© 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.In this study, we propose an adaptive longitudinal flight controller in the sequential loop closure framework using the energy principles. In contrary to traditional SISO classical control theory based flight control architectures, the proposed control is a MIMO controller where the elevator and throttle controls are used simultaneously to track the velocity and altitude commands. An energy management system works in conjunction with an outer loop adaptive controller to achieve the desired velocity and altitude tracking and decoupling performances. With the adaptation in the outer loop, the effects of uncertainties acting on the slow states of the aircraft (e.g. airspeed) are eliminated with the throttle control. In the inner loop adaptive controller, satisfactory pitch response has been attained with the elevator control by suppressing the undesired effects of model uncertainties on the fast aircraft modes such as short period. Eventually, improved coordinated longitudinal control has been accomplished with all the loops closed without any high-frequency oscillations in the pitch response. The efficacy of the proposed algorithm is illustrated through numerical simulations with a high-fidelity nonlinear aircraft model.