Abstract We examine the balancing of economic and environmental goals in long-term airline fleet planning. A multi-objective linear programming model optimizes fleet composition, fleet development, and fleet employment for a 10-year planning horizon. Model inputs include flight plan data, operational, technical, and cost parameters, existing fleet aircraft, and the availability of new, more efficient aircraft. The model determines trade-offs between an economically and an environmentally optimal fleet plan depending on user-defined weightings. Varying these weightings provides alternative Pareto-optimal fleet plans. An example for a major European airline shows that it would have to deviate by approximately 3% from its economic optimum to achieve a 6% improvement in the environmental goal. The study provides insights for policy makers when setting environmental targets for airlines and developing mechanisms to encourage environmental commitment.