This paper addresses the problem of steering a quadrotor vehicle along a prescribed trajectory. The problem is formulated so as to enforce bounds on the thrust actuation and present robustness against possible disturbances resulting from errors in the estimation of the aircraft state. The proposed solution consists of a nonlinear state feedback controller for thrust and torque actuation that i) guarantees asymptotic stability of the closed-loop system in the presence of exponentially decaying observer errors, ii) ensures global regulation of the trajectory tracking errors, and iii) defines the thrust actuation as a saturated function of the position and linear velocity errors. Simulation results are presented to assess the performance and robustness of the proposed controller.