A non-aircraft-propelling auxiliary gas turbine engine assembly includes an auxiliary gas turbine engine and a mixing damper. The auxiliary engine and the mixing damper are installable in an aircraft having at least one aircraft-propelling main gas turbine engine. The auxiliary engine includes a compressor having a compressor inlet. The mixing damper has first and second inlets and has an outlet. The outlet is fluidly connectable to the compressor inlet. The first and second inlets are adapted to receive first and second gas streams which have been compressed by at least one main engine. An aircraft component includes a mixing damper. A controller includes a program which instructs the controller to increase/decrease a first gas stream in response to increasing/decreasing electrical demands on an electric generator operatively connected to an auxiliary gas turbine engine of an aircraft.