Aircraft contrails are considered as one of the emissions towards climate change. Trajectory optimization is one of the methods that can be used to reduce contrail formation and a strategy that can readily be implemented. However, most of the trajectory optimization studies were performed only with clean engines, and engine degradation was not considered. This work provides a novel approach to aircraft trajectory optimization problem by including engine degradation and real aircraft trajectories within the optimization framework. Impact of engine degradation on long range optimum aircraft trajectories were assessed by quantifying the difference in fuel burn and contrail formation, when an aircraft is flying on a trajectory which has been optimized for clean engines and degraded engines. For this study, Contrail prediction model was developed with one clean and two degraded engines, integrated with aircraft performance model in an optimization framework to generate optimum aircraft trajectories. The optimum trajectories generated with degraded engines were compared with the trajectories generated with clean engines. The results have shown, for long range aircraft the persistent contrails can be reduced by 2.1% with low level degraded engines having 50°C EGT increase and 3.84% with highly degraded engines having 100°C EGT increase. However, to achieve zero persistent contrail for the same route there is a significant penalty of 2.3% and 4.2% increase of fuel with low level degraded engines and highly degraded engines. Therefore, impact of engine degradation on contrail optimum aircraft trajectories are significant and in order to reduce contrails aircraft need to fly on an optimized trajectory specifically customized for the degraded engine performance.

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