This paper describes the development of an optimization-based cooperative planning system for the efficient routing and scheduling of flight formations. This study considers the use of formation flight as a means to reduce the overall fuel consumption of civil aviation in long-haul operations. It elaborates on the operational implementation of formation flight, particularly focusing on formation flight routing. A completely decentralized approach is presented, meaning that formation flight is not anticipated pre-flight and is not subjected to any predefined routing restrictions. A greedy communication scheme is defined through which all participating aircraft are allowed to communicate with neighboring aircraft in order to establish flight formations. The communication range of aircraft is used as a system parameter to control the allowed communications. A constraint on formation flight induced additional flight time is introduced in order to suppress the occurrence of large detours in the assembly of flight formations. A transatlantic case study is presented that contains 347 eastbound flights. Assuming a 10% fuel flow reduction for any trailing aircraft in formation, overall obtainable fuel savings were estimated at 4.3% at the expense of an additional flight time of 10.3 minutes per flight on average. In this transatlantic long-haul scenario, a formation flight usage rate of 73% was realized.