Life-Cycle GHG of SAF in Real Flights: Empirical WTW Accounting and Reconciliation with TIM, DEFRA, and Base Empreinte

The growing deployment of Sustainable Aviation Fuels (SAFs) collides with an aviation greenhouse gas (GHG) accounting landscape that remains largely fossil-baseline- and tank-to-wake (TTW)-focused. Operational calculators used for corporate reporting and disclosure—such as Google’s Travel Impact Model, IATA CO₂ Connect, the ICAO Carbon Emissions Calculator, ATP-DEC and the UK DEFRA factors—generally assume 100% conventional jet fuel and offer little structural treatment of SAF. This study quantifies well-to-wake (WTW) CO₂-equivalent emissions for ten commercial flights operated with certified SAF blends and documented pathways, including hydroprocessed esters and fatty acids (HEFAs), Fischer–Tropsch fuels and power-to-liquid e-fuels. Using flight-specific fuel uplift, blend share and aircraft data combined with ISO 14067/14083-consistent life-cycle assessment, the analysis derives WTW intensities per flight, per seat-kilometre and per passenger-kilometre. These empirical results are then compared with estimates from the above calculators, each run under its native distance uplift, passenger-and-cargo allocation and non-CO₂ conventions. The comparison decomposes discrepancies into contributions from the TTW versus WTW scope, treatment of SAF, non-CO₂ assumptions and allocation rules. In addition to climate change impact, the work screens a limited set of further impact categories (such as land-use change, eutrophication potential and water use) to explore trade-offs for SAF produced from dedicated biomass versus waste-based feedstocks. Building on the findings, the paper proposes a minimal, auditable protocol for integrating SAF into existing tools—explicit TTW/WTW disclosure, transparent non-CO₂ options, pathway- and blend-specific WTW factors and book-and-claim rules compatible with SAF certificates—aimed at making SAF deployment visible, comparable and verifiable in Scope 3.6 business-travel accounting.