Air-rail mobility has the potential to play a significant role in addressing European mobility challenges such as emissions reduction and capacity shortages. Rail can complement the air network in different ways: enlarging airport catchment areas, supporting operations in case of disruption or replacing air links to obtain environmental benefits. There is, however, still a need to better understand the potential role of rail when substituting current air links both from a strategic and a tactical mobility perspective, particularly when passenger connections are con- sidered. This was initially assessed, considering passengers’ door-to-door itineraries, as part of the Modus project (H2020 - SESAR 2020) with an innovative approach towards data driven, integrated air-rail modelling. Further considerations, such as the evaluation of strategic and tactical multimodal solutions, will be explored in the MultiModX project (Horizon Europe - SESAR 3). This discussion paper presents the modelling challenges addressed in Modus and the approach defined for MultiModX to evaluate and model multimodal door-to-door solutions.