In the framework of the research activities supported by SESAR JU, dedicated research stream is devoted to investigation of integration of Air Traffic Management (ATM) and aviation into a wider transport system able to support the implementation of Door-to-Door (D2D) travel concept. In this framework, the project X-TEAM D2D (Extended ATM for Door-to-Door Travel) has been funded by SESAR JU under the call SESAR-ER4-10-2019: ATM Role in Intermodal Transport, with Grant Agreement n. 891061. The project aims defining, developing and initially validating a Concept of Operations (ConOps) for the seamless integration of ATM and air transport into an overall intermodal network, including other available transportation means (surface, water), to support the door-to-door connectivity, in up to 4 hours, between any location in Europe, in compliance with the target assigned by the ACARE SRIA FlightPath 2050 goals. The project is focused on the consideration of ConOps for ATM and air transport integration in intermodal transport network serving urban and extended urban (up to regional level) mobility, taking into account the transportation and passengers service scenarios envisaged for the next decades, according to baseline (2025), intermediate (2035) and final (2050) time horizons. In this paper, the outcomes of the first phase of the project activities, aimed to provide the initial definition (concept outline) of the proposed overall ConOps are illustrated, emphasizing the specific activities that have been carried out up to date and the related achievements. In addition, an outlook is provided in the paper on the next project activities, expected to be carried out towards the conclusion of the studies and the validation, by means of dedicated numerical simulation campaigns, of the proposed ConOps.