During full load operation of gas turbine engine operation, a valve system is maintained in a closed position to substantially prevent air from passing through a piping system of a shell air recirculation system. Upon initiation of a turn down operation, which is implemented to transition the engine to a turning gear state or a shut down state, the valve system is opened to allow air to pass through the piping system. A blower is operated to extract air through at least one outlet port of the shell air recirculation system from an interior volume of an engine casing portion associated with the combustion section, to convey the extracted air through the piping system, and to inject the air into the interior volume of the engine casing portion through at least one inlet port of the shell air recirculation system to circulate air within the engine casing portion.