In this paper, the singularly-perturbed design of an auto-pilot system of a high speed fighter aircraft, for the same authors (1985), is modified. The previous suboptimal design based on singular perturbation technique was proper only for aircraft operation near its nominal flight conditions. The new proposed adaptive design would be adequate for all possible changes of aircraft dynamics. The plant with varying parameters, representing aircraft, is controlled to behave nearly similar to a chosen first order reference model. The proposed discrete model reference adaptive control design uses an adaptive algorithm of Suzuki and Takashima (1978), based on augmented error signal concept and Popov's hyperstability theorem. Computer simulation results are presented to demonstrate the usefulness of the proposed design.