The Data Behind the Declaration

Why Airport Scope 3 Emissions Reporting Needs More than Good Intentions

The recent changes to the Airport Carbon Accreditation (ACA) programme mark a significant step forward in aviation’s sustainability ambitions, as from Level 3 onwards, airports are now required to report Scope 3 full-flight aircraft emissions. In practice this means extending the calculations previously required for Landing and Take-Off (LTO) cycles (activity up to 3,000 feet altitude) to also include emissions generated during climb, cruise, and descent (CCD).

This change from ACA is a necessary evolution, but as its member airports grapple with the expanded requirements a more uncomfortable question is emerging: were the previous numbers the airports were publishing actually dependable, and going forward, how will they know if they’re not?

A Step Change in Complexity

For most airports, Scope 1 and 2 reporting have become relatively routine. Energy bills, ground transport fuel invoices, refrigerant top-ups; the data sources are established and the methodologies well-understood. Perhaps most importantly by the emissions verifiers. However, for Scope 3 full-flight emissions, it’s a different proposition entirely. Calculating the CO₂e impact of every aircraft departure from an airport and calculating fuel burn across all flight phases dependent on aircraft type, engine variant, load factor and routing is an analytically intensive exercise.

The ACA Application Manual acknowledges two broad methodological approaches (1) fuel uplift data used as a surrogate for full-flight fuel data and (2) flight by flight calculations based on aircraft and engine specific fuel performance modelling. The manual is candid about the limitations of the simpler fuel uplift approach, noting it “might lead to an overestimation of emissions for airports with high refuelling activity (where fuel is uplifted for several flights of an aircraft) and an underestimation of emissions for airports with little refuelling activity.” In other words, this methodology may misrepresent the very figure the airport is trying to measure.

The Fuel Uplift Problem in Practice

Analysis undertaken by PACE has examined the variance between these two methodological approaches across a range of airport types and traffic profiles, and the findings are conclusive. The directional difference between regional and international airports reflects precisely what the ACA manual warns about: airports with high refuelling activity such as large hubs where aircraft uplift for onward long-haul sectors overstate emissions, while smaller and regional airports where aircraft often arrive with fuel carried from elsewhere to ensure swift turnarounds are understating Scope 3 emissions.

The numbers are quite stark. For regional airports in Europe, PACE’s analysis found the reported emissions to be significantly lower with an average CO₂e variance of -101% when comparing airport’s fuel uplift-based figures against flight-level calculations. In Asia Pacific, the divergence was even more pronounced at -149%.

At international airports, the picture shifts in the opposite direction. European international hubs showed an average CO₂e variance of +13% overestimation relative to flight-level modelling while Asia-Pacific international airports showed a +9% CO₂e overestimation.

What this means in practice is that an airport’s Scope 3 carbon footprint, as reported under ACA, could be materially wrong not because of data entry errors or calculation mistakes, but because the chosen methodology is structurally misaligned with the underlying operational reality. For airports seeking or renewing accreditation and more importantly, for the stakeholders, airlines, regulators, and communities who rely on that accreditation as a credible signal, this is a significant vulnerability.

Risks of Proprietary Tools and Resource Burdens

Faced with the complexity of full-flight emissions modelling, many airports turned to in-house developed spreadsheet tools, often with a dependency on a specific individual. Single-person dependency is endemic in this space, and the individual who built the model is often the only one who fully understands its logic, assumptions and quirks. When that person leaves, moves role, or is simply unavailable during a reporting window, the airport is exposed. As verification under ACA requires independent third parties to attest that reported figures meet the ACA programme requirements, a verifier confronted with a proprietary spreadsheet faces a significant assurance challenge. There is also reputational risk to consider. On the positive side the fact that there is detailed reporting by the airport is important, but in the broader context of ESG reporting scrutiny, a published Scope 3 figure that is later shown to be substantially incorrect risks reputational harm.

Of course, modelling Scope 3 full-flight emissions creates a significant resource burden. Sourcing movement data, assigning aircraft types, reconciling against fuel records and checking outputs for verification can often represent up to a month of analyst time for every annual reporting cycle. The knock-on effect of allocating resources to the calculation effort is reduced capacity to drive initiatives that actually reduce the emissions themselves. A Sustainability team that is busy calculating Scope 3 is not engaging airlines on SAF commitments, designing ground power infrastructure to eliminate APU use, renegotiating ground handler contracts to accelerate GSE electrification, or building the stakeholder partnership plan that ACA Levels 4 and 5 explicitly require.

Reliable Options for Efficient Disclosure

The ambition embedded in the ACA changes through the programme’s expansion to full-flight Scope 3 reporting is a move in the right direction. The path forward requires airports to think critically about two things: the quality of their data and what they do with it once they have it. PACE’s analysis makes it clear that the variance introduced by fuel uplift can be material and shows that flight-level modelling produces figures that are more defensible, more accurate, and more useful for the substantive engagement with airlines that subsequent ACA levels demand.

In addition, breaking the cycle of reporting Scope 3 data as an annual retrospective exercise to providing near real time insights that can inform decision-making helps transform this component of the Sustainability Manager’s responsibilities from calculation to application. Airports that invest in automated emissions data will increase the credibility of disclosures while freeing up the sustainability team to move the environmental needle, engaging airlines, shaping incentives, and building the stakeholder partnerships on which net zero ultimately depends. Airports can set absolute reduction trajectories aligned to IPCC pathways and demonstrate data-driven progress against them.

Rob Neale is Chief Product Officer and founder of PACE, a software platform launched in 2022 that calculates Scope 3 emissions automatically for aviation. Its latest development is PACE for Airports which covers over 99% of commercial flights globally and has been specifically designed to enable Sustainability Managers in Airports to meet their ACA Levels 3 to 5 reporting requirements for Full Flight Emissions.