Digital autopilots: Design considerations and simulator evaluations

The development of a digital autopilot program for a transport aircraft and the evaluation of that system's performance on a transport aircraft simulator is discussed. The digital autopilot includes three axis attitude stabilization, automatic throttle control and flight path guidance functions with emphasis on the mode progression from descent into the terminal area through automatic landing. The study effort involved a sequence of tasks starting with the definition of detailed system block diagrams of control laws followed by a flow charting and programming phase and concluding with performance verification using the transport aircraft simulation. The autopilot control laws were programmed in FORTRAN 4 in order to isolate the design process from requirements peculiar to an individual computer.