Interoperability constituent (IC)

An interoperability constituent is a component or assembly the TSIs single out as safety- or interoperability-critical enough to be certified on its own, before it is ever installed in a subsystem: a wheel, a rail fastening, a pantograph head, a balise, a driver's desk ETCS DMI. The manufacturer obtains an EC declaration of conformity for the IC from a Notified Body against the requirements of the relevant TSI — often by applying the harmonised EN standards the TSI cites — and subsystem-level EC verification then builds on those component certificates instead of re-assessing everything from scratch. The mechanism is what lets a wagon builder buy certified wheelsets on the open market, or a signalling integrator source Eurobalises from any certified vendor, and it is the legal backbone of component-level competition in the EU rail supply market. Each TSI's annexes list which constituents it defines and which assessment modules (design examination, production quality system, and so on) may be used.