A tool to evaluate the turbine cooling air schedule during the flight path is presented. The method is suitable for complex gas turbine engine models where accurate calculation of thermodynamic parameters of a cooling flow used for studies such as specific fuel consumption (SFC), lifing, and operating cost analysis. The method is also applicable for land-based gas turbine engines where the flight path is replaced by load pattern. The method can be employed even if only a little information about the engine is known. The calculation method has been investigated on a model of a high bypass ratio turbofan for long haul application. Using it with an aircraft model and after comparing to conventional cooling air simulations, the reduction of SFC during the flight path has been observed. A comparison has been performed on engine manufacturer’s public domain data where the method shows comparable value of total cooling air needed. The tool returns similar results but estimates a higher proportion of cooling air for the high pressure turbine nozzle guide vanes (NGV) compared with Young and Wilcock’s method.