AIRBUS FLIGHT CONTROL LAWS
High AOA Protection Load Factor Limitation Pitch Attitude Protection
NORMAL LAW
High Speed Protection Flight Augmentation (Yaw) Bank Angle Protection
Low Speed Stability Load Factor Limitation
ALTERNATE LAW
High Speed Stability Yaw Damping Only
Load Factor Limitation
ABNORMAL ALTERNATE LAW w/o Speed Stability
Yaw Damping Only
DIRECT LAW
FLIGHT CONTROL LAWS SUMMARY
NORMAL LAW
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.
Ground
Mode
• 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.
Flight
Mode
• 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.
Flare
Mode
• 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).
ALTERNATE LAW
If Multiple Failures of Redundant Systems occur, the flight controls revert to Alternate Law.
The ECAM displays the message: ALTN LAW: PROT LOST
Ground
Mode The ground mode is identical to Normal Law.
Flight
Mode
• In pitch alternate law the flight mode is a load factor demand law similar to the Normal Law flight
mode, with reduced protections.
• Pitch alternate law degrades to pitch direct law when the landing gear is extended to provide feel
for flare and landing, since there is no flare mode when pitch normal law is lost.
• Automatic pitch trim and yaw damping (with limited authority) is available.
• Turn coordination is lost.
• When pitch law degrades from normal law, roll degrades to Direct Law - roll rate depends on
airspeed.
Protections
• All protections except for load factor maneuvering protection are lost.
• The load factor limitation is similar to to that under Normal Law.
• Amber XX's replace the green = attitude limits on the PFD.
• A low speed stability function replaces the normal angle-of-attack protection
o System introduces a progressive nose down command which attempts to prevent the
speed from decaying further.
o This command CAN be overridden by sidestick input.
o The airplane CAN be stalled in Alternate Law.
　
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