Many global socio-economic systems are based on flows of information, energy or matter. Typically, various organizations and institutions plan, design, implement and operate part of the physical infrastructure necessary to enable the flow, but none of them are the central controlling instance. Collaboration in such self-organized complex systems of flow enables broader market and system connectivity, at the cost of increasing complexity and risk. This paper studies collaborative operator interdependencies by transforming the operators' networks to the network of operators. The proposed approach analyzes collaboration in systems of flow according to four aspects: quantifying collaboration magnitude, evaluating diversity, finding the most important collaborators and illustrating the large-scale structure of collaboration. The presented use case is commercial air transport between Europe and North America, and vice versa. It is found that, while the flow becomes more direct, there is an increasing probability that a connection occurred among different airlines. The proposed method was also able to display the cyclic dynamics of collaboration heterogeneity and identify the most collaborative airlines. A visualization of the network-of-operators illustrates the large-scale structure of collaboration for the system-of-interest. This collaboration network is able to capture real world peculiarities such as formation and separation in airline alliances and mergers in a quantitative way.