This paper develops a novel cascading Proportional-Integral-Derivative (PID) with Model Predictive Control (MPC) formulation for lateral control of a fixed wing aircraft in the presence of a constant load disturbance, with the consideration of actuator constraints. A Constrained Quadratic Programming (QP) problem is used to solve this MPC problem, via the Primal-Dual procedure. Furthermore, a disturbance observer is utilized to estimate this disturbance so that the setpoint calculation can be adjusted accordingly. Numerical simulations demonstrate steady-state tracking of the aircraft’s roll angle whilst rejecting this disturbance. In addition, heading (yaw) control is implemented via the outer PID loop, and perfect tracking is achieved for this as well. Throughout the entire simulation, the aircraft’s control inputs (aileron and rudder) do not violate their position and rate constraints, thus demonstrating the successful performance of the QP algorithm.