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16. Flight controls

16.1. Overview
16.2. Side sticks
16.3. Normal Law & protections
16.4. Reconfiguration laws

16.1. Overview

The primary flight controls consist of:

  • Ailerons

  • Elevators

  • Trimmable Horizontal Stabilizer (THS)

  • Rudder

  • Ground spoilers/ Speed brakes

The ten spoilers (five each side) have several functions, each using different surfaces:

Speed brakes

Use the 3 central surfaces to increase drag.

Roll control

Use the four outer spoilers to assist in rolling the aircraft.

Ground spoilers

Deploy all spoilers to dump lift to get weight on the wheels.

Seven flight control computers take input from the sidestick, analyse it to ensure it is a safe command, then use it to manage the control surface servos. There are:

  • Two Elevator and Aileron Computers (ELAC)

  • Three Spoiler and Elevator Computers (SEC)

  • Two Flight Augmentation Computer (FAC)

Two Flight Control Data Concentrator computers (FCDC) process data from the ELACs and SECs for use by the EIS. The FACs send their data directly. The FCDCs are redundant. Failure of both FCDCs will lead to flight control data not being available to the EIS.

Two FLT CTL panels, one on either side of the overhead panel, are used to control the flight control computers.

Each pair of flight control computers is redundant. The SEC3 is only used for spoiler control, and does not participate in flight control system reconfiguration.

The ailerons, elevators and pitch trim are powered by two independent actuators, each powered by a seperate hydraulic source. The rudder is powered by three independent actuators. Each actuator is controlled by a different computer. At any one time, one actuator will be in active mode, and the other will be in damping mode. In the event of a flight control computer failure, the actuators controlled by that computer will automatically be switched to damping mode, and those controlled by the other computer will become active.

If both ELACs fail, active control of the ailerons is lost and they revert to damping mode. SEC2 takes over control of the elevators and the stabilizer. Roll function is provided by the spoilers. If SEC2 also fails, it will be replaced by SEC1.

With an elevator fault, the remaining elevator remains operative, but its deflection limits are reduced to prevent excessive torsional loads on the tail. Normal flight is possible in this configuration. If the elevators are lost entirely, they are automatically set to the neutral position.

Providing suitable hydraulic power is available, mechanical control of the stabiliser and rudder is always available.

Each spoiler is fitted with a single actuator. If a hydraulic system fails, its associated spoiler will remain in its last position unless pushed down by aerodynamic forces. Spoiler control is shared by the three SECs. Failures are shown on the ECAM F/CTL page by an amber number above the failed spoiler. An amber triangle above the number indicates a failure in the extended position. If possible, the spoiler will be automatically retracted by its controlling SEC and then it and its symmetrical pair on the opposite wing will be inhibited.

Under certain conditions, speed brake extension is inhibited and spoilers are automatically retracted. This may lead to a SPD BRK DISAGREE ECAM caution.

Auto ground spoilers are armed by pulling the spoiler lever up to expose a white collar. A memo on the E/WS confirms arming.

Rudder trim is isolated in flight when the autopilot is engaged. Its position is shown by a blue line on the ECAM F/CTL page.

When the autopilot is engaged, speed brakes will not deploy past approximately half, even if the speed brake lever is moved to full.

The "SPEED BRK" memo on the E/WD will flash amber if speed brakes are extended and any engine is above idle.

Auto ground spoilers deploy automatically when both main gear are compressed and thrust levers are at idle or behind. If only one main gear is compressed, the spoilers only partially deploy. They will automatically retract if power is applied for a go-around.

Lift augmentation devices consist of:

  • Five slats on each leading edge

  • Two flaps on each trailing edge

The lift augmentation devices are hydraulically actuated. They are electrically controlled by two Slat Flap Control Computers (SFCC). Each SFCC has two channels, one for the slats and one for the flaps. The SFCCs are redundant, but a system associated with a failed channel will move at half speed.

When flaps are selected, both ailerons are dropped by about 5°. This is indicated on the ECAM F/CTL page by the aileron position indicator pointing to a boxed position on the scale rather than there normal double dashed position.

The flaps have an auto retract function. In configuration 1+F, the flaps will automatically retract when airspeed reaches 210kt. There is no corresponding automatic slat retraction, so this is known as configuration 1.

When deploying flaps when airborne, selecting 1 on the flap lever only moves the slats - i.e. configuration 1 is acheived rather than 1+F.

Flap and slat faults are indicated in amber on the flap/ slat display on the E/WD. Locked flaps or slats may be caused by the Wing Tip Brakes (WTB) locking the affected surface movement if assymmetry, overspeed, symmetrical runaway or uncommanded movement are detected. WTBs cannot be released in flight. The slats and flaps have independant WTBs, so locked flaps will not cause locked slats, and vice versa. An ALIGNMENT FAULT indicates flap attachment failure.

A-LOCK pulsing blue on the E/WD indicates that the slats have been locked due to high angle of attack and/or low speed.

The rudder deflection is limited depending on speed by the rudder travel limiter. The current rudder travel limit is shown on the F/CTL ECAM page by white ticks below the rudder scale.

16.2. Side sticks

The side sticks are spring loaded to neutral and do not provide feedback. They are not interconnected. If both side sticks are operated at the same time, their inputs are added algebraically. If this happens, a "DUAL INPUT" aural warning is activated and green lights show on the SIDE STICK PRIORITY warning lights. Dual inputs are not recommended.

When the autopilots are engaged, the side sticks are locked in neutral. If the lock is overcome, the autopilot is disconnected.

The button on the side stick is dual function. If an autopilot is engaged, pushing the button will disconnect the autopilot and pushing it a second time will silence the associated warning. If no autopilot is engaged, pressing and holding the button prioritises the side stick. This results in a "PRIORITY LEFT/RIGHT" message and a red arrow indication on the opposite side stick priority warning light. Moving the low priority sidestick now just results in a green light in the side stick priority light on the prioritised side. If both priority buttons are pushed, the last pressed will give priority. The opposite sidestick can be permanently deactivated by pressing and holding the button for 40 seconds. In this case, a momentary push on either button will reactivate the deactivated side stick.

On the ground, a combined side stick deflection indicator is shown as a white cross on the attitude indicator. This only indicates side stick positions, not control surface positions. Control surface positions are shown on the ECAM F/CTL page, which is automatically called if either the sidesticks or the rudder pedals are moved on the ground. The side sticks become operable on the ground as soon as hydraulic power becomes available (i.e. after first engine start).

16.3. Normal Law & protections

Normal law operates in three modes:

Ground mode

Conventional controls when the aircraft is on the ground and electrically and hydraulically powered.

Flight mode

Operates in the air after a gradual transition from ground mode, commencing at lift off.

Flare mode

Introduces conventional feel to the landing phase. This is acheived by memorizing the aircraft attitude at 50ft, then progressively reducing this attitude, meaning the pilots must perform a gentle flare.

In flight mode, control surface deflection is not directly proportional to side stick deflection. Instead, side stick input is a rate of roll demand in roll and a load factor demand in pitch. Control surface movement will occur with no input on the side stick. An attitude is set with the sidestick and the sidestick is then allowed to return to its neutral position. As pitch and roll rate demands are now zero, the flight control computer holds the attitude until further inputs are made with the sidestick. Yaw control is conventional, but turn co-ordination and dutch roll protection are provided, meaning rudder inputs are not generally required.

Normal law provides the following protections:

Load factor limitation

Structural load is limited to:

  • +2.5g to -1g in clean configuration

  • +2g to 0g in flaps extended configuration

Pitch attitude protection

Pitch is restricted to a maximum of between 20° and 30° nose up (depending on configuration and speed) and a maximum of 15° nose down. The current limits are indicated by green dashes on the attitude indicator.

High angle of attack protection

Prevents the aircraft stalling and ensures optimum performance during extreme maneuvres. It takes priority over all other protections. Vα-prot is displayed as the top of an amber barber pole on the speed scale. This is the lowest speed that the aircraft is allowed to reach with the stick neutral. The pilot can override Vα-prot using the side stick and reduce to Vα-max, which is represented by the top of the solid red bar on the speed scale. In the protection range, normal law demand is modified to be an angle of attack demand rather than a load factor demand. If the sidestick is released at Vα-max the speed will increase to Vα-prot.

High speed protection

Prevents exceedance of VMO/MMO. This is shown on the speed scale as the bottom of the red barber pole. Green dashes indicate the speed at which protection activates. Momentary exceedance of VMO/MMO is allowed for maneuvring, but the speed will then return to protection speed. With stick released, the speed returns to VMO/MMO. When high speed protection is active, roll stability is augmented so that the aircraft will roll wings level if the sidestick is released.

Bank angle protection

Bank angle is limited to 67°, shown by green dashes on the bank angle scale on the PFD. The FD bars will disappear if bank angle exceeds 45°. If the side stick is released and the bank angle is >33°, the bank angle will return to 33°. Autotrim is inhibited above 33°. If the angle of attack or the high speed protection is active, bank angle is limited to 45°.

16.4. Reconfiguration laws


Whilst a single failure will not result in degradation of normal law, it is possible that multiple failures may.

Alternate law

Degradation to alternate law is annunciated on the E/WD as F/CTL ALTN LAW (PROT LOST). The effects are:

Ground mode

As in normal law,

Flight mode

Pitch as in normal law. Conventional roll control, i.e surface deflection proportional to side stick deflection. In yaw, turn coordination is lost and damping has limited authority.

Landing mode

Direct law when landing gear is selected down.

Load factor limitation is provided similarly to normal law. Pitch attitude protection is lost, indicated by the green pitch limit dashes on the attitude indicator being replaced by amber crosses. Bank angle protection is lost. Again, this is indicated by the green dashes on the bank angle scale being replaced by amber crosses.

The high angle of attack protection is replaced by low speed stability. Stall warning speed, VSW indicated by a red baber pole on the speed indicator replaces the Vα indications. As speed approaches VSW a progressive nose down pitch input is introduced. This can be overridden with side stick inputs. A "STALL,STALL" aural warning sounds at VSW, and the aircraft will stall if the warning is ignored. Alpha floor protection is also inoperative in alternate law.

High speed stability replaces high speed protection. A nose up input is added when speed is above VMO/MMO. This can be overridden with sidestick inputs. As in normal law, an aural over speed warning is triggerred when VMO/MMO is exceeded.

According to the failures, it is possible that the stabilities will also be lost. In this case only load factor limitation and the stall and overspeed warnings remain.

Direct law

Direct law is indicated by the ECAM message FCTL DIRECT LAW (PROT LOST). In direct law, there is a direct relationship between side stick and control surface positions. There are no protections available, although stall and over speed warnings are still available. Auto-trim is not available. A "USE MAN PITCH TRIM" message appears on the FMA. Auto turn coordination and dutch roll damping are also lost.

Mechanical backup mode

Pitch is controlled solely through the use of manual pitch trim. "MAN PITCH TRIM ONLY" appears on the FMA. Lateral control is solely through the use of the rudder pedals. In most cases, action can be taken to recover to either alternate law or direct law.

Abnormal attitude laws

In the event the aircraft attitude leaving the protected envelope, the flight controls revert to alternate law without the stability enhancements. Once the aircraft is recovered, it stays in alternate law. It will not, however, revert to direct law when the gear is deployed.