Afcs
The AFCS (Automatic Flight Control System)
🧭 1️⃣ What AFCS Means
AFCS = Automatic Flight Control System
It’s the umbrella system that automatically controls the aircraft in flight.
Think of it as the “autopilot family” — it includes everything that helps the aircraft fly itself, stay stable, and follow the desired path.
⚙️ 2️⃣ What It Does
The AFCS helps the aircraft by:
- Stabilizing it — keeps pitch, roll, and yaw steady.
- Guiding it — follows headings, altitudes, speeds, or routes.
- Relieving pilot workload — the pilot monitors instead of manually flying.
🧩 3️⃣ Main Components of an AFCS
| Component | Function | Example |
|---|---|---|
| Sensors | Measure the aircraft’s motion and position | Gyros, accelerometers, air data, radio navigation signals |
| Flight Control Computer(s) | Process signals and decide what control movements to make | Autopilot computer |
| Actuators / Servos | Move the flight controls according to commands | Elevator, aileron, rudder servos |
| Mode Control Panel (MCP / FCU) | Where the pilot selects desired modes (heading, altitude, etc.) | “Autopilot control panel” on flight deck |
| Feedback sensors | Tell the computer what actually happened | Close the control loop for precise control |
✈️ 4️⃣ The Three Control Axes
The AFCS controls all three aircraft axes:
| Axis | Control Surface | Function | Example Mode |
|---|---|---|---|
| Pitch | Elevator | Controls climb/descent | Altitude Hold, Vertical Speed, VNAV |
| Roll | Ailerons / Spoilers | Controls bank & heading | Heading Hold, LNAV, Localizer |
| Yaw | Rudder | Keeps coordinated flight | Yaw Damper, Turn Coordination |
🔄 5️⃣ Levels (or Degrees) of Automation
| Level | Function | Example |
|---|---|---|
| 1 – Stability Augmentation | Basic stability (damps oscillations) | Yaw damper, pitch damper |
| 2 – Attitude Hold | Keeps fixed pitch/bank | Basic autopilot modes |
| 3 – Path Control | Maintains flight path (altitude, heading, airspeed) | ALT HOLD, HDG SEL |
| 4 – Full Guidance | Follows programmed route and approach | LNAV/VNAV, ILS approach, autoland |
🧠 6️⃣ How It Works (in Simple Steps)
- Sensors measure the aircraft’s current motion (attitude, speed, etc.).
- The AFCS computer compares the current state to the selected target (e.g., 10,000 ft, 250 kt).
- It calculates an error signal (difference between target and actual).
- The servo actuators move control surfaces to correct the error.
- Feedback confirms the correction — this is a closed-loop system.
🧩 7️⃣ AFCS Includes These Subsystems
| Subsystem | Purpose |
|---|---|
| Autopilot (A/P) | Controls flight path automatically |
| Flight Director (F/D) | Gives guidance bars to show pilot or A/P what to do |
| Autothrust / Autothrottle (A/THR) | Controls engine power to maintain speed |
| Yaw Damper | Prevents Dutch roll and stabilizes yaw motion |
Together, they form the complete Automatic Flight Control System.
🧭 8️⃣ Simple Analogy
Think of the AFCS as the aircraft’s automatic pilot brain:
- Sensors = Eyes and inner ear
- Computer = Brain (decides what to do)
- Servos = Muscles (move the controls)
- Feedback = Feeling (knows what it’s doing)
✅ 9️⃣ Summary Table
| Feature | Description |
|---|---|
| Name | Automatic Flight Control System (AFCS) |
| Purpose | Stabilize and guide the aircraft automatically |
| Main Components | Sensors, computers, servos, control panel |
| Subfunctions | Autopilot, flight director, autothrust, yaw damper |
| Control Axes | Pitch, Roll, Yaw |
| Type of System | Closed-loop control system |
✈️ In short:
The AFCS is the overall system that combines autopilot, flight director, autothrust, and stability functions to automatically control and guide the aircraft — safely and smoothly — in all flight phases.