Description:

The main aim of Working Group 3 (WG3, Emissions Technical) is to keep ICAO engine emissions and aeroplane CO₂ emissions certification standards (Annex 16, Volume II and Volume III respectively) up to date and effective, while ensuring that the certification procedures are as simple and inexpensive as possible. The CAEP working groups liaise on the interdependencies of ICAO environmental Standards and Recommended Practices (SARPs), and WG3 provides advice on the emissions aspects associated with the ICAO global environmental trends and local air quality analysis.

As a result of the noise-CO₂ integrated dual stringency analyses, in February 2025 CAEP/13 agreed to  recommend the amendments to Annex 16, Volume III – Aeroplane CO₂ Emissions, and the ETM (Doc 9501), Volume III – Procedures for the CO₂ Emissions Certification of Aeroplanes, for consideration by the Council, including the more stringent CO₂ emissions Standards for new subsonic aeroplane types (applicability date of 31 December 2031) and for in-production subsonic aeroplane types (applicability date of 1 January 2035). 

Current work:

The WG3 work programme for the CAEP/14 cycle (2025-2028) includes various topics such as:

• Maintenance of Annex 16, Volumes II and III and ETM (Doc 9501), Volumes II and III.
• Update Doc 9889 to reflect industry best practices, new emissions data for modern aircraft and airport emission sources, airport operational information that affect aviation emissions, and emissions modelling methodologies, including engines not currently regulated for gaseous and nvPM emissions.
• Monitor trends in supersonic technology and assess consequences for engine emissions, aeroplane CO₂ emissions and certification standards.
• nvPM and NO_x (non-CO₂) emissions assessments at cruise and development of the engine-level NO_x metric with the assessment of its ability to control cruise NO_x emissions.
• vPM Emissions measurements and modeling - review scientific community findings on vPM emission measurement procedures, sources, and cruise emissions including analysis of implications, priorities, and timings.
• Electricity and Hydrogen supply assessment – start scoping the work related to additional assessments to understand the requirements that would be needed to track the electricity and hydrogen supply for aircraft propulsion and its potential contribution into CO₂ emissions for international aviation.
• Emission certification databases - maintain aeroplane CO₂ certification database and engine emissions certification databank.
• Monitor developments in aeroplane and engine applications and concepts e.g. blended wing body, or non-classical tube and wing configurations and open-rotor engines etc., and develop methodologies for emissions certification. For less mature products (TRL≤6) that are brought to the attention of WG3, consider implications on future emission certifications.
• Assess potential NO_x reporting point at 57.5% of rated thrust - investigate the feasibility and added value of a potential reporting point for emission index for NO_x at 57.5% sea-level static thrust with the goal to better characterize cruise emissions.
• NO_x LTO Stringency Standard Setting Process – develop new NO_x LTO stringency options based on the existing metric and correlating parameter; assess NO_x emissions mitigation technologies associated with stringency options, including costs.
• Fuel composition and emissions – – quantify exhaust emissions of all regulated pollutants and vPM precursors when using aviation fuels, considering relevant fuel composition topics (e.g. aromatic and hydrogen content).
• Supersonics certification requirements – update all elements of Annex 16, Volume II and ETM Volume II, including the regulatory limits for modern supersonic engines without afterburning technology based on emissions data availability.

Main publications (Reference publications):

• Annex 16 – Volume II, Aircraft Engine Emissions (Fifth Edition, July 2023)
• Annex 16 – Volume III, Aeroplane CO2 Emissions (First Edition, July 2017, including Amendments 1 and 2)
• Doc 9501 – Environmental Technical Manual, Volume II – Procedures for the Emission Certification of Aircraft Engines (Fifth Edition, 2023)
• Doc 9501 – Environmental Technical Manual, Volume III – Procedures for the CO₂ Emissions Certification of Aeroplanes (Third Edition, 2023)
• Doc 9889 - Airport Air Quality Manual (Third Edition, 2023)
• Doc 9884 – Guidance on aircraft emission charges related to local air quality (2007)
• Doc 9887 – Report of the Independent Experts on the LTTG NOx Review and Medium and Long Term Technology Goals for NOx (2008)
• Doc 9953 – Report of the Independent Experts to CAEP/8 on the Second NOx Review and the Establishment of Medium and Long Term Technology Goals for NOx (2010)
• Doc 9963 – Report of the Independent Experts on the Medium and Long Term Goals for Aviation Fuel Burn Reduction From Technology (2010)