This paper presents the design and implementation proposal of a Total Energy Control System (TECS)-based longitudinal autopilot for a conventional twin-engine commercial aircraft, aiming to reduce the complexity of the Automatic Flight Control System.

The challenge addressed in this work is the prioritization between commanded Flight Path Angle and airspeed, specifically under conditions of thrust saturation. Two TECS-based longitudinal autopilot architectures from the literature are analyzed and compared, and one is selected for the implementation of vertical autopilot modes. The evaluation is done using a nonlinear model of the Research Civil Aircraft Model (RCAM), restricted to longitudinal dynamics. The pitch control innerloop is designed via pole placement, while the outerloop is tuned using parameterized optimization. Highlights are given to the nonlinearities introduced in the architecture, such as the automatic mode switching from Path priority to Speed priority, as well as the pitch control authority limitation.

Simulation results demonstrate that TECS is a viable framework for the integration into a modern autopilot structure, satisfying the industry's performance requirements, while keeping the potential of simplifying the Automatic Flight Control System from the system's and pilot's perspective.