Abstract: A system for controlling aircraft main engines cooling during starting operations. An aircraft incorporates a main engine and a pneumatic starter for starting the same, and a pneumatic source fluidly communicated with the pneumatic starter to supply pressurized air thereto. A control system is provided with a data chart containing predetermined pressure values of the pneumatic source, and the values correspond to an ambient condition to obtain a desired rotating speed for the main engine for that ambient condition. The control system is configured to control the pneumatic source air pressure output based on the data chart and to rotate the main engine within a predefined rotating speed range during cooling procedure. A controlled reduced rotating speed during main engines cooling or cranking operation is thus provided before starting main engines, in order to mitigate bowed rotor phenomenon.