Engineering improvements, technology enhancements and advanced operations have an important role to play in reducing aviation fuel consumption and environmental emissions. Currently several organizations worldwide are focusing their efforts towards large collaborative projects whose main objective is to identify the best technologies or routes to reduce the environmental impact and fuel efficiency of aircraft operations. The paper describes the capability of a multi-disciplinary optimization framework named GATAC (Green Aircraft Trajectories under ATM Constrains) developed as part of the Clean Sky project to identify the potential cleaner and quieter aircraft trajectories