It is widely believed that the initiation of cloud formation due to condensation trails formed in cruise flight has a net positive effect on global warming due to the radiative forcing of the cloud coverage. This paper introduces a methodology to optimize 3-dimensional long-hail aircraft trajectories in a wind field with the aim of minimizing the flight time in which the formation of persistent condensation trails may take place, whilst taking into account the effects on flight time and total fuel burn. For this purpose, an advanced optimization algorithm based on optimal control theory was combined with a point-mass aircraft model, an atmospheric model based on historic weather data and a model to predict the formation of persistent condensation trails. An example scenario of a long-haul flight between Amsterdan and Washington D.C. is presented indicating significant potential for the reduction of radiative forcing at relatively small cost in terms of fuel and flight time. @en