Secondary Power Requirements for Large Transport Aircraft

Secondary power generating systems for use in flight and on the ground should be integrated into a unified system for minimum redundancy. The auxiliary power system which is normally used during ground operation of the aircraft can be an effective means of providing power for use in flight in the event of failure of the primary power system. An emergency power source for flight controls in the event all engines fail may be required on aircraft powered by high bypass turbofan engines due to the inherent low windmilling horsepower capability of these engines.