In a fuel fired furnace, it is imperative to ensure the air is always in excess to the fuel during transients so that all fuel entering the furnace is combusted and no un-burnt fuel remains inside (safety objective). Thus, if the firing rate is to be increased, the air rate must increase first followed by the fuel rate. On the other hand, if the firing rate is to be decreased, the fuel rate must decrease first followed by the air rate. Synthesize a control structure that accomplishes the above using appropriate selector blocks and dynamic elements such as a lag or a lead-lag etc. Additional control structure features are: The air and fuel rates are flow controlled. . The demanded air rate is kept in ratio with the demanded fuel rate. The furnace exit stream temperature is controlled by manipulating the demanded fuel rate setpoint. The air-to-fuel ratio setpoint is adjusted by a flue gas oxygen composition controller.