AUTO FLIGHT Flight Control

Airbus Flight Control System

Normal operating configuration of the system. Failure of any single computer does not affect normal law.
Covers 3-axis control, flight envelope protection, and load alleviation. Has 3 modes according to phase of flight.
  • Active when aircraft is on the ground.
  • Direct proportional relationship between the sidestick deflection and deflection of the flight controls.
  • Is active until shortly after liftoff.
  • After touchdown, ground mode is reactivated and resets the stabilizer trim to zero.
  • Becomes active shortly after takeoff and remains active until shortly before touchdown.
  • Sidestick deflection and load factor imposed on the aircraft are directly proportional, regardless of airspeed.
  • With sidestick neutral and wings level, system maintains a 1 g load in pitch.
  • No requirement to change pitch trim for changes in airspeed, configuration, or bank up to 33 degrees.
  • At full aft/fwd sidestick deflection system maintains maximum load factor for flap position.
  • Sidestick roll input commands a roll rate request.
  • Roll rate is independent of airspeed.
  • A given sidestick deflection always results in the same roll rate response.
  • Turn coordination and yaw damping are computed by the ELACs and transmitted to the FACs.
  • No rudder pedal feedback for the yaw damping and turn coordination functions.
  • Transition to flare mode occurs at 50' RA during landing.
  • System memorizes pitch attitude at 50' and begins to progressively reduce pitch, forcing pilot to flare the aircraft
  • In the event of a go-around, transition to flight mode occurs again at 50' RA.
Protections Load factor Limitation
  • Prevents pilot from overstressing the aircraft even if full sidestick deflections are applied.

Attitude Protection

  • Pitch limited to 30 deg up, 15 deg down, and 67 deg of bank.
  • These limits are indicated by green = signs on the PFD.
  • Bank angles in excess of 33 deg require constant sidestick input.
  • If input is released the aircraft returns to and maintains 33 deg of bank.

High Angle of Attack Protection (alpha):

  • When alpha exceeds alpha prot, elevator control switches to alpha protection mode in which angle of attack is proportional to sidestick deflection.
  • Alpha max will not be exceeded even if the pilot applies full aft deflection

High Speed Protection:

  • Prevents exceeding VMO or MMO by introducing a pitch up load factor demand.
  • The pilot can NOT override the pitch up command.

Low Energy Warning:

  • Available in CONF 2, 3, or FULL between 100' and 2, 000' RA when TOGA not selected.
  • Produces aural "SPEED SPEED SPEED" when change in flight path alone is insufficient to regain a positive flight path (Thrust must be increased).
If Multiple Failures of Redundant Systems occur, the flight controls revert to Alternate Law.
The ECAM displays the message: ALTN LAW: PROT LOST

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