A320 PITCH CONTROL

Pitch control is achieved with the elevators and the trimmable horizontal stabilizer (THS). They are both electrically controlled by the ELACs or SECs, and are hydraulically actuated. If both ELACs fail the SECs take over. The stabilizer can be controlled mechanically through cables attached to the cockpit pitch trim wheels, provided there is hydraulic power available. Mechanical pitch trim has priority over electric trim.

Elevators 

The blue and green hydraulic systems power two servojacks on the left elevator and the yellow and blue, two on the right. One jack is active while the other is in damping mode. If the active jack fails then the other one takes over. If electrical control is lost to the jacks, they both go into centering or streamlined mode. If hydraulic control is lost to the jacks, they both go into damping mode. If one elevator is lost, the other will operate at reduced deflection to avoid excessive asymmetric loads on the tail.

Trimmable horizontal stabilizer (THS) 

The stabilizer is electrically controlled by one of three electric motors or mechanically controlled via the trim wheels. A screwjack is hydraulically driven by the green and yellow hydraulic systems to drive the THS. After touchdown the trim returns to 0° automatically.

YAW CONTROL 

Yaw control is achieved by the rudder. Yaw orders for turn coordination and yaw damping are computed by the ELACs and transmitted to the FACs.

Rudder 

The rudder is electrically controlled by the trim motors or mechanically by the rudder pedals. In mechanical control hydraulic pressure is still required to move the surface. Three independent servojacks, operating in parallel, operate the rudder. In automatic operation (turn coordination and yaw damping) a green hydraulic servo actuator drives all three servojacks. A yellow system actuator is always synchronized and takes over if there is a failure.

Rudder travel is limited as a function of speed. If both FACs fail, maximum rudder deflection will be obtained when the slats are extended. The rudder trim is operated by the number one electric motor, controlled by FAC 1, number 2 motor is in synchronized in backup with FAC 2. Electric trim with the autopilot engaged operates at 5°/second up to a maximum of 20°. Engine failure compensation is calculated by the FACs and FMGC as a function of speed, engine power available, bank angle and yaw. 

Manual rudder trim operates at 1°/second up to 20°. Manual trim is not available when the autopilot is engaged. 

Yaw damper 

The yaw damper receives inputs form the ELACs and FACs. The information is sent to the yaw damper servo for damping and turn coordination. There is no feedback from the rudder pedals during these functions.

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