To answer the ever-increasing complexity of aircraft, it becomes of foremost importance to better and earlier assess the interactions among their systems and sub-systems. The study presents the Virtual Integrated Aircraft (VIA) methodology, which allows achieving the integration of aircraft systems with virtual means, complementing and preceding physical integration, which is usually completed at the end of the validation and integration phase. LMS Imagine.Lab platform provides the means for applying this methodology. A simulation architecture, integrating models from different platforms, is built and simulations are run on High Performance Computers (HPC) to cover multiple scenarios and therefore validate the selected architecture and pre-design in the early system development phases. Equipment, systems and subsystems are essential for the performance, safety, reliability and comfort. A large part of the non-propulsive power is allocated to the environmental control system (ECS) through use of air “bleed” from the engine. Reducing the bleed off-take is of major importance to increase engine efficiency while ensuring comfortable cabin conditions. Besides, failure scenarios must be considered and system response has to be compliant with expectations from regulatory authorities. The study presents the application of the VIA methodology for the virtual integration of the ECS and its consumers in case of a middle range aircraft. LMS Imagine.Lab Amesim was used to model the main systems of interest (ECS, air distribution, engine bleed air) along with the aircraft structure. Functional mock-up unit representing a thermal model of equipment was also developed and integrated, with a co-simulation approach. Once integration is performed, different scenarios are considered and simulated to study the overall aircraft system response and check compliance with regards to expectations.