Abstract: A method of detecting partial flame out in a gas turbine engine combustor is provided which involves the steps of establishing a model for performance of the engine during a particular operating mode of the combustor, wherein the model assumes that all fuel supplied during the combustor operating mode is burned, calculating a value for an engine parameter in the model representative of engine performance, obtaining a sensed value for the engine parameter during operation of the engine at the combustor operating mode, and comparing the calculated value of the engine parameter and the sensed value of the engine parameter, wherein partial flame out of the combustor is detected when the sensed value of the engine parameter differs from the calculated value of the engine parameter by a predetermined amount.