Abstract: Aircraft thermal management is optimized by integration of normally separate airframe and engine fuel transfer/heat sink systems into a composite heat sink and secondary power source. Fuel temperature is controlled to limits set by coking and varnishing within the engine fuel nozzles. Fuel in excess of engine demand is returned to the aircraft's main fuel tank after being cooled by either aerodynamic surfaces or by a "fuel to ram-air" heat exchanger. Airframe and engine systems are cooled through use of fuel as coolant passing through heat exchangers mounted in the feed line from the "cool" main tank to the engines. The Engine Electronic Control Unit (ECU) is cooled by the airframe Environmental Control System (ECS) increasing its operational reliability. Controlling engine burn fuel to nozzle temperature limits results in lower main tank fuel temperature, less fuel boiloff, smaller sized ECS, greater heat sink capacity and less dependence on supplemental ram air.