Abstract: A back-up control system is implemented in a single engine aircraft to provide the inactivation of a faulty primary system and engagement of a secondary system, and thereby provide a means of maintaining controllable flight sustaining thrust. The aircraft's hydromechanical main engine control and its companion pressure and temperature sensors can develop faults which can result in the inability of the engine to deliver flight sustaining thrust. The electronic control contains logic functions which indicate failure of the main engine control when all of the following exists for a minimum of three seconds: (a) the power lever is at a position requesting a level of dry thrust which exceeds a predetermned threshold; (b) core engine speed is below that required to deliver the predetermined level of dry thrust; (c) core engine speed is not increasing; and (d) turbine temperature is beneath the maximum allowable limit.

Abstract: The engine includes a main engine fuel flow, an augmentation fuel flow, and a variable area exhaust nozzle. Primary speed control means is powered by first electrical power supply means. Fan speed is controlled by modulation of main engine fuel flow. Loss of electrical power to the primary speed control means during augmented operation results in a reversion from fan speed control to core engine speed control while simultaneously reducing the augmentation fuel flow toward a minimum level and closing the variable area exhaust nozzle. Backup speed control means is coupled to the primary speed control means for limiting fan overspeed in augmented operation during loss of electrical power to the primary speed control means. The backup speed control means is powered by second electrical power supply means which is independent of the first power supply means.