Detailed working notes on ICAO's environmental protection framework for civil aviation: CORSIA, the Long-Term Aspirational Goal (LTAG), sustainable aviation fuels (SAF), and operational green-trajectory measures delivered through ATM. This folder expands the summary in topics/green_atm.md into per-aspect files readable independently.

Files in this folder#

• overview.md -- what Green ATM is, where it sits in the ICAO framework, and the relationship between LTAG, CORSIA, SAF, and operational measures.
• components.md -- the four pillars of the basket of measures: technology, SAF/LCAF, operational improvements, and market-based measures.
• blocks.md -- CORSIA phases (pilot/first/second) mapped as a timeline flow; LTAG trajectory milestones from A37 2010 goals to net-zero 2050.
• threads.md -- the five functional axes: CORSIA MRV, SAF/LCAF deployment, ATM operational measures, CO2 technology standard, regional/EU schemes.
• modules.md -- anatomy of one strand in depth: the CORSIA offsetting obligation cycle (MRV to cancellation) plus a CDO green-trajectory module.
• enablers.md -- institutional, regulatory, infrastructure, and capacity enablers required to implement all four pillars.
• performance_objectives.md -- KPA-keyed performance matrix and KPIs for environment, cost-effectiveness, and flight efficiency.
• timeline.md -- year-keyed table of key dates from A37 (2010) to the LTAG horizon (2050).
• references.md -- consolidated ICAO and authoritative external references.

Reading order#

Start with overview.md for the conceptual framing, then components.md for the basket structure. Read blocks.md for the CORSIA phase chronology and LTAG trajectory. threads.md separates the functional axes. modules.md gives the MRV cycle and a CDO example. enablers.md and performance_ objectives.md support implementation planning. Use timeline.md for date context and references.md for citations.

Source basis#

Content is grounded in:

• Annex 16, Volume IV (CORSIA), Second Edition, July 2023 (applicable 1 January 2024).
• Annex 16, Volume III (Aeroplane CO2 Emissions), First Edition, 2017.
• ICAO Doc 9988 (State Action Plans guidance), Fourth Edition, 2024.
• ICAO Doc 9931 (CDO Manual), First Edition, 2010.
• ICAO Doc 9993 (CCO Manual), First Edition, 2013.
• ICAO Doc 10177 (Environment Manual / Noise Abatement), CAEP.
• ICAO Doc 10184 (41st Assembly Resolutions, 2022): A41-21 (LTAG) and A41-22 (CORSIA).
• ICAO Doc 9750 (GANP), ASBU modules CDO-B0, CCO-B0, FRTO-B0.
• ICAO CORSIA website: https://www.icao.int/environmental-protection/CORSIA/Pages/default.aspx

What Green ATM is#

Green ATM is the shorthand for the environmental agenda of civil aviation and air traffic management: the ICAO policies, technical standards, operational procedures, and market measures designed to reduce CO2 and other greenhouse gas (GHG) emissions from international aviation.

The ICAO Assembly at its 41st Session (September-October 2022) adopted a Long-Term Aspirational Goal (LTAG) of net-zero carbon emissions from international aviation by 2050, in support of the Paris Agreement (Assembly Resolution A41-21, operative clause 7). This goal is collective and aspirational: it does not assign binding emissions-reduction targets to individual States, but each State is expected to contribute within its national circumstances.

Reaching net-zero by 2050 is not achievable through any single instrument. The ICAO Assembly codified the approach as a basket of measures, comprising four interlinked pillars:

1. Technology and standards -- more fuel-efficient aircraft (CO2 certification under Annex 16 Volume III) and cleaner engines (Annex 16 Volume II).
2. Sustainable aviation fuels (SAF) and lower-carbon aviation fuels (LCAF) -- replacing fossil kerosene with fuels of lower lifecycle carbon intensity.
3. Operational improvements -- ATM and airport procedures that reduce actual fuel burn on each flight, including CDO, CCO, free-route airspace, reduced holding, and trajectory-based operations.
4. Market-based measures -- CORSIA at the global level, which requires operators to offset CO2 emissions above the scheme's baseline.

Within the ATM domain, the third pillar is the primary deliverable for ANSPs, airports, and airspace designers. It is often called "green trajectories" -- a family of operational concepts and procedures that combine to reduce track miles flown, avoid unnecessary level segments, eliminate unnecessary holding, and progressively extend optimal trajectory management gate to gate.

Where Green ATM sits in the ICAO framework#

Green ATM is the environmental strand of the Global Air Navigation Plan (GANP, Doc 9750). The GANP explicitly recognises the basket of measures as part of its operational strategy, and the ASBU modules CDO-B0, CCO-B0, FRTO-B0, and OPFL-B1 are the operational-improvement components of the basket. Assembly Resolution A41-21 operative clause 23(a) urges States, operators, and ANSPs to accelerate fuel-efficient routings and air navigation procedures, and to take into account the ASBUs.

CORSIA is the legal-obligation layer. It is codified in Annex 16, Volume IV (Second Edition, July 2023, applicable 1 January 2024). This is the first global market-based measure for any transport sector and is a cornerstone of ICAO's climate leadership.

CAEP (Committee on Aviation Environmental Protection) is the ICAO technical body that develops the environmental SARPs for Annex 16 and provides technical input to the CORSIA periodic review and the LTAG monitoring process.

Why the ATM community is engaged#

Two of the four pillars -- operational improvements and CORSIA -- directly engage the ATM community.

On operational improvements: ANSPs enable CDO and CCO through airspace design, procedure development, and ATC facilitation. Network managers enable free-route airspace and reduce unnecessary holding. Trajectory-based operations extend optimal profile management across the full gate-to-gate flight. EUROCONTROL data shows that CDO and CCO conformance varies significantly by airport and airline, and improving it yields measurable fuel savings at scale.

On CORSIA: States are required to oversee operator MRV compliance, calculate offsetting requirements, and administer emissions unit cancellation. ANSPs facilitate the operational infrastructure that operators use to reduce their offsetting burden -- particularly SAF fuelling logistics and flight profile optimisation.

Relationship to other topics in this workspace#

• ASBU -- the ASBU modules CDO-B0, CCO-B0, FRTO-B0, and OPFL-B1 are the operational-improvement components of the basket of measures. TBO-B2 and TBO-B3 extend green trajectory management to full gate-to-gate optimisation.
• CDO / CCO -- the specific ATM operational measures; deep-dived in those separate topic files.
• TBO -- the long-term trajectory management framework that maximises fuel efficiency through 4D trajectory optimisation.
• A-CDM -- airport collaborative decision-making reduces APU time, taxi time, and airport-related fuel burn.
• ATFM -- network flow management reduces airborne holding and fuel-burn penalties from demand-capacity imbalances.

The basket of measures: four pillars#

ICAO Assembly Resolution A41-21 and Doc 9988 (Fourth Edition, 2024) define the basket of measures as the comprehensive approach to reducing CO2 emissions from international aviation. The basket has four categories.

• Pillar 1: Technology and standards

  • Aircraft CO2 efficiency standard
    • Annex 16 Volume III (First Edition 2017): the ICAO CO2 certification standard for subsonic jet aeroplanes and large propeller-driven aeroplanes
    • First global aircraft CO2 certification standard; sets a maximum CO2 metric value per aeroplane type based on maximum take-off mass and configuration
    • Administered by CAEP; updated with each new CAEP work cycle
  • Engine emissions standards
    • Annex 16 Volume II: NOx, HC, CO, and smoke certification standards for turbine engine emissions during the landing and take-off cycle (LTO)
    • CAEP progressively tightens NOx standards
  • Future technology
    • Hydrogen propulsion, battery-electric and hybrid-electric aircraft: CAEP tracking; no Annex 16 standard yet
    • Sustainable/zero-emissions propulsion for regional and short-haul operations expected to contribute significantly towards 2050

• Pillar 2: Sustainable aviation fuels (SAF) and LCAF

  • CORSIA eligible fuels (defined in Annex 16 Vol IV)
    • CORSIA sustainable aviation fuel: a renewable or waste-derived aviation fuel meeting CORSIA Sustainability Criteria
    • CORSIA lower carbon aviation fuel (LCAF): a fossil-based aviation fuel meeting CORSIA Sustainability Criteria
    • Both types reduce the operator's offsetting requirement
  • Lifecycle carbon assessment
    • CORSIA Sustainability Criteria and Default Life Cycle Emissions Values are maintained as ICAO documents on the CORSIA website
    • Methodology for calculating actual lifecycle emissions also published on the CORSIA website
  • GFAAF and ACT-SAF
    • ICAO Global Framework for Aviation Alternative Fuels (GFAAF, established CAAF/1 2009): tracks SAF conversion processes, airports distributing SAF
    • ACT-SAF programme: capacity-building, training, and partnerships for SAF scale-up in developing States
  • ICAO SAF Vision
    • 2050 ICAO Vision for Sustainable Aviation Fuels adopted at CAAF/2 (October 2017): aspirational path for substituting a significant proportion of aviation fuels with SAF by 2050
    • CAAF/3 (2023) was tasked to review and update the Vision and define a global framework including LCAF and cleaner energies

• Pillar 3: Operational improvements (ATM/CNS layer)

  • Continuous Descent Operations (CDO)
    • ASBU module CDO-B0: fuel-efficient arrival profiles removing level segments
    • Doc 9931 (CDO Manual, 2010): standard for CDO design, implementation, and measurement
    • Benefit: reduced fuel burn, noise, and emissions during approach; typical savings 40-150 kg fuel per arrival (varies by aircraft type and baseline procedure)
  • Continuous Climb Operations (CCO)
    • ASBU module CCO-B0: fuel-efficient departure profiles without intermediate level-offs
    • Doc 9993 (CCO Manual, 2013): standard for CCO design, implementation, and measurement
    • Benefit: reduced fuel burn and noise near departure airports
  • Free Route Airspace (FRA / FRTO-B0)
    • Allows operators to fly direct or user-preferred routes in cruise airspace without mandatory routing via ATS waypoints
    • Doc 9988 records a NAV Portugal example: free route in the Lisbon FIR saved 8,783 tonnes of fuel and 27,000 tonnes of CO2 in the initial implementation period
  • Optimum Flight Levels (OPFL-B1)
    • ASBU module OPFL-B1: improved access to optimum cruise altitude through dynamic re-clearance
    • Prevents fuel penalty from flying at sub-optimal altitudes due to rigid ATS level assignment
  • Reduced Holding and Ground Stops
    • ATFM-driven departure slots replace airborne holding
    • A-CDM target off-block times reduce taxi and APU time
  • Trajectory-Based Operations (TBO-B2/B3)
    • Gate-to-gate 4D trajectory optimisation minimises fuel burn across all phases of flight
    • Integrates CDO, CCO, OPFL, and network-level ATFM into a single managed trajectory

• Pillar 4: Market-based measures

  • CORSIA (global)
    • Annex 16 Volume IV: mandatory MRV, offsetting, and emissions unit cancellation scheme for international aviation
    • Three phases: pilot (2021-2023), first (2024-2026), second/mandatory (2027-2035)
    • Designed to achieve carbon-neutral growth above the baseline; not a reduction scheme
  • EU Emissions Trading System (EU ETS)
    • Covers intra-EEA flights; requires operators to surrender emission allowances for covered flights
    • Regional layer complementary to CORSIA for EU-regulated flights (authoritative source -- not in local library)
  • ReFuelEU Aviation
    • EU regulation mandating SAF blending at EU airports on an escalating schedule starting from 2025
    • Creates a SAF demand floor in Europe (authoritative source -- not in local library)
  • Other national schemes
    • UK ETS (post-Brexit); various carbon pricing mechanisms at national level
    • States encouraged to report these in State Action Plans

CORSIA MRV system components#

The MRV system under Annex 16 Volume IV has five distinct components:

• Monitoring: aeroplane operators monitor fuel use from international flights using an approved Fuel Use Monitoring Method or the ICAO CORSIA CO2 Estimation and Reporting Tool (CERT). Monitoring Plans must be approved by the attributed State.
• Reporting: operators submit annual Emissions Reports to their attributed State; States submit aggregated data to ICAO.
• Verification: an accredited, impartial third-party Verification Body independently verifies each Emissions Report.
• Offsetting calculation: the State calculates each operator's annual offsetting requirement and final compliance-period offsetting requirement (FOR_c), taking into account CORSIA eligible fuel use.
• Cancellation: operators cancel CORSIA Eligible Emissions Units equal to FOR_c; a verified Emissions Unit Cancellation Report is submitted to the State and to ICAO.

References#

• Annex 16, Volume IV (CORSIA), Second Edition, July 2023, applicable 1 January 2024 -- MRV Standards, eligible fuel definitions (Part I, §1.1), offsetting requirements (Chapter 3), emissions units (Chapter 4).
• Annex 16, Volume III (Aeroplane CO2 Emissions), First Edition, 2017, applicable 1 January 2018 -- CO2 certification standard for aeroplanes.
• Annex 16, Volume II (Aircraft Engine Emissions) -- NOx and LTO emissions certification.
• Doc 9988 (State Action Plans Guidance), Fourth Edition, 2024, Chapter 4, §4.5 -- operational improvements as part of the basket of measures; CDO-B0 and CCO-B0 reference.
• Doc 9931 (CDO Manual), First Edition, 2010 -- CDO design and measurement.
• Doc 9993 (CCO Manual), First Edition, 2013 -- CCO design and measurement.
• Doc 10184 (41st Assembly Resolutions, 2022) -- A41-21 operative clause 7 (LTAG), §23(a) (ATM operational improvements), basket of measures definition (§2782).

Two parallel timelines#

Green ATM has two distinct time axes that must not be confused:

1. CORSIA phase timeline -- the statutory compliance windows defined in Annex 16, Volume IV and Assembly Resolutions.
2. LTAG trajectory -- the long-term CO2 reduction pathway from baseline goals (2010) to net-zero by 2050.

Mapping these against ASBU block availability dates shows how operational ATM improvements interlock with the policy milestones.

CORSIA phases#

For the second phase, the growth factor split changes within the period: from 2027-2029, sectoral 100% / individual 0%; from 2030-2032, sectoral 100% / individual 0%; from 2033-2035, sectoral 85% / individual 15%.

Applicability: an operator must participate if it conducts international flights (as defined in Annex 16 Vol IV Chapter 1) between States both of which are in the CORSIA States for Chapter 3 State Pairs list for that compliance year.

CORSIA compliance period cycle#

Each compliance period is three years. The key milestones within each compliance period:

• Year 1-3: operators monitor fuel use annually.
• By 31 May each year: verified Emissions Report for the prior year submitted to State and ICAO.
• After final year: State calculates FOR_c (final offsetting requirement for the compliance period).
• Within 9 months of period end: operators cancel CORSIA Eligible Emissions Units equal to FOR_c.

LTAG trajectory milestones#

ATM operational improvement milestones aligned#

The ASBU operational measures align with the CORSIA timeline:

• CDO-B0 / CCO-B0 / FRTO-B0: Block 0, available from 2013. States implementing these modules deliver fuel/CO2 savings that reduce operators' total emissions and thus their CORSIA offset burden.
• OPFL-B1: Block 1, from 2019. Improved access to optimum cruise levels through dynamic re-clearance further reduces fuel burn.
• TBO-B2: Block 2, from 2025. Trajectory-based operations extend optimisation gate-to-gate during the second phase of CORSIA.
• TBO-B3: Block 3, from 2031. Full trajectory contracts within the CORSIA second phase, maximising green trajectory benefits.

References#

• Annex 16, Volume IV (CORSIA), Second Edition, July 2023, §3.1 and Appendix 1 -- phase applicability dates, compliance period timelines, and offsetting calculation formulas.
• Doc 10184 (41st Assembly Resolutions, 2022) -- A41-21 operative clause 7 (LTAG net-zero 2050); A41-22 §2 and §3 (CORSIA phases and post-pilot baseline).
• Doc 9988 (State Action Plans), Fourth Edition, 2024, §1.1.3 -- LTAG operative clause 7 and State Action Plan linkage.
• Doc 9750 (GANP), ASBU modules CDO-B0, CCO-B0, FRTO-B0, OPFL-B1 -- operational improvement block availability (authoritative source -- not in local library; see https://ganpportal.icao.int/).

Five functional axes#

Green ATM is best understood through five functional threads. Each thread represents a distinct axis of work with its own regulatory basis, implementing actors, and performance indicators. The threads are interdependent: reducing actual emissions (Threads 2 and 3) directly reduces CORSIA offsetting obligations (Thread 1).

• Thread 1: CORSIA MRV and offsetting

  • Monitoring, reporting, and verification
    • Operators use approved Fuel Use Monitoring Methods or the ICAO CORSIA CO2 Estimation and Reporting Tool (CERT)
    • Emissions Monitoring Plans approved by the attributed State
    • Annual verified Emissions Reports submitted to State and ICAO
  • Offsetting calculation and compliance
    • State calculates annual and final offsetting requirements
    • Operator cancels CORSIA Eligible Emissions Units each compliance period
  • Eligible fuels credit
    • Use of CORSIA-eligible SAF or LCAF reduces the offsetting requirement (claimed in the Emissions Report)
  • Periodic review
    • CORSIA reviewed every three years from 2022; results feed into Assembly decisions on phase design

• Thread 2: SAF and LCAF deployment

  • Feedstock and production
    • SAF: renewable or waste-derived (e.g. HEFA, AtJ, FT-SPK pathways approved by ASTM)
    • LCAF: fossil-based but meeting CORSIA Sustainability Criteria
  • Lifecycle carbon assessment
    • Default Life Cycle Emissions Values for eligible fuels published on the ICAO CORSIA website and periodically updated
    • Actual lifecycle calculation methodology also published
  • ACT-SAF programme
    • ICAO capacity-building and partnerships to scale SAF production and delivery, particularly in developing States
  • Regional mandates
    • EU ReFuelEU Aviation: escalating SAF blending mandate at EU airports from 2025 (authoritative source -- not in local library)
  • SAF into-plane logistics
    • Airport infrastructure for SAF delivery; into-plane uplift documentation for CORSIA eligible fuel claims

• Thread 3: ATM operational green measures

  • Continuous Descent Operations (CDO)
    • Design of arrival routes and STARs enabling continuous 3D profiles from top of descent
    • ATC facilitation: reducing speed and altitude instructions during descent
    • Measurement: EUROCONTROL CDO/CCO performance dashboard tracks seconds of level flight during descent by airport and airline
  • Continuous Climb Operations (CCO)
    • Standard Instrument Departures (SIDs) designed without altitude constraints except where operationally necessary
    • ATC facilitation: minimising early level-offs after departure
  • Free Route Airspace (FRA)
    • Airspace structure allowing operators to fly user-preferred routes without mandatory ATS route adherence in cruise
    • Implemented subregionally: ICAO EUR (EUIRFRAF area), APAC (advancing), NAT (oceanic tracks advancing)
  • Reduced holding and ground delay
    • ATFM departure slots replace airborne holding; time-based metering (TBFM) further reduces arrival holding
    • A-CDM target off-block times reduce taxi and APU fuel burn
  • TBO integration
    • TBO-B2 and TBO-B3 extend trajectory optimisation gate to gate; 4D trajectory management locks in CDO/CCO/FRA benefits across the full flight profile

• Thread 4: CO2 technology standard (certification)

  • Annex 16 Volume III standard
    • CO2 metric value certification for new aeroplane types and new deliveries of existing types above threshold masses
    • Standard tightened over each CAEP work cycle
  • Engine emissions (Annex 16 Volume II)
    • NOx certification stringency progressively tightened
    • Local air quality benefits as well as global climate benefit
  • Noise (Annex 16 Volume I)
    • Noise abatement procedures (CDO/CCO) also reduce noise around airports; dual benefit
  • Fleet renewal tracking
    • States Action Plans expected to include fleet modernisation projections; retiring older aircraft reduces per-unit burn

• Thread 5: Regional and unilateral market measures

  • EU ETS -- aviation
    • Cap-and-trade system covering intra-EEA flights; operators surrender allowances (authoritative source -- not in local library)
  • ReFuelEU Aviation
    • EU SAF mandate creating a SAF demand floor in Europe; escalating blending obligation from 2025 (authoritative source -- not in local library)
  • National carbon pricing
    • UK ETS, Swiss ETS, and various State-level carbon pricing schemes complement CORSIA for domestic and bilateral traffic
  • Relationship to CORSIA
    • CORSIA and regional measures must be designed to avoid double counting; ICAO and regional bodies coordinate on accounting

Thread interdependencies#

The threads form a reinforcing system:

• More CDO/CCO/FRA (Thread 3) reduces total emissions per flight, directly reducing each operator's CORSIA offsetting requirement (Thread 1).
• More SAF (Thread 2) further reduces the offsetting requirement through eligible fuel credits, and also reduces lifecycle CO2.
• Better aircraft technology (Thread 4) reduces baseline fuel burn, compressing the absolute amount that must be offset or displaced.
• Regional market measures (Thread 5) create economic incentives for operators and airports to invest in all four threads simultaneously.

References#

• Annex 16, Volume IV (CORSIA), Second Edition, July 2023 -- MRV (Chapter 2), offsetting (Chapter 3), emissions units (Chapter 4), eligible fuel definitions (Part I).
• Doc 9931 (CDO Manual), First Edition, 2010 -- CDO procedure design and measurement.
• Doc 9993 (CCO Manual), First Edition, 2013 -- CCO procedure design and measurement.
• Doc 10177 (Environment Manual / Noise Abatement), CAEP -- §2.6.4 EUROCONTROL CDO/CCO performance dashboard methodology.
• Doc 9988 (State Action Plans), Fourth Edition, 2024, Chapter 4, §4.5 -- operational improvement measures including CDO, CCO, free route.
• Doc 10184 (41st Assembly Resolutions, 2022) -- A41-21 §23(a) operational improvements; §2782 basket of measures; A41-22 §6 SAF credit mechanism.

Two representative modules are worked through here: the CORSIA offsetting obligation cycle (Thread 1), and a CDO green-trajectory module (Thread 3). Together they illustrate how the market-based and operational dimensions of Green ATM function at the level of a single operator and a single airport, respectively.

Module A: CORSIA offsetting obligation cycle#

This module describes one aeroplane operator completing a three-year compliance period under Annex 16, Volume IV.

1. Scope determination#

The operator identifies which of its international routes connect State pairs both of which appear in the ICAO document "CORSIA States for Chapter 3 State Pairs" for the applicable compliance period. Only emissions from those State-pair routes count toward offsetting requirements.

The operator checks whether it qualifies as a "new entrant" (defined in Annex 16 Vol IV §1.1): operators whose annual CO2 from routes in scope is 10,000 tonnes or less in any year are exempt. New entrants are also exempt for up to three years from first meeting the threshold.

2. Monitoring#

The operator selects an eligible Fuel Use Monitoring Method (Annex 16 Vol IV Appendix 2) or uses the ICAO CORSIA CO2 Estimation and Reporting Tool (CERT, Appendix 3). The method must be approved by the attributed State via an Emissions Monitoring Plan before the compliance period begins.

The operator records fuel uplift and consumption for each flight in scope, including any CORSIA eligible fuel (SAF or LCAF) to be claimed. Data gaps may not exceed 5 per cent of covered flights for 2021-2035 (Annex 16 Vol IV §2.5.1.1).

3. Annual reporting and verification#

By 31 May each year, the operator submits an Emissions Report for the prior calendar year to its attributed State and authorises the verification body to submit its Verification Report independently.

The Verification Body -- an accredited, impartial third party -- reviews the Emissions Report against the monitoring plan and data trails. Reasonable assurance level is required (Annex 16 Vol IV Appendix 6).

The State conducts an order-of-magnitude check and submits validated data to ICAO. ICAO publishes aggregate data on the CORSIA website.

4. Offsetting requirement calculation#

The State calculates the operator's annual offsetting requirement (OR) using the formula in Annex 16 Vol IV §3.2. The formula compares the operator's emissions on covered routes against the applicable growth factor applied to the sector baseline.

For the pilot and first phases (2021-2026): the growth factor is sectoral only (100% of sector growth, 0% individual operator growth).

For the second phase (2027-2035): for 2027-2029 still sectoral 100% / individual 0%; for 2030-2032 sectoral 100% / individual 0%; for 2033-2035 sectoral 85% / individual 15%.

If the operator used CORSIA eligible fuels, the attributed lifecycle CO2 reduction is subtracted from the offsetting requirement, reducing the units the operator must cancel.

5. Emissions unit cancellation#

At the end of the three-year compliance period, the State notifies the operator of its Final Offsetting Requirement (FOR_c), which is the sum of the three annual requirements minus eligible fuel credits.

The operator cancels CORSIA Eligible Emissions Units (from ICAO- approved programmes) in a quantity equal to FOR_c. Only units listed in the ICAO document "CORSIA Eligible Emissions Units" and meeting the CORSIA Emissions Unit Eligibility Criteria qualify.

The operator submits a verified Emissions Unit Cancellation Report to the State. The State submits to ICAO. CORSIA programme registries make cancellation records publicly visible.

Outcome#

The operator has offset the net growth in its international aviation CO2 emissions above the scheme baseline for the period. This does not reduce the absolute emissions -- it compensates for the growth above the baseline through independently verified carbon units.

Module B: CDO green-trajectory module at a busy airport#

This module describes the implementation and measurement of a CDO procedure at a medium-to-large airport under Doc 9931 and ASBU CDO-B0.

Problem statement#

A typical radar-vectored descent at a busy airport involves multiple level segments totalling 3-7 minutes. Each minute of level flight at low altitude burns significantly more fuel than a continuous descent at idle thrust. CDO removes or reduces those level segments.

Design step#

The ANSP designs a Standard Terminal Arrival Route (STAR) with a continuous vertical profile from top of descent to the Initial Approach Fix (IAF). Altitude constraints along the STAR are minimised to those required for safety separation (for example, terrain clearance or crossing restrictions with departures). Speed constraints are designed to allow maximum FMS autonomy.

The procedure is flight-checked, published in the AIP, and briefed to airlines and controllers.

Controller facilitation#

ATC issues STAR clearances early (before top of descent where practicable) so the FMS can compute the optimal vertical profile from cruise altitude. Speed instructions are limited to those required for separation, allowing the FMS to manage idle-thrust descent.

When traffic demand requires vectoring, controllers aim to rejoin the STAR above the minimum level to preserve as much of the continuous profile as possible.

Performance measurement#

The EUROCONTROL CDO/CCO performance framework (described in Doc 10177 Chapter 4) defines the metric as time in level flight during a defined measurement window (typically from 6,000 ft AAL to the runway threshold). A CDO conformance rate of zero seconds of level flight represents a perfect CDO.

The EUROCONTROL CCO/CDO performance dashboard tracks conformance by airport and by airline, allowing comparison across the European network. The same methodology is recommended for States implementing CDO globally.

Benefits#

A well-implemented CDO at a busy airport typically saves 40-150 kg of fuel per arrival, depending on aircraft type and the depth of the vertical profile change. At high-traffic airports (100,000+ annual arrivals), system-wide savings of thousands of tonnes of CO2 per year are achievable. Additional benefits include reduced noise under the approach path and reduced controller workload when demand is moderate.

Integration with ASBU#

CDO-B0 is a Block 0 module in the GANP framework. It is a prerequisite for OPFL-B1 and TBO-B2 benefits in the arrival phase: once CDO is established, TBO extends the profile management upstream into the cruise phase, delivering further fuel savings through optimised top- of-descent placement and reduced speed interventions.

References#

• Annex 16, Volume IV (CORSIA), Second Edition, July 2023, Part II Chapters 2, 3, and 4 -- MRV, offsetting calculation, emissions unit requirements (full Module A text).
• Doc 9931 (CDO Manual), First Edition, 2010 -- Module B CDO design and measurement basis.
• Doc 10177 (Environment Manual), CAEP, Chapter 4, §4.2 -- CDO definition, noise and fuel burn benefits.
• Doc 10177, §2.6.4 -- EUROCONTROL CCO/CDO Task Force and European performance dashboard methodology.
• Doc 9988 (State Action Plans), Fourth Edition, 2024, §4.3.2 and Appendix A -- CDO example state measures and benefit quantification.

What must be in place#

Delivering Green ATM across all four pillars requires enablers in five categories: institutional and regulatory, infrastructure and data, economic and financial, human factors and training, and international coordination. Weak enablers in any category create implementation gaps even when the technical standards and procedures exist.

Institutional and regulatory enablers#

ICAO governance#

The ICAO Assembly sets the policy goals (LTAG, CORSIA baseline, basket of measures). The Council oversees implementation, conducts periodic reviews (CORSIA review every three years from 2022), and adopts Annex 16 amendments through the CAEP work cycle.

CAEP (Committee on Aviation Environmental Protection) is the primary technical body: it develops SARPs for Annex 16 Volumes I-IV, maintains the CORSIA Sustainability Criteria and eligible fuel documentation, and assesses the environmental impact of proposed measures.

State attribution and oversight#

Each aeroplane operator is attributed to a single State for CORSIA purposes. That State must approve the operator's Emissions Monitoring Plan, conduct an order-of-magnitude check on verified Emissions Reports, calculate the operator's offsetting requirements, and submit data to ICAO on schedule. States without strong aviation regulatory capacity face a significant burden; ACT-SAF and the No Country Left Behind (NCLB) initiative address this gap.

Verification body accreditation#

CORSIA requires operators to have their Emissions Reports verified by an accredited, impartial Verification Body. States must publish a list of accredited bodies and update it when changes occur. In States with limited regulatory infrastructure, establishing an accreditation framework is a prerequisite for CORSIA compliance.

Annex 16 State obligations#

States are required to ensure that aeroplane operators attributed to them comply with the Standards in Annex 16 Volume IV. Failure to submit verified data to ICAO, or failure to ensure operators cancel the required emissions units, constitutes a breach of the Standards.

Infrastructure and data enablers#

Fuel monitoring infrastructure#

Operators need fuel uplift data from all international airports. Many airports have mature into-plane fuel delivery records. For airports where paper fuelling records dominate, digitisation is an enabler. The CERT tool is the fallback for operators without sufficient data.

SAF supply chain and blending#

SAF production facilities, transport logistics (pipeline, truck, barge), airport fuel farm integration, and into-plane uplift are all required before operators can make CORSIA eligible fuel claims. The supply chain remains the primary bottleneck for SAF scale-up globally.

CORSIA Eligible Emissions Units registries#

Operators can only cancel units from ICAO-approved programmes. Those programmes must operate public, auditable registries. ICAO publishes the list of eligible programmes on the CORSIA website. Registry accessibility and unit availability are supply-side enablers.

ATM infrastructure for green trajectories#

CDO enablers at the ATM layer:

• RNAV/PBN approach and arrival procedures replacing radar vectors.
• Controller training in facilitating idle-thrust continuous descents.
• Traffic flow management that sequences arrival streams before top of descent, reducing last-minute speed interventions.

CCO enablers:

• SID redesign removing unnecessary altitude constraints.
• Airspace integration to de-conflict departure and arrival flows.

Free Route Airspace enablers:

• Controller tool support for direct routings in cruise sectors.
• Neighbouring FIR coordination agreements for cross-border free route.
• SWIM-based flight-object sharing to propagate FRA routing downstream.

Economic and financial enablers#

Carbon market liquidity#

The CORSIA offsetting mechanism requires liquid, high-integrity carbon markets. Eligible Emissions Units must be available in sufficient quantity and at prices that do not undermine scheme integrity. CAEP periodically assesses market supply.

SAF economics#

SAF currently costs 3-5 times more than conventional jet fuel. Government incentives, SAF mandates (e.g. ReFuelEU Aviation), and long-term supply contracts are required to close the price gap. Doc 9988 Chapter 4 notes that SAF deployment should be considered from a medium-term perspective as the only route to physically reducing aviation emissions in tandem with technology progress.

State Action Plan financing#

Doc 9988 Chapter 5 and Resolution A41-21 operative clause 17 recognise that LTAG implementation requires substantial investment, particularly in developing States. ICAO coordinates with multilateral development banks, the Global Environment Facility (GEF), and national green finance instruments to direct funding toward aviation decarbonisation.

Human factors and training enablers#

Controller training for green trajectories#

Delivering CDO and CCO requires controllers to modify working practices. Training programmes must cover the fuel and environmental benefits of continuous profiles, the phraseology and tactics for facilitating them under traffic load, and the metrics used to measure performance. The Swedish LFV example in Doc 9988 demonstrates a practical approach: a 2-hour training module covering ATC behaviour, flight efficiency, environmental impact, and the fuel consequences of different operational choices.

Pilot and FMS proficiency#

CDO conformance depends on pilots being briefed on STAR design philosophy and on FMS programming for idle-thrust continuous descent. Airline flight operations manuals and line training must reinforce CDO technique.

SAF handling training#

Airport fuelling staff need training for SAF handling, blending documentation, and into-plane delivery records that will support CORSIA eligible fuel claims.

International coordination#

State pairs and reciprocity#

CORSIA applies only to flights between State pairs both of which are in the CORSIA States for Chapter 3 list. Expanding CORSIA coverage requires States to opt in (for the pilot and first phases) or meet the mandatory threshold (from 2027). Diplomatic engagement between States is an enabler for scheme breadth.

Regional green trajectory harmonisation#

CDO and CCO benefits compound when implemented consistently across multiple FIRs. Cross-border AMAN (XMAN) extends arrival management upstream, enabling CDO profiles to begin from cruise altitude rather than after transfer. SESAR 3 JU / Digital European Sky coordinates the European CDO/CCO task force and dashboard. APAC regional bodies promote CDO/CCO harmonisation under the APAC Seamless ATM Plan.

ReFuelEU and EU ETS coordination with CORSIA#

ICAO and the European Commission coordinate to ensure that the EU ETS and ReFuelEU Aviation are designed to avoid double-counting with CORSIA. States in the EEA apply specific accounting rules to prevent operators from claiming both a CORSIA credit and an EU ETS credit for the same emission reduction.

References#

• Annex 16, Volume IV (CORSIA), Second Edition, 2024, Chapter 1 (State attribution), Chapter 2 (MRV), Appendix 6 (verification bodies) -- institutional and MRV enabler basis.
• Doc 9988 (State Action Plans), Fourth Edition, 2024, Chapter 5 (assistance) and §4.5 (operational improvements) -- economic and ATM enabler reference.
• Doc 10177 (Environment Manual), CAEP, §2.6.4 -- EUROCONTROL CDO/CCO Task Force as a model for collaborative ATM enabler development.
• Doc 10184 (41st Assembly Resolutions, 2022) -- A41-21 operative clause 17 (financing for LTAG) and §23(a) (ATM/ANSP acceleration).
• Doc 9931 (CDO Manual), 2010 -- §2.3-2.5 controller facilitation guidance.
• Doc 9993 (CCO Manual), 2013 -- §3.3.2-3.3.4 controller facilitation and airspace design guidance.

The performance lens#

Green ATM maps onto the ICAO Key Performance Areas (KPAs) defined in Doc 9854 (Global ATM Operational Concept) and Doc 9883 (Manual on Global Performance of the Air Navigation System). Environmental impact is the primary KPA driver, but the basket of measures also contributes significantly to flight efficiency, cost-effectiveness, and predictability.

KPA contribution matrix#

The following matrix shows the contribution of each Green ATM pillar to the ICAO KPAs (1 = some benefit, 2 = clear benefit, 3 = primary driver).

The ATM operational pillar scores highest on flight efficiency and cost-effectiveness because CDO, CCO, and free-route airspace reduce actual flight time and fuel burn, delivering direct cost savings to operators alongside the environmental benefit.

Performance objectives#

Key Performance Indicators (KPIs)#

Environment KPIs#

• Total CO2 emissions from international aviation per year (tonnes).
• CO2 per revenue tonne kilometre (RTK): tracks fleet-wide efficiency improvement against the 2% per annum aspirational goal.
• Offsetting requirement per compliance period: operator-level CORSIA measure; indicates net gap between emissions and baseline.
• SAF and LCAF volume blended as a percentage of total jet fuel uplift.

Flight efficiency KPIs (ATM operational layer)#

• CDO conformance rate: seconds of level flight during descent (measurement window typically 6,000 ft AAL to threshold). Lower is better. Tracked per airport and per airline by EUROCONTROL dashboard.
• CCO conformance rate: seconds of level flight during climb (typical window from lift-off to cruise level). Lower is better.
• Fuel savings per movement attributed to CDO and CCO versus baseline radar-vector procedure: estimated using the ICAO Fuel Savings Estimation Tool (IFSET).
• Free route utilisation rate: percentage of eligible flights exercising user-preferred direct routing vs. ATS route structure.
• Track-mile extension (KEP/KEA): planned and actual flight distance versus great-circle; reduction indicates FRA and direct routing benefit.

Cost-effectiveness KPIs#

• Fuel cost savings per movement: monetised benefit of operational improvements attributable to CDO, CCO, and FRA.
• Carbon unit expenditure per tonne offset: CORSIA compliance cost per tonne; tracks market efficiency and operator burden.
• IFSET-calculated marginal abatement cost of operational measures: used in State Action Plan prioritisation (Doc 9988 Appendix F).

Predictability KPI (indirectly linked)#

• Arrival time predictability: CDO conformance correlates with more predictable landing times; measured as standard deviation of actual vs. scheduled landing time.

Reporting framework#

CORSIA performance is reported globally through the ICAO CORSIA website: verified emissions data aggregated by State, CORSIA eligible fuel volumes claimed, and emissions units cancelled per compliance period.

State Action Plans submitted to ICAO every three years report each State's selected basket of measures, quantified expected environmental benefits, and progress against prior plan commitments.

ATM operational performance is reported regionally:

• EUR: EUROCONTROL Performance Review Body; CDO/CCO dashboard.
• APAC: APANPIRG environmental reporting under the Seamless ATM Plan.
• Global: ICAO ASBU implementation monitoring covering CDO-B0, CCO-B0.

References#

• Doc 9854 (Global ATM Operational Concept) -- eleven KPAs as the performance measurement framework.
• Doc 9883 (Manual on Global Performance of the Air Navigation System) -- KPI definitions and ATM performance reporting.
• Doc 9988 (State Action Plans), Fourth Edition, 2024, §4.8 -- prioritisation of basket of measures; MAC curve tool reference.
• Doc 10177 (Environment Manual), CAEP, §2.6.4 -- EUROCONTROL CDO/CCO performance dashboard; conformance metrics.
• Annex 16, Volume IV (CORSIA), Second Edition, 2024, Chapter 2 -- MRV methodology underpinning CO2 per RTK and offsetting KPIs.

Two timelines to keep distinct#

When reading dates in Green ATM documents, two distinct timelines apply:

1. Policy and regulatory timeline: ICAO Assembly sessions, Annex 16 editions, CORSIA phase boundaries, and LTAG milestones.
2. ATM operational improvement timeline: ASBU block availability dates for CDO-B0, CCO-B0, FRTO-B0, OPFL-B1, and TBO-B2/B3.

These timelines interact: ATM operational improvements reduce the absolute emissions level against which CORSIA calculates its baseline, and TBO improvements extend into the CORSIA compliance horizon.

Key dates table#

GANP/ASBU operational improvement availability dates#

The ASBU modules contributing to Green ATM follow the standard ASBU block cadence from the 5th edition GANP baseline:

• CDO-B0 (continuous descent), CCO-B0 (continuous climb), FRTO-B0 (free-route airspace): Block 0, available from 2013.
• OPFL-B1 (optimum flight levels): Block 1, available from 2019.
• TBO-B2 (initial 4D trajectory management): Block 2, available from 2025.
• TBO-B3 (full gate-to-gate trajectory contracts): Block 3, available from 2031.

These are global notional availability dates. Individual States and ANSPs may implement earlier or later depending on traffic levels, fleet equipage, and regulatory readiness. The benefit from these measures is immediate upon implementation: every CDO or free-route flight reduces actual fuel burn regardless of whether the CORSIA compliance period has reached a given phase.

CORSIA periodic review cycle#

CORSIA is reviewed every three years from 2022 (per A39-3 and A40-19). Review inputs include CAEP analyses of: COVID-19 and demand impacts; cost impacts on States and operators; market distortion risks; and SAF/LCAF contribution levels. Council recommendations go to the next Assembly session for decision. The 2022 review produced the key changes codified in Annex 16 Vol IV Second Edition: new pilot-phase baseline (2019 instead of 2019-2020 average), and the 85% post-pilot baseline.

References#

• Annex 16, Volume IV (CORSIA), Second Edition, July 2023, Foreword -- edition history (First Edition 2018, Second Edition 2023, applicable 1 January 2024) and compliance timeline (Appendix 1).
• Doc 10184 (41st Assembly Resolutions, 2022) -- A37-19 background (§137); A41-21 operative clause 7 (LTAG); A41-22 §2 (CORSIA phases).
• Doc 9750 (GANP), ASBU block availability -- Block 0 from 2013, Block 1 from 2019, Block 2 from 2025, Block 3 from 2031 (authoritative source -- not in local library; see https://ganpportal.icao.int/).
• Doc 9988 (State Action Plans), Fourth Edition, 2024, §1.1.2-1.1.4 -- LTAG and Action Plan timeline.

Primary ICAO sources#

Annex 16 -- Environmental Protection#

• Annex 16, Volume I (Aircraft Noise), current edition -- noise certification standards and Balanced Approach policy for noise management at airports.
• Annex 16, Volume II (Aircraft Engine Emissions), current edition -- NOx, HC, CO, smoke certification standards for turbine engines; LTO cycle methodology.
• Annex 16, Volume III (Aeroplane CO2 Emissions), First Edition, July 2017, applicable 1 January 2018 -- first global CO2 certification standard for aeroplanes; developed under CAEP/10.
• Annex 16, Volume IV (CORSIA), Second Edition, July 2023, applicable 1 January 2024 -- MRV Standards (Part II Chapter 2), offsetting requirements (Chapter 3), emissions units (Chapter 4), eligible fuel definitions (Part I, §1.1), compliance timeline (Appendix 1). Supersedes First Edition (2018).

ICAO Assembly Resolutions (Doc 10184)#

• Doc 10184, Resolution A41-21 (Consolidated statement of continuing ICAO policies and practices related to environmental protection -- Climate change) -- operative clause 7: LTAG of net-zero carbon emissions from international aviation by 2050; basket of measures definition; §23(a): ATM/ANSP acceleration of fuel-efficient routings; operative clause 11: State Action Plans.
• Doc 10184, Resolution A41-22 (CORSIA) -- post-pilot baseline at 85% of 2019 emissions; offsetting growth factor splits by period.

ICAO Manuals and Guidance#

• Doc 9931 (Continuous Descent Operations (CDO) Manual), First Edition, 2010 -- CDO definition, airspace design, procedure design, ATC facilitation, and performance measurement.
• Doc 9993 (Continuous Climb Operations (CCO) Manual), First Edition, 2013 -- CCO definition, procedure design, ATC facilitation.
• Doc 9988 (Guidance on the Development of State Action Plans on CO2 Emissions Reduction Activities: Towards LTAG Implementation), Fourth Edition, 2024 -- basket of measures overview (Chapter 4); CDO-B0 and CCO-B0 as operational improvement measures (§4.5); free-route example data (§4.5); LTAG State Action Plan framework; IFSET tool reference.
• Doc 10177 (Environment Manual -- Noise Abatement Procedures), CAEP -- Chapter 3 (CCO guidance), Chapter 4 (CDO guidance), §2.6.4 (EUROCONTROL CDO/CCO Task Force and European performance dashboard), §1.2.1 (CAEP noise policy).
• Doc 9854 (Global ATM Operational Concept) -- KPA framework (eleven areas); management-by-trajectory and environmental performance linkage.
• Doc 9883 (Manual on Global Performance of the Air Navigation System) -- KPI definitions; environmental KPIs including fuel burn and CO2 per flight.
• Doc 9750 (Global Air Navigation Plan, GANP) -- ASBU modules CDO-B0, CCO-B0, FRTO-B0, OPFL-B1 as operational improvement components of the basket of measures (authoritative source -- not in local library; see https://ganpportal.icao.int/).

CORSIA-specific documents (on ICAO CORSIA website)#

• CORSIA States for Chapter 3 State Pairs -- current list of participating States per compliance year.
• CORSIA Sustainability Criteria for CORSIA Eligible Fuels -- requirements for SAF and LCAF to qualify as eligible.
• CORSIA Default Life Cycle Emissions Values for CORSIA Eligible Fuels -- default carbon intensities by pathway.
• CORSIA Eligible Emissions Units -- list of ICAO-approved offset programmes and unit types.
• ICAO CORSIA CO2 Estimation and Reporting Tool (CERT) -- fallback monitoring tool for operators without full fuel measurement.
• (All documents above are authoritative sources maintained on the ICAO CORSIA website -- not in local library.)

External authoritative sources#

• https://www.icao.int/environmental-protection/CORSIA/Pages/default.aspx - ICAO CORSIA website; all CORSIA operational documents and tools.
• https://www.icao.int/environmental-protection/Pages/env2050.aspx - ICAO LTAG page; net-zero 2050 goal, monitoring, and State Action Plans portal.
• https://www.icao.int/environmental-protection/Pages/SAF.aspx - ICAO SAF and LCAF page; GFAAF, CAAF outcomes.
• https://www.icao.int/environmental-protection/Pages/act-saf.aspx - ACT-SAF programme; capacity-building and partnerships for SAF deployment.
• https://www.icao.int/environmental-protection/Pages/CAEP.aspx - CAEP page; committee mandate, work programme, and Annex 16 development.
• https://www.icao.int/environmental-protection/Pages/ifset.aspx - ICAO Fuel Savings Estimation Tool (IFSET); quantification of CDO, CCO, and FRA benefits.
• https://www.eurocontrol.int/tool/cdo-cco-performance-dashboard - EUROCONTROL CDO/CCO performance dashboard; Europe-wide conformance data by airport and airline (authoritative source -- not in local library).
• https://transport.ec.europa.eu/transport-modes/air/environment/refueleu-aviation_en - ReFuelEU Aviation regulation; EU SAF mandate blending schedule (authoritative source -- not in local library).
• https://ganpportal.icao.int/ - ICAO GANP Portal; ASBU modules CDO-B0, CCO-B0, FRTO-B0, OPFL-B1 operational details.