Automatic Flight Control System

Automatic Flight Control System (AFCS): key concepts for ATPL candidates

The Automatic Flight Control System integrates the autopilot, flight director, associated sensors, and servo actuators to assist pilots in maintaining the desired flight path with precision and safety. In ATPL training, you’ll study how the AFCS uses inputs from gyros/IRS, air data computers, navigation receivers (e.g., localizer and glideslope), and the radio altimeter to compute guidance and drive control surfaces. A useful way to visualize the architecture is by “inner loops” and “outer loops.” Inner-loop (stability/attitude) controllers manage rotations about the aircraft’s center of gravity—pitch, roll, and yaw—while outer-loop guidance monitors and commands the motion of the aircraft’s center of gravity in three dimensions to follow a target path, altitude, or approach profile.

The flight director (FD) provides visual steering cues on the Attitude Director Indicator (ADI). Its command bars translate the AFCS guidance into pilot-friendly instructions: the horizontal bar indicates pitch corrections required, and the vertical bar indicates roll/lateral corrections. In localizer (LOC) mode during a manual final approach, the FD may momentarily present a centered vertical command bar if the pilot is already correcting toward the beam and the tracking trend is satisfactory—reminding you that FD cues reflect both error and rate-of-closure logic, not just raw displacement. Control Wheel Steering (CWS) is another common mode: when engaged, the autopilot treats the aircraft’s current pitch and roll attitudes as targets, holding them once the pilot releases control pressure, which is useful for quick, temporary attitude changes without selecting a new managed mode.

Automatic approach and landing capability is classified by both system performance and failure-response behavior. A fail-passive system, upon a single fault, disengages or relaxes to a condition that does not cause a significant out-of-trim or abrupt flight-path change; the crew must complete the landing manually because the automatic landing will not continue. A fail-operational system retains sufficient redundancy (often multi-channel autopilot) so that, after a single failure, the approach, flare, and touchdown can still be completed automatically. For Category II/III operations under aviation regulations, the radio altimeter is the primary height source for low-altitude guidance, flare initiation, and callouts. Regardless of category, standard procedures emphasize correct mode selection, continuous monitoring of AFCS annunciations, cross-checks against raw data, and readiness to disconnect and go around if required minima, alerts, or system status demand.

What this question bank covers

• AFCS architecture: inner-loop attitude control versus outer-loop guidance and how they interact with aircraft systems.
• Flight director indications on the ADI, meaning of horizontal/vertical command bars, and LOC/GS tracking logic.
• Autopilot modes and procedures, including Control Wheel Steering (CWS), approach modes, and mode engagement/transition.
• Autoland classifications: fail-passive versus fail-operational behavior, redundancy, and crew actions after a failure.
• Use of the radio altimeter for CAT II/CAT III automatic approaches, flare logic, and minima considerations under aviation regulations.
• Pilot monitoring, mode awareness, decision making (continue, disconnect, or go-around), and best practices for ATPL exams.