Abstract: The cessation of stall/surge in the compressor of a twin spool gas turbine engine is detected by comparing by digital electronics the engine's sensed burner pressure with a burner pressure calculated from corrected low pressure compressor speed and sensed airplane Mach number which has been compensated to approximate engine dynamics.

Abstract: A control system for a twin spool gas turbine engine for synthesizing a control parameter for the engine (such as the ratio of high compressor inlet temperature to low compressor inlet temperature) includes a function generator responsive to an engine operating parameter (such as corrected rotor speed) to generate a simulated value of the control parameter for a base engine configuration. A second function generator, responsive to an engine operating parameter, generates a simulated value of the difference between the value of the control parameter for the base engine configuration and the value of the parameter for another configuration. This difference is operated upon to correct it to the actual engine configuration. The corrected difference is added to the simulated value of the control parameter for the base configuration to give a simulated value of the control parameter for the actual engine configuration.