Historically, Turboprop engines have been controlled via two levers in the cockpit -- one adjusting engine speed and the other controlling engine power. Engine power was controlled by speed lever and fuel flow (a function of power lever angle). The pilot had to adjust the speed lever to obtain the desired engine speed setting, then he would “close the loop” on torque (his primary control parameter) by watching a gage and moving the power lever angle (PLA). This resulted in significant pilot effort in readjusting the engine to different power levels/operating modes.
The control system for the TPF351-20 engine, as applied to the Embraer CBA123 aircraft, is designed to reduce pilot workload by providing a single lever system that controls the engine to a torque commanded by the power lever position. This was made possible by the use of a Full-Authority Digital Engine Control (FADEC).
In order to maximize the use of the FADEC in the reduction of pilot workload, it is tied via various serial data busses on the aircraft to the Air Data Computer, the Autopilot, and Engine Indication and Crew Alerting System (EICAS). These inputs allow the FADEC to schedule torque linearly versus power lever command, and to hold each engine to within 1 percent torque of each other which prevents undesirable power lever splits or aircraft yaw.
The FADEC also uses the Autopilot inputs to adjust engine power during approach to keep the aircraft on the specified glide slope. Pilot workload, aircraft performance, and maintainability are significantly improved by the state-of-the-art advances made in control of turboprop engines on the TPF351-20.