1. A method for improving fuel efficiency in an aircraft having a digital avionics system and at least first and second engines wherein the digital avionics system communicates first control signals from a first full-authority digital engine control (FADEC) system to the first engine to thereby control operating parameters of the first engine and communicates second control signals from a second full-authority digital engine control (FADEC) system to the second engine to thereby control operating parameters of the second engine, said method comprising: providing at least one processor programmed with a differential specific fuel consumption (DSFC) algorithm, a first engine optimization algorithm and a second engine optimization algorithm; and communicatively coupling the at least one processor and the DSFC algorithm through a first outer loop with the first FADEC system and through a second outer loop with the second FADEC system, and communicatively coupling the first engine optimization algorithm through a first inner loop with the first FADEC system and the second engine optimization algorithm through a second inner loop with the second FADEC system, wherein implementation of the DSFC algorithm, first engine optimization algorithm and second engine optimization algorithm by the at least one processor during operation of the aircraft includes: (a) determining first and second desired thrust values for the first and second engines respectively as a function of estimated differential specific fuel consumption of each of the first and second engines with the DSFC algorithm; determining first and second DSFC throttle adjustments for the first and second engines respectively as a function of the first and second desired thrust values and contemporaneous estimated thrust values for the first and second engines; and communicating the first and second DSFC throttle adjustments to the first and second FADEC systems respectively; (b) determining a first adjustment to at least one operating parameter of the first engine as a function of fuel efficiency and the desired first thrust value for the first engine with the first engine optimization algorithm and communicating the first adjustment to the first FADEC system; and (c) determining a second adjustment to at least one operating parameter of the second engine as a function of fuel efficiency and the desired second thrust value for the second engine with the second engine optimization algorithm and communicating the second adjustment to the second FADEC system.