According to one embodiment of the invention, an apparatus comprises a passive cooling system and a portion of an air vehicle which receives thermal energy. The passive cooling system is disposed adjacent the portion of the air vehicle and comprises a fluid transfer chamber. A fluid transfer element and a coolant are disposed within the fluid transfer chamber. The fluid transfer element wicks a portion of the coolant towards the portion of the air vehicle. The portion of the coolant wicked towards the portion of the air vehicle absorb at least a portion of the thermal energy in a boiling heat transfer.