PURPOSE: To stably maintain control of an aircraft by providing a high speed spool for driving auxiliary driving machines and a low speed spool for driving an emergency power unit at losing propulsion power on a turbofan engine.

CONSTITUTION: A turbofan engine 12 drives an auxiliary driving machine (AMAD) 18 mounted on the airframe through a high speed spool 14 and a clutch 20, and supplies electric power and the like. Next when an emergency condition such as flame-out or combustion stop is generated during flight at high altitude, it is detected by a propulsion power losing sensor 32 to combine together a combination unit 26, an emergency power unit 28 is driven by rotating inertia of a low speed spool 22 and operation as a windmill turbine, and required power in the aircraft is supplied until the aircraft lowers to the altitude at which the engine 12 is restarted. Hence control of the aircraft can be stably maintained.