The proposed project is part of the Cleansky activities for the “More electric” aircrafts.Such aircrafts require more power electronics integration and so “traditional” cooling systems (natural or forced convection, liquid loops,…) may reach their maximal performances because of the too high thermal dissipation density of these components. A need of heat spreading is clearly identified by the users.In this way, two-phase fluid capillary pumped heat transfer systems appear as more efficient alternative solutions thanks to their high heat transport capacity and their passive pumping capacity.Several passive cooling systems can be considered for these applications such as vapour chambers, heat pipes, high temperature loop heat pipes,…Such systems have background on space systems and environments; however, the demonstration of their functioning in avionic application, by modeling and experimental tests, is required before being equipped on an airplane.The EHP proposal will address the development, design, manufacturing and demonstration in a relevant environment - TRL6 (technology Readiness Level) - of a two-phase passive cooling system to be used on aeronautical applications.The size of equipment to be cooled is close to an A4 format.One hundred of watts are dissipated over several localized areas with a heat flux density around 30W/cm².The equipment is located in a harsh environment characterized by an ambient temperature of160°C and a low heat exchange coefficient. Despite these conditions, the equipment maximal temperature should not exceed 200°C.The EHP activities will consist in the following points:- Bibliographic review- Technology selection- Fluid selection- Cooling system sizing / modeling- Prototype construction- Experimental validation