Does Compliance Certainty Deliver Decarbonization? Comparing Mandate and Incentive Governance for Sustainable Aviation Fuel

Does governance design determine whether aviation decarbonization advances or stalls? This article introduces compliance certainty—the degree to which policy compels actors to secure supply, contract forward, and reconfigure operations—as the pivotal mechanism distinguishing directed from adaptive transition pathways. Comparing EU blending mandates under ReFuelEU Aviation with US production tax credits under the Inflation Reduction Act, the study uses theory-testing process tracing (2019–2025) and 49 causal process observations drawn from legal texts, regulatory guidance, and audited corporate filings. Evidence indicates that EU mandates generate strong compliance certainty: airlines explicitly cite binding quotas as drivers of offtake contracts and supply-chain investment. US credits narrow cost gaps but, absent purchase obligations, produce weaker compliance certainty and voluntary, price-contingent uptake. However, compliance certainty alone is insufficient. Both pathways confront acute planning constraints: waste feedstocks can support only ~10% of 2050 demand, and synthetic e-fuels require final investment decisions by 2026 to meet EU sub-targets while facing costs 3–5× above conventional SAF. The article contributes a replicable process-tracing design for hard-to-abate sectors and concludes that effective decarbonization governance must pair compliance certainty with feasibility planning.