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Primary Flight Control System
Consists of:
- ailerons (driven by conventional control cables connected to hydro-mechanical actuators)
- multi-function roll spoilers (FBW)
- elevators (FBW)
- rudder (FBW)
The controls are comprised of two complementary parts: the P-ACE and the FCM.
Roll control system
Includes conventional hydro-mechanical ailerons and FBW multi-function spoilers providing roll control. The 3 outboard pairs of spoilers are used for roll control. A feel and centering unit is provided. Trim commands are limited to 3s. 2 sets of aileron cables run from forward torque tubes in the flight deck to aft torque tubes at the wing spar. A second set of cables begins at the aft torque tubes and runs to the aileron PCUs.
2 PCUs control each aileron surface in active/active mode. If 1 PCU fails, the other PCU operates normally but with half the force authority. If hydraulic supply to a PCU is lost, it acts as a damper.
If the two control column jam, there is a disconnect mechanism between the two torque tubes, which is activated through the aileron disconnect handle. The feel mechanism is on the pilot's side, so if the pilot's side jams, the copilot retains control of the right aileron without feel and trim. Only one pair (? set) of multi-function spoilers remain functional after disconnection. Ground maintenance is required to reset the system.
Spoiler control system
There are 3 pairs of multi-function spoilers outboard (L3 to L5, and R3 to R5), and 2 pairs of dedicated ground spoilers inboard. The multi-function spoilers provide roll augmentation, speedbrake, and ground deployment (with the ground spoilers). Inflight the limit is 30° for full spoilers. The speedbrake retracts automatically when flap 2 is selected, or with a TLA of 70°. The spoilers are differential spoilers.
Normal mode
Roll spoilers are gain scheduled with airspeed by the FCM.
Direct mode
If 1 FCM fails, only the associated spoilers change to direct mode. Those spoilers will not deploy as speedbrakes or ground spoilers.
Elevator control system
An FBW electro-hydraulic control system. Moves the left and right elevator surfaces which are attached to the horizontal stabiliser. FCM and P-ACE logic is used to control 2 PCUs per elevator surface which operate in active and standby mode. In standby mode, the PCU acts as a damper and provides flutter protection. The PCU functions are alternated each start. Independent feel units provide feel and centering to the control columns. Pitch trim resets the horizontal stabiliser. 4 P-ACE channels independently control each of the 4 PCUs.
If the two control column jam, there is a disconnect mechanism between the two torque tubes, which is activated through the elevator disconnect handle. Ground maintenance is required to reset the system.
Normal mode
The elevator authority reduces with increasing airspeed. The FCM performs ETC and angle of attack limiting functions.
Direct mode
If airspeed is lost, the FCM is removed from the loop, and the P-ACE uses gain schedules for flap/slat extended or retracted.
Rudder control system
2 PCUs (an upper and a lower) operate in active or standby mode. They are alternated each day, or switched if required after a failure. There is also an artificial feel and centering unit. For autoland aircraft, the AP controls the rudder in addition to the rudder pedals and FCMs. The 4 FCMs augment the system, providing yaw damping, turn coordination, and gain scheduling with airspeed.
In the event of a jam in the rudder pedals, the rudder remains active and is actuated by the high-level FCM functions for yaw damping and turn coordination. If a PCU jams, the rudder is locked and control is via the ailerons and roll spoilers.
Normal mode
Rudder gain is reduced by the FCM with airspeed.
Direct mode
Allows up to 30° of rudder deflection.
See also
Secondary Flight Control System