Аннотация
This work describes quantitative calculation-experimental methodic of evaluation and prediction of formation and existence of condensation trails and condensation cirrus clouds during flights of civil aviation jet aircraft. Methodic approbation is made basing on concrete examples of aircraft (engine types) and flight routes. Here are presented the recommendations on it utilization for ecological optimization of flight routes with accounting of season and time of the day under condition of valid information on atmospheric conditions availability.