in a control system for a gas turbine engine , a degradation level of the gas turbine engine is estimated according to a deviation of an output of an internal temperature sensor when the engine is producing a target output at a target rotational speed from a prescribed reference temperature , and a correction value for correcting the engine operation map is computed according to the degradation level of the gas turbine engine . thereby , even when the degradation of the engine has progressed to a certain extent typically owing to the aging of various component parts , the engine operation map can be corrected in such a manner that the level of fuel supply is optimally selected and the acceleration , efficiency and other items of performance of the engine can be improved .