Refer to figures.
The basic function of an Automatic Flight Control System (AFCS) is to provide long-term stability for "hands-off" flight of the helicopter. This is achieved using a basic inner loop control system with reference to attitude information to control the aircraft around its Center of Gravity and hold the altitude and heading (pitch and roll control). This would be a 2-axis autopilot. However, large commercial helicopters use a 4-axis system incorporating collective and yaw control.

The Automatic Flight Control System (AFCS), except for the basic function, can also control airspeed, climb and descent, navigation commands, engine power, and hover. These are termed flight path modes, and the control system is modified by adding an outer loop control.

The outer loop system drives parallel actuators to operate the flight control systems. The outer loop modes are selected via several labelled buttons on an AFCS control panel.

The automatic transition to hover is a complex maneuver that involves control of the aircraft in multiple axes. Thus, a four-axis autopilot is necessary for the precision required during the transition to hover.

In contrast, a three-axis autopilot typically handles roll, pitch, and yaw control, but lacks the specific control over vertical motion needed for a controlled transition to hover. Therefore, the automatic transition to hover is generally engaged on a four-axis autopilot to ensure comprehensive control over all relevant aircraft movements during this intricate phase of flight.