Fly-By-Wire (FBW)

081-05-07Pablo Asensio Martínez2026-04-011 min

Concept

Replaces mechanical linkages (cables/rods) with electrical signals.

  • Pilot input -> Computer -> Actuator -> Control Surface.
  • Computers can modify inputs to ensure stability and prevent exceeding limits.

Flight Envelope Protection

FBW systems (like Airbus Laws) prevent the pilot from stalling or overstressing the aircraft.

  1. High Speed Protection: Automatically pitches up or reduces thrust to prevent overspeed.
  2. High Angle of Attack Protection (Alpha Protection):
    • Alpha Floor: Automatically applies TO/GA thrust if speed/AoA gets critically dangerous.
    • Alpha Max: Limits the maximum AoA the pilot can command (elevator authority is reduced).
  3. Bank Angle Protection: Limits bank angle (e.g., to 67° or 33° depending on mode).
  4. Load Factor Protection: Limits G-load (e.g., +2.5g / -1.0g).

Normal Law vs Direct Law

  • Normal Law: Full protections active.
  • Direct Law: No protections. Direct stick-to-surface relationship (like a Cessna). happens if multiple computers/sensors fail.