Aircraft CO2 and non-CO2 emissions contribute significantly to climate change. Sustainable aviation fuels (SAFs) and climate-optimized flight planning are among the most immediate measures to mitigate these impacts. However, SAFs are more production-intensive and costly than conventional kerosene fuel, limiting their short-term scalability. Moreover, climate-optimized routing incurs additional costs and may lead to operational issues such as capacity-demand imbalances and increased complexity. In this work, we present a framework that strategically combines these two measures in a targeted manner to maximize climate benefits while accounting for the challenges associated with limited fuel availability and operational constraints.

We conducted a year-long analysis of the 150 most-traveled European routes in 2023. Results indicate that smartly allocating only 2% SAF to business-as-usual trajectories, specifically targeting flights that form strongly warming contrails, can deliver contrail-related climate benefits comparable to those achieved with uniform 100% SAF usage, yielding approximately 40% mitigation. This effectiveness is attributed to the reduction in soot particle emissions from SAF combustion, which shortens contrail lifetime and reduces associated radiative forcing.  Furthermore, the strategic allocation of SAF on climate-optimized trajectories can achieve an additional 30-40% reduction in contrail-related climate impact compared to operating the same routes with kerosene alone. Notably, these benefits saturate at around 5% SAF usage, indicating that increased SAF availability does not necessarily yield proportional additional mitigation for contrail impacts.