Which of the following is NOT one of the five basic AFCS subsystems?

• A. Stabilator
• B. SAS
• C. FPS
• D. APU

Answer: (D)

The automatic flight control system is made up of subsystems that actively manage and stabilize the helicopter’s attitude and flight path, reducing pilot workload and maintaining commanded flight conditions. Within that system, the Stabilator handles automatic pitch stabilization, the Stability Augmentation System provides roll stability, and the Flight Path Stabilization subsystem helps keep the aircraft on a desired flight path. An Auxiliary Power Unit, on the other hand, is a power source used to start the engines and supply electrical and hydraulic power; it does not participate in automatic flight control. So the APU is not one of the AFCS subsystems.