Patent ID: 8661832

Claim:
An apparatus for controlling a gas turbine engine comprising a plurality of compressors, the apparatus comprising: a controller having an input for receiving at least one measured engine parameter and an output for transmitting control signals for controlling engine variables; wherein the controller is configured to determine, from said at least one measured engine parameter, an indication of surge margin for each of at least two compressors; a surge margin operating map, the surge margin operating map comprising; a first dimension corresponding to the indication of surge margin in one of the at least two compressors; a second dimension corresponding to the indication of surge margin in a second of the at least two compressors, and a plurality of control domains; wherein the controller is configured to use said indications of surge margin to determine a current engine operating point on the surge margin operating map, and wherein the controller is configured to generate at least one control signal for controlling at least one engine variable based on the location of the current engine operating point on the surge margin operating map.