 / 3/33/33-05-003.022 

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Lambda 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Mode

Lambda

Lambda 0.839 0.807 0.785 0.701 0.837 0.822 0.765 0.716 0.839 0.82 0.743 0.757 0.85 0.817 0.749 0.683

TO CL DWD Final TO CL DWD Final TO CL DWD Final TO CL DWD Final

Figure 80: Lambda during four aerodrome circuits (TO = Take off roll, CL = Climb at vy, DWD = downwind), flown 

with second pilot (ECERT 62, HBKIA) 

5.b) Discussion 

In contrast to the engines of HBEYS and HBKEZ, the engine of HBKIA is auto-leaned (see 5, Introduction). This can be seen in figures 74 and 80. Lambda values at take-off are around 0.83 to 0.85, significantly higher than the values of the previously measured engines at “full rich” mixture. A lambda 

value of 0.85 corresponds approximately to best power mixture. However, engine cylinder head temperatures reach easily its limits at this condition and therefore considerable care must be taken, not to 

exceed engine temperature limits during climb. At low power settings, the auto-lean feature does not 

seem to have an effect. The engine is running extremely rich again (lambda around 0.7), like the previously measured engines at “full rich” mixture adjustment. 

The second pilot has been flying the circuits very regularly compared to the first pilot. This can be seen 

in the variation of the engine manifold pressure, lambda, fuel flow and emission factors. 

Due to auto-lean at high power, CO emission factors are lowest and NOx emission factors highest for 

high power setting (take-off and climb). Interestingly, HC emission factors are highest as well for high 

power settings. Normally HC correlates to CO and HC would have been expected to be lowest at high 

power settings. 

5.c) Inventory: Total emissions of HBKIA in aerodrome circuits and comparison between two 

pilots 

For this comparison of total emissions in the circuits, we used the same mean circuit times as in 3.g) 

and the data of 5.a). In order to obtain more general results, we used mean FOCA standard times 

instead of Grenchen circuit times for this comparison. 

Table 4: 

Mode Times in Mode (s) 

TAKE-OFF 20 

CLIMB OUT 75 

DOWNWIND 90 

BASE 105 

FINAL 20 

 

Emission factors were taken from the previously discussed measurements, with mixture control in “full 

rich” position and the engine doing auto-lean, as discussed in 5.b). Because of very incomplete combustion (as described in section 3 of this Appendix), the mean emission factor for CO2 is far below the 

theoretical 3.17 kg / kg fuel. For this calculation we assume again a conservative factor of 2 kg CO2 / 

kg fuel and 1.2 kg H2O / kg fuel. The lead content in AVGAS 100LL is considered 0.794 g / kg fuel, the 

fuel density 0.72 kg / liter. 

Table 5: Total emissions for 1 circuit (emissionsinventar.volten.HBKIA_060921_rit) 

HBKIA fuel (kg) CO (g) HC (g) NOx (g) CO2 (kg) H20 (kg) lead (g)

Pilot 1 4.10 3291 52 24 8.19 4.92 3.25

Pilot 2 3.88 3371 62 20 7.77 4.66 3.08
Reference: 0 / 3/33/33-05-003.022 

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5.d) Discussion 

During 1 circuit, HBKIA burns around 4 kg fuel and produces roughly 3 kg CO, 50 g HC and 20 g NOx, 

8 kg CO2, 5 kg H2O and 3 g lead. 

From the existing measurement experience, FOCA assumes that significant differences in the results 

between pilot 1 and pilot 2 of more than 5% can be attributed to pilot operations. Table 5 shows that 

pilot 2 was flying more efficient. This can be explained by lower power settings, especially in the downwind leg (see figures 79 and 73). Part of this gain would be compensated by longer downwind time. 

The lower power setting results in slightly higher CO and HC emissions and lower NOx emissions, as 

can be seen in table 5. CO2, H2O and lead emissions are directly proportional to fuel burn, hence are 

lower for pilot 2 operations. 

Generally speaking, the differences between the two measurement sets and the influence of the pilot 

are not significantly high for this aircraft during circuit flying. This may be attributed mainly to the fact, 

that the engine of HBKIA is automatically leaned and hence produces similar combustion conditions in 

both cases. Remaining differences outside possible measurement statistical errors may be caused 

from different power settings in the downwind, base and final leg of the circuit. 

5.e) Additional high altitude circuit flight testing at Samedan Airport (5600ft AMSL), Switzerland 

As in 3.e) we wanted to investigate the emissions performance at a high altitude airport. The function 

of the auto-lean feature of the tested engine and the effect on emissions was of particular interest. 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO 1151 1040 860 882 882 742 1385 809 727 1388 808 871 745 1274 821 858 732 1051

TA MC 

Check TO TO/CL CL DWD Final TO DWD Final TO CL DWD Final TO CL DWD FinalHRPM

Figure 81: CO emission factors during four aerodrome circuits (TA = Taxi, MC = Magneto Check, TO = Take off 

roll, CL = Climb at vy7

, DWD = downwind), flown at Samedan Airport (ECERT 59, HBKIA) 

 

7

 Vy = indicated airspeed for best rate of climb 
Reference: 0 / 3/33/33-05-003.022 

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HC Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel) HC NDIR 42 24 26 20 20 9 24 41 11 23 52 25 11 19 59 27 12 18

TA MC 

Check TO TO/CL CL DWD Final TO DWD Final TO CL DWD Final TO CL DWD FinalHRPM

Figure 82: HC emission factors during four aerodrome circuits (TA = Taxi, MC = Magneto Check, TO = Take off 

roll, CL = Climb at vy, DWD = downwind), flown at Samedan Airport (ECERT 59, HBKIA) 

NOx Emission Factors 

0

2

4

6

8

10

12

Mode

Mass (g/kg Fuel) NOx 1 2 6 6 6 7 1 8 9 1 8 6 10 1 7 6 10 2

TA MC 

Check TO TO/CL CL DWD Final TO DWD Final TO CL DWD Final TO CL DWD FinalHRPM

Figure 83: NOx emission factors during four aerodrome circuits (TA = Taxi, MC = Magneto Check, TO = Take off 

roll, CL = Climb at vy, DWD = downwind), flown at Samedan Airport (ECERT 59, HBKIA) 

Fuel Flow 

0

10

20

30

40

50

60

70

80

90

Mode

Fuel Flow (l/h)

Fuel 18 26 81 81 79 61 36 79 57 39 80 80 59 42 81 78 61 57

TA MC 

Check TO TO/CL CL DWD Final TO DWD Final TO CL DWD Final TO CL DWD FinalHRPM

Figure 84: Fuel flow during four aerodrome circuits (TA = Taxi, MC = Magneto Check, TO = Take off roll, CL = 

Climb at vy, DWD = downwind), flown at Samedan Airport (ECERT 59, HBKIA) 

?

? ? 
Reference: 0 / 3/33/33-05-003.022 

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Manifold Pressure 

0

5

10

15

20

25

Mode

Manifold Pressure (in Hg)

Man. Pr. 12 12.2 23 23 22.8 21 10 23 19.5 11 23.2 23.2 20 12 23 23 20 15

TA MC 

Check TO TO/CL CL DWD Final TO DWD Final TO CL DWD Final TO CL DWD FinalHRPM

Figure 85: Manifold pressure during four aerodrome circuits (TA = Taxi, MC = Magneto Check, TO = Take off roll, 

CL = Climb at vy, DWD = downwind), flown at Samedan Airport (ECERT 59, HBKIA) 

Lambda 

0

0.2

0.4

0.6

0.8

1

Mode

Lambda

Lambda 0.903 0.741 0.788 0.781 0.781 0.819 0.624 0.798 0.823 0.623 0.797 0.782 0.819 0.664 0.792 0.785 0.822 0.735

TA MC 

Check TO TO/CL CL DWD Final TO DWD Final TO CL DWD Final TO CL DWD FinalHRPM

Figure 86: Lambda during four aerodrome circuits (TA = Taxi, MC = Magneto Check, TO = Take off roll, CL = 

Climb at vy, DWD = downwind), flown at Samedan Airport (ECERT 59, HBKIA) 

5.f) Discussion 

The circuits at Samedan have been flown by the same pilot, as in ECERT 62 (circuits at Grenchen 

airport, see 5.a). Therefore the results of ECERT 62 are compared to that of ECERT 59 (circuits at 

Samedan airport). ECERT 59 data do not contain the base leg. In Samedan, the base leg consists 

basically of a 180° turn. 

First of all, it can be seen from figures 79 and 85 that the four circuits flown in Samedan did not show a 

consistent repetitive power setting. There is no clear repetition of the power setting pattern as shown 

in figure 79. This can be explained by the fact that the wind conditions in the alpine valley were very 

variable, resulting in different power adjustments. Because of the high altitude (in fact the density altitude varied between 6800 and 7800ft in the circuits), maximum manifold pressure at take off was only 

at 23 In Hg8

 (figure 85) and maximum engine power was approximately as low as normal cruise 

power. 

From comparison between figures 80 and 86 it can be seen that the auto-lean mixture adjustment for 

take-off power was not as good as in the lower altitude measurement (5.a). The engine ran still very 

rich. In fact, it seems that the measured engine does not automatically fully compensate the air-fuelmixture for the lower air density and additional manual leaning would have been necessary in this 

situation. The result can be seen with higher CO and HC values at high power settings compared to 

ECERT 62. Once again, HC values are highest for take-off. We were not able to find out, whether this 

was real and resulted from the particular engine condition with low manifold pressure in the air intake, 

richer conditions and the throttle fully open or resulted from a systematic error in the measurement. 

(figure 82). 

 

8 In Hg = Inches mercury column, 23 In Hg = 779 hPa
Reference: 0 / 3/33/33-05-003.022 

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5.g) Inventory: Comparison of total emissions of HBKIA in the low and high altitude aerodrome 

circuit 

For this comparison of total emissions in the circuits, we used the same mean circuit times as in 3.g), 

5.c) and the data of 5.e). In order to obtain more general results, we used mean FOCA standard times 

instead of Samedan circuit times for this comparison. 

Table 6: 

Mode Times in Mode (s) 

TAKE-OFF 20 

CLIMB OUT 75 

DOWNWIND 90 

BASE 105 

FINAL 20 

 

Emission factors were taken from the previously discussed measurements, with mixture control in “full 

rich” position and the engine doing auto-lean, as discussed in 5.b) and 5.f). Because of very incomplete combustion (as described in section 3 of this Appendix), the mean emission factor for CO2 is far 

below the theoretical 3.17 kg / kg fuel. For this calculation we assume again a conservative factor of 2 

kg CO2 / kg fuel and 1.2 kg H2O / kg fuel. The lead content in AVGAS 100LL is considered 0.794 g / 

kg fuel, the fuel density 0.72 kg / liter. 

The missing base leg data in ECERT 59 has been interpolated between “downwind” and “final”. 

Table 7: Total circuit emissions (1 circuit), calculated with mean values from Grenchen and Samedan measurements and table 6. 

fuel (kg) CO (g) HC (g) NOx (g) CO2 (kg) H20 (kg) lead (g)

Samedan (ECERT 59) 3.81 3309 72 22 7.63 4.58 3.03

Grenchen (ECERT 62) 3.88 3371 62 20 7.77 4.66 3.08

5.h) Discussion 

The result for high altitude circuits with HBKIA suggests similar total emissions, which are within 

measurement uncertainties. The higher emission factors of the richer running engine are partly compensated by a lower fuel burn during the high power segments of the circuit. For emission inventories 

with TCM IO-550 engine, the following values are suggested for 1 circuit (based on table 6 times): 

Table 8: Suggested emission totals for 1 aerodrome circuit with TCM IO-550 B. (33-05-003 emissionsinventar.volten.HBKIA_060921_rit) 

TCM IO-550 B fuel (kg) CO (g) HC (g) NOx (g) CO2 (kg) H20 (kg) lead (g)

1 Aerodrome circuit 3.9 3300 60 22 7.8 4.6 3.1

5.i) Systematic measurements at full power settings between 3000 and 6000ft flight altitude 

The following measurements, ECERT 58, 61 and 65 have been performed on three different days, 

with different meteorological conditions. Measurements for take-off, climb and approach have been 

separated into different sets of figures. 
Reference: 0 / 3/33/33-05-003.022 

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CO Emission Factors 

0

200

400

600

800

1000

1200

Mode

Mass (g/kg Fuel)

CO 710 818 879 855 823 734 829 785 821 803 737 718 721 724 855 806 802

TO 

2300

TO 

3000

TO 

4000

TO 

5000

TO 

6000

TO 

5000

TO 

6000

TO 

3000

TO 

4000

TO 

5000

TO 

6000

TO 

3000

TO 

3000

TO 

3000

TO 

4000

TO 

4000

TO 

4000

Figure 87: CO emission factors for full power climb, measured at different flight altitudes, e.g. TO 2300 means 

take-off measurement at 2300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT 65). 

HC Emission Factors 

0

5

10

15

20

25

Mode

Mass (g/kg Fuel) HC NDIR 16 15 17 18 18 18 16 12 12 13 14 14 14 15 14 16 16

TO 

2300

TO 

3000

TO 

4000

TO 

5000

TO 

6000

TO 

5000

TO 

6000

TO 

3000

TO 

4000

TO 

5000

TO 

6000

TO 

3000

TO 

3000

TO 

3000

TO 

4000

TO 

4000

TO 

4000

Figure 88: HC emission factors for full power climb, measured at different flight altitudes, e.g. TO 2300 means 

take-off measurement at 2300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT 65). 

NOx Emission Factors 

0

2

4

6

8

10

12

Mode

Mass (g/kg Fuel) NOx 9 7 4 5 6 10 7 8 4 4 4 10 9 9 6 7 7

TO 

2300

TO 

3000

TO 

4000

TO 

5000

TO 

6000

TO 

5000

TO 

6000

TO 

3000

TO 

4000

TO 

5000

TO 

6000

TO 

3000

TO 

3000

TO 

3000

TO 

4000

TO 

4000

TO 

4000

Figure 89: NOx emission factors for full power climb, measured at different flight altitudes, e.g. TO 2300 means 

take-off measurement at 2300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT 65). 
Reference: 0 / 3/33/33-05-003.022 

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Fuel Flow 

0

10

20

30

40

50

60

70

80

90

100

Mode

Fuel Flow (l/h)

Fuel 90 89 88 87 80 87 80 91 88 86 83 91 91 91 90 90 89

TO 2300 TO 3000 TO 4000 TO 5000 TO 6000 TO 5000 TO 6000 TO 3000 TO 4000 TO 5000 TO 6000 TO 3000 TO 3000 TO 3000 TO 4000 TO 4000 TO 4000

Figure 90: Fuel flow for full power climb, measured at different flight altitudes, e.g. TO 2300 means take-off measurement at 2300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from ECERT61 and No 

12 – 17 from ECERT 65). 

RPM 

0

500

1000

1500

2000

2500

3000

Mode

RPM (1/Min.)

RPM 2550 2550 2550 2540 2550 2580 2550 2610 2580 2610 2600 2580 2580 2560 2580 2580 2590

TO 2300 TO 3000 TO 4000 TO 5000 TO 6000 TO 5000 TO 6000 TO 3000 TO 4000 TO 5000 TO 6000 TO 3000 TO 3000 TO 3000 TO 4000 TO 4000 TO 4000

Figure 91: Engine revolutions per minute for full power climb, measured at different flight altitudes, e.g. TO 2300 

means take-off measurement at 2300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 

from ECERT61 and No 12 – 17 from ECERT 65). 

Manifold Pressure 

0

5

10

15

20

25

30

Mode

Manifold Pressure (in Hg)

Man. Pr. 26.2 25.6 24.8 23.8 23 24 22.9 25.6 24.9 23.9 23 26 26 26 25 25 25

TO 2300 TO 3000 TO 4000 TO 5000 TO 6000 TO 5000 TO 6000 TO 3000 TO 4000 TO 5000 TO 6000 TO 3000 TO 3000 TO 3000 TO 4000 TO 4000 TO 4000

Figure 92: Manifold pressure for full power climb, measured at different flight altitudes, e.g. TO 2300 means takeoff measurement at 2300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT65).
Reference: 0 / 3/33/33-05-003.022 

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Lambda 

0

0.2

0.4

0.6

0.8

1

1.2

Mode

Lambda

Lambda 0.985 0.932 0.9 0.898 0.895 0.918 0.987 0.81 0.798 0.802 0.819 0.829 0.828 0.826 0.788 0.803 0.803

TO 2300 TO 3000 TO 4000 TO 5000 TO 6000 TO 5000 TO 6000 TO 3000 TO 4000 TO 5000 TO 6000 TO 3000 TO 3000 TO 3000 TO 4000 TO 4000 TO 4000

Figure 93: Lambda for full power climb, measured at different flight altitudes, e.g. TO 2300 means take-off measurement at 2300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from ECERT61 and No 

12 – 17 from ECERT65).

5.j) Discussion 

From figure 93 it can be seen that the engine was running significantly less rich in ECERT58 than in 

ECERT61 and 65. This could be attributed to a different general engine adjustment before and after 

regular maintenance. In ECERT65, after some pilot training and in calm air, power settings and aircraft 

attitude were more stable, resulting in less fluctuating values. All measurements were made with the 

mixture lever in “full rich” position. Auto lean works in function of density altitude, therefore the results 

are showing differences even at the same pressure altitude, because of different ambient air temperatures. The same is true for the following results (5.k and l), measured at climb and approach power 

settings. 

5.k) Systematic measurements at climb power settings between 3000 and 6000ft flight altitude 

CO Emission Factors 

0

200

400

600

800

1000

1200

Mode

Mass (g/kg Fuel)

CO 832 872 849 826 752 796 754 753 701 737 737 708 758 743

CL 3300 CL 4000 CL 5000 CL 6000 CL 3000 CL 4000 CL 5000 CL 6000 CL 3000 CL 3000 CL 3000 CL 4000 CL 4000 CL 4000

Figure 94: CO emission factors for AFM9 climb power, measured at different flight altitudes, e.g. CL 3300 means 

climb measurement at 3300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT 65). 

 

9

 AFM = Airplane Flight Manual 
Reference: 0 / 3/33/33-05-003.022 

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HC Emission Factors 

0

5

10

15

20

25

Mode

Mass (g/kg Fuel) HC NDIR 18 19 19 19 14 15 16 16 15 15 15 15 17 18

CL 3300 CL 4000 CL 5000 CL 6000 CL 3000 CL 4000 CL 5000 CL 6000 CL 3000 CL 3000 CL 3000 CL 4000 CL 4000 CL 4000

Figure 95: HC emission factors for AFM climb power, measured at different flight altitudes, e.g. CL 3300 means 

climb measurement at 3300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT 65). 

NOx Emission Factors 

0

2

4

6

8

10

12

Mode

Mass (g/kg Fuel) NOx 6 6 6 7 9 6 5 5 10 9 9 10 8 8

CL 3300 CL 4000 CL 5000 CL 6000 CL 3000 CL 4000 CL 5000 CL 6000 CL 3000 CL 3000 CL 3000 CL 4000 CL 4000 CL 4000

Figure 96: NOx emission factors for AFM climb power, measured at different flight altitudes, e.g. CL 3300 means 

climb measurement at 3300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT 65). 

Fuel Flow 

0

10

20

30

40

50

60

70

80

90

100

Mode

Fuel Flow (l/h)

Fuel 84 82 80 76 87 85 81 79 89 87 87 83 85 85

CL 3300 CL 4000 CL 5000 CL 6000 CL 3000 CL 4000 CL 5000 CL 6000 CL 3000 CL 3000 CL 3000 CL 4000 CL 4000 CL 4000

Figure 97: Fuel flow for AFM climb power, measured at different flight altitudes, e.g. CL 3300 means climb measurement at 3300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from ECERT61 and No 

12 – 17 from ECERT 65). 
Reference: 0 / 3/33/33-05-003.022 

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RPM 

0

500

1000

1500

2000

2500

3000

Mode

RPM (1/Min.)

RPM 2440 2450 2450 2450 2470 2470 2470 2480 2440 2470 2450 2470 2470 2460

CL 3300 CL 4000 CL 5000 CL 6000 CL 3000 CL 4000 CL 5000 CL 6000 CL 3000 CL 3000 CL 3000 CL 4000 CL 4000 CL 4000

Figure 98: RPM for AFM climb power (Reference 2500 RPM), measured at different flight altitudes, e.g. CL 3300 

means climb measurement at 3300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT 65). 

Manifold Pressure 

0

5

10

15

20

25

30

Mode

Manifold Pressure (in Hg)

Man. Pr. 25.2 24.9 23.9 23 25.8 24.9 24 23 26 26 26 25 25 25

CL 3300 CL 4000 CL 5000 CL 6000 CL 3000 CL 4000 CL 5000 CL 6000 CL 3000 CL 3000 CL 3000 CL 4000 CL 4000 CL 4000

Figure 99: Manifold pressure for AFM climb power, measured at different flight altitudes, e.g. CL 3300 means 

climb measurement at 3300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT 65). 

Lambda 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Mode

Lambda

Lambda 0.886 0.896 0.883 0.888 0.818 0.804 0.814 0.815 0.832 0.832 0.832 0.83 0.816 0.82

CL 3300 CL 4000 CL 5000 CL 6000 CL 3000 CL 4000 CL 5000 CL 6000 CL 3000 CL 3000 CL 3000 CL 4000 CL 4000 CL 4000

Figure 100: Lambda for AFM climb power, measured at different flight altitudes, e.g. CL 3300 means climb measurement at 3300ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from ECERT61 and No 

12 – 17 from ECERT 65). 
Reference: 0 / 3/33/33-05-003.022 

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5.l) Systematic measurements at approach power settings between 3000 and 6000ft flight altitude 

CO Emission Factors 

0

200

400

600

800

1000

1200

Mode

Mass (g/kg Fuel)

CO 556 585 677 832 616 659 786 819 1024 822 991 903 933 937

AP 6000 AP 5000 AP 4000 AP 3000 AP 6000 AP 5000 AP 4000 AP 3000 AP 3000 AP 3000 AP 3000 AP 4000 AP 4000 AP 4000

Figure 101: CO emission factors for approach power, measured at different flight altitudes, e.g. AP 6000 means 

approach measurement at 6000ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT 65). 

HC Emission Factors 

0

5

10

15

20

25

Mode

Mass (g/kg Fuel)

HC NDIR 7 8 8 9 8 10 11 11 11 11 10 11 12 11

AP 6000 AP 5000 AP 4000 AP 3000 AP 6000 AP 5000 AP 4000 AP 3000 AP 3000 AP 3000 AP 3000 AP 4000 AP 4000 AP 4000

Figure 102: HC emission factors for approach power, measured at different flight altitudes, e.g. AP 6000 means 

approach measurement at 6000ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT 65). 

NOx Emission Factors 

0

2

4

6

8

10

12

14

16

18

20

Mode

Mass (g/kg Fuel) NOx 17 16 12 7 14 12 8 7 4 8 4 5 5 5

AP 6000 AP 5000 AP 4000 AP 3000 AP 6000 AP 5000 AP 4000 AP 3000 AP 3000 AP 3000 AP 3000 AP 4000 AP 4000 AP 4000

Figure 103: NOx emission factors for approach power, measured at different flight altitudes, e.g. AP 6000 means 

approach measurement at 6000ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from 

ECERT61 and No 12 – 17 from ECERT 65). 
Reference: 0 / 3/33/33-05-003.022 

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Fuel Flow 

0

10

20

30

40

50

60

70

80

90

100

Mode

Fuel Flow (l/h)

Fuel 57 55 57 58 51 51 52 53 52 52 52 52 53 52

AP 6000 AP 5000 AP 4000 AP 3000 AP 6000 AP 5000 AP 4000 AP 3000 AP 3000 AP 3000 AP 3000 AP 4000 AP 4000 AP 4000

Figure 104: Fuel flow for approach power, measured at different flight altitudes, e.g. AP 6000 means approach 

measurement at 6000ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from ECERT61 

and No 12 – 17 from ECERT 65). 

RPM 

0

500

1000

1500

2000

2500

Mode

RPM (1/Min.)

RPM 2280 2280 2290 2290 2270 2250 2250 2250 2240 2230 2240 2250 2280 2250

AP 6000 AP 5000 AP 4000 AP 3000 AP 6000 AP 5000 AP 4000 AP 3000 AP 3000 AP 3000 AP 3000 AP 4000 AP 4000 AP 4000

Figure 105: Engine RPM for approach power, measured at different flight altitudes, e.g. AP 6000 means approach 

measurement at 6000ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from ECERT61 

and No 12 – 17 from ECERT 65). 

Manifold Pressure 

0

5

10

15

20

25

Mode

Manifold Pressure (in Hg)

Man. Pr. 20 20 20 19.8 17.5 17.5 17.5 17.5 17 17 17 17 17 17

AP 6000 AP 5000 AP 4000 AP 3000 AP 6000 AP 5000 AP 4000 AP 3000 AP 3000 AP 3000 AP 3000 AP 4000 AP 4000 AP 4000

Figure 106: Manifold pressure settings for approach power, measured at different flight altitudes, e.g. AP 6000 

means approach measurement at 6000ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 

from ECERT61 and No 12 – 17 from ECERT 65). In ECERT65, manifold pressure has been kept constant during 

descent. 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Lambda 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Mode

Lambda

Lambda 0.898 0.902 0.871 0.829 0.854 0.845 0.811 0.805 0.745 0.8 0.754 0.778 0.769 0.768

AP 6000 AP 5000 AP 4000 AP 3000 AP 6000 AP 5000 AP 4000 AP 3000 AP 3000 AP 3000 AP 3000 AP 4000 AP 4000 AP 4000

Figure 107: Lambda for approach power, measured at different flight altitudes, e.g. AP 6000 means approach 

measurement at 6000ft pressure altitude (From left to right: No 1 – 7 from ECERT58, No 8 – 11 from ECERT61 

and No 12 – 17 from ECERT 65). 

5.m) Standard flight profile emission measurement Bern - WIL10 - Bern, Switzerland 

The following flight profile has been flown at two different days by two different pilots: 

- Departure at LSZB (Bern) 

- Outbound route E 

- Continuous climb to 5500ft 

- Level off at 5500ft and maintain 

- Track WIL VOR 

- Cruise power setting, first full rich (CR 5510), then three measurements (CR 5500) at mixture “25°F 

rich side of EGT11 peak according to AFM12, followed by “best power mixture, 125°F rich of EGT peak” 

(CR 5500 BP) and again two measurements at mixture “25°F rich side of EGT peak”. After that, one 

measurement (CR 5500) at mixture “25°F lean of EGT peak” according to AFM and the last cruise 

measurement at mixture “25°F rich side of EGT peak” as before. 

- Descent and approach were at pilot’s discretion and the two pilots were told to always fly according 

to AFM. 

- 180° turn at WIL VOR and return to LSZB (Bern) 

- Approach and Landing at LSZB 

CO Emission Factors 

0

200

400

600

800

1000

1200

1400

1600

Mode

Mass (g/kg Fuel)

CO Pilot 1 1105 747 807 856 891 866 793 396 325 350 603 491 313 14 425 345 293 461 494 619 604 938 1161 1133

CO Pilot 2 1136 772 811 852 862 808 794 612 390 386 400 392 25 26 27 723 783 1020 850 1154 992 1393 970

TA 

167

3

TO 

170

0

CL 

230

0

CL 

300

0

CL 

400

0

CL 

500

0

CR 

551

0

CR 

550

0

CR 

550

0

CR 

550

0

CR 

550

0 BP

CR 

550

0

CR 

550

0

CR 

550

0

CR 

550

0

DCT 

540

0

DCT 

510

0

DCT 

480

0

DCT 

430

0

DCT 

420

0 R

DCT 

370

0

AP 

320

0

AP 

240

0

Fina

l 

190

Figure 108: CO emission factors comparison for both flights. TA = taxi, TO = take-off roll, CL = climb, CR = cruise, 

DCT = descent, AP = approach. The number below the flight mode indicates flight pressure altitude, e.g. DCT 

5100 = measurement during descent at 5100ft. (ECERT 57 and 64) 

 

10 WIL = Willisau VOR (Radio Navigation Facility) 11 EGT = Exhaust Gas Temperature, at this aircraft, measured in the collector of the exhaust muffler on the right side of the 

engine (= exhaust gas temperature mixture of three cylinders out of six). 

12 AFM = Airplane Flight Manual 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

HC Emission Factors 

0

10

20

30

40

50

Mode

Mass (g/kg Fuel) HC Pilot 1 114 16 16 16 17 17 17 11 10 10 12 11 11 5 12 8 7 8 8 8 9 13 13 15

HC Pilot 2 50 17 17 18 19 19 18 11 10 10 10 11 4 4 4 6 9 13 11 18 13 48 14

TA 

167

TO 

170

CL 

230

CL 

300

CL 

400

CL 

500

CR 

551

CR 

550

CR 

550

CR 

550

CR 

550

CR 

550

CR 

550

CR 

550

CR 

550

DCT 

540

DCT 

510

DCT 

480

DCT 

430

DCT 

420

DCT 

370

AP 

320

AP 

240

Fina

l 

Figure 109: HC emission factors comparison for both flights. TA = taxi, TO = take-off roll, CL = climb, CR = cruise, 

DCT = descent, AP = approach. The number below the flight mode indicates flight pressure altitude, e.g. DCT 

5100 = measurement during descent at 5100ft. (ECERT 57 and 64) 

NOx Emission Factors 

0

10

20

30

40

50

Mode

Mass (g/kg Fuel) NOx Pilot 1 0 9 7 4 3 5 8 28 35 32 15 20 35 87 26 32 39 24 22 16 15 5 2 2

NOx Pilot 2 1 9 3 1 2 3 3 10 29 29 28 29 38 37 32 11 8 3 6 2 3 0 3

TA 

167

3

TO 

170

0

CL 

230

0

CL 

300

0

CL 

400

0

CL 

500

0

CR 

551

0

CR 

550

0

CR 

550

0

CR 

550

0

CR 

550

0 BP

CR 

550

0

CR 

550

0

CR 

550

0

CR 

550

0

DCT 

540

0

DCT 

510

0

DCT 

480

0

DCT 

430

0

DCT 

420

0 R

DCT 

370

0

AP 

320

0

AP 

240

0

Fina

l 

190

Figure 110: NOx emission factors comparison for both flights. TA = taxi, TO = take-off roll, CL = climb, CR = 

cruise, DCT = descent, AP = approach. The number below the flight mode indicates flight pressure altitude, e.g. 

DCT 5100 = measurement during descent at 5100ft. (ECERT 57 and 64) 

Fuel Flow 

0

20

40

60

80

100

Mode

Fuel Flow (l/h)

Fue Pilot 1 17 91 89 89 87 85 79 65 64 64 68 65 64 49 65 57 58 55 56 58 56 47 45 45

Fuel Pilot 2 18 95 95 87 84 81 80 66 64 64 64 64 49 49 49 52 52 51 49 53 49 36 61

TA 

1673

TO 

1700

CL 

2300

CL 

3000

CL 

4000

CL 

5000

CR 

5510

CR 

5500

CR 

5500

CR 

5500

CR 

5500 

CR 

5500

CR 

5500

CR 

5500

CR 

5500

DCT 

5400

DCT 

5100

DCT 

4800

DCT 

4300

DCT 

4200 

DCT 

3700

AP 

3200

AP 

2400

Final 

1900

Figure 111: Fuel flow comparison for both flights. TA = taxi, TO = take-off roll, CL = climb, CR = cruise, DCT = 

descent, AP = approach. The number below the flight mode indicates flight pressure altitude, e.g. DCT 5100 = 

measurement during descent at 5100ft. (ECERT 57 and 64) 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

RPM 

0

500

1000

1500

2000

2500

3000

Mode

RPM (1/Min.)

RPM Pilot 1 1120 2550 2540 2530 2530 2530 2530 2300 2310 2320 2320 2300 2300 2300 2310 2310 2310 2300 2310 2310 2170 2170 2160 2150

RPM Pilot 2 1160 2640 2470 2470 2460 2460 2460 2250 2250 2230 2250 2240 2060 2060 2060 2250 2290 2290 2280 2280 2270 1930 2440

TA 

1673

TO 

1700

CL 

2300

CL 

3000

CL 

4000

CL 

5000

CR 

5510

CR 

5500

CR 

5500

CR 

5500

CR 

5500 

CR 

5500

CR 

5500

CR 

5500

CR 

5500

DCT 

5400

DCT 

5100

DCT 

4800

DCT 

4300

DCT 

4200 

DCT 

3700

AP 

3200

AP 

2400

Final 

1900

Figure 112: Engine RPM comparison for both flights. TA = taxi, TO = take-off roll, CL = climb, CR = cruise, DCT = 

descent, AP = approach. The number below the flight mode indicates flight pressure altitude, e.g. DCT 5100 = 

measurement during descent at 5100ft. (ECERT 57 and 64) 

Manifold Pressure 

0

5

10

15

20

25

30

Mode

Manifold Pressure (in Hg)

Man. Pr. Pilot 1 13.5 27 26.5 26 25 24 23.2 23.4 23 23 23 23 23 23 23 20 21 19.8 19.9 20 21 16.2 15 15

Man. Pr. Pilot 2 13.2 27 26.5 26 24.8 24 23.5 23 23 23 23 23 22.5 22.5 22.5 17 17 16.2 16 17 16.5 11 17

TA 

1673

TO 

1700

CL 

2300

CL 

3000

CL 

4000

CL 

5000

CR 

5510

CR 

5500

CR 

5500

CR 

5500

CR 

5500 

CR 

5500

CR 

5500

CR 

5500

CR 

5500

DCT 

5400

DCT 

5100

DCT 

4800

DCT 

4300

DCT 

4200 

DCT 

3700

AP 

3200

AP 

2400

Final 

1900

Figure 113: Manifold pressure comparison for both flights. TA = taxi, TO = take-off roll, CL = climb, CR = cruise, 

DCT = descent, AP = approach. The number below the flight mode indicates flight pressure altitude, e.g. DCT 

5100 = measurement during descent at 5100ft. (ECERT 57 and 64) 

Lambda 

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Mode

Lambda

Lambda Pilot 1 0.883 0.821 0.825 0.818 0.809 0.815 0.837 0.925 0.943 0.957 0.9 0.944 1.02 1.269 1.011 1.008 1.031 0.974 0.972 0.937 0.943 0.84 0.848 0.826

Lambda Pilot 2 0.902 0.812 0.798 0.787 0.784 0.799 0.803 0.852 0.909 0.91 0.907 0.908 1.251 1.25 1.259 0.829 0.812 0.747 0.795 0.705 0.754 0.633 0.761

TA 

1673

TO 

1700

CL 

2300

CL 

3000

CL 

4000

CL 

5000

CR 

5510

CR 

5500

CR 

5500

CR 

5500

CR 

5500 

CR 

5500

CR 

5500

CR 

5500

CR 

5500

DCT 

5400

DCT 

5100

DCT 

4800

DCT 

4300

DCT 

4200 

DCT 

3700

AP 

3200

AP 

2400

Final 

1900

Figure 114: Lambda comparison for both flights. TA = taxi, TO = take-off roll, CL = climb, CR = cruise, DCT = 

descent, AP = approach. The number below the flight mode indicates flight pressure altitude, e.g. DCT 5100 = 

measurement during descent at 5100ft. (ECERT 57 and 64) 

5.n) Discussion 

Taxi, Take-off, Climb 

During taxi, take-off and climb, there are no significant differences between the results of ECERT57 

(pilot 1) and 64 (pilot 2). Both pilots operate the aircraft in a similar way with a power reduction to 25 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

inHG manifold pressure in the climb phase. Manual mixture control is set to “full rich” and the engine is 

doing automatic lean, producing similar emission factors in both flights. This is also true for the first 

cruise power setting with mixture “full rich”. 

Cruise 

The task for the two pilots, to adjust the mixture to “25°F rich of EGT peak”, best power “125°F rich of 

EGT peak” and economy power “25°F lean of EGT peak” (which is an allowed operating condition for 

this type of engine), was definitely leading to different results. Most sensitive to differences in mixture 

are NOx emission factors (figure 110) and CO emission factors (figure 108). It can also be seen, that 

the mixture settings of pilot 2 are more constant than those of pilot 1. At “lean of EGT peak” mixture, 

pilot 2 was able to adjust the engine repeatedly to smooth running lean conditions (lambda around 

1.2) with CO and HC emissions falling drastically (figure 108 / 109 middle) and without increasing NOx

emissions (figure 110) too much. [It must also be noted that engine cylinder head temperatures were 

falling from around 150°C to 140°C during that operating condition and airspeed was reduced by a few 

knots due to power loss]. From previous results and the results of the cruise phase measured during 

these flights, it can be concluded: 

From point of view of emissions, the “lean of EGT peak” setting is preferred, producing lowest 

possible emissions. All emission factors and the fuel flow are lower than with “rich of EGT peak” 

setting. This is especially true for NOx, because these emissions are highest with the “rich of EGT 

peak” setting, mainly because of the highest combustion temperatures. Very strict “lean of EGT peak” 

conditions lead to lower cylinder head temperatures. 

However, from point of view of operations, the “lean of EGT peak” setting has a lot of limitations: 

- The rather simple engine technology of the measured type (air cooled, fuel injection system, 

not taking individual cylinder operating condition into account) leads to uneven mixture distribution and cylinder filling in the six cylinders (uneven “charging weight”), causing all six cylinders to be in six different operating conditions at a certain mixture setting. There is the risk of 

one or more cylinders being at higher operating conditions which can cause vibrations, additional wear and valve damage. 

- Safety margins for engine operations are more limited, because one or more cylinders may 

go into the self detonation or flame out condition, if the pilot does not observe the engine 

carefully or if the pilot forgets to enrich the mixture for descent. At “rich conditions”, the margins for safe operations are much higher. 

- Pilots need to be well trained as “lean conditions” require even more attentive engine observation which can distract from the primary air work. 

For the emission inventory application, it can be concluded that it is probably more representative 

to take “rich of EGT peak” conditions as the reference for the cruise phase, because in most cases, 

such engines will be operated at “rich” conditions. As could be seen in the in-flight tests with HBKEZ 

and HBEYS, “rich of EGT peak” conditions typically lead to a lambda of around 0.93 to 0.95 which 

can be a basis value for engine on ground measurements at cruise power setting. This value for “rich 

of EGT peak” condition has been confirmed with the HBKIA flights. 

Descent and Approach 

Within the limits of the AFM, pilots were free to choose the “top of descent” point and the power settings for descent and approach. Figure 113 shows that pilot 2 was choosing less power during descent. [Pilot 1 started the descent early, with a small rate of descent and higher power.] The effect of 

lower power setting in the case of pilot 2 can be seen in lower instantaneous fuel consumption (figure 

111) and lower NOx emission factors but significantly higher CO and HC emission factors. The effect 

on total emissions will be discussed in the next section 5.o/p). In the first part of the approach, both 

pilots used similar power settings (around 17 InHg manifold pressure and similar selected propeller 

RPM. In the second part of the approach, pilot 2 reduced engine power further but later had to increase power during final above the pilot 1 power setting. 

For the emission inventory application, it can be seen that the descent and approach phase are 

very dependent on pilots operational choice (whether forced by the environment, weather etc or not) 

and therefore, sort of mean power settings have to be derived for standardized ground measurements. From the sum of the in-flight tests with HBEYS, HBKEZ and HBKIA it can be concluded, that a 

preferred power setting for this phase of flight seems to be around 18 InHg with a fuel flow of 40 to 

45% of the maximum take-off power fuel flow. These values are taken as the basic values for engine 

ground measurements at approach power setting. 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

5.o) Inventory: Total emissions of HBKIA in a flight, defined in 5.m) 

Figure 115: ECERT 57 (Defined Flight from Bern to Wilisau VOR and back to Bern, flown by pilot 1). The altitude 

profile is plotted in dark blue. Engine RPM, manifold pressure and fuel flow have been added to the same figure. 

The theoretical LTO and cruise phase boundaries are shown with red and blue darts on top of the figure. 

5 Minutes after engine start up, the sharp rise in fuel flow indicates the beginning of the take off roll. After lift-off, 

manifold pressure is slightly reduced and the fuel flow slightly decreases (at around 6 minutes on the time axis). 

During level flight at cruise, the pilot was given different tasks for air/fuel mixture settings. Please note, that all 

variations of fuel flow (the light blue curve) during cruise level, are caused by different choice of engine operating 

air/fuel mixture conditions at constant RPM and constant manifold pressure (see 5.m)! At around 15 minutes on 

the time axis, the engine is run at slightly rich air/fuel mixture. At about 18 minutes the mixture is further enriched 

for best power, followed by the previous setting. At about 23 minutes, the air/fuel mixture is set to lean conditions, 

which is shown by a significant reduction of fuel flow. During descent and the first part of the approach, the fuel 

flow does not significantly fall below cruise fuel flow. This is due to the standard mixture enrichment for approach, 

causing the engine to run less efficiently. Because of the auto lean capabilities of the tested engine, the effect is 

not as pronounced as it was with HBKEZ (see figure 61). 

Figure 116: ECERT 64 (Defined Flight from Bern to Wilisau VOR and back to Bern, as above, flown by pilot 2). In 

contrast to pilot 1, pilot 2 was achieving only two different manual mixture settings during cruise: 25°F rich of peak 

EGT and lean of peak EGT. There is a long lean of EGT peak phase, showing significantly lower fuel consumption. The power setting during cruise and the first part of descent is slightly lower than that chosen by pilot 1. During cruise, the aircraft was flying slower than that of pilot 1, resulting in a longer flight time. The descent starts 

later and with higher descent rate than that chosen by pilot 1. Pilot 2 was performing rather big power corrections 

during landing. 

Flight-Profile LSZB - WIL - LSZB, HB-KIA, Pilot 1, ECERT 57

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 5 10 15 20 25 30 35 40 45

Time (Min)

Index

Flightprofile RPM Man. Pressure Fuel Flow

manual mixture full rich mixture 25°F rich of EGT peak

best pow er mix lean of EGT peak

manual mixture full rich

LTO (Climb) Cruise (Descent) LTO 

Flight-Profile LSZB - WIL - LSZB, HB-KIA, Pilot 2, ECERT 64

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 5 10 15 20 25 30 35 40 45

Time (Min)

Index

Flightprofile RPM Man. Pressure Fuel Flow

mixture 25°F rich of EGT peak

manual mixture full rich

lean of EGT peak

manual mixture full rich

LTO (Climb) Cruise LTO (Descent)
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Figure 117: Variation of CO emission factor during flight. LTO and cruise phase are indicated in red and blue 

darts, mixture settings in black darts. (ECERT 57) 

Figure 118: Variation of HC emission factor during flight. LTO and cruise phase are indicated in red and blue 

darts, mixture settings in black darts. (ECERT 57) 

Figure 119: Variation of NOx emission factor during flight. LTO and cruise phase are indicated in red and blue 

darts, mixture settings in black darts. During cruise, at a mixture setting 25°F rich of peak EGT, the EI NOx is 

around 35 g/kg fuel. Please note, that at lean of EGT peak operation, the EI NOx would decrease below rich of 

EGT peak value. During this flight, this does not occur: The EGT aircraft instrumentation in HBKIA does not give 

individual cylinder EGT. This measurement reveals that although the mean indicated EGT value has dropped with 

this mixture setting, at least one of the six cylinders must have been running very hot, at peak EGT, thus producing a very high EI NOx! (ECERT 57) 

CO Emission Factor Variation During Flight HBKIA, ECERT 57

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30 35 40 45

Time (Min)

EI CO (g/kg)

EI CO

manual mixture full rich mixture 25°F rich of EGT peak

best pow er mix lean of EGT peak

manual mixture full rich

LTO (Climb) Cruise (Descent) LTO 

HC Emission Factor Variation During Flight HBKIA, ECERT 57

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40 45

Time (Min)

EI HC (g/kg)

EI HC

manual mixture full rich mixture 25°F rich of EGT peak

best pow er mix lean of EGT peak

manual mixture full rich

LTO (Climb) Cruise (Descent) LTO 

NOx Emission Factor Variation During Flight HBKIA, ECERT 57

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

0 5 10 15 20 25 30 35 40 45

Time (Min)

EI NOx (g/kg)

EI NOx

manual mixture full rich mixture 25°F rich of EGT peak

best pow er mix lean of EGT peak

manual mixture full rich

LTO (Climb) Cruise (Descent) LTO 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

For comparison of the two flights and to calculate cumulative emissions, the cruise phase values have 

to be generalized. The most common mixture setting with this engine is 25°F rich of peak EGT, so for 

both flights, the measured values for this setting have been taken for the entire level flight at cruise: 

 

Figure 120: Pilot 1 Flight Profile, used for emission inventory. (ECERT57) 

Figure 121: Pilot 2 flight profile, used for emission inventory. (ECERT 64) 

Figure 122: Comparison of CO emission factor variation during flights with pilot 1 and 2. Please note, that the 

increase of EI CO P2 (pilot 2) between 23 and 32 minutes after off-block is artificial, because of missing data 

points. 

Flight-Profile LSZB - WIL - LSZB, HB-KIA, Pilot 1, ECERT 57

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 5 10 15 20 25 30 35 40 45

Time (Min)

Index

Flightprofile RPM Man. Pressure Fuel Flow

Flight-Profile LSZB - WIL - LSZB, HB-KIA, Pilot 2, ECERT 64

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 5 10 15 20 25 30 35 40 45

Time (Min)

Index

Flightprofile RPM Man. Pressure Fuel Flow

CO Emission Factor Variation During Flight HBKIA, Pilot 1 and 2

0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25 30 35 40 45

Time (Min)

EI CO (g/kg)

EI CO P2 EI CO P1
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Figure 123: Comparison of HC emission factor variation during flights with pilot 1 and 2. The much higher HC 

emission factor during taxi (pilot 1) can be explained by lower engine RPM. At low engine RPM, EI HC drastically 

increases with decreasing engine RPM. 

Figure 124: Comparison of NOx emission factor variation during flights with pilot 1 and 2. Please note, that the 

decrease of EI NOx P2 (pilot 2) between 23 and 32 minutes after off-block is artificial, because of missing data 

points, as in figure 122. 

Figure 125: Comparison of cumulative fuel consumption during flight with pilot 1 and 2. In this example, pilot 2 

chooses reduced cruise power. Hence the flight time is longer. Together with a suboptimal approach pattern, this 

adds up to higher total fuel consumption. 

HC Emission Factor Variation During Flight HBKIA, Pilot 1 and 2

0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30 35 40 45

Time (Min)

EI HC (g/kg)

EI HC P2 EI HC P1

NOx Emission Factor Variation During Flight HBKIA, Pilot 1 and 2

-10

0

10

20

30

40

50

0 5 10 15 20 25 30 35 40 45

Time (Min)

EI NOx (g/kg)

EI NOx P2 EI NOx P1

Cumulative Fuel Consumption HBKIA, Pilot 1 and 2

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35 40 45

Time (Min)

Fuel (kg)

Fuel Consumption P2 Fuel Consumption P1
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Figure 126: Comparison of cumulative CO emissions during flight with pilot 1 and 2. In this example, the lower 

power setting chosen by pilot 2 results in higher CO emissions. The highest portion of CO emissions occurs during taxi and take-off. 

Figure 127: Comparison of cumulative HC emissions during flight with pilot 1 and 2. In this example, the lower 

power setting during taxi, chosen by pilot 2 results in higher HC emissions. During flight, HC emissions seem to 

be very similar between the two flights. The highest portion of HC emissions occurs during taxi and take-off. 

Figure 128: Comparison of cumulative NOx emissions during flight with pilot 1 and 2. In this example, the lower 

power setting during cruise and descent, chosen by pilot 2 results in lower NOx emissions. The highest portion of 

NOx emissions occurs during cruise. 

Cumulative CO Emissions HBKIA, Pilot 1 and 2

0

5000

10000

15000

20000

25000

0 5 10 15 20 25 30 35 40 45

Time (Min)

CO (g)

CO Emissions P2 CO Emissions P1

Cumulative HC Emissions HBKIA, Pilot 1 and 2

0

100

200

300

400

500

600

0 5 10 15 20 25 30 35 40 45

Time (Min)

HC (g)

HC Emissions P2 HC Emissions P1

Cumulative NOx Emissions HBKIA, Pilot 1 and 2

-100

0

100

200

300

400

500

600

0 5 10 15 20 25 30 35 40 45

Time (Min)

NOx (g)

NOx Emissions P2 NOx Emissions P1
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

5.p) Emissions summary for a HBKIA mission, defined in 5.m) (300 HP injected traditional aircraft piston engine) 

Table 9 

HBKIA Pilot 1 Pilot 2

LTO Fuel (kg) 11.1 11.2

LTO CO (g) 9159 10932

LTO HC (g) 384 382

LTO NOx (g) 57 30

CR Fuel (Mission kg) 17 18

CR CO (Mission g) 7325 10108

CR HC (Mission g) 180 173

CR NOx (Mission g) 476 342

CR Fuel (kg/h) 49 43

CR CO (g/(h) 20929 24259

CR HC (g/h) 514 415

CR NOx (g/h) 1360 822

Taxi Time (Min.) 11 11

Take-off Time (Min.) 1 1

Climb Time (Min.) 3.5 3.5

Cruise Time (Min.) 21 25

Approach Time (Min.) 7.5 7.5

6) HBHFX (Carburated Engine Lyc O-320 Series) 

6.a) HBHFX high accuracy in-flight measurements: Installation of OBS2200 

The FOCA low-cost in-flight measurement system described in Appendix 1 has some limitations for 

total HC and NOx and therefore, correction factors have to be applied, as described in Appendix 5. It 

was not clear, how good these corrections would work for the in-flight measurements, because calibration was only possible at ground level static conditions. Until then, no system could be found in the 

marked, which was portable, with a potential for installation in a small aircraft and which –at the same 

time - was showing emission certification accuracy. 

Through relations network and pure chance, HORIBATM company got to know about FOCA in-flight 

measurements and presented their portable emission measurement system (PEMS), originally designed for on-road high quality measurements of diesel trucks and cars. FOCA was interested to see 

whether the HORIBATM system would show comparable results to the low-cost system. HORIBATM 

was interested to know, whether their system (OBS2200) was able to operate in an aircraft, facing 

rather quick changes of ambient conditions. At this time, the OBS2200 was not yet officially on the 

market. It was known from car measurements and tests in the Swiss alps, that the system would work 

at least down to an air pressure of about 850 hPa. 

A major difference in the measurement principle between the FOCA low-cost measurement system 

and the OBS2200 lies in the determination of mass flow (see Appendix 1). FOCA uses actual fuel flow 

meters (that have to be installed in the fuel lines) and OBS2200 measures actual and ISA corrected 

exhaust volume flow. The HORIBATM exhaust flow meter (which is a patented design) has to be installed in a straight part of the exhaust tube of the engine. In a first step, the OBS2200 was used for 

ground static measurements of HBKEZ (see Appendix 3). The calculated fuel flow from exhaust flow 

and exhaust carbon content measurement (OBS2200) and the actual measured fuel flow in the fuel 

line were compared. Those measurements matched very well (within 1 to 3% difference). Former 

ground based measurements and calculated emission factors of HBKEZ could be compared to 

OBS2200 measurements. This was part of validation work for the results that were obtained with 

FOCA low-cost measurement system (Appendix 3). It would have been very useful to compare also 
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FOCA and HORIBATM in-flight measurements of HBKEZ and HBEYS. Unfortunately, there was no 

way for proper and safe installation of the HORIBATM exhaust flow meter on the wooden and plastic 

covered airframe of HBKEZ and HBEYS without drilling holes and altering the airframe structure. So 

FOCA was looking for another aircraft with similar engine and chose the AS02 (HBHFX). The installed 

engine, Lyc O-320-E2A is practically identical to the one installed in HBEYS, rated at 150 HP instead 

of 180 HP (HBEYS). The AS02 aircraft is a full metal design, very robust, mainly used for pilot school 

and training. For noise reduction purposes, an additional muffler had been fitted and closer examination showed that the exhaust flow meter could be mounted instead of the muffler. 

Picture 8: HB-HFX with original exhaust muffler (Gomolzig). 

Moreover, the two large batteries, necessary for running the OBS2200 and the heated sampling line, 

could be installed below the seats, near the centre of gravity. However, zero fuel weight came close to 

maximum take-off weight which meant that planned flight time would be limited to half an hour per 

flight with a 45 minutes fuel reserve. 

Details of the temporary major modification of HBHFX: 

- The exhaust sample line is much thicker (40 mm diameter) than the FOCA system line. So we 

screwed the line directly to the airframe, using aircraft clamps and existing screw holes. 

- The fixation of the exhaust probe system was a sheer replacement of the Gomolzig muffler by 

a stainless steel tube with the exhaust flow meter between. The exhaust system replacing the 

Gomolzig muffler had exactly the same weight (3.6 kg). Exhaust flow was not hindered inside 

the tube. We had tested the installation during a one hour ground test, also at take off power, 

without anything becoming loose or falling off and without any noticeable drop in engine performance. During the ground test we also rolled on the runway, without taking off and the 

whole measurement system fully operating. 

- No existing aircraft systems were affected. Power supply was independent from aircraft. 

Technical Influence 

Limitations: 

- Vne = 120 MPH 
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- Max. Altitude 7000 ft QNH 

- Max. vertical acceleration = + 2g 

- Neg. vertical accelerations to be avoided 

Cabin Safety: 

- CO detector necessary 

- Emergency procedure: Emission measurement unit emergency stop button, closing down the 

whole system and valves immediately. 

- Gas main valves have to be closed manually. 

Documents Affected: 

- Flight Manual (AFM) (Including weight and balance for all possible test configurations) 

Applicable Airworthiness Requirements 

None, restricted admission for emission measurements 

Installation documentation: 

Exhaust system installed in lieu of the 

Gomolzig silencer. Stainless steel pipe 

with D = 60 mm, wall thickness 2.5 mm. 

Steel support welded, identical to holder 

of Gomolzig silencer, including rubber 

suspension. With flow meter in between. 

Mounting on the HBHFX. The flow meter 

between the supports is clamped to the 

pipe with a stainless steel muff. It can not 

fall, even if the rubber muffs were to be 

broken due to high temperature. The 

pipes have only a minimal spacing at the 

transition point underneath the muffs. 

Detail of the flow meter. During the inflight measurements, a 0,5 mm aluminium plate is clamped between the metallic bridle and the rubber muff to prevent 

damaging. 

The connexions with the flow meter are 

welded. The measurement line is visible 

to the right on the picture. It is fixed on 

the fuselage by existing screws. 
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Battery with plastic cover, specially created for the installation. Installation of both batteries underneath 

the front seats. They are fitting perfectly 

in the place and can't slide. The lids protecting the batteries' contacts are open 

on the photo. 

The back seat was taken off and a 2 cm 

thick wooden board was fixed on the 

fuselage. On the left side is the metallic 

support for the two little gas bottles. 

Batteries are mounted. Any possible 

upward movement of the batteries is 

prevented by the front seats once these 

are back in place. 

Installation of the on board measurement 

system. The fixation is done with two 

clamps which are passing underneath 

the wooden board. The gas bottles 

(synth. air and He/H2) are fixed with 4 

clamps to the metallic support. The pipe 

for He/H2 is made out of stainless steel 

with a reserve length of 1 m. The various 

links on the gas lines are tested with 

special gas leakage spray. A pressure 

drop during measurement would be signalled by the system. 

Collector pipe is directly fixed to the fuselage by choke collars. 
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Collector pipe is fixed with choke collars 

directly screwed on the fuselage. The 

turbulences created by the collector pipe 

were investigated during the rolling test 

on runway in LSZB and did not interfere 

with the controls. In emergency, the canopy can be slide backward without hindrance. 

The airplane wears the inscription "Experimental" on both sides of the cockpit. 

AFM Supplement 

1. Description

Temporary installation of a measurement system for in-flight emission measurements. 

 

2. Operational Limits

VNE is reduced to 120 MPH.

Maximum pressure altitude is limited to 7000ft. 

Maximum vertical acceleration is limited to +2g. Negative vertical accelerations shall be avoided. 

Load planning: With a mass of 158 kg for Pilot and Expert, maximum ramp fuel is limited to 57 liter. 

Therefore, measurement flights are restricted to 30 minutes duration (plus reserve). (see point 6) 

3. Emergency Procedures

Supplements to the primary AFM are: 

1. Push emergency stop switch of OBS2200 (By doing so, all systems are cut off, all gas valves closed 

immediately) 

2. The main valves of the two fuel gas bottles have to be closed manually by the measurement expert. 

4. Normal Procedures

No change to basic AFM. 

5. Performance

No change to basic AFM. 

6. Mass and Balance

Basic empty mass, after 

- Removing of Gomolzig Silencer and back seat 

- Mounting of Exhaust Flow Meter and wooden board 

= 678 kg 
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Mass and Centre of Gravity: 

Mass (kg) Moment (mkg) Remarks 

Basic empty 678 547 

System 

 (OBS 34kg, 

Gas 11kg) 45 85 Back seat position 

Batteries (2 

peaces, 40 kg 

each) 80 110

Underneath front seats, position backend of 

pilot seats 

 

Dry operating 

without crew 803 742 Lies within envelope (AFM B 5-2) 

 

Configuration 

for first test 

flight 

Dry operating 

without crew 803 742 

Pilot 79 80 

 

Zero Fuel 882 822 Lies within envelope (AFM B 5-2) 

 

Take-off 

mass for first 

test flight 

Dry operating 

without crew 803 742 

Pilot 79 80 

fuel (138 l) 100 85 

 

 982 907 Lies within envelope (AFM B 5-2) 

 

Dry operating 

with full crew 

Dry operating 

without crew 803 742 

Pilot + Expert 158 158 

 

 961 900 Lies within envelope (AFM B 5-2) 

 

Take-off 

mass with full 

crew 

Dry operating 

without crew 803 742 

Pilot + Expert 158 158 

fuel ( 53 l) 38 33

Max allowable ramp fuel = 57 

Liter 

 

 999 933 Lies within envelope (AFM B 5-2) 
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7. System Description (see Installation Documentation)

Replacement of the Gomolzig silencer by an exhaust flow meter (according picture documentation). 

Collector pipe fixed along fuselage, guided through the left cockpit window to the OBS2200 analyzer. 

Closed analyzer exhaust loop: Pumped exhaust sample and water condensate are guided outside the 

cockpit. 

Two little gas bottles (He/H2, synthetic air) used for the analyzer are mounted on the metallic support 

on the wooden board. The measurement system provides an emergency shut down switch, which is 

positioned within reach of the measurement expert. 

The energy used for operating the measurement system and the heated sampling line is provided 

independently from the electrical system of the aircraft. Two pressure compensating dry batteries are 

fixed below the pilot and copilot seats. The batteries can not move in any direction and their contacts 

are covered. 

Monitoring of the cabin CO concentration is done with a CO-sensor (Quantum Eye) which is placed on 

the right hand side of the cockpit panel, clearly visible for the crew. 

8. Maintenance

No change to basic AFM. 

6.b) Real time emission mass determination during flight 

CO, HC, NOx and CO2 emission factors and the geographical coordinates from the GPS receiver have 

been displayed and recorded in real time during flight. The data recording interval was 1 second. 

Picture 9: First departure of HB-HFX with OBS2200 fully operating. 
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The flight pattern used for HBKEZ and KIA had to be shortened because of the limited fuel and therefore limited flight time: 

- Departure at LSZB (Elevation 1673ft) 

- Continuous Climb to 5000ft (TO end at 4673ft) 

- Level off at 5000ft and maintain 

- Cruise phase with cruise lean at 5000ft 

- Descent and approach (L begin at 4673ft) 

- Landing at LSZB 

Actual in- and outbound routes were chosen according to the visual approach chart (VAC), the meteorological and traffic situation. 

Figure 129: Visualization of the flight track and the NOx mass from flight HBHFX 1537 (22.03.2006). Important 

phases of the flight and pilot operations, which affect emissions, are labelled with yellow flags. The flight begins at 

Bern-Belp airport (LSZB) (right hand side of the picture). The aircraft is taking off from runway 32 and departure is 

flown outbound route Whiskey, leading first towards Bern (the capital of Switzerland). The climb continues in 

westerly direction. “End of LTO” marks the point, where the aircraft reaches 3000ft above airport elevation. In this 

example, the coloured track indicates the amount of NOx mass flow in grams per second. A light blue and thin 

track means NOx mass emissions in the order of 0.005 grams/second, a red and large track means about 0.2 

grams NOx per second. At top of climb, the aircraft is levelled off and accelerates for cruise. Cruise power is set 

and the air fuel mixture is adjusted to less rich conditions. With the leaning procedure described in 1.c), NOx 

emissions get very high as peak EGT is reached (see red dot after “acceleration”). At the end of the adjustment 

(which is still a rich air/fuel mixture), NOx emissions stay rather high (orange track). This is the cruise phase, with 

the engine running more efficient, but with rather high NOx emissions. The orbit, which is shown on the left hand 

side of the picture, was only flown to demonstrate the wind situation. The aircraft was turning right with constant 

bank angle. The medium westerly wind produces a ground track with narrow turn, when the aircraft is turning 

towards the wind, and a wider turn, when the aircraft is flying with tail wind. That is why the ground track orbit is 

not a closed circle. Top of descent and the point where the aircraft is down at 3000ft above airport elevation are 

labelled accordingly. You can also see the effect of air/fuel mixture adjustments and the use of carburetor heat on 

the NOx emissions during descent and approach. With the air/fuel mixture enrichment, NOx emissions are reduced. At the end of downwind (right hand side of the picture), the NOx emissions get very low, as the power is 

very low and the mixture lever in the “full rich” position. 
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Picture 10: HBHFX cockpit during measurement flight with cabin CO-detector (right hand side) 

Picture 11: OBS2200 Laptop monitor during measurement flight with HB-HFX at 2340 seconds after engine startup. The top line shows measured concentrations over time. At the bottom right, instantaneous values of the exhaust flow meter are displayed. 
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Table 10: Extract from data recording from 15:54:15 to 15:54:17 local time during take-off acceleration on the 

runway, showing the measured concentrations, sensor values and calculated values. (HBHFX, 1537, 22.03.2006) 

FILLER_01 FILLER_02 ANALYZER_VANALYZER_VANALYZER_VANALYZER_VANALYZER_VANALYZER_VFILLER_03

absolute relative CO conc. CO2 conc. THC conc. NOx conc. H2O conc. A/F Alarm

[s] [vol%] [vol%] [ppmC] [ppm] [vol%]

15:54:15 440 5.59 9.46 2078.00 396.00 11.37 12.66

15:54:16 441 5.69 9.38 2056.00 400.30 11.37 12.65

15:54:17 442 5.74 9.35 2041.00 394.00 11.37 12.64

SENSOR_01 SENSOR_02 SENSOR_03 SENSOR_04 SENSOR_05 SENSOR_06 GPS_01 GPS_02 GPSAV_01

Exh. Flow Exh. Temp. Exh. Press. Amb. Temp. Amb. Press. Amb. Humid. Latitude Longitude Altitude

[m3/min] [degC] [kPa] [degC] [kPa] [%RH] [N/S] [W/E] [m]

5.65 491.22 97.77 12.98 94.56 61.92 N46.54.33.65 E7.30.10.656 508.90

5.55 507.67 97.71 13.00 94.56 61.91 N46.54.33.994E7.30.10.218 508.90

5.48 518.11 97.83 12.98 94.56 61.89 N46.54.34.384E7.30. 9.731 509.00

GPSAV_02 SENSOR_08 ANALYZER_MANALYZER_MANALYZER_MANALYZER_MANALYZER_MANALYZER_MANALYZER_MASS08

Velocity Battery CO mass CO2 mass THC mass NOx mass Fuel Power NOx corre. mass

[km/h] [V] [g/s] [g/s] [g/s] [g/s] [g/s] [] [g/s]

46.00 22.83 6.13 16.30 0.11 0.07 8.27 129.96 0.07

51.50 22.83 6.13 15.88 0.11 0.07 8.13 127.81 0.07

57.00 22.95 6.10 15.62 0.11 0.07 8.03 126.25 0.06

NOx Mass (g/s) Emissions during Flight

46.88

46.89

46.9

46.91

46.92

46.93

46.94

46.95

46.96

7.1 7.15 7.2 7.25 7.3 7.35 7.4 7.45 7.5 7.55

Longitude

Latitude

Figure 130: NOx emissions during flight HBHFX 1537 (22.03.2006), the same flight as shown in figure 129 but 

without geographical background information. With this illustration (“NOx worm”) the variation of NOx mass emissions during the flight can be seen very clearly. One “bubble” contains the NOx emissions integrated over 10 seconds flight time. The bubble size goes from around 0.05 to 2 grams NOx per 10 seconds. 
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CO Mass Emissions during Flight

46.88

46.89

46.9

46.91

46.92

46.93

46.94

46.95

46.96

7.1 7.15 7.2 7.25 7.3 7.35 7.4 7.45 7.5 7.55

CO (g/s)

 Figure 131: CO emissions during flight HBHFX 1537 (22.03.2006), the same flight as shown in figure 129 but 

without geographical background information. CO emissions are practically contrary to NOx: Very high during 

take-off and climb, lower during cruise and high during approach. The bubble size goes from around 9 to 70 (!) 

grams CO per 10 seconds. 

Total HC Mass Emissions during Flight

46.88

46.89

46.9

46.91

46.92

46.93

46.94

46.95

46.96

7.1 7.15 7.2 7.25 7.3 7.35 7.4 7.45 7.5 7.55

Total HC (g/s)

Figure 132: Total HC emissions during flight HBHFX 1537 (22.03.2006), the same flight as shown in figure 129 

but without geographical background information. HC emissions are particularly high during take-off and climb, 

lower during cruise and higher during approach. The bubble size goes from around 0.4 to 1.2 grams HC per 10 

seconds. 
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Fuel Consumption during Flight

46.88

46.89

46.9

46.91

46.92

46.93

46.94

46.95

46.96

7.1 7.15 7.2 7.25 7.3 7.35 7.4 7.45 7.5 7.55

Fuel (g/s)

Figure 133: Fuel flow during flight HBHFX 1537 (22.03.2006), the same flight as shown in figure 129 but without 

geographical background information. The fuel flow is particularly high during take-off and climb, lower during 

cruise, stays practically the same during descent and is even increasing during approach! This can be explained 

by the fact, that according to the AFM, the mixture was set to full rich conditions at the end of the approach check. 

The bubble size goes from 83 grams of fuel per 10 seconds at take-off, to 55 grams per 10 seconds during cruise 

(around 27 liters per hour), 56 grams per 10 seconds during descent and 60 grams per 10 seconds in downwind 

before base and final turn. The final approach bubbles represent 33 grams of fuel per 10 seconds. 

6.c) OBS2200 confirms typical emission factors for Lycoming carbureted engines 

Table 10: Mean emission factors for Lyc O-320-A3A. 

Fuel EF CO EF HC EF NOx EF CO2

[kg/s] [g/kg] [g/kg] [g/kg] [g/kg]

TA mean 0.0013 690 16.0 1.6 2044

TO mean 0.0083 815 12.6 6.7 1857

CL mean 0.0079 837 15.1 6.9 1816

CR mean 0.0058 410 11.6 37.0 2498

AP mean 0.0048 696 13.7 19.4 2042

In-fight emission factors obtained with HBEYS and the FOCA low-cost measurement system are confirmed with HBHFX and OBS2200. 

In addition to that, the emission factor for CO2 is calculated during the whole flights of HBHFX, in one 

second intervals. The low mean value of around 2 kg CO2 per kg fuel, which is shown above, is not 

surprising, because of the low combustion efficiency with very high CO emission factors. The theoretical CO2 emission factor for complete combustion and AVGAS100LL would be 3.17 kg CO2 per kg fuel. 

For LTO CO2 calculations of typical aircraft piston engines, it is suggested to use 2 kg CO2 per kg fuel 

instead of 3.17 kg CO2 per kg fuel (see also 3.g), if CO emissions are counted separately. 
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6.d) OBS2200 time trend chart and confirmation of high HC emission factors at flight idle 

Figure 134: This is the same flight as shown in section 6.b) (HBHFX, 1537, 22.03.06) displayed as 

time trend chart from OBS2200. On top of the figure, you can see the CO concentration in red and the 

CO2 concentrations in blue colour. In the middle, NOx concentrations are given in yellow and total HC 

(THC) concentrations in green colour. The part on the bottom of the figure shows the fuel flow in orange and the flight vertical profile (GPS altitude) in violet colour. 

At about 200 seconds on the time scale there is a significant NOx, THC, CO and fuel flow peak. This is 

the moment, when the pilot performs the engine run-up with magneto check. The next peaks during 

taxi indicate a short engine RPM increase to accelerate the aircraft after a stop. At about 450 seconds, 

the engine goes to full power (maximum fuel flow) for take-off. During climb, NOx concentrations decrease and CO concentrations increase due to decreasing air density and fixed mixture setting. At 

about 1050 seconds, the aircraft is levelled off and accelerated, which can be seen on the increased 

fuel flow. At about 1100 seconds, power is reduced and the air/fuel mixture adjusted to less rich conditions. There is a significant increase in NOx and decrease in CO concentration, as shown in figures 

130 and 131. THC is not reduced very much, which is also corresponding to FOCA previous results, 

obtained with the low-cost measurement system. Top of descent is at about 1400 seconds. As explained before, the fuel flow does not decrease significantly, because the mixture is set to richer conditions. Turning base and final approach begin at about 2000 seconds. Shortly before touch-down the 

engine is set to flight idle. At this point of time there is a drastic increase in THC concentration (black 

dart). This is a confirmation of the results obtained with FOCA low-cost measurement system (see 3.c 

with explanations for this effect). 
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Picture 12: Ready for airborne measurements 

Picture 13: The HB-HFX project team 
33-05-003 Piston Engine Emissions_Swiss FOCA_Appendix3_070605_rit 

Federal Department of the Environment, Transport, Energy and 

Communications DETEC 

Federal Office of Civil Aviation FOCA 

Aviation Policy and Strategy 

Environmental Affairs 

AIRCRAFT PISTON ENGINE EMISSIONS 

Appendix 3: Power Settings and Procedures 

for Static Ground Measurements 

 Picture 1: Ground measurement (HB-KIA) 

FOCA, CH-3003 Bern

Reference: 0 / 3/33/33-05-003 ECERT 

Contact person: Theo Rindlisbacher 

Tel. +41 31 325 93 76, Fax +41 31 325 92 12, theo.rindlisbacher@bazl.admin.ch

This document has been released for publication by FOCA, Aviation Policy and Strategy, Director M. Zuckschwerdt, 11.06.2007 
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Contents 

 Page 

1. The problem of piston engine power definitions 3 

2. Theoretical power calculation 3 

3. Engine manifold pressure (MAP) and RPM for power determination 3 

4. Correlation of fuel flow and propeller power 4 

5. Adjustment of ground measurement power settings (Fuel Flow Method) 7 

5.1 Step 1: Comparison of in-flight and static ground measurements of HBKEZ (example) 7 

5.2 Step 2: Power setting methodology for static ground measurements 8 

5.2.1 Determination of maximum fuel flow 8 

5.2.2 Power settings other than maximum propeller power 9 

5.3 Step 3: Application of the power setting methodology (step 2) 9 

5.3.1 Comparison of ground and later in-flight measurements 11 

5.3.2 Adjustments to the fuel flow method for complex aircraft/engines 14 

5.3.3 Temperature corrections for normally aspirated carburetted piston engines 15 

6. Recommended ground measurement power setting procedures for emission tests 17 

6.1 Selection of methodology 17 

6.2 Procedure for determination of maximum fuel flow 17 

6.2.1 Fuel flow calibration 17 

6.2.2 Preparing the aircraft for a maximum fuel flow (and emission) measurement 18 

6.3 Simple fuel flow method 19 

6.3.1 Fuel flow for all modes 19 

6.3.2 Recommended procedure 20 

6.4 Combined MAP & fuel flow method 21 

6.4.1 Preparations 21 

6.4.2 Recommended procedure 22 

7. Example for measurement documentation 23 
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1. The problem of piston engine power definitions 

The term „horse power“ is not very well defined. Generally, quite a variety of definitions and measurement methodologies are used which cause (at least) slight variations in the final numbers. As far as 

aircraft piston engines and propeller aircraft are concerned, the following terms could be identified: 

- Brake horsepower (BHP): Strictly speaking, BHP is the measure of an engine's horsepower without 

the loss in power caused by the gearbox, generator, water pump and other auxiliaries. The prefix 

"brake" refers to where the power is measured: at the engine's output shaft, as on an engine dynamometer. In aircraft piston engine manuals, power is often given in brake horsepower. 

- Propeller horsepower: The horsepower that is delivered to the propeller. Most of the tested aircraft 

piston engines do not have a reduction gear or other auxiliaries that might cause a significant loss of 

power through e.g. friction. Therefore, propeller horsepower is considered very near brake horse 

power under these circumstances. 

- Rated horsepower: The normal maximum allowable power output of the aircraft piston engine. In 

power charts of aircraft piston engine manuals, this number is often equal to maximum brake horse 

power. 

2. Theoretical power calculation (scientific SI-system1

) 

The power (P) which is delivered to the propeller is calculated by multiplying the torque (M) by the 

angular velocity (ω ) of the propeller shaft. 

P = M ⋅ω (1) 

Angular velocity and RPM ( n ) have the following relationship: 

ω = 2π ⋅ n (2) where n is the number of revolutions per second. 

Equation (2) in (1): 

P = M ⋅ 2π ⋅ n (3) 

At 2400 RPM (= 40.00 per second) and a torque of 400 Newtonmeter, the power equals about 100 

Kilowatt (around 135 HP, depending on the definition). 

This simple example shows that when knowing RPM and torque at the propeller shaft, engine propeller power is defined and can be determined exactly. Piston engine aircraft cockpits give information 

about engine RPM but do not usually have a torque indicator. It would have been very costly to install 

a torque meter between engine shaft and propeller and to make this design airworthy for the in-flight 

tests. So, this straightforward way of determining propeller power for the emission measurements 

could not be followed. 

3. Engine manifold pressure (MAP) and RPM for power determination 

MAP indicates the absolute pressure of the air/fuel mixture between the throttle and the cylinder inlet 

valve. The measuring gauge has a sealed capsule and a capsule that is exposed to manifold pressure. It is normally calibrated to inches of mercury, where 29.92 In Hg is the standard pressure. At full 

throttle, and in the case of a normally aspirated engine, the MAP will indicate nearly the value of the 

absolute pressure of the ambient air. For such engines, at full throttle, MAP is always a little bit lower 

 

1

 SI = système international, kg, meter, second,... 
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than ambient air pressure due to losses in the induction system. If the throttle is reduced, the MAP 

decreases. If the engine has stopped, the MAP shows ambient absolute air pressure. A turbocharged 

engine achieves MAP above ambient pressure. 

BHP (and propeller horsepower as described in a)) are almost directly related to MAP and engine 

RPM. The power output from a piston engine depends on both, engine RPM and the difference in 

pressure between the inside of the cylinders and the atmosphere outside the engine. 

But one has to be careful: When climbing at constant MAP and RPM, since the pressure in the manifold is constant, the reduction in ambient temperature increases the density of air in the manifold, resulting in a gradual increase in power. Constant MAP is maintained by opening the throttle during 

climb until the throttle is fully open. In other words: 23 In Hg is more power at 10 000 feet than it is at 

sea level. This has to be taken into account for ground measurement power settings, if they are based 

on MAP. 

4. Correlation of fuel flow and propeller power 

First of all, it must be noted, that for a given thrust, the fuel flow is NOT constant. The problem with 

piston engine thrust is that we get less thrust for the same fuel flow, as velocity is increased. (This is 

completely different from what happens in a jet). But: 

Piston engine fuel flow is constant for a given amount of power. This was the starting point to 

look for the correlation between fuel flow and propeller power. 

Table 1: Determination of propeller horsepower with HBEYS. Example sheet (source: “In flight Abgasmessung 

BAZL/CCUW”, R = rich, L = lean, FT = full throttle) 

HBEYS (DR400-180R)

O-360-A3A

Sensenich 76EM8S5-0-58

Gomolzig

AVGAS100LL

Stargas 898

Flights from 30.04.03, 13.08.03 and 21.08.03:

Flight Altitude 

QNH (ft) Date Nr.

Ambient 

Air 

Pressure 

(hPa)

Pressure 

Altitude (ft)

Relative 

Humidity 

(%) 

(rounded)

OAT 

(°C)

"Powersetting"RPM 

(1/min)

MAP 

(In Hg) Fuel Mixt.

T Zyl. 

(°C)

T Oil 

(°C)

Fuel 

Flow 

(l/h)

4000 30.4. cruise 2400 20 R 200 80 35

4000 cruise 2500 23 R 205 80 49

2000 13.8. 2 952 1647 40 24 FT, acceler. 2410 27 R 210 80 56

2000 3 923 2430 40 23 FT, vy 2500 27 R 200 80 58

2000 5 905 2916 40 23 Reduced 2050 18 R 210 85 26

2000 7 928 2295 40 23 Approach 1580 14 R 180 80 14

2000 9 924 2403 40 23 FT, vy 2510 28 R 200 80 59

2000 11 907 2862 40 23 Reduced 2080 17 R 200 85 26

2000 13 928 2295 40 23 Approach 1520 12 R 170 80 10

4000 13.8. 3 855 4266 30 22 FT, vy 2500 25 R 210 92 57

4000 5 841 4644 30 21 Reduced 2070 17 R 200 95 28

4000 7 863 4050 30 21 Approach 1580 12 R 180 95 15

4000 9 859 4158 30 22 FT, vy 2530 25 L 210 85 40

4000 11 842 4617 30 21 Reduced 2050 16 L 220 98 20

4000 13 863 4050 30 21 Approach 1410 11 L 190 92 10

6000 13.8. 3 799 5778 30 20 FT, vy 2510 24 R 210 95 55

6000 5 781 6264 30 18 Reduced 2060 15 R 200 92 25

6000 7 803 5670 30 18 Approach 1440 10 R 180 85 8

6000 9 795 5886 30 20 FT, vy 2570 24 L 210 82 44

6000 11 780 6291 30 18 Reduced 2070 16 L 210 90 20

6000 13 801 5724 30 18 Approach 1490 10 L 180 82 11

4000 21.8. 2 866 3969 50 16 cruise 2440 20 R 210 75 38

4000 3 868 3915 50 16 cruise 2330 20 lambda =1 200 80 29

Measurement System

Fuel

Silencer

Propeller

Engine

Aircraft
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Propeller horsepower calculations were based on ambient air pressure values and hand written power 

curves from Textron/Lycoming. Figure 1 shows an example for the engine model O-360 A series, marvel carburettor and an engine cylinder compression ratio of 8.5 : 1. 

Propeller Load Horsepower O-360 A Series

Marvel Carburetor, Compression Ratio 8.5 : 1

40

65

90

115

140

165

190

1700 1900 2100 2300 2500 2700

Drehzahl [1/min]

Brake Horsepower [hp]

Figure 1: Power Curve Lycoming Model O-360 A Series, Curve No. 10350-A (Textron/Lycoming) digitalized. 

Propeller horsepower was assumed very near brake horsepower (see section a)). The calculated values for propeller horsepower, the measured fuel flow, MAP, ambient air pressure and flight mode were 

normalized and plotted together (figures 2 and 3). 

 HB-EYS, "mixture rich" 

ambient air pressure 781 bis 952 hPa

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1

Share on maximum fuel flow

Propeller horsepower

Manifold pressure (MAP)

RPM

Ambient air pressure

Flight mode (Final, Downwind,

Cruise, Take-off)

Linear (Propeller horsepower)

Figure 2: Normalized selected engine parameters in function of fuel flow (mixture rich). Example: At 45% (=0.45) 

of maximum fuel flow, propeller power is at 40% (=0.4), manifold pressure at 60% (=0.6) and engine RPM at 82% 

(=0.82) of the maximum value.
Reference: 0 / 3/33/33-05-003.022 

6/29

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

 HBEYS, mixture lean, 

ambient air pressure 780 to 868 hPa

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1

Share on maximum fuel flow

Propeller horsepower

Manifold pressure (MAP)

RPM

Ambient air pressure

Flight mode (Final,

Downwind, Cruise, Take-off)

Linear (Propeller

horsepower)

Figure 3: Normalized selected engine parameters in function of fuel flow (mixture lean)

It can be seen from figures 2 and 3 that for the investigated engine, propeller horsepower and fuel flow 

correlate quite nicely (R2

 = 0.98), better than MAP or RPM. 

MAP is also directly related to ambient pressure and figure 2 shows that for a certain propeller power, 

the MAP is varying, although fuel flow and propeller horsepower are kept constant. 

Fuel Flow versus Brake HP Analysis for Lyc IO-360 A Series @ Best Power Mixture

40

50

60

70

80

90

100

40 50 60 70 80 90 100

Percent of max. Brake HP

Percent of max. Fuel Flow @ Best Power Mixture

2700 RPM Best Power

2600 RPM Best Power

2400 RPM Best Power

2200 RPM Best Power

Figure 4: In-flight fuel flow versus brake horsepower for different propeller adjustments (HBKEZ). Restrictions: Especially for low power settings below 40% of maximum fuel flow, significant deviations 

from the linear relationship can occur, because the piston engine efficiency is not a constant over the 

full power range. This can be seen in this figure, which shows an analysis for an injected aircraft piston 

engine with variable pitch propeller at best power mixture (HBKEZ, Appendix 2). 
Reference: 0 / 3/33/33-05-003.022 

7/29

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Generally, the linear relationship between propeller horsepower and fuel flow at higher power settings 

could be reproduced, also for other engine-propeller combinations. Fuel flow was equally found useful 

to account for changes in ambient conditions. As ambient air pressure and air density decrease2, 

engine power decreases which is well translated into fuel flow decrease (at constant mixture setting). 

Therefore it is considered sufficiently accurate for those emission measurements, which are not intended for certification, to use fuel flow as the major parameter for engine propeller horsepower settings. 

The FOCA low cost emission measurement system (see Appendix 1 and 5) requires a direct fuel flow 

measurement. The fuel flow transducer, which has to be installed and calibrated on the aircraft, can 

therefore serve as propeller horsepower setting device at the same time. 

5. Adjustment of ground measurement power settings (Fuel Flow Method) 

FOCA tries to produce emission factors and fuel flow data for emission inventory purposes at the 

highest possible cost efficiency. Therefore, besides a low-cost measurement system with sufficient 

accuracy (as described in Appendix 1), a methodology for static ground measurements is needed. 

Primary goal: Find ground power settings that are representative of typical in-flight modes and emissions. 

Results from in-flight emission tests (see Appendix 2) were used to select appropriate settings for 

ground measurements. 

• Step 1: Take in-flight measurement results and try to reproduce them at static ground measurements. 

• Step 2: Derive power setting methodology for static ground measurements 

• Step 3: Take an aircraft that has not been measured in-flight, apply the power setting methodology (step 2) for static ground measurements, followed by in-flight measurements to validate 

the methodology. 

5.1 Step 1: Comparison of in-flight and static ground measurements of HBKEZ (example) 

Normalised Emission Factors HBKEZ, full throttle

On the left: in-flight, On the right: static on ground measurement

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Rel. EF CO 0.864 0.907 0.884 0.923 0.903 0.905 0.904 0.895 0.898 0.902 0.912 0.914 0.916 0.946 0.94 0.967 0.985 1 0.88 0.88 0.88 0.897 0.914 0.922 0.933 0.945

Rel. EF HC 0.669 0.827 0.74 0.972 0.743 0.83 0.788 0.738 0.771 0.745 0.767 0.796 0.791 1 0.802 0.964 0.987 0.997 0.7 0.662 0.649 0.774 0.799 0.859 0.775 0.808

Rel. EF NOx 1 0.882 0.745 0.537 0.482 0.482 0.472 0.399 0.369 0.519 0.514 0.495 0.474 0.478 0.582 0.412 0.333 0.304 0.628 0.609 0.587 0.69 0.706 0.817 0.761 0.837

Normalised Fuel Flow 0.972 0.958 0.986 0.986 0.986 0.986 0.986 1 1 1 0.986 0.986 0.986 0.972 0.944 0.958 0.944 0.93 0.93 0.93 0.93 0.944 0.972 0.986 0.986 0.972

TO 

1673f

TO 

1673f

TO 

2300f

TO 

3000f

TO 

3500f

TO 

3500f

TO 

3500f

TO 

3500f

TO 

3500f

TO 

3500f

TO 

3500f

TO 

3500f

TO 

3500f

TO 

4000f

TO 

4300f

TO 

5000f

TO 

6000f

TO 

7000f

TO 

Stand

TO 

Stand

TO 

Stand

TO 

Stand

TO 

Stand

TO 

Stand

TO 

Stand

TO 

Stand

Figure 5: Comparison of emission factors for CO, HC and NOx from in-flight and static on ground tests at full throttle. Flights were performed up to a pressure altitude of 7000ft and different ambient conditions. NOx is highest at 

ground level, CO and HC are highest at high altitude (mixture full rich). Please note that all HC measurements 

were based on NDIR, not on FID. 

 

2

 Air density decrease: Mainly through increase of ambient air temperature. Humidity increase had little effect 
Reference: 0 / 3/33/33-05-003.022 

8/29

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Normalised Emission Factors HBKEZ, Climb

On the left: in-flight, On the right: static on ground measurement

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Rel. EF CO 0.973 0.953 0.949 0.945 0.942 0.94 0.937 0.601 0.596 0.531 0.429 0.47 0.521 0.509 0.542 0.985 0.971 0.972 0.972 1 0.994 0.962 0.942 0.951 0.918 0.952

Rel. EF HC 0.759 0.787 0.813 0.814 0.852 0.857 0.865 0.492 0.518 0.664 0.498 0.392 0.4 0.692 0.701 0.79 1 0.768 0.76 0.792 0.794 0.838 0.682 0.678 0.714 0.68

Rel. EF NOx 0.091 0.07 0.07 0.072 0.07 0.071 0.071 0.526 0.54 0.787 0.849 1 0.807 0.896 0.799 0.078 0.088 0.086 0.083 0.095 0.095 0.084 0.074 0.068 0.085 0.07

Normalised Fuel Flow 1 0.983 1 0.983 1 1 1 0.8 0.8 0.767 0.767 0.767 0.767 0.75 0.75 0.867 0.85 0.85 0.85 0.85 0.867 0.883 0.983 0.983 0.883 0.983

CL 

3000f

CL 

3500f

CL 

3500f

CL 

3500f

CL 

3500f

CL 

3500f

CL 

3500f

CL 

3500f

CL 

3500f

CL 

3500f

CL 

3500f

CL 

3600

CL 

4500

CL 

4500f

CL 

5500f

CL 

Stand 

CL 

Stand 

CL 

Stand 

CL 

Stand 

CL 

Stand 

CL 

Stand 

CL 

Stand 

CL 

Stand 

CL 

Stand 

CL 

Stand 

CL 

Stand 

Figure 6: Comparison of emission factors for CO, HC and NOx from in-flight and static on ground tests at climb. 

Flights were performed up to a pressure altitude of 5500ft and different ambient conditions. The second set of inflight measurements starting from 3500ft to 5500ft (in the middle of the figure) has been measured with fuel mixture adjustment during climb (as described in Appendix 2, section 4.f)). All ground measurements were performed 

with mixture full rich, with fuel flow guided power setting (suffix “alt”) and MAP guided power setting (“v3”). Please 

note that all HC measurements were based on NDIR, not on FID. 

Normalised Emission Factors HBKEZ, Approach

On the left: in-flight, On the right: static on ground measurement

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Rel. EF CO 0.87 0.75 0.97 0.93 0.9 0.9 0.85 0.97 0.88 0.96 0.96 0.95 0.94 0.94 0.94 0.93 0.93 0.92 0.93 0.92 0.92 0.92 1 1 0.99 0.99 0.99 0.99 0.99 1 0.94 0.94 0.94 0.9

Rel. EF HC 0.75 0.79 1 0.88 0.72 0.73 0.75 0.89 0.74 0.83 0.76 0.78 0.78 0.79 0.8 0.83 0.78 0.79 0.77 0.77 0.81 0.8 0.91 0.79 0.79 0.84 0.86 0.8 0.88 0.79 0.76 0.74 0.77 0.75

Rel. EF NOx 0.63 1 0 0.15 0.57 0.56 0.81 0.06 0.57 0.14 0.48 0.45 0.44 0.44 0.49 0.52 0.49 0.52 0.55 0.5 0.43 0.44 0.35 0.38 0.39 0.41 0.37 0.39 0.37 0.47 0.46 0.46 0.48 0.5

Normalised Fuel Flow 0.68 0.49 0.36 0.19 0.96 0.91 1 0.6 0.45 0.91 0.68 0.79 0.77 0.74 0.74 0.72 0.7 0.77 0.72 0.79 0.79 0.77 0.66 0.66 0.66 0.66 0.66 0.66 0.68 0.72 0.66 0.66 0.66 0.77

AP 

160

AP 

200

AP 

250

AP 

260

AP 

320

AP 

320

AP 

320

AP 

320

AP 

350

AP 

350

AP 

350

AP 

350

AP 

350

AP 

350

AP 

350

AP 

350

AP 

350

AP 

350

AP 

350

AP 

350

AP 

350

AP 

350

AP 

Sta

AP 

Sta

AP 

Sta

AP 

Sta

AP 

Sta

AP 

Sta

AP 

Sta

AP 

Sta

AP 

Sta

AP 

Sta

AP 

Sta

AP 

Sta

Figure 7: Comparison of emission factors for CO, HC and NOx from in-flight and static on ground tests at approach. Flights were performed from a pressure altitude of 3500ft and different ambient conditions. Flight measurements show significant variations coming from different approach power settings. All ground measurements 

were performed with mixture full rich, with fuel flow guided power setting (suffix “alt”) and MAP guided power 

setting (suffix “v3”). Please note that all HC measurements were based on NDIR, not on FID. 

5.2 Step 2: Power setting methodology for static ground measurements 

The first version of the methodology is solely based on fuel flow measurements for power settings at 

ground level. 

5.2.1 Determination of maximum fuel flow 

Generally, in order to get measurement results that are near standard sea level conditions, it is helpful 

if the test location is situated at low altitude airports. Many airports in the Swiss Midlands are at about 

1500ft AMSL. If measurements are performed during cold days in winter and high ambient air pressure, the density altitude can be reduced to around 0ft AMSL. Under these conditions a normally aspirated piston engine can produce its maximum rated propeller power and its maximum fuel flow. Moreover, measurements at low ambient temperatures have the advantage of better engine cooling and 

better prevention of “hot spots” inside the engine cowling during the static tests. 
Reference: 0 / 3/33/33-05-003.022 

9/29

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

For practical reasons, it was not possible for FOCA to do all the ground static tests at density altitudes 

around 0ft AMSL. 

However, the maximum fuel flow at different ambient conditions between winter and summer showed 

relatively small differences. Although, high humidity also reduces air density, the significant portion of 

difference is generated by ambient air temperature variations (see also section 5.3.3). Additionally, 

part of the variation has to be attributed to the fuel flow transducers limited accuracy. 

Examples for total variations (all flights, take-off and all ground measurements, full throttle, high RPM): 

HBEYS 57 < max. fuel flow < 60 liters/hour 

HBKEZ 68 < max. fuel flow < 71 liters/hour 

Keeping in mind that the emission measurements were primarily designed for inventory purposes, 

reflecting operational conditions, the variation seemed acceptable. However, when ever possible, 

FOCA tried to measure normally aspirated piston engines at low density altitude, giving highest possible propeller power and fuel flow at full throttle. Of course, influence of ambient air pressure was not 

an issue for ground level static tests in the case of turbocharged engines. And: 

There was no significant difference in maximum fuel flow at full throttle with the aircraft standing or 

with the aircraft accelerating on the runway. 

For details of the measurement procedure, see section 6. 

5.2.2 Power settings other than maximum propeller power 

Table 2 was generated from in-flight and ground measurement comparisons in order to match fuel flow 

and emissions obtained with ground measurements as good as possible to in-flight conditions. (Examples are given in figures 5 to 7 of section 5.1) 

Table 2: Percent of maximum fuel flow for all selected aircraft modes (mixture “full rich”) 

Mode % of maximum fuel flow 

Take off 100 

Climb out 85 

Cruise 65 

Approach 45 

Taxi AFM 

 

The power setting for the different modes is established by adjusting the throttle to bring the indicated 

fuel flow to the corresponding % fuel flow calculated value. The taxi mode is treated differently: The 

engine is running at the recommended RPM for warm up according to AFM/engine operation manual. 

(Details in section 6) 

Example: Max. fuel flow 70 liter / hour -> Climb out setting 70 liter /hour * 0.85 = 60 liter / hour

5.3 Step 3: Application of the power setting methodology (step 2) for static ground measurements with an aircraft that has not been measured in-flight, followed by in-flight measurements 

The fuel flow methodology developed in step 2 was applied to the high performance piston engine 

aircraft HBKIA. It was considered demanding to match static ground and in-flight measurements of 

such an aircraft, because of variable pitch propeller and an automatic air/fuel mixture adjustment of the 

engine (Appendix 2, Section 5). Therefore, this aircraft was considered an interesting choice to test the 

fuel flow method. 
Reference: 0 / 3/33/33-05-003.022 

10/29

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Picture 2: Preparations for ground static emission measurements of HB-KIA 

Picture 3: Preparations for ground static emission measurements of HB-KIA 
Reference: 0 / 3/33/33-05-003.022 

11/29

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

5.3.1 Comparison of ground and later in-flight measurements 

General remark: The in-flight tests following the ground static tests have been flown in very different 

ambient conditions, pressure altitudes and sometimes including individual operational behaviour of 

different pilots (Appendix 2). It could not be the aim to match a certain flight exactly with a certain 

ground measurement. The main goal was, to develop the methodology so far that emission factors 

(resulting from ground measurements) were in the range of values occurring in-flight. The following 

figures show emission factors and fuel flow in relation to their maximum values obtained within all the 

measurements. If the engine and the measurement system would perform absolutely identical at each 

flight, all in-flight pillars in the figure would be equal to 1. In reality, there are already significant differences within a certain flight mode. We consider the methodology useful, if it is able to produce the 

same pillar height range as compared to the in-flight pillars for the different species and the fuel flow 

(see figures below). 

Normalised Emission Factors HBKIA, full throttle

On the left: static on ground, On the right: in-flight

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Rel. EF CO 0.932 0.922 0.922 0.952 0.985 0.985 0.764 0.772 0.757 0.753 0.707 0.812 0.795 0.878 0.85 0.858 0.836 0.808 0.817 0.82 0.824 0.894 0.931 0.87 0.949 0.973 0.917

Rel. EF HC 0.461 0.491 0.491 0.637 0.53 0.53 0.791 0.797 0.836 0.837 0.807 0.74 0.782 0.584 0.557 0.77 1 0.563 0.484 0.484 0.529 0.412 0.534 0.478 0.484 0.5 0.546

Rel. EF NOx 0.354 0.504 0.569 0.558 0.463 0.463 0.927 0.907 0.932 0.943 1 0.823 0.686 0.756 0.753 0.676 0.719 0.778 0.824 0.812 0.805 0.724 0.565 0.675 0.662 0.531 0.624

Normalised Fuel Flow 0.96 0.96 0.96 0.952 0.952 0.952 0.98 0.98 0.993 0.993 0.962 0.962 0.962 1 0.962 0.962 0.962 0.951 0.96 0.96 0.96 0.96 0.941 0.962 0.941 0.952 0.952

TO 

0000

TO 

0000

TO 

0000

TO 

0000

TO 

0000

TO 

0000

TO 

LSZG

TO 

LSZG

TO 

LSZG

TO 

LSZG

TO 

LSZG

TO 

LSZG

TO 

LSZG

TO 

1700

TO 

1700

TO 

LSZB

TO 

LSZB

TO 

2300

TO 

3000

TO 

3000

TO 

3000

TO 

3000

TO 

3000

TO R 

3000

TO R 

3500

TO 

4000

TO 

4000

Figure 8: Comparison of normalized emission factors for take-off power settings of all ground and in-flight measurements of HBKIA. The ground static results are represented by the first six sets of columns on the left. HC 

emissions were measured with NDIR (Appendix 1). 

 

Mean differences between ground an in-flight measurements

HB-KIA, take-off

0

20

40

60

80

100

120

140

EF CO EF HC EF NOx Fuel Flow

%

Ground measurement

In-flight measurement

Figure 9: Relative difference in mean emission factors between ground and in-flight measurements with 

indicated standard deviation for HB-KIA, take-off. 

Discussion of take-off mode: The take-off fuel flow is stable within 5% for all measurements. CO emission factors tend to be higher at static conditions by around 10% with the exception of high altitude 

take-offs. NOx emission factors seem to be around 30% lower at static conditions. However, in absolute terms, the difference is in the order of grams / kg fuel. HC emission factors have a tendency to be 

lower than in-flight at low altitudes. 
Reference: 0 / 3/33/33-05-003.022 

12/29

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Normalised Emission Factors HBKIA, climb mode

On the left: static on ground, On the right: in-flight

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Rel. EF CO 0.904 0.882 0.847 0.812 0.821 0.831 0.801 0.737 0.879 0.838 0.837 0.878 0.814 0.977 0.837 0.911 0.995 0.906 0.956 0.787 0.827 0.827 0.918 0.843 0.961 0.933 0.968

Rel. EF HC 0.501 0.511 0.548 0.709 0.838 0.823 0.712 0.562 0.749 1 0.71 0.603 0.674 0.66 0.828 0.715 0.865 0.671 0.759 0.642 0.641 0.627 0.654 0.597 0.67 0.775 0.815

Rel. EF NOx 0.374 0.614 0.757 0.806 0.782 0.722 0.831 1 0.521 0.816 0.668 0.278 0.746 0.542 0.786 0.245 0.368 0.651 0.13 0.921 0.841 0.856 0.521 0.826 0.342 0.61 0.182

Normalised Fuel Flow 0.948 0.948 0.948 0.921 0.928 0.921 0.92 0.856 0.921 0.962 0.877 0.877 0.877 0.921 0.92 1 0.92 0.941 0.921 0.941 0.921 0.921 0.846 0.921 0.941 0.888 0.892

CL 

0000

CL 

0000

CL 

0000

CL 

LSZG

CL 

LSZG

CL 

LSZG

CL 

LSZG

CL 

LSZG

CL 

LSZG CL R CL LSZG

CL 

LSZG

CL 

LSZG

CL 

0000 CL R CL 2300 CL R CL 2300

CL 

3000

CL 

3000

CL 

3000

CL 

3000

CL R 

3000

CL 

3000

CL 

3000

CL 

3300

CL 

4000

Figure 10: Comparison of normalized emission factors for climb mode of all ground and in-flight measurements of 

HBKIA. The ground static results are represented by the first three sets of columns on the left. HC emissions were 

measured with NDIR (Appendix 1). 

Mean differences between ground and in-flight 

measurements, HB-KIA, climb mode

0

20

40

60

80

100

120

140

EF CO EF HC EF NOx Fuel Flow

%

Ground measurement

In-flight measurement

Figure 11: Relative difference in mean emission factors between ground and in-flight measurements with indicated standard deviation for HB-KIA, climb mode. 

Discussion of climb mode: The variation of in-flight emission factors can be rather significant. In this 

example, this is especially the case for NOx emission factors. Nevertheless, matching of mean values 

for all in-flight emission factors to the ground measurement values is considered acceptable with the 

exception of EF HC. It must be noted, that HC emissions had been measured with NDIR instead of 

FID (Appendix 1) only. Therefore, the composition of HC had an influence on the total value and this 

could be part of the difference. 

Normalised Emission Factors HBKIA, approach mode

On the left: static on ground, On the right: in-flight

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Rel. EF CO 0.9225 0.8976 0.9133 0.9002 0.8941 0.8887 1 0.9614 0.7058 0.882 0.7082 0.854 0.8084 0.855 0.6775 0.7779 0.8039 0.8074 0.7743 0.7446 0.7591

Rel. EF HC 0.9157 0.9601 0.9228 0.9441 1 0.9962 0.9409 0.933 0.7817 0.7652 0.8024 0.74 0.9145 0.9502 0.7552 0.8021 0.8505 0.8075 0.7592 0.8507 0.7715

Rel. EF NOx 0.3176 0.3438 0.2592 0.2755 0.2857 0.3128 0.2315 0.2546 0.8716 0.4581 0.9936 0.5168 0.6037 0.404 1 0.6615 0.5878 0.5793 0.5062 0.5854 0.5489

Normalised Fuel Flow 0.9283 0.9283 0.9283 0.9283 0.9283 0.8491 0.8491 0.9245 0.9925 0.9849 0.9849 0.9849 0.8868 0.9245 0.9849 0.9849 1 0.9849 0.9623 0.9245 0.9434

AP 

0000

AP 

0000

AP 

0000

AP 

0000

AP 

0000

AP 

0000

AP 

2400

AP 

3000

AP 

3000

AP 

3000

AP 

3000

AP 

3000

AP 

3200

AP 

3200

AP 

4000

AP 

4000

AP 

4000

AP 

4000

AP 

4500

AP 

5000

AP 

5000

Figure 12: Comparison of normalized emission factors for approach mode of ground and in-flight measurements 

of HBKIA. The ground static results are represented by the first six sets of columns on the left. 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Mean differences between ground and in-flight 

measurements, HB-KIA, approach mode

0

20

40

60

80

100

120

140

EF CO EF HC EF NOx Fuel Flow

%

Ground measurement

In-flight measurement

Figure 13: Relative difference in mean emission factors between ground and in-flight measurements with indicated standard deviation for HB-KIA, approach mode. 

Discussion of approach mode: NOx emission factors have the tendency to be significantly lower at 

ground tests than in flight. The contrary is true for CO and HC. This can be explained by the fact that 

the engine is running at a less rich air/fuel mixture during flight, most probably due to the automatic 

mixture adjustment in the engine (Appendix 2, section 5). 

Normalised Emission Factors HBKIA, cruise mode

On the left: static on ground, On the right: in-flight

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

Rel. EF CO 0.97 0.94 0.94 0.81 0.80 0.79 0.79 0.81 0.66 1.00 0.71 0.87 0.64

Rel. EF HC 0.34 0.38 0.38 0.86 0.87 0.80 0.86 0.88 0.82 0.93 0.80 1.00 0.87

Rel. EF NOx 0.60 0.67 0.67 0.80 0.81 0.83 0.81 0.80 1.00 0.57 0.92 0.74 0.99

Normalised Fuel Flow 1.00 1.00 1.00 0.92 0.92 0.92 0.92 0.94 0.93 0.94 0.93 0.94 0.93

0 CR LR 

GND

0 CR LR 

GND

0 CR LR 

GND CR 5500 CR 5500 CR 5500 CR 5500 CR 5500 CR 5500 CR 5500 CR 5500 CR 5500 CR 5500

Figure 14: Comparison of normalized emission factors for cruise mode of ground and in-flight measurements of 

HBKIA. The ground static results are represented by the first three sets of columns on the left. HC emissions were 

measured with NDIR (Appendix 1). Mixture was set “rich of EGT peak”. (For details see section 6) 

Mean differences between ground and in-flight 

measurements, HB-KIA, cruise mode

0

20

40

60

80

100

120

140

EF CO EF HC EF NOx Fuel Flow

%

Ground measurement

In-flight measurement

Figure 15: Relative difference in mean emission factors between ground and in-flight measurements with indicated standard deviation for HB-KIA, approach mode.
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Discussion of cruise mode: Cruise mode emission factors are extremely dependent on pilot’s choice 

for the mixture setting (Appendix 2). In-flight results show the variation between settings of different 

pilots. It was found that the mean value for lambda (Appendix 5, section c)) for the standard mixture 

setting condition “rich of EGT peak” was around 0.93 to 0.95. In ground tests, after setting the power 

reference, the mixture setting was adjusted to this range of lambda (see section 6 for details). It is 

interesting to see, that although CO emission factors seem to be higher and NOx emission factors 

lower for the ground measurement, the HC emission factors are significantly lower. A similar situation 

can be seen in climb mode (figure 11). No logical explanation could be found, because HC emission 

factors should normally correlate with CO. However, as mentioned before, HC emissions had been 

measured with NDIR instead of FID (Appendix 1) only. 

5.3.2 Adjustments to the fuel flow method for complex aircraft/engines 

For aircraft equipped with manifold pressure gauge, the fuel flow method was combined with manifold 

pressure preset values (section 6.4). This procedure further improved matching between ground and 

in-flight data. For the engine Teledyne/Continental IO-550-B of HB-KIA, the following ground based 

emission factors were obtained with this method: 

Table 3: Fuel flow and mean emission factors for TCM IO-550-B (times are not relevant here) 

The data presented in table 3 have been checked against the flights ECERT 57 and 64 (Appendix 2, 

sections 5.o) and 5.p)) in order to show a better match with in-flight measured emission inventories. 

Table 4: Comparison of emission results from in-flight full mission measurements (ECERT 57 and 64) and emission results based on the ground measurement data sheet (Table 3). For the calculation based on the data sheet, 

the average pilot 1 and pilot 2 times were used, as indicated on the bottom of the table. 

HBKIA Pilot 1 Pilot 2 Average Pilot 1 and 2 Based on Data Sheet

LTO Fuel (kg) 11.1 11.2 11.1 11.8

LTO CO (g) 9159 10932 10046 11337

LTO HC (g) 384 382 382 218

LTO NOx (g) 57 30 43 40

CR Fuel (Mission kg) 17 18 17.5 19.1

CR CO (Mission g) 7325 10108 8716.5 9008

CR HC (Mission g) 180 173 176.5 103

CR NOx (Mission g) 476 342 409 438

CR Fuel (kg/h) 49 43 46 49.7

CR CO (g/(h) 20929 24259 22594 23498

CR HC (g/h) 514 415 464.5 268

CR NOx (g/h) 1360 822 1091 1142

Taxi Time (Min.) 11 11 11 11

Take-off Time (Min.) 1 1 1 1

Climb Time (Min.) 3.5 3.5 3.5 3.5

Cruise Time (Min.) 21 25 23 23

Approach Time (Min.) 7.5 7.5 7.5 7.5
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Comparison of in-flight emission results for a full mission and emission 

results based on data sheet (HB-KIA)

0

20

40

60

80

100

120

140

160

LTO Fuel (kg)

LTO CO (g)

LTO HC (g)

LTO NOx (g)

CR Fuel (Mission kg)

CR CO (Mission g)

CR HC (Mission g)

CR NOx (Mission g)

CR Fuel (kg/h)

CR CO (g/(h)

CR HC (g/h)

CR NOx (g/h)

%

Average Pilot 1 and 2

Based on Data Sheet

Figure 16: Relative comparison of in-flight emission results for a full mission and emission results based on the 

data sheet of table 3. Emission results based on ground measured data for fuel, CO and NOx match the emissions of the selected flights by 3 to 8% difference. HC emissions, based on the data sheet, are significantly lower 

(by 42%). It looks as if the differences in HC emissions between in-flight and ground measurements are systematic. It must be noted that the HC emission factors presented in table 3 were measured with a FID for total HC. Inflight measurement of HC could only be done with the NDIR sensor and total HC had to be estimated (see Appendix 5). Standard deviations for in-flight emissions are only based on the two flights and are therefore not statistically robust. 

5.3.3 Temperature corrections for normally aspirated carburetted aircraft piston engines 

The value of ambient air density (which is a function of ambient air temperature) can influence the 

air/fuel ratio in the carburettor significantly, much more than ambient humidity. Changing air/fuel ratio 

(and therefore changing lambda) changes the value of emission factors (even with all other factors 

remaining constant). 

To compensate for temperature effects on emission factors for normally aspirated carburetted engines, two simple correction formulas are suggested, shifting the values to approximately 15°C outside 

air temperature (see Appendix 5). The correction represents present state of investigation and has not 

been developed any further. 

Table 5: Generally, lambda gets lower at higher temperatures (the engine runs „richer“). The taxi mode of this 

particular engine is behaving differently and is not representative for this class of engines. (Example from HBEYS, LycO-360, Marvel carburettor). 

Mode lambda 10.03.04 

/1°C 

lambda 17.03.04 / 20°C cold minus warm 

TO 0.708 0.704 0.004 

TO 0.704 0.692 0.012 

TO 0.701 0.689 0.012 

CL 0.759 0.747 0.012 

CL 0.762 0.743 0.019 

CL 0.757 0.732 0.025 

CR 0.827 0.813 0.014 

CR 0.834 0.811 0.023 

CR 0.827 0.806 0.021 

AP 0.763 0.746 0.017 

AP 0.766 0.748 0.018 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

AP 0.772 0.75 0.022 

TA 1.338 1.371 -0.033 

TA 1.333 1.359 -0.026 

TA 1.343 1.386 -0.043 

CR L 0.994 0.96 0.034 

CR L 1.001 0.973 0.028 

CR L 0.996 0.966 0.03 

CO emission factor in function of ambient temperature and pressure at full throttle 

HB-EYS 

1100

1200

1300

Mode

EFCO (g/kg Fuel)

CO 1167 1183 1192 1225 1231 1247 1260 1259 1271 1279 1264

TO 1°C 

946hPa

TO 1°C 

946hPa

TO 1°C 

946hPa

TO 20°C 

960hPa

TO 20°C 

960hPa

TO 22°C 

954hPa

TO 22°C 

954hPa

TO 27°C 

951hPa

TO 30°C 

951hPa

TO 30°C 

952hPa

TO 30°C 

952hPa

Figure 17: Example for temperature dominated EF CO increase. Ambient pressure is QFE. Several measurements at the same temperature and QFE also show statistical differences resulting from measurement inaccuracies and engine performance fluctuations. 

EF CO (T)

y = 3.1259x + 1176.5

R2

 = 0.9381

1160

1180

1200

1220

1240

1260

1280

1300

0 5 10 15 20 25 30 35

Ambient Air Temperature (°C)

EF CO (g/kg Fuel)

Figure 18: Example of linear correction of EF CO in function of ambient air temperature. At 15°C, the EF CO is 

assumed to be 1223 g/kg fuel (HB-EYS). See Appendix 5, section f) for first order approximation formulas. 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

6. Recommended ground measurement power setting procedures for emission tests 

6.1 Selection of methodology 

. 

6.2 Procedure for determination of maximum fuel flow 

6.2.1 Fuel flow calibration 

The fuel flow measurement system, either already existing in the aircraft or installed for the measurements only, should be calibrated. This can normally only be done with flight testing, which requires to 

certify the installation. The fuel flow transducer used by FOCA (Appendix 1) is a certified design and 

can be installed in terms of a major aircraft modification. Calibration of the transducer was achieved by 

- Marking the position of the aircraft wheels before first refuelling. 

- Refuelling the aircraft with the fuel reaching a clearly defined optical reference. 

- Running the fuel flow system during flights, which last several hours. 

- Noting the time integrated fuel consumption indicated by the fuel flow system until next refuelling. 

- Parking the aircraft with the same balance exactly at the position where the previous refuelling 

took place. 

- Refuelling the aircraft to the previously defined optical reference. 

- Noting the relation between tanked amount of fuel and fuel flow system indicated fuel consumption. 

- Correcting the calibration factor according to the fuel flow transducer manual. 

After installation in the aircraft, the factory pre-calibration value of the fuel flow transducer was often 

within 5% of the determined calibration value. 

Aircraft/Engine 

combination with 

installed and calibrated fuel flow 

transducer 

Combined MAP & 

fuel flow method 

Section 6.4 

Manifold pressure (MAP) 

gauge installed & MAP 

values existent in flight 

manual? 

Simple fuel flow 

method 

Section 6.3 

Determination of 

maximum fuel flow

Section 6.2 

NO YES 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

6.2.2 Preparing the aircraft for a maximum fuel flow (and emission) measurement 

As mentioned before, determination of maximum fuel flow (maximum propeller horsepower) of normally aspirated piston engines should be made at low density altitudes (low ambient air temperature 

and high ambient air pressure conditions). At a density altitude of 0 ft, the engine will behave similar to 

sea level due to a similar “weight of charge” in the inlet. Practical recommendations: 

• Wheels are secured with wheel chocks and fully braked by the pilot 

• The measurement car is placed behind the main wing and in a sufficient distance to the tail 

wing, outside the propeller stream and without obstructing the aircraft, should the aircraft 

move forward. 

• If the engine is equipped with a variable pitch propeller, the pitch setting is “high RPM”. 

• The engine has to be perfectly warmed up. 

• When going to full throttle, the aircraft is observed from outside with permanent radio contact 

between observer and pilot. 

• Full throttle static conditions should generally not last more than one minute. Engine temperatures have to be observed carefully. 

• This configuration can be used for the whole emission measurement 

Picture 4: Determination of maximum fuel flow (static measurement). The aircraft brakes are fully applied and the 

wheels secured by wheel chocks. 

After determination of maximum fuel flow, the engine is idling at the RPM which is suggested according to the aircraft flight manual (AFM), in order to cool down. During this time, the corresponding fuel 

flows, belonging to Climb out, Cruise (mixture rich) and Approach can be calculated, as described in 

section 6.3 and 6.4 respectively. 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Picture 5: Emission measurement of a Microlight (Swiss Ecolight) aircraft, normally used for glider towing. The 

power to weight ratio of this aircraft is such that the towing rope is necessary to hold the aircraft in position during 

full throttle operation. 

6.3 Simple fuel flow method 

6.3.1 Fuel flow for all modes 

All power settings are derived from the following table: 

Table 6: Percent of maximum fuel flow for all selected aircraft modes (mixture “full rich”) 

Mode % of maximum fuel flow 

Take off 100 

Climb out 85 

Cruise 65 

Approach 45 

Taxi AFM 

 

The power setting for the different modes is established by adjusting the throttle to bring the indicated 

fuel flow to the corresponding % that has been calculated out of the maximum fuel flow. 

Important: 

• If the engine has manual mixture adjustments, all settings from table 6 correspond to mixture 

“full rich”. 

• The taxi mode is treated differently: The engine is running at the recommended RPM for warm 

up according to the AFM/engine operation manual. Therefore, in order to measure taxi mode, 

the engine power is set by the recommended engine RPM and the resulting fuel flow is measured. 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

• Cruise power for engines with manual mixture control: The initial power setting is adjusted with 

“mixture full rich” at 65% of maximum fuel flow, according to table 6. The final cruise setting 

(CRUISE LEAN) for the measurement will be obtained by leaning the mixture to lambda = 

0.93 (see 5.3.1), while maintaining the RPM from the initial power setting. (It is recommended 

to use an exhaust emission measurement system, which is capable of computing the lambda 

values from measured concentrations instantly, see more details in 6.3.2.) 

Example: Max. fuel flow = 70 liter / hour 

Î Climb out setting = 70 liter /hour * 0.85 = 60 liter / hour

Î Cruise initial setting with mixture full rich = 46 liter / hour 

Î Cruise lean setting by leaning to lambda = 0.93 and maintaining RPM. Now, the fuel flow and 

emission concentrations are measured. Fuel flow is usually between 50 and 55% of maximum 

fuel flow and would result in around 37 liter / hour for this example 

Î Approach setting = 32 liter / hour 

Î Taxi setting = Taxi RPM according engine/aircraft manual, usually around 7 liters / hour. 

6.3.2 Recommended procedure 

• We recommend going from high power to low power measurements, at least three measurements per power mode and a VHF radio communication between pilot and measurement 

team. 

• The first measurement would be again the maximum fuel flow (max. power) measurement. At 

this occasion, the repetition of maximum fuel flow is a check for the first maximum fuel flow 

measurement. 

• As soon as measured concentrations are stable, data are recorded. The pilot should note at 

least fuel flow, RPM and engine temperatures during the measurements. (This can be a demanding task, with the airframe vibrating and having to hold the throttle lever in its position.) 

• After the measurements, the engine power is reduced to the recommended Taxi/Idle setting 

for cooling down. 

• The measurement for climb out mode is prepared and if necessary, measurement equipment 

is checked again for calibration and zero points. 

• The pilot is then asked to set the throttle to reach the climb out fuel flow value, calculated as 

described above. As soon as the fuel flow reading is reported to be stable and measured concentrations are stable, the next data recording begins. The pilot should note at least fuel flow, 

RPM and engine temperatures during the measurements, as above. 

• After measurement, the engine power is again reduced to the recommended Taxi/Idle setting 

for cooling down. 

• This procedure is repeated down to taxi mode. 

Cruise mode: 

• As described in the example above, the measurement of the cruise mode is special, if the 

engine is equipped with a manual mixture adjustment. The pilot is asked to set the throttle 

to reach the cruise fuel flow value at mixture “full rich”, calculated as described above. As 

soon as the fuel flow reading is reported to be stable, the mixture is slowly leaned to lambda = 

0.93. The corrections (“a bit richer, a bit leaner”) are transmitted from the measurement team 

to the pilot. The pilot has to make sure that RPM remain constant. If not, a throttle adjustment 

is necessary, followed by a mixture adjustment. At stable conditions, the data recording begins. The pilot should again note at least fuel flow, RPM and engine temperatures after stable 

conditions have been established, as mentioned above. The adjustment of static cruise power 

can take more than one minute and therefore it is vital to observe engine temperatures carefully. Engine cylinder head temperatures are rising and there is less engine cooling, because 

the aircraft is not moving forward. 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

6.4 Combined MAP & fuel flow method 

More complex aircraft, especially those fitted with a variable pitch propeller or even constant 

speed propeller need a MAP gauge, which is generally a reasonable power indicator (see section 

3). Engine parameter comparison of in-flight and ground measurements showed a potential for 

improvements by use of MAP. This method is referred as “V5” in FOCA piston engine emissions data sheets. 

6.4.1 Preparations 

From Airplane Operations Manual (AFM), typical MAP values for climb and cruise mode are recorded. We suggest a reference pressure altitude of sea level for climb mode and 5000ft for cruise 

mode. 

Normally, no MAP values are given in the AFM for approach mode. From in-flight test we recommend a pre-selected mean value of 18 InHg and minimum 44% of maximum fuel flow at 

mixture “full rich” (Appendix 2). 

The MAP values are input to the measurements, as shown with the orange fields in figure 19. 

For take-off mode, no pre-selected MAP value is necessary. However, at full power with a normally aspirated engine, the value is an indication for ambient air pressure. Near sea level it can 

read around 29 InHg (Because of some inefficiencies in the engine induction system it does not 

fully reach the value of ambient air pressure with the engine running at full power). However, it is 

possible to get nearly 100% of rated maximum propeller horsepower at 27 InHg too, if the air is 

cold and therefore dense enough. That is one reason, why we recommend doing the measurements at low altitude airports and cold ambient temperatures (low density altitudes). With the variable pitch propeller, a pre-selected RPM value, normally the maximum allowed RPM for take-off, 

is necessary. This is indicated in the dark blue fields in figure 19. For all static ground measurements we recommend to leave propeller pitch at “high RPM”. 

Taxi mode power is selected by RPM, according to AFM, as with the simple fuel flow method. 

RPM input is indicated in light blue in figure 19. MAP and fuel flow for taxi mode will result from 

measurements. 

US gal/h US gal/h or l/h 1/min. 1/min.

Max. FF R (AFM/Test) RPM TA RPM TO (AFM)

In HG ft In HG ft

MAP 65%CR (AFM) MAP 85% CL (AFM)

In HG ft In HG ft

MAP AP (Test) MAP TA (Test)

Meas. Nr. Mode/Mixt. MAP FF FF/ MFF (%) FF Check MAP RPM input RPM λ input λ

1 TO F.T. min. 95

2 TO F.T. min. 95

3 TO F.T. min. 95

4 CL 0.0 min.77

5 CL 0.0 min.77

6 CL 0.0 min.77

7 CR R 0.0 min. 51

8 CR R 0.0 min. 51

9 CR R 0.0 min. 51

10 CR L 0.0 min. 45 0.93

11 CR L 0.0 min. 45 0.93

12 CR L 0.0 min. 45 0.93

13 AP 0.0 min. 44

14 AP 0.0 min. 44

15 AP 0.0 min. 44

16 TA 0.0 min. 09

17 TA 0.0 min. 09

18 TA 0.0 min. 09

Figure 19: Engine data input and recording sheet used by FOCA. All entries from measurements 

go into the yellow coloured fields, brown fields are MAP predefined values, red fields the calculated relations of measured fuel flow to maximum fuel flow and green fields contain minimum percentage of maximum fuel flow that should be achieved in the power setting (fuel flow check). 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

6.4.2 Recommended procedure 

• We recommend going from high power to low power measurements with at least three measurements per power mode 

• There should be a VHF radio communication between the pilot and the measurement team. 

• All measurements should be done with propeller pitch “high RPM”. 

• The first measurement would be again the maximum fuel flow (max. power) measurement. At 

this occasion, the repetition of maximum fuel flow is a check for the first maximum fuel flow 

measurement. 

• As soon as measured concentrations are stable, data are recorded. The pilot should note at 

least fuel flow, RPM and engine temperatures during the measurements. (This can be a demanding task, with the airframe vibrating and having to hold the throttle lever in its position.) 

• After the measurements, the engine power is reduced to the recommended Taxi/Idle setting 

for cooling down. 

• The measurement for climb out mode is prepared and if necessary, measurement equipment 

is checked again for calibration and zero points. 

• The pilot is then asked to set the throttle to reach the climb out MAP value. As soon as the 

MAP reading is reported to be stable and measured concentrations are stable, the next data 

recording begins. The pilot should note at least fuel flow, RPM and engine temperatures during the measurements, as above. The fuel flow is transmitted to the measurement team and it 

is checked that the value fulfills the minimum requirement (E.g. minimum 77% of the maximum fuel flow for climb, see figure 17, green column). If the minimum fuel flow is not reached, 

throttle should be increased accordingly. 

• After measurement, the engine power is again reduced to the recommended Taxi/Idle setting 

for cooling down. 

• This procedure is repeated down to taxi mode. 

Cruise mode: 

• As described in the simple fuel flow method, the measurement of cruise mode following the 

climb mode is special, if the engine is equipped with a manual mixture adjustment. The 

pilot is asked to set the throttle to reach the cruise MAP value at mixture “full rich”. As soon as 

the MAP, RPM and fuel flow reading are reported to be stable, the mixture is slowly leaned to 

lambda = 0.93. The corrections (“a bit richer, a bit leaner”) are transmitted from the measurement team to the pilot. The pilot has to make sure that RPM remain constant. If not, a throttle 

adjustment is necessary, followed by a mixture adjustment. At stable conditions, the data recording begins. The pilot should again note at least fuel flow, RPM and engine temperatures 

after stable conditions have been established, as mentioned above. Again, the adjustment of 

static cruise power can take more than one minute and therefore it is vital to observe engine 

temperatures carefully. Engine cylinder head temperatures are usually rising and there is less 

engine cooling, because the aircraft is not moving forward. 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

7. Example for measurement documentation 

FOCA Groundmeasurement VERSION I.V5 Injected Eng./CS Prop. Meas. Nr. 78 A/C Reg. HB NCO

Aircraft Commander 114 Full Cycle

Engine Lyc IO-540-T4A5D Engine Hours 1817

Crew

Prop HC-C2YR-1 Fuel Injector standard PIC G. Staude

Expert rit

Silencer standard Rated P. (HP) 260 Warm up

Block Time Flight Time

Fuel AVGAS 100LL 13:20

14:05

Equipment Stargas 898, Mexa-1150 HFID Check Oil Temp.> 60°C

Day 13. Dez 06 Wind (° / kn) calm Dewpoint (°C) NIL Airport (ft) 1575

PA 1071

Begin LT 14.57 Uhr Air T (°C) 3 QNH (hPa) 1031 DA 9

US gal/h US gal/h or l/h 1/min. 1/min.

Max. FF R 85 (AFM/Test) RPM TA 1000 2700 RPM TO (AFM)

In HG ft In HG ft

MP 65% CR 22.5 SL (AFM) MP 85% CL 25 SL (AFM)

In HG ft In HG ft

MP AP 17.9 SL (Test) MP TA 11.8 (Test)

Meas. Nr. Mode/Mixt. % Power FF FF/ MFF (%) FF Check MP RPM input RPM λ input λ

1 TO F.T. 84 99 min. 95 27.2 2700 2620 0.749

2 TO F.T. 83 98 min. 95 27.2 2700 2620 0.749

3 TO F.T. 83 98 min. 95 27.2 2700 2620 0.749

4 CL 25.0 74 87 min.77 25 2590 0.76

5 CL 25.0 74 87 min.77 25 2590 0.759

6 CL 25.0 74 87 min.77 25 2590 0.757

7 CR R 22.5 61 72 min. 51 22.5 2480 0.773

8 CR R 22.5 61 72 min. 51 22.5 2480 0.773

9 CR R 22.5 61 72 min. 51 22.5 2480 0.771

10 CR L 22.5 49 58 min. 45 22.5 2350 0.93 0.947

11 CR L 22.5 49 58 min. 45 22.5 2350 0.93 0.95

12 CR L 22.5 49 58 min. 45 22.5 2350 0.93 0.943

13 AP 17.9 37 44 min. 44 18 2120 0.809

14 AP 17.9 37 44 min. 44 18 2120 0.811

15 AP 17.9 37 44 min. 44 18 2120 0.812

16 TA 11.8 12 14 min. 09 11.8 1000 1000 0.8

17 TA 11.8 12 14 min. 09 11.8 1000 990 0.794

18 TA 11.8 13 15 min. 09 11.8 1000 980 0.781

Figure 20: Practical example of the engine data input file for a Lyc IO-540 measurement (Aircraft HB-NCO). The 

file contains relevant aircraft and engine data, ambient conditions and (in this case) predefined MAP values from 

AFM, measured fuel flow, MAP, RPM and lambda (compare to figure 19). 

Stargas NDI Horiba FID

Meas. Nr. Mode/Mixture FF CO (Vol. %) CO2 (Vol. %) HC (ppm) HC (ppmC) O2 (Vol. %) NO (ppm) Lambda Airpr. (hPa) Humidity Air T (°C)

1 TO 84 9.027 8.68 170 2300 0.16 198 0.749 964 3

2 TO 83 8.954 8.79 136 2000 0.09 165 0.749 964 3

3 TO 83 8.994 8.79 136 2200 0.09 127 0.749 964 3

4 CL 74 8.528 8.85 164 2200 0.17 226 0.76 964 3

5 CL 74 8.522 8.92 145 2100 0.11 180 0.759 964 3

6 CL 74 8.571 8.85 137 2100 0.1 137 0.757 964 3

7 CR R 61 7.877 8.97 149 2400 0.15 251 0.773 964 3

8 CR R 61 7.877 8.97 149 2100 0.15 251 0.773 964 3

9 CR R 61 7.96 9.07 135 2100 0.1 216 0.771 964 3

10 CR L 49 2.058 12.63 64 1400 0.25 2191 0.947 964 3

11 CR L 49 1.945 12.64 57 1400 0.24 2296 0.95 964 3

12 CR L 49 2.116 12.61 62 1300 0.2 2066 0.943 964 3

13 AP 37 6.782 9.49 155 2500 0.35 364 0.809 964 3

14 AP 37 6.664 9.61 136 2200 0.3 389 0.811 964 3

15 AP 37 6.649 9.59 130 2300 0.31 389 0.812 964 3

16 TA 12 8.173 7.89 744 6400 1.77 42 0.8 964 3

17 TA 12 8.389 7.8 655 6600 1.7 39 0.794 964 3

18 TA 13 8.547 7.86 538 7000 1.34 40 0.781 964 3

Figure 21: Measured exhaust concentrations (Measurement HB-NCO). Data entries are checked for plausibility and variation (First measurement quality check). 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

NDIR FID

Meas Nr. EI CO [g/kg] EI HC [g/kg] EI HC [g/kg] EI NOx [g/kg] LTO

1 1015.51348 18.0651925 14.8165072 3.041351843 TO

2 1006.90822 14.4248084 12.8788933 2.53347117 TO

3 1008.03576 14.3923887 14.1195705 1.94350651 TO

4 977.859871 17.7578546 14.4453432 3.538319905 CL

5 974.182434 15.6446866 13.746553 2.809509427 CL

6 980.950534 14.8000098 13.7629223 2.140895179 CL

7 930.226235 16.6431938 16.2298584 4.047256074 CR R

8 931.862325 16.6431938 14.2261031 4.054374423 CR R

9 931.68529 14.9187271 14.0750912 3.451986958 CR R

10 280.070402 8.20343786 10.9100221 40.71209449 CR L

11 266.544 7.35811704 10.9863414 42.96159664 CR L

12 287.420635 7.92668518 10.111635 38.31702853 CR L

13 828.306316 17.9240617 17.4843281 6.070071338 AP

14 815.276508 15.7268266 15.4123325 6.497985909 AP

15 814.676326 15.0659279 16.1373549 6.50785081 AP

16 987.375305 86.835632 44.2747876 0.692802229 TA

17 1004.68735 75.897227 45.2626966 0.637741339 TA

18 1008.17031 61.5586021 47.281799 0.644227734 TA

Figure 22: Calculated emission factors (according Appendix 5) 

Figures 23 and 24: Visualization of CO and HC emission factors for the measured engine modes. 

CO Emission Factors 

0

200

400

600

800

1000

1200

Mode

Mass (g/kg Fuel)

CO 1016 1007 1008 977.9 974.2 981 930.2 931.9 931.7 280.1 266.5 287.4 828.3 815.3 814.7 987.4 1005 1008

TO TO TO CL CL CL CR R CR R CR R CR L CR L CR L AP AP AP TA TA TA

HC Emission Factors 

0

10

20

30

40

50

60

Mode

Mass (g/kg Fuel)

HC NDIR 18.07 14.42 14.39 17.76 15.64 14.8 16.64 16.64 14.92 8.203 7.358 7.927 17.92 15.73 15.07 86.84 75.9 61.56

HC FID 14.82 12.88 14.12 14.45 13.75 13.76 16.23 14.23 14.08 10.91 10.99 10.11 17.48 15.41 16.14 44.27 45.26 47.28

TO TO TO CL CL CL CR R CR R CR R CR L CR L CR L AP AP AP TA TA TA
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Figure 25: Visualization of NOx emission factors for the measured engine modes. Visualization is used for a second measurement quality check. 

Figures 26 and 27: Visualization of measured fuel flow and RPM. During subsequent measurements of one particular power mode, fuel flow and RPM should be maintained constant. 

NOx Emission Factors 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel)

NOx 3.0414 2.5335 1.9435 3.5383 2.8095 2.1409 4.0473 4.0544 3.452 40.712 42.962 38.317 6.0701 6.498 6.5079 0.6928 0.6377 0.6442

TO TO TO CL CL CL CR R CR R CR R CR L CR L CR L AP AP AP TA TA TA

Fuel Flow 

0

10

20

30

40

50

60

70

80

90

Mode

Fuel Flow (l/h)

Fuel 84 83 83 74 74 74 61 61 61 49 49 49 37 37 37 12 12 13

TO TO TO CL CL CL CR R CR R CR R CR L CR L CR L AP AP AP TA TA TA

RPM 

0

500

1000

1500

2000

2500

3000

Mode

RPM (1/Min.)

RPM 2620 2620 2620 2590 2590 2590 2480 2480 2480 2350 2350 2350 2120 2120 2120 1000 990 980

TO TO TO CL CL CL CR R CR R CR R CR L CR L CR L AP AP AP TA TA TA
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Figures 28 and 29: Visualization of measured MAP and lambda. During subsequent measurements of one particular power mode, MAP should be maintained constant and lambda should result in practically constant values. 

(Third check for measurement quality). For engines with manual air/fuel mixture adjustment, like the engine 

measured in this example, the CR L (cruise leaned) lambda value should be kept constant as well, with a value 

around 0.93, as described in 6.3.1, 6.3.2 and 6.4.2. In this example, the CR L lambda values vary between 0.943 

and 0.95. 

Statistical Basis for Calculation

Number of Measurements

per powersetting

3

Factor for 90% Confidence Level 

(T-Test, Assumption: Normal Distribution)

2.92

Figure 30: Before computing mean values per power mode, the statistical functions for determining a 90% confidence interval are defined. For this very small sample of only three measurements per power mode, a T-test is 

suggested. 

Manifold Pressure 

0

5

10

15

20

25

30

Mode

Manifold Pressure (in Hg)

Man. Pr. 27.2 27.2 27.2 25 25 25 22.5 22.5 22.5 22.5 22.5 22.5 18 18 18 11.8 11.8 11.8

TO TO TO CL CL CL CR R CR R CR R CR L CR L CR L AP AP AP TA TA TA

Lambda 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Mode

Lambda

Lambda 0.749 0.749 0.749 0.76 0.759 0.757 0.773 0.773 0.771 0.947 0.95 0.943 0.809 0.811 0.812 0.8 0.794 0.781

TO TO TO CL CL CL CR R CR R CR R CR L CR L CR L AP AP AP TA TA TA
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

TO Emp. Mean Emp. St.Dev. Mean stat. Error 90% CI Fuel Flow (kg/s)

EI CO [g/kg] 1010.15 4.68 2.70 4.47 0.0167

EI HC [g/kg] 13.94 0.98 0.57 2.05

EI NOx [g/kg] 2.51 0.55 0.32 1.53

CL Emp. Mean Emp. St.Dev. Mean stat. Error 90% CI Fuel Flow (kg/s)

EI CO [g/kg] 977.66 3.39 1.96 3.80 0.0148

EI HC [g/kg] 13.98 0.40 0.23 1.30

EI NOx [g/kg] 2.83 0.70 0.40 1.73

CR Emp. Mean Emp. St.Dev. Mean stat. Error 90% CI Fuel Flow (kg/s)

EI CO [g/kg] 931.26 0.90 0.52 1.96 0.0122

EI HC [g/kg] 14.84 1.20 0.69 2.26

EI NOx [g/kg] 3.85 0.35 0.20 1.21

AP Emp. Mean Emp. St.Dev. Mean stat. Error 90% CI Fuel Flow (kg/s)

EI CO [g/kg] 819.42 7.70 4.45 5.73 0.0074

EI HC [g/kg] 16.34 1.05 0.61 2.12

EI NOx [g/kg] 6.36 0.25 0.14 1.03

TA Emp. Mean Emp. St.Dev. Mean stat. Error 90% CI Fuel Flow (kg/s)

EI CO [g/kg] 1000.08 11.14 6.43 6.89 0.0025

EI HC [g/kg] 45.61 1.53 0.88 2.56

EI NOx [g/kg] 0.66 0.03 0.02 0.36

CR L Emp. Mean Emp. St.Dev. Mean stat. Error 90% CI Fuel Flow (kg/s)

EI CO [g/kg] 278.01 10.59 6.11 6.72 0.0098

EI HC [g/kg] 10.67 0.48 0.28 1.44

EI NOx [g/kg] 40.66 2.32 1.34 3.15

Figure 31: Calculation of empirical mean, empirical standard deviation, mean statistical error and 90% confidence 

interval based on T-test. Mean HC emission factors are only based on the FID values. The fuel flow in kg/s is 

calculated from fuel flow in litres/hour by using a fuel density of 0.72 kg/litre, if actual density at 15°C is not known. 

Carbonmonoxide CO

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

TO CL CR AP TA CR L

Mode

EF [g/kg Fuel]

Figure 32: Visualization of mean statistical error and 90% confidence interval (two bars with emission factor value 

for each power mode) for EF CO. 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Hydrocarbons HC

0.00

10.00

20.00

30.00

40.00

50.00

60.00

TO CL CR AP TA CR L

Mode

EF [g/kg Fuel]

Figure 33: Visualization of mean statistical error and 90% confidence interval (two bars with emission factor value 

for each power mode) for EF HC (based on FID). 

Nitrous Oxydes NOx

0.00

10.00

20.00

30.00

40.00

50.00

TO CL CR AP TA CR L

Mode

EF [g/kg Fuel]

Figure 34: Visualization of mean statistical error and 90% confidence interval (two bars with emission factor value 

for each power mode) for EF NOx. Please note the limitations for NOx measurements with the FOCA low-cost 

measurement system, as described in Appendix 1 and 5. Systematic errors are not included in this statistical 

analysis. 

Picture 6: Documentation of the fuel flow transducer installation (in the middle of the picture). The orange wire 

leaving to the left is carrying the pulses from the transducer to the fuel flow indicator in the cockpit. This installation is NOT certified for in-flight operation. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Federal Office of Civil Aviation, Environmental Affairs

ENGINE EXHAUST EMISSIONS MEASUREMENT

PISTON ENGINES

ENGINE IDENT Lyc IO-540-T4A5D INJECTOR standard

UNIQUE ID NUMBER PF12 INJECTION NOZZLE -

ENGINE TYPE 6Cyl. 4Stroke RATED POWER (Poo) (HP) 260

Air cooled

PROPELLER TYPE HC-C2YR-1

DATA STATUS TEST ENGINE STATUS

x EMISSION INVENTORY NEWLY MANUFACTURED ENG.

PRE-REGULATION x USED ENGINE

CERTIFICATION DEDICATED TO PRODUCTION 

REVISED OTHER (SEE REMARKS)

MEASUREMET STATUS CURRENT ENGINE STATUS

GROUND BASED FIXED PITCH PROP x IN PRODUCTION

x GROUND BASED VARIABLE PITCH PROP OUT OF PRODUCTION

OUT OF SERVICE

EMISSIONS STATUS

DATA CORRECTED TO REFERENCE TEMPERATURE

DATA CORRECTED TO REFERENCE (ANNEX 16 VOLUME II)

IV5 CALCULATION METHODOLOGY VERSION NUMBER

MEASURED DATA

MODE

POWER

SETTING (%)

TIME

(minutes)

FUEL FLOW

(kg/s) EI HC (g/kg) EI CO (g/kg) EI NOx (g/kg)

PM

(...) (...)

TAKE-OFF 100 0.3 0.0167 13.9 1010 3

CLIMB OUT 85 2.5 0.0148 14.0 978 3

CRUISE 65 60 0.0122 14.8 931 4

APPROACH 45 3 0.0074 16.3 819 6

TAXI 12 12 0.0025 45.6 1000 1

CRUISE LEAN 65 60 0.0098 10.7 278 41

LTO TOTAL FUEL (kg) or EMISSIONS (g) 5.63 138 5341 17

CRUISE 1HOUR FUEL (kg) or EMISSIONS (g) 35.3 376 9808 1435

NUMBER OF TESTED ENGINES 1111

NUMBER OF TESTS 3333

ATMOSPHERIC CONDITIONS FUEL

BAROMETER QNH (hPa) 1031 SPEC AVGAS 100LL

TEMPERATURE (°C)) 3 HC C7H13

DEW POINT (°C) -

DENSITY ALTITUDE (ft) 9

MANUFACTURER: REFERENCE:

TEST ORGANIZATION: FOCA 33-05-003.001 groundmeasurement78.injected.

TEST LOCATION: LSPL constantspeed.IV5.1.HBNCO_061213_rit

TEST DATES: 13. Dez 06 Expert: T. Rindlisbacher

REMARKS:

 Figure 35: Final data sheet for Lyc IO-540-T4A5D as provided by FOCA for download. 
33-05-003 Piston Engine Emissions_Swiss FOCA_Appendix4_070605_rit 

Federal Department of the Environment, Transport, Energy and 

Communications DETEC 

Federal Office of Civil Aviation FOCA 

Aviation Policy and Strategy 

Environmental Affairs 

AIRCRAFT PISTON ENGINE EMISSIONS 

Appendix 4: Nanoparticle Measurements and 

Research for Cleaner AVGAS 

 

Picture 1: Nanoparticle measurements of two different aircraft piston engines fuelled with leaded and 

unleaded aviation gasoline. (Oberpfaffenhofen Airport (EDMO), Germany) 

FOCA, CH-3003 Bern

Reference: 0 / 3/33/33-05-003 ECERT 

Contact person: Theo Rindlisbacher 

Tel. +41 31 325 93 76, Fax +41 31 325 92 12, theo.rindlisbacher@bazl.admin.ch

This document has been released for publication by FOCA, Aviation Policy and Strategy, Director M. Zuckschwerdt, 11.06.2007 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Contents 

 Page 

1. Background, motivation and project partners 3 

1.1 Research programme 3 

1.2 Research goals 3 

2. General results for nanoparticle emissions of an aircraft gasoline engine, running 3 

under rich air/fuel conditions (AVGAS 100 LL) 

2.1 Preparations 3 

2.2 SMPSTM system layout and description for particle measurements 4 

2.3 Results 6 

2.4 Picture documentation of first non-volatile nanoparticle measurements 9 

3. Looking for particle emission improvements: First tests with unleaded 11 

AVGAS (AVGAS 91/96 UL) 

3. 1 Introduction and description of AVGAS 91/96 UL 11 

3.2 Composition of measured AVGAS 100LL (560 mg Pb / liter) 11 

3.3 Used aircraft 12 

3.4 Results for HB-EYS 12 

3.5 Conclusion for HB-EYS tests 13 

3.6 Results for SE-KEI 13 

3.7 Air/fuel mixture ratio for HB-EYS and SE-KEI 14 

3.8 Discussion 15 

3.9 Conclusions for AVGAS 91/96 UL 15 

4. Change from SMPSTM to Engine Exhaust Particle SizerTM (EEPS 3090TM) system for 15 

aircraft piston engine nanoparticle measurements 

4.1 Introduction 15 

4.2 EEPSTM system description 15 

4.3 Application of EEPSTM for aircraft piston engine measurements 16 

4.4 EEPSTM results 18 

4.5 First conclusions for EEPSTM measurements 19 

5. Research for AVGAS 100LL substitution and emission reduction 19 

5.1 Test fuels 20 

5.2 Test location 20 

5.3 Used aircraft 20 

5.4 Measurement systems 20 

5.5. Power settings 21 

5.6 Results 22 

5.7 Discussion 31 

5.8 First conclusions 32 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

1. Background, motivation and project partners 

The results for most in-flight tests documented in Appendix 2 showed engine operation at extremely 

rich air/fuel ratios. It is known that fuel rich conditions can form soot nanoparticles even in gasoline 

engines. Given the fact that standard aviation gasoline is still leaded today, there was even more evidence for possible nanoparticle emissions. 

Through the European AERONET network, Swiss FOCA started collaboration with the Institute of 

Combustion Technology of the German Aerospace Centre (DLR) in Stuttgart (Germany), recognizing 

their vast experience in nanoparticle measurement techniques and their high reputation in research of 

aero engine combustion processes. DLR Oberpfaffenhofen (Germany) provided the necessary infrastructure for the aircraft on ground measurements at Oberpfaffenhofen Airport (Germany). 

At the same time and through AERONET as well, Swiss FOCA got to know Swedish HjelmcoTM Company, the only producer of lead free AVGAS worldwide, which is meeting ASTM D910 AVGAS specifications. The company can in 2007 claim more than 26 years of lead free AVGAS flying experience in 

Sweden. 

At a later step, collaboration started with German TSITM. The company provided their fast response 

engine exhaust particle sizer (EEPSTM) for in-field testing. 

Research for cleaner, lead free AVGAS was done in Switzerland, at St. Stephan Airport (LSTS) in the 

Swiss Alps. The airport is a former military airport, privately owned and belongs to the company “prospective concepts”, which generously provided their infrastructure. 

1.1 Research programme: 

Step 1: Nanoparticle measurements of a gasoline piston aircraft engine running under rich air/fuel 

conditions, using standard leaded AVGAS (AVGAS 100LL) 

Step 2: Nanoparticle measurements of gasoline piston aircraft engines running under rich air/fuel conditions, using AVGAS 100LL (leaded) and the Swedish AVGAS 91/96 UL (unleaded). 

Step 3: Optimization of AVGAS 91/96 UL for higher knocking margin and lowest possible emissions. 

Use of three aircraft (three different engines) and ten different fuels. 

1.2 Research goals: 

1) Development and testing of a ground and in-field nanoparticle measurement methodology and 

measurement system. 

2) Determination of nanoparticle emissions from aircraft piston engines. 

3) Investigating possible emission improvements by use of unleaded AVGAS. 

4) Use of knowledge for support, development and application of nanoparticle measurements also for 

jet engines. This goal is connected with international activities in ICAO CAEP1

 of Swiss FOCA. 

2. General results for nanoparticle emissions of an aircraft gasoline engine, 

running under rich air/fuel conditions (AVGAS 100 LL) 

2.1 Preparations 

Step one of the research program started in April 2004. Measurements took place in Oberpfaffenhofen 

EDMO (Germany). The test aircraft was HB-KEZ whose engine (Lyc IO-360 series) had shown very 

rich combustion at mixture “full rich” conditions (see Appendix 2, section 4d). 

 

1

 Commitee on Aviation Environmental Protection of the International Civil Aviation Organization, defining standards and recommended practices also for environmental aircraft/engine certification. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Gaseous emissions of HB-KEZ were measured with the FOCA “low cost” system as described in Appendix 1. The methodology, which was used for the ground power settings, is described in Appendix 

3, section 6.4. 

Table 1: Measured CO and CO2 concentrations of HBKEZ on 13th April 2004 for different standard power settings, as described in Appendix 3, section 6.4. (TO = take-off, CL = climb, CR = cruise (rich), AP = approach, TA = 

taxi, CR L= cruise lean). Running on very rich air/fuel ratio is represented by extremely high CO concentrations 

and low CO2 concentrations. The measurement numbers were assigned for the particle measurements 

Meas. Nr. LTO CO (Vol. %) CO2 (Vol. %)

- TO 12.506 6.99

6 CL 12.654 6.84

9 CR 12.674 6.82

12,11 AP 13.665 6.23

13,15 TA 10.536 8.06

18 CR L 1.42 13.63

2.2 SMPSTM system layout and description for particle measurements 

Non-volatile nanoparticles are extremely small particles in the range of 10 to 500 nanometers (one 

hundred thousandth of a millimeter). There is growing concern about negative health effects from such 

particles. They are formed as a result of incomplete combustion. Some of them are potentially toxic 

and the small size allows them to easily enter the human body deep into the lungs and to penetrate 

even into nerve cells and the brain. Measurement systems (including sampling processes) need to be 

sophisticated. General metrics are the size and number distribution (concentration). 

The first measurements were performed with a SMPSTM (Scanning Mobility Particle Sizer) System TSI 

3080TM. Such a system classifies the particles first by their size. The classification is done with electrostatic forces in a so called DMA (Differential Mobility Analyzer). When a certain size class is “filtered”, the number per volume (controlled by sample flow and known dilution) is counted in a CPC 

(Condensation Particle Counter) (figure 1). The scanning and counting through the size range of 10 to 

500 nm usually can take several minutes. This is the measurement time per power mode. 

Figure 1: System layout for nanoparticle measurements with an electrostatic classifier and CPC. Explanations are given in the text. [TSITM] 

Diluter 

CPC 

Pure Nitrogen 

Exhaust Probe 

Heated Line 

Diluter 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Figure 2: Scheme of a CPC (Condensation Particle Counter) used for counting the number of particles 

of a certain class of size (Example: TSITM Model 3775). [TSITM] 

Picture 2: Stainless steel exhaust probe and heated sampling line (150°C). Total length 4.5 meters. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

For best measurement results, the sampling line has to be as straight and as short as possible. The 

DLR sampling line measures 4.5 meters only. The material has to be stainless steel, heated to 150°C. 

Other materials like TeflonTM would absorb fractions of the particles. The exhaust is diluted by a 

heated DekatiTM diluter 1:10. Dilution air is nitrogen with a minimum quality of 4.5. For calibrating sampling line losses, DLR/Wahl has developed and patented a nanoparticle generator, which produces 

particles at defined and adjustable sizes. Calibration of sampling lines for size dependent losses has 

been carried out. However, absent such calibration in the international measurement community for 

the time being, it has not been applied to the measurements, for reasons of comparison with other 

engine types and engine technology. 

2.3 Results 

Figure 3 shows a typical example of a particle size distribution from an aircraft gasoline piston engine, 

running on AVGAS 100LL (leaded fuel) under rich air/fuel ratio. For the different power modes, •

 the mean diameter varied between 49 and 108 nm and •

 the total concentration between 5.7 to 8.6 times 10 million particles per cubic centimeter.

With an assumed specific density for soot of 1.2, •

 the estimated mass concentration was around 10 000 micro grams per cubic meter. 

(see picture 3) 

The result for this gasoline engine is very comparable to the number-size distribution of a typical 

diesel passenger car engine without particle filter (see figure 4)!

 

Figure 3: Number-size distribution of HB-KEZ engine at approach mode. The mean particle diameter 

is around 100 nm and the total concentration is in the order of 10 million particles per cubic centimeter.

 

Figure 4: Number-size distribution of a typical diesel passenger car (CDI) at 2000 RPM (increased 

idle) for comparison to the HB-KEZ measurements [C. Wahl/M. Kapernaum/DLR 2004l] 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

At lower power settings, exhaust has been pumped through sample cartridges at controlled flow rate 

for later HC speciation with HPLC (High Performance Liquid Chromatography). Pumping time usually 

was 2 minutes. Figure 5 shows the result for the measurement of Carbonyls at approach mode. The 

speciation was obtained by analysis of the filter material with a gas chromatograph and mass spectrometer. Surprising was the amount of produced formaldehyd (see figure 6). 

Figure 5: Detected carbonyls at approach mode. [C. Wahl/M. Kapernaum/DLR 2004] 

 

Figure 6: Summary of carbonyl measurements at climb mode (nr. 6), approach mode (nr. 12) and taxi 

mode (nr. 15). [C. Wahl/M. Kapernaum/DLR 2004] 

Formaldehyde is dominating carbonyl emissions of the tested engine, running on AVGAS 100LL at 

standard very rich air/fuel mixture. 

Blindwert

ppb mg/kg Fuel ppb mg/kg Fuel ppb mg/kg Fuel ppb

Formaldehyd 8337,48 92,49 6346,26 68,98 5867,59 68,24 21,29

Acetaldehyd 999,68 16,27 744,04 11,87 848,79 14,48 7,08

Propanal 639,90 13,73 532,20 11,19 707,13 15,91 0

Aceton 98,92 2,12 95,11 2,00 95,59 2,15 10,26

1-Buten-3-on 831,43 21,53 781,08 19,82 862,45 23,41 0

Methacrolein 213,53 5,53 184,10 4,67 198,74 5,40 0

Butanal 87,75 2,34 0 0 0 0 0

Benzaldehyd 347,12 13,61 297,51 11,43 333,92 13,72 0

o-Toluolaldehyd 162,52 7,21 141,79 6,17 136,54 6,35 0

m-Toluolaldehyd 294,13 13,06 260,23 11,32 281,54 13,10 0

p-Toluolaldehyd 79,40 3,52 80,54 3,50 71,96 3,75 0

Summe 12091,88 191,42 9462,85 150,95 9404,27 166,51 38,63

 Nr. 6 Nr. 12 Nr. 15

0 10 20 30 40 50 60 70

0

50

100

150

200

250

300

350

1,3-Dinitrobenzene

DNPH

HPLC-chromatogram carbonylcompounds sample No. 12 o-,m-,p-Toluenealdehyde Acetone 1-Buten-3-one Methacrolein Benzaldehyde Propionaldehyde Acetaldehyde Formaldehyde Acetyl-DNPH

Absorption (365 nm)

t [min]
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Picture 3: Poster presented at the 8th International ETH-Conference on Combustion Generated Particles, 16th – 18th August 2004, Zurich, Switzerland [C. Wahl/M. Kapernaum/DLR] 
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2.4 Picture documentation of first non-volatile nanoparticle measurements 

Picture 4: “In-field laboratory” at Oberpfaffenhofen Airport (EDMO) and candidate aircraft HB-KEZ. 

Picture 5: SMPS (on the left) with DMA (the vertical tube). The CPC is installed behind the Laptop. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Picture 6: This picture was taken during approach mode measurement. The SMPS is placed in the 

back compartment of the car (as shown in picture 5) and is brought as nearly as possible to the aircraft, for shortest possible sampling line and lowest possible particle losses. 

Picture 7: Measurement team which performed – to our knowledge – the first successful measurement 

of non-volatile nanoparticles of an aircraft gasoline piston engine. From left to right: Manfred Kapernaum, Claus Wahl (both DLR Stuttgart), Werner Bula, Theo Rindlisbacher (both FOCA) 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

3. Looking for particle emission improvements: First tests with unleaded 

AVGAS (AVGAS 91/96 UL) 

3. 1 Introduction and description of AVGAS 91/96 UL 

Through AERONET network, FOCA came into contact with Lars Hjelmberg from Swedish HjelmcoTM 

Oil company, which in 2007 is producing unleaded AVGAS since more than 26 years. Unleaded AVGAS has become a standard fuel in Sweden. Because it meets the AVGAS standard ASTM D910, no

Supplemental Type Certificate (STC) for the aircraft is needed to use that fuel. It is important to notice, 

that the AVGAS specifications do not prescribe any minimum lead content. The only limitation for the 

use of the Swedish fuel comes from the lower aviation octane rating compared to the leaded AVGAS 

100LL. The engine manufacturer Textron Lycoming has included AVGAS 91/96UL, which is Hjelmco,s 

second generation of unleaded AVGAS, as an approved alternate aviation gasoline for a large number 

of their engines already in the year 1995. The engines with type numbers are listed in service instruction No. SI 1070. Generally speaking, only highest pressure ratio engines, especially turbocharged 

gasoline piston engines, can not use AVGAS 91/96 UL in their standard configuration. 

Swiss FOCA had AVGAS 91/96 UL analyzed and some interesting properties were found: 

- The fuel is composed of a surprisingly low number of components compared to 100LL 

- The components are extremely pure 

- There is no benzene, no sulphur 

- There is no dye (the fuel is clear like water) 

- The fuel meets AVGAS specification ASTM D910 

A hypothesis was set up, that the use of AVGAS 91/96 UL instead of AVGAS 100LL could significantly reduce particle emissions, both in terms of mass and in terms of number. 

To test the hypothesis, two aircraft whose engines are in the manufacturers list for running on 

unleaded AVGAS 91/96 UL, were selected. Both engines were run on AVGAS 100LL ( max lead content 560 mg / liter) and on unleaded 91/96 UL. DLR used the SMPS (as described in section 2), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) for particle properties 

investigation. Additionally, DLR performed aldehyde tests (DNPH method). Engine power for selected 

power modes (Take-off, Climb, Cruise, Approach and Taxi) was adjusted according to the FOCA 

methodology for static on-ground tests, as described in Appendix 3, sections 6.2 and 6.3. 

3.2 Composition of measured AVGAS 100LL (max 560 mg Pb / liter) 

Figure 7: Composition of measured AVGAS 100LL [C. Wahl/M. Kapernaum/DLR] 
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3.3 Used aircraft 

HB-EYS Type: Robin DR400 SE-KEI Type: Piper PA28 Warrior II 

 Owner: Swiss Confederation Owner: Hjelmco Oil, Sweden 

 Engine: Lyc O-360 series, 180 HP Engine: Lyc O-320 series, 160 HP 

 Carburetor Carburetor 

 

 

3.4 Results for HB-EYS 

Figure 8: Non-volatile particle number concentrations for AVGAS 100LL and 91/96 UL in function of 

propeller power (HB-EYS). [C. Wahl/M. Kapernaum/DLR] 

Figure 9: Total non-volatile particle mass concentration for AVGAS 100LL and 91/96 UL in function of 

propeller power (HB-EYS) [C. Wahl/M. Kapernaum/DLR] 
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Figure 10: Using EDX, both, Lead (Pb) and Bromide (Br) containing particles from AVGAS 100LL exhaust could be identified (HB-EYS). In the picture on the left, the location of the spectrum 1 is indicated with a tag. [C Wahl/DLR]. 

3.5 Conclusion for HB-EYS tests 

- AVGAS 100LL forms soot and lead bromide particles. 

- Besides lead additive, also bromides must be contained in AVGAS 100LL. (Bromides are actually used as scavenger, which should help to reduce lead deposits in the engine...) 

- Running HB-EYS on AVGAS 91/96 UL (lead free) still gives some lead bromides, which can 

be explained by the fact that the engine has been running on leaded fuel for its whole life and 

there are huge lead deposits e.g in the oil pan of the engine. 

The use of AVGAS 91/96 UL in HB-EYS gives a significant reduction in non-volatile particle concentration and mass. 

3.6 Results for SE-KEI 

Figure 11: Non-volatile particle number concentrations for AVGAS 100LL and 91/96 UL in function of 

propeller power (SE-KEI). [C. Wahl/M. Kapernaum/DLR] 
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Figure 12: Total non-volatile particle mass concentration for AVGAS 100LL and 91/96 UL in function of 

propeller power (SE-KEI) [C. Wahl/M. Kapernaum/DLR] 

3.7 Air/fuel mixture ratio for HB-EYS and SE-KEI 

Combustion quality is greatly influenced by the air/fuel mixture. The air/fuel mixtures at different power 

settings were recorded, using the FOCA analyzer described in Appendix 1. 

0.6

0.7

0.8

0.9

1

1.1

1.2

TAKE-OFF

CLIMB OUT

CRUISE

APPRAOCH

TAXI

CRUISE Lean

Lambda

Lyc O-360

Lyc O-320

Figure 13: Comparison of air/fuel mixture (Lambda) between the measured Lyc O-360 (HB-EYS) and 

Lyc O-320 (SE-KEI) for different power modes during the AVGAS 100LL measurements. The engine 

Lyc O-360 of HB-EYS runs on a significantly richer air/fuel mixture than that of SE-KEI, with the exception of the taxi mode. For explanation of lambda, see Appendix 5. 
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3.8 Discussion 

The carburetor system of SE-KEI is behaving differently from that of HB-EYS. Especially at high 

power, the engine of SE-KEI is running less rich than that of HB-EYS. Apart from different carburetor 

systems and tuning, the four blade propeller of SE-KEI might add to that effect, providing the air intake 

system with slightly increased manifold pressure. As a result of this different behavior, the shapes of 

the corresponding curves in figures 8 and 11, and in figures 9 and 12 respectively, are very different. 

However, in both cases, with use of AVGAS 91/96 UL, the mass and number concentrations are significantly reduced. 

3.9 Conclusions for AVGAS 91/96 UL 

• The use of AVGAS 91/96 UL gives a significant reduction in non-volatile particle concentration and mass, compared to AVGAS 100LL 

• AVGAS 91/96 UL has no lead and no bromide emissions. 

• As described in the introduction, the highest pressure ratio piston engines equipped with a 

RPM invariant ignition system are not allowed to use AVGAS 91/96 UL. 

Given the fact, that 

• unleaded AVGAS has a significantly superior environmental performance, 

• unleaded AVGAS can increase engine operational safety (no spark fouling, no lead deposits, 

still tight aviation gasoline specs, more than 26 years Swedish experience) 

• unleaded AVGAS is needed for state-of-the art engine management and the use of exhaust 

after treatment systems like catalysts, 

research and regulatory initiatives are necessary to further develop and promote AVGAS 91/96 

UL as a full substitute for AVGAS 100LL (see section 5). 

4. Change from SMPSTM to Engine Exhaust Particle SizerTM (EEPS 3090TM) system for aircraft 

piston engine nanoparticle measurements 

4.1 Introduction 

The Engine Exhaust Particle SizerTM (TSI EEPS 3090TM) spectrometer is a fast-response instrument 

that measures very low particle number concentrations in diluted exhaust. It offers a time resolution of 

10 times per second, which makes it well-suited for dynamic and transient tests. It was developed for 

continuous measurement of entire test cycles. It measures the size distribution and number concentration of engine exhaust particle emissions in the range from 5.6 to 560 nanometers. Compared to the 

SMPSTM, the TSI EEPS 3090TM system 

• measures fast response (real time) particle number-size-distributions (+) 

• significantly reduces engine running time (+) 

• makes particle emissions in transient power settings visible (+) 

• shows whether a certain power setting produces stable emissions (+) 

• has a reduced size resolution and a reduced overall accuracy (-) 

4.2 EEPSTM system description 

[Source: TSITM]: The instrument draws a sample of the exhaust flow into the inlet continuously. Particles are positively charged to a predictable level using a corona charger. Charged particles are then 

introduced to the measurement region near the center of a high-voltage electrode column and transported down the column surrounded by HEPA-filtered sheath air. A positive voltage is applied to the 

electrode and creates an electric field that repels the positively charged particles outward according to 

their electrical mobility. (Figure 14) 

Charged particles strike the respective electrometers and transfer their charge. A particle with higher 

electrical mobility strikes an electrometer near the top; whereas, a particle with lower electrical mobility 

strikes an electrometer lower in the stack. This multiple-detector arrangement using highly sensitive 

electrometers allows for simultaneous concentration measurements of multiple particle sizes. 
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The Model 3090 uses a real-time data inversion to deconvolute data. The inversion accounts for variability in particle charge, image charge, multiple voltages on the center rod, and detection time to present a size distribution 

Figure 14: EEPSTM flow schematic [TSITM] 

4.3 Application of EEPSTM for aircraft piston engine measurements 

Between 29th March and 4th April 2005, one year after the first non-volatile nanoparticle measurements 

in Oberpfaffenhofen, Germany, the same aircraft (HB-KEZ) with the same engine was measured 

again, this time with TSI EEPS 3090TM. The main goals were: 

• Application test for in-field measurement with EEPSTM at low ambient temperatures 

• Comparison to SMPSTM measurements 

• Reproducibility test 

The measurement arrangement and the sampling line were identical to the measurements of April 

2004 (see section 2.2) with the exception that the SMPSTM was replaced by the EEPSTM and the dilution ratio adjusted to 1 : 100. 

Ambient temperatures were as low as 9°C with a relative humidity of nearly 100%. At those ambient 

conditions, the EEPSTM was working in-field without any problems. However, measurements for comparison with SMPSTM results were made later, at dry ambient conditions. 

The methodology, which was used for the ground power settings of the engine, was identical to the 

procedure of 2004 (as described in Appendix 3, section 6.4). In 2004, the SMPSTM measurements 

were limited to low power settings, due to the necessary sampling time of two minutes and the limited 

engine running time, with the aircraft standing on ground. 

With EEPSTM it was possible to measure the high power settings as well: The measurement team 

could visually follow the stabilization of the number-size distribution on the PC screen. Engine running 

times at high power with the aircraft standing could be reduced to less than half a minute. 

Exhaust 
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Picture 8: EEPSTM measurements with HB-KEZ at Oberpfaffenhofen (EDMO), Germany, March 2005 

 Picture 9: EEPSTM installed in the back Picture 10: Small ground power unit for 

compartment of a car. In-field supply of electricity. 
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4.4 EEPSTM results 

Figure 15: While the power setting is constant, the number-size distributions show a constant shape in 

successive measurements at a rate of 10 times per second. (Proof for engine emission flow rate stability and combustion and measurement stability.) 

Figure 16: Example of a number-size distribution of non-volatile particles for approach mode of the 

HB-KEZ engine, measured with EEPSTM. With a mean diameter of 100 nm and an overall total concentration of 8 * 107 particles / cm3, the SMPSTM values for approach mode were confirmed. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Figure 17: EEPSTM measurement of a power cycle. Each slice represents the mean of 1 second 

measurement time. The left axis shows the measurement time, the x-axis in front the particle size and 

the z-axis on the right shows the particle number per cm3, as measured after dilution. The first set of 

number-size distributions on top of the figure belongs to the climb power setting, followed by cruise 

power (12.33.57), approach power (12.34.37) and taxi power setting (12.35.00). The approach power 

number-size distribution shown in figure 16 is taken from this cycle and is marked in light blue. 

4.5 First conclusions for EEPSTM measurements 

• The system showed robustness with respect to low ambient temperatures and high relative 

humidity 

• The results of the SMPSTM measurements have generally be confirmed for the different 

modes (see section 2.3, picture 3) 

• For the first time, nanoparticle emissions during transient aircraft piston engine power conditions could be observed. 

• Engine running time was very short compared to SMPSTM measurements. 

5. Research for AVGAS 100LL substitution and emission reduction 

Following the conclusions from section 3.9, the Swedish producer of unleaded AVGAS, Hjelmco Oil, 

provided FOCA with a variety of different unleaded AVGAS fuels. The main goal was to find a lead 

free AVGAS that would have a similar high aviation octane rating like 100LL with superior emissions 

performance and economically feasible production costs. In other words: The research is aimed to find 

an environmentally beneficial and safe full substitute for AVGAS 100LL. Please note that aviation octane rating is not directly comparable to the research octane number (ROZ) used e.g. for car gasoline. 

An AVGAS 100 may have a ROZ well above 105. So, an aviation fuel rated at “100” has a significantly 

higher octane rating than lead free car gasoline. 

The composition of the research fuels is known to DLR and FOCA but is part of a confidentiality 

agreement because this is proprietary data. Therefore, the fuels from HjelmcoTM are just labeled “A” to 

“H” in this documentation. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

5.1 Test fuels 

Fuel A: Standard unleaded AVGAS 91/96UL, as tested before (section 3). 

Fuel B to H: unleaded AVGAS which, in comparison to Fuel A, had one ore more components 

replaced and/or additives. 

Fuel I: Standard leaded AVGAS 100LL 

Fuel J: Standard MOGAS (lead free car gasoline with 98 ROZ, tested in Rotax engine) 

Fuels D, F and G have the highest aviation octane rating of all tested unleaded fuels, with fuel G 

reaching nearly 100, so being comparable to AVGAS 100LL from that point of view. 

 

5.2 Test location 

The test location was St. Stephan (LSTS), a former military Airport in the Swiss Alps. The infrastructure was generously provided by the private company “prospective concepts”. 

Picture 11: Test location St. Stephan, Swiss Alps 

5.3 Used aircraft 

HB-EYS Type: Robin DR400 SE-KEI Type: Piper PA28 Warrior II 

 Owner: Swiss Confederation Owner: Hjelmco Oil, Sweden 

 Engine: Lyc O-360 series, 180 HP Engine: Lyc O-320 series, 160 HP 

 Carburetor (Fuels A to I) Carburetor (Fuels A to I) 

HB-WAD Type: Ikarus C-42 (Microlight/Ecolight) 

 Owner: A. Liechti, Switzerland 

 Engine: Rotax 912S, 100HP, Carburetor (Fuels A to C and J) 

5.4 Measurement Systems 

For gaseous emissions, the FOCA measurement system as described in Appendix 1 was used. For 

particle emissions, the EEPSTM measurement system, described in section 4 of this appendix, was 

used. Simultaneous measurement with both systems was made possible by two separate heated sampling lines. In addition, at lower power settings, exhaust has been pumped through sample cartridges 

at a controlled flow rate for later HC speciation (Carbonyl measurements). Pumping time usually was 2 

minutes. The speciation was obtained by analysis of the sample cartridges with HPLC (High Performance Liquid Chromatography) in the DLR laboratory. 
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Picture 12: Gaseous emission analyzers in the white car on the left (FOCA), particle analyzers in the 

blue-green car on the right (DLR). 

5.5 Power settings 

Engine power for selected power modes (Take-off, Climb, Cruise, Approach and Taxi) was adjusted 

according to the FOCA methodology for static on-ground tests, as described in Appendix 3, sections 

6.2 and 6.3.It must be noted that the airport elevation of 3274 ft AMSL (with the prevailing air density 

at the time of measurement) reduced the maximum propeller power output of the tested engines to 

about 88%, compared to sea level standard conditions. 

Picture 12: Measurement of SE-KEI engine 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

5.6 Results 

As described in section 3.7, the two tested Lycoming engines have a quite different air/fuel mixture 

characteristic. The Rotax engine is running less rich at high power than the Lycoming engines. Therefore, if all three engines independently show the same trend, we consider this as a more general effect, not only valid for one particular aircraft piston engine. As far as particle emissions are concerned, 

we focus on the results for the SE-KEI engine. The reason is given by the fact that the engine of HBEYS has been running on leaded fuel for its whole life (more than 1600 hours). With a lot of lead deposits in the engine, significant amounts of particles have been detected in the exhaust even with 

unleaded fuel. The SE-KEI engine has the same basic design as the HB-EYS engine. 

5.6.1 Ranking of the fuels in terms of emission factors for gaseous emissions 

The resulting fuel consumption for a certain power setting in terms of fuel mass did not differ significantly between the tested fuels. This means that measured differences in emission factors directly 

translate in different emission levels. 

The figures 18, 19, 21 and 22 show the CO and HC emissions ranking of the tested fuels for full 

throttle and climb out mode of SE-KEI and HB-EYS. Two groups of fuel can be distinguished: A, E, I, 

H and C, D, B, G, F. The second group shows a significant drop in CO and HC emissions. This effect 

is shown with both, the SE-KEI and the HB-EYS engine. For the lower CO and HC emissions group of 

fuel, one of the original components of the fuel A had been replaced by another. 

The figures 20 and 23 show the CO and HC emissions ranking between fuels A, B, C and J, as tested 

with HB-WAD and the Rotax engine. The lowest emissions have been measured for fuel B and C, 

confirming the result and corresponding to fuel group two above. Fuel J (MOGAS) showed the lowest 

total HC emissions of the four fuels, but significantly the highest carbonyl emissions, which is shown in 

tables 2 to 4. 

For the HC speciation (Carbonyl measurements), the following carbonyls have been detected: 

Formaldehyde CH2O 

Acetaldehyde CH3CHO 

Propargylaldehyde CHCCHO 

Acetone CH3OCH3 

Propionaldehyde CH3CH2CHO 

Crotonaldehyde CH3CHCHCHO 

i-Butanale i-C3H7CHO 

Benzaldehyde C6H5CHO 

Methylglyoxal CH3COCHO 

o-Toluene – aldehyde CH3C6H4CHO 

m-Toluene – aldehyde CH3C6H4CHO 

p-Toluene – aldehyde CH3C6H4CHO 

The ranking for the total carbonyl emissions has been analyzed for different power settings (see 

examples in tables 2 to 4). A representative ranking is given below. It is given with falling total carbonyl 

emissions from left to right: 

• SE-KEI (no carbonyl measurement for fuel B) 

F, G, D, C (first group) and H, A, E, I (second group) 

• HB-EYS 

B, D, C, F, G (first group) and E, H, A, I (second group) 

• HB-WAD 

J (MOGAS), B, C (first group) and A (second group) 

Interestingly, the fuels with the lowest CO and lowest total HC emissions produce the highest total 

carbonyl emissions. In contrast, the (leaded) AVGAS 100LL produces the lowest total carbonyl emissions. 
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Relative Comparison of CO emission factors for different fuels (SE-KEI, St. Stephan, Switzerland, 

May 2006)

0

20

40

60

80

100

FUEL A FUEL E FUEL I FUEL H FUEL C FUEL D FUEL B FUEL G FUEL F

F.T. / CL

Figure 18: Ranking of the CO emission factors for the tested fuels (SE-KEI engine in climb out 

mode/full throttle). AVGAS 100LL (Fuel I) is set to 100%. 

Relative Comparison of CO emission factors for different fuels (HBEYS, St. Stephan, Switzerland, 

May 2006)

0

10

20

30

40

50

60

70

80

90

100

FUEL A FUEL E FUEL I FUEL H FUEL C FUEL D FUEL B FUEL G FUEL F

F.T. / CL

Figure 19: Ranking of the CO emission factors for the tested fuels (HB-EYS engine in climb out 

mode/full throttle). AVGAS 100LL (Fuel I) is set to 100%. 
Reference: 0 / 3/33/33-05-003.022 

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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Relative Comparison of CO emission factors for different fuels (HB-WAD, St. Stephan, Switzerland, 

June 2006)

0

20

40

60

80

100

120

FUEL A FUEL J FUEL B FUEL C

F.T. / CL

Figure 20: Ranking of the CO emission factors for the tested fuels A, B, C and J with the ROTAX engine at climb out/full throttle setting. MOGAS (car gasoline, fuel J) is set to 100%. 

Relative Comparison of HC emission factors for different fuels (SE-KEI, St. Stephan, Switzerland, 

May 2006)

0

20

40

60

80

100

FUEL I FUEL A FUEL E FUEL H FUEL D FUEL B FUEL F FUEL C FUEL G

F.T. / CL

Figure 21: Ranking of the HC emission factors for the tested fuels (SE-KEI engine in climb out 

mode/full throttle). AVGAS 100LL (Fuel I) is set to 100%. 
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Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Relative Comparison of HC emission factors for different fuels (HBEYS, St. Stephan, Switzerland, 

May 2006)

0

10

20

30

40

50

60

70

80

90

100

FUEL I FUEL A FUEL E FUEL H FUEL D FUEL B FUEL F FUEL C FUEL G

F.T. / CL

Figure 22: Ranking of the HC emission factors for the tested fuels (HB-EYS engine in climb out 

mode/full throttle). AVGAS 100LL (Fuel I) is set to 100%. 

Relative Comparison of HC emission factors for different fuels (HBWAD, St. Stephan, Switzerland, 

June 2006)

0

20

40

60

80

100

120

FUEL A FUEL C FUEL B FUEL J

F.T. / CL

Figure 23: Ranking of the HC emission factors for the tested fuels A, B, C and J with the ROTAX engine at climb out/full throttle setting. MOGAS (car gasoline, fuel J) is set to 100%. 
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Table 2: Carbonyl emission factors for fuel A, B, C and J (MOGAS). Results for approach mode 

(HBWAD).[DLR C. Wahl/M. Kapernaum] 

Approach mode Carbonyls Fuel J Fuel C Fuel B Fuel A

mg/kg Fuel mg/kg Fuel mg/kg Fuel mg/kg Fuel

Formaldehyde 338.25 269.39 290.64 282.20

Acetaldehyde 44.95 97.56 83.22 49.41

Propargylaldehyde 4.55 4.52 5.43 2.20

Acrolein 34.33 34.83 32.66 22.67

Propanaldehyde 2.61 0.79 0.81 3.56

i-Butanaldehyde 24.46 13.04 12.21 15.36

Benzaldehyde 79.70 7.95 8.26 72.43

Methacrolein 69.24 145.73 101.76 69.64

o-Toluolaldehyde 19.709 0 0 2.48

p-Toluolaldehyde 43.42 0 0 1.37

m-Toluolaldehyde 0 0 0 2.73

2,5-Dimethylbenzaldehyde 13.586 000

3,4-Dimethylbenzaldehyde 23.059 000

2,4-Dimethylbenzaldehyde 24.297 000

Sum 722.16 573.82 534.98 524.05

Table 3: Carbonyl emission factors for fuel A, B, C and J (MOGAS). Results for cruise mode 

(HBWAD). [DLR C. Wahl/ M. Kapernaum] 

Cruise 65% power Carbonyls Fuel J Fuel C Fuel B Fuel A

mg/kg Fuel mg/kg Fuel mg/kg Fuel mg/kg Fuel

Formaldehyde 306.36 261.48 288.23 269.60

Acetaldehyde 55.62 103.62 96.84 36.69

Propargylaldehyde 3.65 2.50 2.75 1.29

Acrolein 23.42 23.34 22.38 16.15

Propanaldehyde 3.89 0.94 1.44 2.55

i-Butanaldehyde 28.53 9.56 9.38 0

Benzaldehyde 89.38 5.34 9.60 66.84

Methacrolein 82.01 92.48 88.73 60.57

o-Toluolaldehyde 21.90 0 0 1.45

p-Toluolaldehyde 17.97 0 0 1.60

m-Toluolaldehyde 34.57 0 0 2.79

2,5-Dimethylbenzaldehyde 15.97 0 0 0

3,4-Dimethylbenzaldehyde 26.55 0 0 0

2,4-Dimethylbenzaldehyde 28.34 0 0 0

Sum 738.14 499.25 519.35 459.51
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Table 4: Carbonyl emission factors for fuel A, B, C and J (MOGAS). Results for climb mode/full throttle 

(HBWAD) [DLR C. Wahl/ M. Kapernaum] 

Climb/Full throttle Carbonyls Fuel J Fuel C Fuel B Fuel A

mg/kg Fuel mg/kg Fuel mg/kg Fuel mg/kg Fuel

Formaldehyde 389.16 344.79 386.22 230.63

Acetaldehyde 71.34 220.80 234.52 39.41

Propargylaldehyde 4.02 2.09 2.92 1.37

Acrolein 55.55 74.15 69.53 20.55

Propanaldehyde 7.49 3.26 2.46 0.71

i-Butanaldehyde 15.43 9.88 10.60 30.76

Benzaldehyde 130.85 15.99 25.70 62.24

Methacrolein 142.81 154.95 154.60 0

o-Toluolaldehyde 29.67 0 0 2.67

p-Toluolaldehyde 71.01 0 0 1.74

m-Toluolaldehyde 0.00 0 0 2.74

2,5-Dimethylbenzaldehyde 22.06 0 0 0

3,4-Dimethylbenzaldehyde 37.57 0 0 0

2,4-Dimethylbenzaldehyde 41.44 0 0 0

Sum 1018.39 825.91 886.56 392.81

The figures 24, 25 and 26 show the NOx emissions ranking of the tested fuels. The two groups of 

fuels mentioned for the CO and HC emissions ranking are confirmed with all engines, but this time the 

ranking of the fuels is the other way round, with MOGAS and the C, D, B, G, F fuels producing the 

highest NOx emissions. 

Relative Comparison of NOx emission factors for different fuels (SE-KEI, St. Stephan, Switzerland, 

May 2006)

0

50

100

150

200

FUEL F FUEL G FUEL B FUEL D FUEL C FUEL H FUEL E FUEL I FUEL A

F.T. / CL

Figure 24: Ranking of the NOx emission factors for the tested fuels (SE-KEI engine in climb out 

mode/full throttle). AVGAS 100LL (Fuel I) is set to 100%. 
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Relative Comparison of NOx emission factors for different fuels (HBEYS, St. Stephan, Switzerland, 

May 2006)

0

20

40

60

80

100

120

140

FUEL F FUEL G FUEL B FUEL D FUEL C FUEL H FUEL E FUEL I FUEL A

F.T. / CL

Figure 25: Ranking of the NOx emission factors for the tested fuels (HB-EYS engine in climb out 

mode/full throttle). AVGAS 100LL (Fuel I) is set to 100%. 

Relative Comparison of NOx emission factors for different fuels (HB-WAD, St. Stephan, Switzerland, 

June 2006)

0

10

20

30

40

50

60

70

80

90

100

FUEL J FUEL B FUEL C FUEL A

F.T. / CL

Figure 26: Ranking of the NOx emission factors for the tested fuels A, B, C and J with the ROTAX 

engine at climb out/full throttle setting. MOGAS (car gasoline, fuel J) is set to 100%. 
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5.6.2 Ranking of the fuels in terms of particle emissions 

0 10 20 30 40 50 60 70 80 90 100

0

1x108

2x108

3x108

4x108

5x108

SE

 Fuel A

 Fuel B

 Fuel C

 Fuel D

 Fuel E

 Fuel F

 Fuel G

 Fuel H

 Fuel I

# / cm3

Power %

Figure 24: Particle number concentration for the different test fuels (SE-KEI engine) in function of propeller power. [DLR, C. Wahl, M. Kapernaum] 

0 10 20 30 40 50 60 70 80 90 100

0

1x1015

2x1015

3x1015

4x1015

5x1015

6x1015

SE

 Fuel A

 Fuel B

 Fuel C

 Fuel D

 Fuel E

 Fuel F

 Fuel G

 Fuel H

 Fuel I

EI Soot [# /kg Fuel]

Power %

Figure 25: Emission factor for the number of soot particles per kg fuel for the different test fuels (SEKEI engine) in function of propeller power. [DLR, C. Wahl, M. Kapernaum] 
Reference: 0 / 3/33/33-05-003.022 

30/32

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

0 20 40 60 80 100

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

SE

 Fuel A

 Fuel B

 Fuel C

 Fuel D

 Fuel E

 Fuel F

 Fuel G

 Fuel H

 Fuel I

Geometric Mean [nm]

Power %

Figure 26: Geometric mean diameter of emitted nanoparticles for the different test fuels (SE-KEI engine) in function of propeller power. [DLR, C. Wahl, M. Kapernaum] 

0 10 20 30 40 50 60 70 80 90 100

0

1

2

3

4

5

6

7

8

9

SE

 Fuel A

 Fuel B

 Fuel C

 Fuel D

 Fuel E

 Fuel F

 Fuel G

 Fuel H

 Fuel I

 mg/m3

Power %

Figure 27: Emitted particle mass per exhaust volume for the different test fuels (SE-KEI engine) in 

function of propeller power. [DLR, C. Wahl, M. Kapernaum] 
Reference: 0 / 3/33/33-05-003.022 

31/32

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

0 10 20 30 40 50 60 70 80 90 100

0

10

20

30

40

50

60

70

80

90

100

SE

 Fuel A

 Fuel B

 Fuel C

 Fuel D

 Fuel E

 Fuel F

 Fuel G

 Fuel H

 Fuel I

EI Soot [mg/kg Fuel]

Power %

Figure 28: Emission factor for emitted particle mass for the different test fuels (SE-KEI engine) in function of propeller power. [DLR, C. Wahl, M. Kapernaum] 

5.7 Discussion: 

For gaseous emissions, an effect of different additives can not be clearly identified. If differences existed, they would be below the measurement accuracy of the FOCA analyzer system. However, differences occurring from different composition of the fuels are clearly visible: 

One way to maintain an acceptable level of octane number without using lead-tetra-ethyl is by adding 

oxygen containing substances to the fuel. The effect of this is most pronounced with the tested lead 

free car gasoline (MOGAS, fuel J). The additional oxygen provided by the fuel reduces CO and total 

HC emissions and increases NOx emissions. In fact, the tested MOGAS contained large amounts of 

MTBE2

. This substance might be the cause for the significantly high carbonyl emissions of the tested 

MOGAS. In addition to that, a substance like MTBE can pose a certain risk for the contamination of 

drinking water. 

In order to rank the tested fuels with respect to particle emissions, the fuels can be separated into 

three groups: 

The fuels A, B and C have the lowest particle number concentrations and the smallest particle diameter, leading to the lowest particle mass emissions. (group 1) 

Fuel I (AVGAS 100LL) has the highest particle number concentrations and the highest particle diameters, leading to the highest particle mass emissions. (group 3) 

The fuels D, E, F, G, and H (group 2) are situated between the group 1 and 3 fuels. The higher particle 

emissions of this group of fuels compared to group 1 can be explained by a fuel additive, which is 

missing in the group 1 fuels. However, particle number concentrations and particle mass emissions 

are still lower than with AVGAS 100LL (group 3). 

 

2

 MOGAS sold in Switzerland and analyzed in 2006 contained quite large quantities of MTBE (Methyl tert-butyl ether). 
Reference: 0 / 3/33/33-05-003.022 

32/32

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

As we have seen, there is no lead free highest octane fuel producing the lowest possible emissions 

(CO, total HC, Carbonyls, NOx and particles) among the tested fuels. A compromise seems to be 

needed, weighing the different trade-offs. 

5.8 First conclusions 

As far as particle emissions are concerned, the standard unleaded AVGAS 91/96UL (Fuel A) has 

again proven its superior environmental performance. 

If not highest octane number is required, an AVGAS like fuel C seems to be a valuable compromise. 

Fuel G, which would have the potential to fully replace AVGAS 100LL from point of view of aviation 

octane rating, has a better environmental performance than AVGAS 100LL, but worse than e.g. fuel C. 

Picture 13: The measurement team. From left to right: C. Wahl, M. Kapernaum (both DLR), L. Hjelmberg (Hjelmco), T. Rindlisbacher, W. Bula (both FOCA) 

Picture 14: HB-WAD (with Rotax engine) was generously provided for the fuel tests by A. Liechti, Switzerland. Many thanks also to K. Moser (first to the right, the pilot of HB-WAD), who contributed to the 

measurements in his spare time. 
33-05-003 Piston Engine Emissions_Swiss FOCA_Appendix5_070605_rit 

Federal Department of the Environment, Transport, Energy and 

Communications DETEC 

Federal Office of Civil Aviation FOCA 

Aviation Policy and Strategy 

Environmental Affairs 

AIRCRAFT PISTON ENGINE EMISSIONS 

Appendix 5: Calculation of Emission Factors 

 

FOCA, CH-3003 Bern

Reference: 0 / 3/33/33-05-003 ECERT 

Contact person: Theo Rindlisbacher 

Tel. +41 31 325 93 76, Fax +41 31 325 92 12, theo.rindlisbacher@bazl.admin.ch

This document has been released for publication by FOCA, Aviation Policy and Strategy, Director M. Zuckschwerdt,11.06.2007 

CO

HC

NO

CO2

O2

H20

N2

CO Emissions 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO

CO 1207.6 1224 1232.5 1039.6 1027.9 1045.1 801.15 780.35 808.13 1064.5 1058.2 1038.5 920.14 888.48 890.31 230.95 219.4 227.63

TO TO TO CL CL CL CR CR CR AP AP AP TA TA TA CR L CR L CR L

HC Emissions 

0

2

4

6

8

10

12

14

16

18

20

Mode

Mass (g/kg Fuel)

HC

HC 12.957 13.139 13.154 10.12 10.14 10.121 9.4066 9.5797 9.7432 14.778 15.452 15.106 17.61 17.436 17.832 3.435 4.4517 4.6837

TO TO TO CL CL CL CR CR CR AP AP AP TA TA TA CR L CR L CR L

NOx Emissions 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel)

NOx

NOx 1.6541 1.636 1.5795 3.0254 3.1254 3.0511 7.8972 10.021 9.0769 2.6446 2.6857 2.8899 1.8298 1.7986 1.6997 42.887 42.905 42.92

TO TO TO CL CL CL CR CR CR AP AP AP TA TA TA CR L CR L CR L

Measured

Concentrations

Emissions g/kg fuel

Calculation Methodology

CO

HC

NO

CO2

O2

H20

N2

CO Emissions 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO

CO 1207.6 1224 1232.5 1039.6 1027.9 1045.1 801.15 780.35 808.13 1064.5 1058.2 1038.5 920.14 888.48 890.31 230.95 219.4 227.63

TO TO TO CL CL CL CR CR CR AP AP AP TA TA TA CR L CR L CR L

HC Emissions 

0

2

4

6

8

10

12

14

16

18

20

Mode

Mass (g/kg Fuel)

HC

HC 12.957 13.139 13.154 10.12 10.14 10.121 9.4066 9.5797 9.7432 14.778 15.452 15.106 17.61 17.436 17.832 3.435 4.4517 4.6837

TO TO TO CL CL CL CR CR CR AP AP AP TA TA TA CR L CR L CR L

NOx Emissions 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel)

NOx

NOx 1.6541 1.636 1.5795 3.0254 3.1254 3.0511 7.8972 10.021 9.0769 2.6446 2.6857 2.8899 1.8298 1.7986 1.6997 42.887 42.905 42.92

TO TO TO CL CL CL CR CR CR AP AP AP TA TA TA CR L CR L CR L

CO Emissions 

0

200

400

600

800

1000

1200

1400

Mode

Mass (g/kg Fuel)

CO

CO 1207.6 1224 1232.5 1039.6 1027.9 1045.1 801.15 780.35 808.13 1064.5 1058.2 1038.5 920.14 888.48 890.31 230.95 219.4 227.63

TO TO TO CL CL CL CR CR CR AP AP AP TA TA TA CR L CR L CR L

HC Emissions 

0

2

4

6

8

10

12

14

16

18

20

Mode

Mass (g/kg Fuel)

HC

HC 12.957 13.139 13.154 10.12 10.14 10.121 9.4066 9.5797 9.7432 14.778 15.452 15.106 17.61 17.436 17.832 3.435 4.4517 4.6837

TO TO TO CL CL CL CR CR CR AP AP AP TA TA TA CR L CR L CR L

NOx Emissions 

0

5

10

15

20

25

30

35

40

45

50

Mode

Mass (g/kg Fuel)

NOx

NOx 1.6541 1.636 1.5795 3.0254 3.1254 3.0511 7.8972 10.021 9.0769 2.6446 2.6857 2.8899 1.8298 1.7986 1.6997 42.887 42.905 42.92

TO TO TO CL CL CL CR CR CR AP AP AP TA TA TA CR L CR L CR L

Measured

Concentrations

Emissions g/kg fuel

Calculation Methodology
Reference: 0 / 3/33/33-05-003.022 

2/7

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

Contents 

 Page 

a) Introduction 3 

b) List of abbreviations 3 

c) Calculation of EF (Equations used for FOCA ground measurements and data sheets) 3 

d) Equations for "low cost" measurement system described in Appendix 1 for AVGAS 4 

 (used for FOCA in-flight measurements and comparative ground measurements) 

e) Equations for "low cost" measurement system described in Appendix 1 for DIESEL 6 

f) Correction of ambient air temperature influence on normally aspirated piston engines 7 

g) Statistical checks 7 

h) Fuel flow 7 
Reference: 0 / 3/33/33-05-003.022 

3/7

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

a) Introduction 

Measured concentrations are converted to emission factors (EF) on the basis of molar masses. The 

fuel flow measurement is necessary for power setting checks (Appendix 3) and to calculate LTO emissions. 

The basic calculation is taken from „Advisory Circular“ AC34-1A of the Federal Aviation Administration 

(FAA). If a low cost gas measurement system is used, as described in appendix 1, some corrections 

(section d) and the use of equation (5) for the calculation of air/fuel ratio to stoichiometric air/fuel ratio 

are suggested. 

b) List of abbreviations 

MAir Molar mass of dry air 28.966 g/mol 

MHC Molar mass of exhaust-HC, as Methane CH4 16.040 g/mol 

MCO Molar mass of CO 28.011 g/mol 

MNO2 Molar mass of NO2 46.088 g/mol 

MNO Molar mass of NO 30.010 g/mol 

MNOx Molar mass of NOx, 15% NO2, 85% NO 32.412 g/mol 

MC Molar mass of carbon C 12.011 g/mol 

MH Molar mass of hydrogen H 1.008 g/mol 

VCO2 Volume fraction of CO2 in dry air 0.0003 

[HC] Mean concentration of exhaust-HC vol/vol 

[CO] Mean concentration of CO vol/vol wet 

[CO2] Mean concentration of CO2 vol/vol wet 

[NOx] Mean concentration of NOx (NO+NO2) vol/vol wet [NOx] = 1.18 [NO] 1

m Number of C atoms in char. fuel molecule 7 (AVGAS / MOGAS), 12 (JET A1) 

n Number of H atoms in char. fuel molecule 13 (AVGAS / MOGAS), 23 (JET A1) 

c) Calculation of EF (Equations used for FOCA ground measurements and data sheets) 

[ ]

[ ][ ][ ] ( )

[ ][ ][ ] ( )

[ ][ ][ ] ( ) 1 (3) ( / )

[ ] 1.18 10 ( )

1 (2) ( / )

[ ] 10 ( )

1 (1) ( / )

10 ( )

2

3

2

2

3

2

2

3

2

CO

C H

NOx

CO

C H

HC

CO

C H

CO

A V

M n m M

M

CO CO HC

NO EF NOx

A V

M n m M

M

CO CO HC

HC EF HC

A V

M n m M

M

CO CO HC

CO EF CO

+ ⋅ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ +

⋅ =

+ ⋅ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ + =

+ ⋅ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ + =

where 

( )

Air

C H

M

M n m M A + ( / ) = λ

 (4) and λ with equation (5) or directly calculated by system. 

The calculation of λ (Lambda) is done with the following approximation (5) where CO2, O2 und CO 

are measured concentrations in volume% and HC6NDIR the NDIR HC reading in Hexane ppm.

 

1

 Conservative assumption FOCA / DLR 
Reference: 0 / 3/33/33-05-003.022 

4/7

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

0.0088 ( 2 6 6 10 ) 4

1.7261 1

0.0088 ( 2 )

2

3.5

3.5

4

1.7261 2

2

2

−4 ⎟⋅ + + ⋅ ⋅ ⎠

⎞ ⎜

⎝

⎛ + −

⋅ +

⎪

⎪

⎭

⎪⎪

⎬

⎫

⎪

⎪

⎩

⎪⎪

⎨

⎧

−

+

+ + + ⋅

=

CO CO HC NDIR

CO CO

CO

CO O CO CO

λ (5) 

General definition of λ (Lambda): 

lean rich

Airmass Fuelmass stoichiometric

Airmass Fuelmass measured

1: 1:

: ( )

: ( )

> <

=

λ λ

λ

d) Equations for “low cost” measurement system described in Appendix 1 for AVGAS/MOGAS 

engines (used for FOCA in-flight measurements and comparative ground measurements) 

EF(HC) 

Many NDIR HC analyzers (like the one that FOCA uses for in-flight tests) read HC concentrations in 

hexane equivalents. Please note that in the standard calculation formulas for EF(CO), (HC) and (NOx) 

above, the HC concentrations have to be methane based. Parallel measurements with a hot FID HC 

analyzer have shown that correction factors for the NDIR HC values can be derived. The HC correction factor counts for hexane to methane conversion and for partial to total HC measurement. Because 

of fuel, engine and power dependent HC composition, the factor is not a constant: 

Relation of FID HC to NDIR HC EF without correction 

(AVGAS/MOGAS) 

0

5

10

15

20

25

30

35

40

8-10 10-12 12-14 14-16 16-18 18-20 20-22 22-24 24-26 26-28 28-30

Classified Correction Factor

Frequency

Figure 1: Distribution of the HC correction factor, based on 141 measurements with 8 different engines 

and all power modes. The derived mean correction factor for EF(HC) is 16.3. Depending on the engine, the engine power condition and the fuel, the error band of the NDIR HC measurement compared 

to the total HC measurement with FID will be +- 25%. 

The magnitude of possible errors in EF(HC), when using NDIR HC measurement systems can be 

considered acceptable for the purpose of emission inventories, but it is significant. Therefore, FOCA 

uses an additional hot FID for all ground measurements and FOCA engine datasheets are all based 

on hot FID measurements where no estimations and HC correction factors are necessary. 
Reference: 0 / 3/33/33-05-003.022 

5/7

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

EF(CO) 

The effect on EF(CO) when using NDIR HC values instead of FID HC values is small. On the basis of 

90 measurements with 5 different engines, the resulting correction factor is 0.9839. When using this 

correction and NDIR HC values, the error band is +- 1% compared to FID HC. 

EF(NOx) 

The effect on EF(NOx) when using NDIR HC values instead of FID HC values is small. On the basis of 

90 measurements with 5 different engines, the correction factor is 0.9839, equal to E( CO) correction. 

The error band - when using this correction and NDIR HC values - is +- 1% compared to FID HC. 

The electrochemical NOx sensor which is used in the FOCA low cost measurement system (Appendix 

1) is in fact a NO sensor and does not account for NO2. After comparative measurements the correction factor for NO to NOx conversion was set to 1.18 together with an assumption for MNOx (as defined 

in section b). The possible error band is assumed +- 10%. 

Equations: 

[ ]

[ ][ ][ ] ( )

[ ][ ][ ] ( )

[ ][ ][ ] ( ) 1 (8) ( / )

10

6

[ ] 1.18 ( ) 0.9839

1 (7) ( / )

10

6

[ 6 ] ( ) 16.3

1 (6) ( / )

10

6 ( ) 0.9839

2

3

2

2

3

2

2

3

2

CO

C H

NOx

CO

C H

HC

CO

C H

CO

A V

M n m M

M

CO CO HC NDIR

NO EF NOx

A V

M n m M

M

CO CO HC NDIR

HC NDIR EF HC

A V

M n m M

M

CO CO HC NDIR

CO EF CO

+ ⋅ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ +

⋅ = ⋅

+ ⋅ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ + = ⋅

+ ⋅ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ + = ⋅

used together with equations (4) and (5). 

- INTENTIONALLY LEFT BLANK -
Reference: 0 / 3/33/33-05-003.022 

6/7

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

e) Equations for “low cost” measurement system described in Appendix 1 for DIESEL engines 

Similarly to what has been said in section d), correction factors for HC have been derived for diesel 

engines: 

Relation of FID HC to NDIR HC EF without correction 

(Diesel Engine)

0

5

10

15

20

2-4 4-6 6-8 8-10 10-12

Classified Correction Factor

Frequency

Figure 2: Distribution of the HC correction factor, based on 36 measurements with 2 different engines 

and all power modes. The derived mean correction factor for EI(HC) is 5.8. Depending on the engine, 

the engine power condition and the fuel, the error band of the NDIR HC measurement compared to 

the total HC measurement with FID can be +- 40%. 

EF(CO) 

The effect on EI(CO) when using NDIR HC values instead of FID HC values is very small. On the basis of 36 measurements with 2 different engines, the correction factor is 0.9976. When using this correction and NDIR HC values the error band is +- 0.3% compared to FID HC. 

EF(NOx) 

The effect on EI(NOx) when using NDIR HC values instead of FID HC values is small. On the basis of 

36 measurements with 2 different engines, the correction factor is 0.9976, equal to EI(CO) correction. 

When using this correction and NDIR HC values the error band is +- 0.3% compared to FID HC. 

The electrochemical NOx sensor which is used in the FOCA low cost measurement system (Appendix 

1) is in fact a NO sensor and does not account for NO2. After comparative measurements the correction factor for NO to NOx conversion was set to 1.18 together with an assumption for MNOx (as defined 

in section b). The possible error band is assumed +- 10%. 

Equations (next page): 
Reference: 0 / 3/33/33-05-003.022 

7/7

Federal Office of Civil Aviation (FOCA), Environmental Affairs, CH-3003 Bern 

[ ]

[ ][ ][ ] ( )

[ ][ ][ ] ( )

[ ][ ][ ] ( ) 1 (11) ( / )

10

6

[ ] 1.18 ( ) 0.9976

1 (10) ( / )

10

6

[ 6 ] ( ) 5.8

1 (9) ( / )

10

6 ( ) 0.9976

2

3

2

2

3

2

2

3

2

CO

C H

NOx

CO

C H

HC

CO

C H

CO

A V

M n m M

M

CO CO HC NDIR

NO EF NOx

A V

M n m M

M

CO CO HC NDIR

HC NDIR EF HC

A V

M n m M

M

CO CO HC NDIR

CO EF CO

+ ⋅ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ +

⋅ = ⋅

+ ⋅ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ + = ⋅

+ ⋅ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ + = ⋅

used together with equations (4) and (5). 

 

f) Correction of ambient air temperature influence on normally aspirated piston engines 

HC and CO emission factors for normally aspirated piston engines have been shown to be significantly 

temperature dependent, mainly because of air density variations and its influence on the air/fuel mixture. To correct the emission factors to 15°C, the following equations are suggested: 

CO Measurement :EF CO(15°C) = 3.1259*(15 - T) + EF CO(T) (12) 

HC Measurement: EF HC(15°C) = 0.0164*(15 - T) + EF HC(T) (13) 

Ambient air humidity primarily seems to have an effect on NOx emissions. However, these emissions 

are very low at “full rich” conditions and therefore no significant correction could be established. 

g) Statistical checks 

For each engine and power mode, a minimum of three valid measurements has been defined. The 

confidence interval (90% Conf. Level) is determined with a T-Test and assumed normal distributed 

values. 

h) Fuel flow 

The fuel flow is normally measured in liters/hour or US gallons/hour. The standard calculation of the 

fuel flow in kg/s is done with a mean fuel density of 0.72 kg / liter for AVGAS/MOGAS and of 0.80 kg / 

liter for DIESEL/JETA1.