A method for calculating vertical trajectory values is provided. The method obtains aircraft performance data for a particular aircraft and atmospheric condition data associated with an air route; calculates a cost-efficient vertical trajectory for the air route, based on the aircraft performance data and the atmospheric condition data, wherein the cost-efficient vertical trajectory comprises a plurality of altitude values for minimizing cost for the particular aircraft during travel of the air route; obtains an altitude consistency threshold; and adjusts the cost-efficient vertical trajectory using the altitude consistency parameter, to create an optimized vertical trajectory for the aircraft route.