What would happen to the rudder of an A320 if both Flight Augmentation Computer (FAC) systems completely failed during mid-flight? Would the auto pilot immediately pass control back to the pilots or if they failed would that be it? Would it be impossible for the cockpit to communicate with the mechanisms which control the rudder or is manual operation possible in an A320?
Also, I know this maybe a more difficult/impossible questions but what would cause the malfunction of one of the FAC computers? Are there any likely scenarios or previous cases?
The A320 has a mechanical link from the rudder pedals to the hydraulic rudder actuators. Computer-generated rudder commands for yaw damping and turn coordination are added to the mechanical signal from the rudder pedals, but in the event of a two-sided computer failure the rudder can still be controlled.
The elevator trim wheels are also mechanically connected, so rudimentary control of the aircraft remains even in the event of a total electronic failure, as long as there's hydraulic power.
The Flight Augmentation (FAC) performs the following functions:
Yaw damper Rudder travel limiting
Monitoring of the flight envelope and computation of maneuvering speed
Yaw autopilot order
Bite fuction of the AFS
The trim actuator, the yaw damper servoactuators and the travel limitation unit are normally controlled by the flight Augmentation Computer (FAC 1) and FAC 2 being in standby.
The rudders are controlled either mechanically from the pedals or electrically when the auto pilot is engaged. Therefore if both FACs fail, the rudder control remains unaffected. However the autopilot is no longer available.