OPERATIONS MANUAL

Flight Controls
Rudder Control:
Flaps Control:
Yaw control is provided by the upper and lower rudder surfaces on the vertical
stabilizer. They are controlled by pushing the rudder pedals on the flight deck.
Pedal motion is mechanically transferred via cables to the aircraft tail where the
system is linked with a feel and trim mechanism. Two ratio changers in the tail
control the upper and lower rudder hydraulic actuators. The SRMs compute the
ratio; it gradually decreases with the rising airspeed. Rudder autopilot servos
provide autocontrol during autoland and multi-channel go-around.
The yaw damper system increases the directional stability of the aircraft. Both
the upper and lower yaw dampers are active when the aircraft is airborne.
The flap lever angle is sensed by three rotary variable differential
transformers (RVDTs) which are monitored by three flap control units
(FCUs). At least one RVDT and one FCU must be operative to provide flap
lever control. The FCUs operate either in primary mode or in secondary
mode. In primary mode, the leading edge (LE) flaps are moved by pneumatic
drives, and the trailing edge (TE) flaps are moved by hydraulic drives. When a
flap does not reach the commanded position within a specific time, the FCUs
automatically switch to secondary mode. In that mode, the entire group, to
which the failed flap belongs, will be symmetrically moved by electric drives.
When an electric drive fails as well, and the LE flaps are asymmetrically
extended, the respective LE groups on both wings are stopped. TE flaps
incorporate a mechanical asymmetry protection: the left wing inboard TE
flaps are interconnected with the right wing inboard TE flaps; and the left wing
outboard TE flaps are interconnected with the right wing outboard TE flaps.
The LE flaps in the midspan and inboard sections are labeled as group A; and
the outboard LE flaps as group B. In primary mode, group A extends when
the flap lever is set to 1. When the lever is set to 5, group B extends and the TE
flaps start to extend.—The retraction is scheduled as follows: When the flap
lever is set from 5 to 1, the TE flaps are commanded to retract completely, and
during the retraction, when the inboard TE flaps pass 4.5 units, group B starts
to retract. When the flap lever is set to UP and the outboard TE flaps are up,
group A starts to retract.
When the alternate mode is activated on the main instrument panel, the FCUs
are bypassed and a simplified retraction and extension control commands the
electric drives.
The FCUs provide a flap load relief function. When the flaps are manually
set to 25 or 30, and the flap limit speed of the respective aircraft model
is exceeded, the FCUs automatically retract the flaps to the next best flap
position, but to not less than flaps 20.
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