THIS PAPER IS directed to aircraft Environmental Control System (ECS) designers and is intended to provide insight into problems with the allocation of ECS chilled air for the thermal control of avionics systems. The basic thermal design concepts and design procedures used by Texas Instruments in the development of airborne military avionics systems are described. A recent FLIR system was selected as an excellent example of a system that requires the effective use of aircraft ECS-conditioned air to provide thermal control. This paper describes the manner in which the ECS-conditioned air is divided between two LRUs and the unique design problems afforded by each of these LRUs. This paper also contains a comparison between two methods of allocating cooling air to avionics systems. The method used on the example FLIR system allows the system to operate within the specifications and meet all of the stated design goals. Another cooling air allocation method in common use by aircraft ECS designers fails to meet the design goal at all design conditions. Provisions must be made in the design of future aircraft ECS to provide enough cooling air for the effective thermal control of FLIR systems which are unique among avionics systems. It is no longer adequate to regard a “kW” as “just another kW.” There are unique “kWs” in the avionics systems that must interface with the aircraft ECS.