A fuel control system (10) for a power unit used for generating power used for operating an airframe in accordance with the invention includes an air supply (18) for supplying pressurized air blown down from a storage vessel (14) to a combustor (16) which generates a gas stream by burning fuel supplied by a fuel supply (32) driving a turbine (50) to produce the power; a pressure sensor (26) coupled to the air supply for producing an analog signal proportional to pressure upstream in the air supply from the combustor; a digital to analog converter (54) having an offset input coupled to a signal proportional to the sensed pressure, a digital input for receiving a digital input signal, and an analog output which varies in proportion to the sum of the signal applied to the offset input and the digital input signal; a fuel control valve (38) contained with the fuel supply which is controlled as a function of the analog output signal of the digital to analog converter; an analog to digital converter (56) having at least one input and at least one output with the analog to digital converter outputting a digital signal proportional to each input signal applied to the at least one input of the analog to digital converter; and a system controller (24), responsive to the at least one output of the analog to digital converter, controlling the fuel with a periodically generated digital input signal applied to the digital to analog converter.