The Vessel Traffic Service (VTS) is a complex system tasked with ensuring the safety of navigation within specified areas known as VTS areas. Earlier research in the domain has often focused on the decision support systems and other tools employed by the VTS operators to provide the vessels in the area with VTS services. Consequently, less effort has gone into looking at the system itself and the human factors aspects of the system.

This study uses the Functional Resonance Analysis Method (FRAM) to create a functional model of the VTS. It looks at how a VTS works, what the different components are and how these components are related. The main purpose of the FRAM model is to serve as a basis for future application by identifying the functions that constitute the system, and to illuminate the potential variability therein. To demonstrate how it might be used, an instantiation of an observed scenario will be presented. A structural description of the VTS is also presented, which aims to serve as an introduction to the domain for readers who are previously unfamiliar with it.

The functional model shows that a lot of the potential variability seems to lie in the functions that rely heavily on human interaction, which is to be expected, as human performance is highly variable. It also shows that the availability and reliability of relevant information is crucial in order to be able to provide the VTS services, and if the information for some reason is unavailable or insufficient it seems likely to cause variability.