Evaluating Soft and Hard Contrail Avoidance Strategies in Commercial Flight Planning: Implementation and Effectiveness Analysis

Linear contrails and induced cirrus clouds contribute significantly to aviation's climate impact, potentially accounting for double the Effective Radiative Forcing (ERF) of the cumulative carbon dioxide (CO2) since 1940. While various mitigation strategies exist, operational contrail avoidance through flight planning presents the most immediate and cost-effective solution. This study evaluates different contrail avoidance strategies using FLIGHTKEYS commercial flight planning system and CoCiP contrail prediction model provided by Breakthrough Energy/Contrails.org through the Contrails API, analyzing 11,172 flights over a two-week period in March 2025. We compare soft constraints (cost-based optimization with shadow prices of 5, 20, and 50 USD/tonne CO 2e,100) against hard constraints (polygon-based airspace restrictions). Results demonstrate that cost-based strategies achieve superior environmental outcomes (49-59% reduction in contrail warming energy forcing) with minimal operational cost increases (0.23-0.49%), outperforming polygon restrictions, which achieve only a 34% reduction. Importantly, despite the increased fuel consumption from rerouting, all strategies maintain net positive climate benefits across both CO 2e,100 and CO 2e,20 metrics, confirming that contrail avoidance delivers genuine climate mitigation even when accounting for additional emissions. These findings support the implementation of market-based mechanisms for contrail mitigation, demonstrating that soft constraints offer superior operational flexibility and environmental effectiveness compared to rigid airspace restrictions.