An aircraft system having a first set of components for performing a function of the aircraft system, and a second, alternative, set of components for performing the function of the aircraft system. The aircraft system has and a controller configured to receive scenario data indicative of a scenario during which the function of the aircraft system is to be performed, and, where each of the first and second sets of components are operational, the controller is configured to select between the first or the second set of components to perform the aircraft system function during the scenario based on the received scenario data. The controller is configured to control the selected set of components to perform the function during the scenario.