cooling assembly 26 is selected according to the particular operating conditions at which heat transfer is desired thermal energy added to air in the fan bypass duct 50 raises the temperature and pressure of that air which contributes to thrust output of the engine 10 and lessens energy loss due to the vapor cooling assembly 26 in traditional gas turbine engine cooling systems using cooling air to cool both static and rotating engine components approximately twice as much cooling air by volume goes toward cooling static components as toward cooling rotating components the present invention allows cooling air expenditures for static components to be reduced or eliminated thereby allowing approximately two thirds savings in cooling air expenditure over prior art systems furthermore by decreasing cooling air expenditure the present invention allows the use of significantly smaller volume cooled cooling air assemblies than would otherwise be needed allowing the overall weight of a hybrid cooling system of the present invention to be approximately half the weight of cooling systems that would utilize only cooling air to cool both static and rotatable components of an engine for example smaller volume cooled cooling air assemblies can utilize smaller heat exchangers which can greatly contribute to weight reductions these features of the present invention help provide engine.