Fly-by-Wire Flight Control Systems

Conventional vs. Fly-by-Wire Systems

Conventional Aircraft: Control movements transferred through cables and pulleys to control surfaces.
Fly-by-Wire (FBW) System (A320 Family): Cables and pulleys replaced by electrical wires.
- Advantages: Saves weight, enhances stability, improves safety, and reduces pilot workload.
- Components: Electrical signals from side stick → Flight control computers → Surface hydraulic actuators (Servo controls).

Components: Ailerons, Elevators, Trimmable Horizontal Stabilizer (THS), Rudder, Spoilers.
Functions:
- Ailerons and Elevators: Green index on white scale shows movement.
- Rudder: Green rudder symbol on white scale, blue line for trim. Rudder deflections limited based on speed via Rudder Travel Limiter (green brackets).
- Pitch Trim: Indicated by THS deflection in degrees.

Functions: Speed brake, roll control, ground spoiler function.
Types and Indicators:
- 3 central surfaces for speed brake function.
- 4 outer surfaces for roll control function.
- All surfaces for ground spoiler function.
- Spoiler extended position indicated by small arrows on ECAM flight controls page.

Types: 7 computers manage flight control surfaces.
- 2 Elevator and Aileron Computers (ELAC).
- 3 Spoiler and Elevator Computers (SEC).
- 2 Flight Augmentation Computers (FAC) - not displayed on ECAM page.
Data Concentration:
- 2 Flight Control Data Concentrator Computers (FCDC) acquire data from ELAC and SEC and send to EIS.
- Data from FAC sent directly to EIS.
Status Indications: Only ELAC and SEC statuses indicated on ECAM flight control page.

Power: 3 independent hydraulic systems (G, B, Y) power flight control surfaces.
Indications: Hydraulics for each surface shown on ECAM flight control page (e.g., Rudder powered by G, B, Y).

Side Sticks: Control pitch and roll.
Priority Lights: Related to side sticks, detailed in separate module.
Pitch Trim Wheels: Located on the center pedestal.
Rudder Pedals: Conventional, mechanically interconnected, with trim panel on the pedestal.
Speed Brake Lever: Located on the left side of the pedestal.
Control Panels: Two panels on overhead panel for flight control computers.

Components: 5 slats on leading edge, 2 flaps on trailing edge.
Control and Actuation:
- Hydraulically actuated, electrically controlled by 2 Slat Flap Control Computers (SFCC).
- Each SFCC has 2 channels (1 for flaps, 1 for slats).
Flap Lever: Multiple positions (0, 1, 2, 3, 4, Full).
- Positions: Can be set among various configurations depending on speed.
Indications: Flap and slat positions indicated by white dots on engine warning display.
- Position 1: Corresponds to 2 configurations depending on speed (1 or 1+F).

Detection: Surface asymmetry, attachment failure, overspeed, and uncommanded movement.

Pitch Trim Values: Indicated for takeoff CG settings (must be set in green band).
- Example: Takeoff CG set at 26.5% aligns with THS setting at 0.5 nose up.
- In-Flight: Pitch trim shown on ECAM flight control page (checked during taxi).
Side Stick Operation: Inoperative without hydraulic pressure, becomes operable with power.
- Ground Mode: Enables pilots to check control surfaces and perform pre-takeoff checks.

Takeoff Operations:
- Flap Lever Positioning: Set to 1, 2, or 3 for takeoff.
- Indications: Blue number and markers show selected position.
- Automatic Flap Retraction: Occurs at certain speeds.
Speed Brakes Operation: Lever pushed and moved rearwards; memo displayed based on lever position and thrust levels.

Flare Mode: Activates at 50 ft radio altitude, system memorizes attitude, and progressively reduces pitch.
Ground Spoilers: Armed, indicated by white band and green memo.
- Deployment: Automatic at touchdown based on specific conditions.
- Retraction: If thrust is no longer idle or reverse is not selected.