(c) UK SAF and carbon emission regulations affecting the aviation sector in the UK
Similar to ReFuelEU, the UK SAF Mandate imposes mandatory SAF blconcludeing obligations on qualifying fuel suppliers. To demonstrate compliance with the obligations, relevant suppliers must either apply for SAF Certificates or pay the acquire-out price. To obtain the former, fuel suppliers must display that their fuel is both eligible and sustainable. You can find a detailed overview of these obligations in our
The UK ETS also operates a cap-and-trade scheme wherein a limit is set on the total greenhoutilize gas emissions from sectors covered by the scheme, including the aviation industest. It came into force on 1 January 2021, following the UK’s withdrawal from the EU, and supersedes the EU ETS for UK flight plans, although it preserves many of the features from EU ETS. Importantly, eligible SAF is ‘zero-rated’ fuel under both the UK ETS and the EU ETS, which means aircraft operators may be exempt from surrconcludeering emissions allowances in relation to their utilize of qualifying SAF.
The UK Carbon Border Adjustment Mechanism (“UK CBAM”) is similar to EU CBAM, in that it covers emission intensive goods imported into the UK, including aluminium, steel and hydrogen from 1 January 2027. The introduction of other emission intensive goods is under review.
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Both EU ETS and UK ETS place a cap on total emissions, whilst ReFuelEU and UK SAF impose an obligation to meet a minimum SAF threshold, but all four regulations allow for a level of flexibility that enable the relevant stakeholders to meet their obligations by trading certificates between them. Those airline operators who go above and beyond their obligations can build a profit, whilst those who fall short are able to pay a fee to attribute other airline operators’ compliance to themselves, thereby also meeting their own obligations.
On 19 May 2025, the UK and EU announced plans to link and to align the UK ETS and EU ETS regimes and on 16 December 2024, the UK government issued a consultation on the incorporation of CORSIA into UK law, with the aim of maximising compliance with CORSIA in a form consistent with UK ETS.
How different flight paths are affected under the different SAF/carbon reduction regimes in the aviation sector?
The map below¹ is designed to display how the regulations apply depconcludeing on the flight path taken by the aircraft with which the relevant stakeholders are involved.
Image Credit: European Union
Flight plans into and out of the EU
- Flight Plan A: aircraft flying from the EU to outside the EU/EEA: CORSIA applies to the relevant airline operator (where the destination is an ICAO member state) and ReFuelEU applies to (i) the fuel supplier fuelling the flight; and (ii) the departure union airport;
- Flight Plan B: aircraft flying from outside the EU/EEA into the EU/EEA: CORSIA applies to the airline operator (where it originates from an ICAO member state);
- Flight Plan C: flights within EU/EEA countries: Both EU ETS and ReFuelEU apply to the airline operators, and ReFuelEU also applies to (i) the departure union airport; and (ii) the qualifying fuel suppliers;
- Flight Plan D: aircraft flying from the UK into the EEA: UK ETS applies to the relevant airline operators and the UK SAF Mandate applies to the relevant fuel suppliers;
- Flight Plan E: aircraft flying within the UK: UK ETS applies to the relevant airline operators and the UK SAF Mandate applies to the relevant fuel suppliers;
- Flight Plan F: aircraft flying from the UK to outside EEA – CORSIA and UK ETS apply to the relevant airline operators (where destination an ICAO member state, in the case of CORSIA) and UK SAF applies to fuel suppliers in relation to the fuel supplied in the UK; and
- Flight Plan G: aircraft flying from outside the EEA into the UK – CORSIA applies to airline operators (where these originate from an ICAO member state) and UK SAF applies to fuel suppliers but only to the fuel supplied in the UK (in this context, for refuelling at UK airports, for example).
Example
To provide a more comprehensive example, imagine an aircraft that first flies (Flight 1) from New York to London, then (Flight 2) from London to Edinburgh, then (Flight 3) from Edinburgh to Paris, then (Flight 4) from Paris to Frankfurt, and finally (Flight 5) from Frankfurt to New York.
Flight 1: CORSIA would apply to the airline operator.
Flight 2: UK ETS applies to the relevant airline operators and the UK SAF Mandate applies to the relevant fuel suppliers if fuel was being provided in the UK in preparation for Flight 2 (if the airline has enough fuel to proceed onto Edinburgh without refuelling at this stage, UK SAF Mandate does not bite).
Flight 3: UK ETS applies to the relevant airline operators and the UK SAF Mandate applies to the relevant fuel suppliers if fuel was being provided in the UK in preparation for Flight 3 (if the airline has enough fuel to proceed onto Paris without refuelling at this stage, UK SAF Mandate does not bite).
Flight 4: Both EU ETS and ReFuelEU apply to the airline operators, and ReFuelEU also applies to (i) the departure union airport; and (ii) the qualifying fuel suppliers.
Flight 5: CORSIA applies to the relevant airline operator (since the USA is an ICAO member state) and ReFuelEU applies to (i) the fuel supplier fuelling the flight; and (ii) the departure union airport in Frankfurt (Frankfurt Main or Frankfurt Hahn).
Navigating the different environmental regulations applicable to the aviation sector is complex, as the regulations listed above – whilst being complementary – were not designed in a unified way.
The relevant industest stakeholders necessary to continuously monitor their compliance with the regulations, as and when they may apply depconcludeing on the flight plan the aircraft takes. Given that each regulation imposes its own eligibility requirements, sustainability and monitoring, verification and reporting requirements and compliance rules, this is no straightforward feat.
Below we highlight a few of the key differences in terms of eligibility criteria for sustainable aviation fuels (“SAF”) and whether carbon offsets or ETS allowance trading is permissible under each of CORSIA, UK ETS, EU ETS, and the SAF Mandates.
SAF Eligibility Criteria
| Regime | What is covered | Eligible Fuels | Carbon emission reduction requirement | Carbon Credit offsets / ETS allowances trading |
|---|---|---|---|---|
| CORSIA (International) |
Global scheme for aviation emissions under ICAO. Applies to international flights. | SAF or lower carbon aviation fuel. SAF production accepts a wider range of feedstocks (including certain crop-based materials) than the other schemes listed below. The feedstocks must not come from land or water systems with high carbon stock. Additional sustainability criteria apply, for example, water, soil, air, conservation, human rights and food security. |
At least 10% reduction compared to fossil jet fuel. | Carbon credits can be utilized via Eligible Emissions Units (“EEUs”) approved by CORSIA. |
| UK ETS | UK Emissions Trading Scheme for aviation emissions from applicable flights. | Addresses aviation emissions from applicable flights rather than fuel type. SAF has a zero-emission factor under UK ETS. | SAF must achieve ≥40% GHG reduction vs fossil fuel. | ETS allowances may be traded SAF certificates cannot offset ETS tarobtains. |
| EU ETS | EU Emissions Trading Scheme for aviation emissions from applicable flights. | Same as UK ETS – addresses emissions from flights, not fuels. SAF has a zero-emission factor under EU ETS. | No specific % stated (zero-emission factor applies). When an airline utilizes SAF, the associated CO₂ emissions are considered zero, so they don’t necessary to surrconcludeer ETS allowances for those emissions. Airlines obtain the full emissions benefit from SAF utilize – every litre counts without necessarying to meet a minimum reduction threshold. This creates a strong financial incentive to utilize SAF, as it reduces compliance costs under ETS. | ETS allowances may be traded.
SAF certificates cannot offset ETS tarobtains. |
| UK SAF Mandate | UK mandate requiring a minimum share of SAF in aviation fuel supply. | SAF from biomass, waste, residues; power-to-liquid fuels (renewable or nuclear-derived); recycled carbon fuels; low-carbon hydrogen. Crop-based biofuels not eligible. HEFA-based fuel is capped at specific percentages of the total SAF obligation (100% in 2026, gradually decreasing to 71% by 2023). The intention is to encourage suppliers to utilize newer SAF technology – like power-to-liquid or fuels from municipal waste -which tconclude to have higher greenhoutilize gas savings (often achieving 60-70% reduction compared with 40% for HEFA) Fuels must meet defined environmental and social standards to qualify under government incentives. These are typically verified through a sustainability certification or life-cycle assessment (LCA) process. |
≥40% GHG reduction vs fossil fuel (baseline: 89 gCO₂e/MJ). | SAF certificates transferable only for compliance with SAF mandate. |
| EU SAF Mandate (ReFuelEU) | EU mandate requiring SAF blconcludeing in aviation fuel. | SAF from waste/residues, recycled carbon fuels, synthetic fuels (renewable hydrogen + captured carbon). Crop-based biofuels not eligible. Sustainability criteria apply. | ≥70% reduction for synthetic fuels; ≥65% for biofuels (baseline: 94 gCO₂e/MJ). | SAF certificates transferable only for compliance with SAF mandate. |
Importantly, the table above displays that there are variances as regards fuel eligibility criteria, sustainability criteria and carbon emission reduction requirements for fuels across the regulations. By way of example, UK SAF Mandate has a sub-cap for HEFA and there are variances as regards eligibility of crop derived biofuels. In terms of operation, unlike the EU ETS, UK ETS and SAF Mandates, CORSIA does not impose a carbon emission cap, but rather an offset scheme, requiring airlines to offset emissions over a defined baseline. Under CORSIA, only CORSIA-approved carbon credits can be utilized for compliance; this is a significantly tinyer pool than the broader carbon market.
This creates a challenging landscape for airline operators and fuel suppliers to navigate as they either necessary to have different SAF for different flight plans or narrow the SAF supply to such SAF which is compliant to all their relevant flight plans and associated regulations (the latter in practice is more likely).
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