An aircraft engine includes an aircraft engine controller configured to detect an actual peak exhaust gas temperature of a cylinder assembly. The aircraft engine controller detects an intersection between a first function representing a relationship between a set of rich exhaust gas temperature signals and a corresponding set of rich fuel-air ratio values and a second function representing a relationship between a set of lean exhaust gas temperature signals and a set of lean fuel-air ratio values. Based upon the intersection between the first and second functions, the engine controller detects an actual peak fuel-air ratio value for the cylinder assembly and can determine if a correction in the fuel-air ratio of a fuel-air mixture provided to the cylinder assembly is required. Accordingly, the engine controller provides each cylinder assembly of the aircraft engine with an accurate fuel-air mixture to allow for operation of the engine with optimal fuel economy.