The objective of the work discussed within this paper is to present a modeling methodology to assess thermal management system (TMS) concepts for aircraft to determine adequacy in meeting thermal requirements and constraints for the duration of the flight1. To accomplish this, an analysis tool that has the capability to investigate steady state and transient thermal hydraulic conditions on a component to system-wide level is employed. This is achieved by simulating the conditions within a cooling network to provide temperature, pressure and mass flow rate distributions, as well as the temperature of surrounding engine and airframe structures.With today's reduced budgets, new aircraft systems will be less common and retrofitting existing high performance aircraft will become more common. Pushing these technologies to their thermal limits is resulting in cooling requirements that were not present or even contemplated during their original designs. As it is unlikely that airframe materials will be changed, the need to use on board fuel for cooling will become prevalent. A thermal analysis code becomes a useful and time saving tool in the identification of possible options to handle these new cooling requirements, while meeting physical size and weight limitations.